Contents
Welcome!..........................................................2
How to Use This Manual ...........................2

Important Safety Instructions........................ 3
Instructions de Sécurité Importantes (French)......4
Beim Benutzen dieses Produktes beachten Sie
bitte die folgenden Sicherheitshinweise: (German).........................................................................6
CE Declaration of Conformity..............................7

Quick Start Guide ........................................... 8
Step 1: Hook it up ..............................................8
Step 2: Set the Controls .....................................8
Phantom ..................................................8
Input ........................................................8
VU Meter Range.......................................8
Mute Switch..............................................8
Gain (Coarse 5 dB and Fine 1 dB) .............8
Rise Time............................................... 10
Impedance Selector ................................ 10
Hi-Pass .................................................. 10
Polarity................................................... 10
About the Instrument Input ............................... 11
Step 3: Experiment .......................................... 11

Connections .................................................. 12

Frequently-Asked Questions ................... 21
About Vacuum Tubes ...................................... 22
Theory................................................... 22
Impedance of tubes ................................ 22
About Class A circuitry............................ 22
Care and feeding of vacuum tubes .......... 23
Tube Replacements................................ 23
The VU Meter.................................................. 24
Clip LEDs............................................... 24
VU Meter Range Control......................... 24
Gain Controls.................................................. 25
GAIN Setting Procedures........................ 25
Overload characteristic .................................... 26
Rise Time ....................................................... 27
The Output Transformer................................... 27
Mute Switch .................................................... 28
Standby .......................................................... 28
Block Diagram................................................. 29

Microphone & Preamp Theory....................31
About Impedance ............................................ 31
The importance of impedance ................. 31
About Noise .................................................... 32
Thermal Noise........................................ 32
Microphone Self-Noise............................ 32
Acoustic Noise ....................................... 32

Unpacking and Inspection ................................ 12
Installing in a Rack........................................... 12Power ............................................................. 13
Avoiding ground loop noise ..................... 14
Basic Connections ........................................... 15
Output To a Mixing Console .................... 15
Connecting Microphones.................................. 18
Connecting Instruments ................................... 18
Connecting Line Inputs..................................... 18

Troubleshooting.............................................33

About the Vipre ............................................. 19

Dimensional drawing ....................................... 37

Why is the microphone preamplifier so important?
....................................................................... 19
The Input Section............................................. 20
About the Input Transformer .................... 20

Troubleshooting Index ..................................... 33
Care and Maintenance..................................... 33
Cleaning ................................................ 33
Refer All Servicing to Groove Tubes ........ 34
Obtaining Repair Service ........................ 35

Specifications.................................................36
Index................................................................38
Groove Tubes Limited Warranty.................39

Introduction/Safety Instructions

Welcome!
Thank you for making Groove Tubes' Vipre™ part ofyour studio. This is a truly unique product, so to take fulladvantage of the Vipre’s functions and enjoy long andtrouble-free use, please read this user’s manual
carefully.

How to Use This ManualThis manual is divided into the following sections
describing the various functions and applications
for the Vipre. While it's a good idea to readthrough the entire manual once carefully, thosehaving general knowledge about microphonepreamplifiers should use the table of contents tolook up specific functions.
Chapter 1: Quick Start. This will get you
started using the Vipre right away. It's a shortguide to the essential elements of hooking it up
and using it for the first time.
Chapter 2: Connection. This chapter gives
detailed instructions for connecting the Vipre toa variety of typical audio systems.
Chapter 3: About the Vipre. This section gives
detailed information on the unique technology of
the Vipre and how to use it.
Chapter 4: Microphone and Preamp Theory
covers deep background information that will
help you use your Vipre, and all microphones, totheir greatest capability.
Chapter 5: Troubleshooting. This chapter
contains troubleshooting tips and service
information should problems occur.
Helpful tips and advice are highlighted ina shaded box like this.

J

2

When something important appears in
the manual, an icon (like the one on theleft) will appear in the left margin. Thissymbol indicates that this information isvital when operating the Vipre.

Vipre Reference ManualImportant Safety
Instructions
Safety symbols used in this productThis symbol alerts the user that there areimportant operating and maintenance instructions in
the literature accompanying this unit.

This symbol warns the user of uninsulated
voltage within the unit that can cause dangerous
electric shocks.

This symbol warns the user that output
connectors contain voltages that can cause
dangerous electrical shock.

Please follow these precautions whenusing this product:

1. Read these instructions.
2. Keep these instructions.
3.

Heed all warnings.

4.

Follow all instructions.

5.

Do not use this apparatus near water.

6. Clean only with a damp cloth. Do not spray
any liquid cleaner onto the faceplate, as thismay damage the front panel controls or
cause a dangerous condition.

8. Do not install near any heat sources such asradiators, heat registers, stoves, or otherapparatus (including amplifiers) that produce
heat.

9.
Do not defeat the safety purpose of
the polarized or grounding-type plug. A
polarized plug has two blades with one wider
than the other. A grounding-type plug has
two blades and a third grounding prong. The
wide blade or the third prong are provided foryour safety. When the provided plug does
not fit into your outlet, consult an electrician
for replacement of the obsolete outlet.
10. Protect the power cord from being walked onor pinched, particularly at plugs, convenience
receptacles, and the point where they exitfrom the apparatus.
11. Use only attachments or accessories
specified by the manufacturer.
12. Use only with a cart, stand, bracket, or table
designed for use with professional audio ormusic equipment.
In anyinstallation, make sure that injury or
damage will not result from cables
pulling on the apparatus and its
mounting. If a cart is used, use
caution when moving the cart/apparatus
combination to avoid injury from tip-over.
13. Unplug this apparatus during lightning storms
or when unused for long periods of time.

7. Install in accordance with the manufacturer's
instructions.
3

Vipre ReferenceIntroduction/Safety Instructions

14. Refer all servicing to qualified service
personnel. Servicing is required when theapparatus has been damaged in any way,such as when the power-supply cord or plugis damaged, liquid has been spilled or objects
have fallen into the apparatus, the apparatus
has been exposed to rain or moisture, does
not operate normally, or has been dropped.
15. This unit produces heat when operated
normally. Operate in a well-ventilated areawith at least six inches of clearance fromperipheral equipment.
16. This product, in combination with an amplifier
and headphones or speakers, may becapable of producing sound levels that could

cause permanent hearing loss. Do not
operate for a long period of time at a highvolume level or at a level that is
uncomfortable.
If you experience any
hearing loss or ringing in the ears, you should
consult an audiologist.
17. Do not expose the apparatus to dripping or
splashing. Do not place objects filled withliquids (flower vases, softdrink cans, coffeecups) on the apparatus.
18. WARNING: To reduce the risk of fire orelectric shock, do not expose this apparatus
to rain or moisture.

Instructions de Sécurité Importantes (French)
Symboles utilisés dans ce produit

Ce symbole alèrte l’utilisateur qu’il existe
des instructions de fonctionnement et de maintenancedans la documentation jointe avec ce produit.

Ce symbole avertit l’utilisateur de laprésence d’une tension non isolée à l’intérieur del’appareil pouvant engendrer des chocs électriques.

Ce symbole prévient l'utilisateur de laprésence de tensions sur les raccordements de sorties,
représentant un risque d'électrocution.

Veuillez suivre ces précautions lors del’utilisation de l’appareil:

1. Lisez ces instructions.

5. N’utilisez pas cet allareil à proximité del’eau.
6. Ne nettoyez qu’avec un chiffon humide.
Il est potentiellement dangereux
d'utiliser des pulvérisateurs ou
nettoyants liquides sur cet appareil.
7. Installez selon les recommandations duconstructeur.
8. Ne pas installer à proximilé de sourcesde chaleur comme radiateurs, cuisinière
ou autre appareils (don’t lesamplificateurs) produisant de la chaleur.
9. Ne pas enlever la prise de terre ducordon secteur. Une prise murale avec
terre deux broches et une troisièrme
reliée à la terre. Cette dernière est
présente pour votre sécurité. Si lecordon secteur ne rentre pas dans laprise de courant, demandez à unélectricien qualifié de remplacer la prise.

2. Gardez ces instructions.
3. Tenez compte de tous les avertissements.

10. Evitez de marcher sur le cordon secteur
ou de le pincer, en particulier au niveau
de la prise, et aux endroits où il sor del’appareil.

4. Suivez toutes les instructions.

4

Vipre Reference ManualIntroduction/Safety Instructions

11. N’utilisez que des accessoires spécifiés par leconstructeur.
12. N’utilisez qu’avec un stand, ou table conçus
pour l’utilisation d’audio professionnel ou
instruments de musique.
Dans touteinstallation, veillez de ne rien endommager àcause de câbles qui tirent sur des appareils etleur support.
13. Débranchez l’appareil lors d’un orage ou
lorsqu’il n’est pas utilisé pendant longtemps.
14. Faites réparer par un personnel qualifié. Uneréparation est nécessaire lorsque l’appareil aété endommagé de quelque sorte que ce soit,
par exemple losrque le cordon secteur ou laprise sont endommagés, si du liquide a coulé
ou des objets se sont introduits dans l’appareil,si celui-ci a été exposé à la pluie ou àl’humidité, ne fonctionne pas normalement ou
est tombé.

Vipre Reference Manual

15. Puisque son fonctionement normale
génère de la chaleur, placez cet
appareil au moins 15cm. deséquipments péripheriques et assurez
que l’emplacement permet la circulation
de l’air.
16. Ce produit, utilisé avec un amplificateur
et un casque ou des enceintes, est
capable de produite des niveauxsonores pouvant engendrer une perte
permanente de l’ouïe. Ne l’utilisez pas
pendant longtemps à un niveau sonoreélevé ou à un niveau non confortable.
Si vous remarquez une perte de l’ouïe
ou un bourdonnement dans les oreilles,
consultez un spécialiste.

5Introduction/Safety Instructions

Beim Benutzen dieses Produktes beachten Sie bitte die folgenden
Sicherheitshinweise: (German)
1. Lesen Sie die Hinweise.

2. Halten Sie sich an die Anleitung.
3. Beachten Sie alle Warnungen.
4. Beachten Sie alle Hinweise.
5. Bringen Sie das Gerät nie mit Wasser in
Berührung.
6. Verwenden Sie zur Reinigung nur ein weiches
Tuch. Verwenden Sie keine flüssigen
Reinigungsmittel. Dies kann gefährliche Folgen
haben.
7. Halten Sie sich beim Aufbau des Gerätes an die
Angaben des Herstellers.
8. Stellen Sie das Gerät nich in der Nähe von
Heizkörpern, Heizungsklappen oder anderen
Wärmequellen (einschließlich Verstärkern) auf.
9. Verlegen Sie das Netzkabel des Gerätes
niemals so, daß man darüber stolpern kannoder daß es gequetscht wird.
10. Benutzen Sie nur
empfohlene Zubehör.

das vom Hersteller

11. Verwenden Sie ausschließlich Wagen, Ständer,oder Tische, die speziell für professionelle
Audio- und Musikinstrumente geeignet sind.
Achten Sie immer darauf, daß die jeweiligen
Geräte sicher installiert sind, um Schäden undVerletzungen zu vermeiden. Wenn Sie einen
Rollwagen benutzen, achten Sie darauf, dasdieser nicht umkippt, um Verletzungenauszuschließen.

6

12. Ziehen Sie während eines Gewittersoder wenn Sie das Gerät über einen
längeren Zeitraum nicht benutzen den
Netzstecher aus der Steckdose.
13. Die Wartung sollte nur durch
qualifiziertes Fachpersonal erfolgen.
Die Wartung wird notwendig, wenn das
Gerät beschädigt wurde oder aber das
Stromkabel oder der Stecker,
Gegenstände oder Flüssigkeit in das
Gerät gelangt sind, das Gerät dem
Regen oder Feuchtigkeit ausgesetzt war
und deshalb nicht mehr normal arbeitet
oder heruntergefallen ist.
14. Dieses Gerät produziert auch im
normalen Betrieb Wärme. Achten Sie
deshalb auf ausreichende Lüftung mit
mindestens 15 cm Abstand von anderen
Geräten.
15. Dieses Produkt kann in Verbindung mit
einem Verstärker und Kopfhörern oder
Lautsprechern
Lautstärkepegel
erzeugen,dieanhaltende
Gehörschäden verursachen. Betreiben
Sie es nicht über längere Zeit mit hoher
Lautstärke oder einem Pegel, der Ihnen
unangenehm is.
Wenn Sie ein
Nachlassen des Gehörs oder ein
Klingeln in den Ohren feststellen, sollten
Sie einen Ohrenarzt aufsuchen.

Vipre Reference ManualIntroduction/Safety Instructions

CE Declaration of Conformity

Manufacturer’s Name:
Manufacturer’s Address:

Groove Tubes llc
1543 Truman Street
San Fernando, CA 91340
USA

declares, that the product:
Product Name:
Model Type:

Vipre
Microphone preamplifier

conforms to the Standards for Safety and EMC for this product listed on the Internet site:www.groovetubes.com

Vipre Reference Manual

7

chapter 1

Quick Start Guide
The Groove Tubes Vipre™ is a unique product, but its
basic hookup and operation is similar to otheroutboard microphone preamplifiers in most respects.
This chapter is a "shorthand" guide for those whowant to start using the Vipre right away. If you havequestions about any of the features, don’t worry –later chapters will unveil the mysteries of the Vipre's
special features.

Step 1: Hook it up

Phantom
If the mic requires phantom power (48 volt), turn the
PHANTOM switch on. (WARNING-DO NOT use
Phantom Power with a Ribbon Microphone-Serious
Damage may occur!)

Input

1. Pull the Vipre out of the package, and plug it into agrounded AC power source with the supplied
power cable.

Since we’re using a microphone in this example, set
the INPUT switch to BALANCED XFMR. If you want
to bypass the input transformer and use anelectronically-balanced input, set the switch to
BALANCED BRIDGE.

2. Connect the output of a microphone to the MIC
INPUT on the back of the Vipre.

VU Meter Range

3. Connect the LINE OUT of the Vipre to a line
input—not a microphone input—of a mixing
console or recording device.

For now, set this to 0 dB. (You can experiment withother settings after you’ve set the initial gain.)

4. For now, set the 5 dB GAIN control to minimum(20, full counter-clockwise).

After 60 seconds of warm up, switch this to NORMAL.
Use this feature when changing microphones.

5. Turn the STANDBY switch to the right (STBY
position—the red light will light).
6. Turn the MUTE switch to the right MUTE position
for now. (The yellow light will light.)
7. Turn the Vipre's POWER switch ON.

J Remember that the Vipre has an all-tube
signal path, and it will take about 20 seconds
for the tubes to warm up before you would be
able to hear audio. Tube life will be prolonged
if you leave the unit in STANDBY mode for atleast 30 seconds before turning STANDBY tothe B+ ON position.
8. After 30 seconds or so, turn the STANDBY switch
to the left (B+ ON position—the red light will turn
off).

8

Step 2: Set the Controls

Mute Switch

Gain (Coarse 5 dB and Fine 1 dB)
These are the most important controls to set in any
microphone preamp. The Vipre uses two rotary-stepswitches to set the gain with laboratory precision. The
left control goes from 20 dB to 70 dB of gain in 5 dB
steps; the right control allows you to change it insingle-dB increments, ± 5 dB. Typical gain settings onlead vocals range from 30 to 50 dB, but that of course
depends upon the microphone and source, and the
input sensitivity of the mixer or recorder connected to
the Vipre's output.
There are two different methods commonly used to
set the gain of any mic preamp. The nominal level
method maximizes headroom; the peak method
maximizes the dynamic range of the system by using
up as much headroom as desired.

Vipre Referencechapter 1 • quick start guideTo set the gain at nominal level:

To set the gain using the peak method:

1. Make sure the VU METER RANGE switch is
set to "0".

1. Set the Vipre's VU METER RANGE switch to"+10 Vu".

2. With the source playing into the microphone,raise the 5 dB GAIN control until the VU meterof the Vipre is peaking at "0" or just barely
going "into the red". Raise or lower the 1 dB
GAIN control as necessary.

2. With the source playing into the microphone,raise the 5 dB GAIN control until the meter ofthe receiving unit (the mixer or recorder theVipre is feeding) is nearing its maximum level.

The average level of the output will be nominal(+4 dBu at the balanced line out, -10 dBV at theunbalanced line out) with peaks typically 8-10 dB
above that. The Vipre's green and red SIGNAL
lamps should never flash with this method.

NOTE: Preparing the Vipre rotary switches
for silent operation.
Vipre uses special ceramic rotary switches tomaintain a fully balanced signal path. Low
noise resistors and high grade capacitors are
hand soldered onto these rotary switch decks.
These caps can become “charged” during thewarmup period and this can cause a loudpopping sound in some positions the firsttime they are activated. To eliminate this fromhappening we recommend:
1) Engage the mute switch to silence the Vipre .
2) Exercise all positions of the front panel rotaryswitches, switch them from full left to right .
3) Restore the Mute switch to Normal position.
4) This will insure silent operation. This step willneed to be repeated each time the Vipre isturned off for any period of time. Leaving theVipre in “Standby operation” (B+ off) will keep
the capacitors charged and so this step will
not need to be repeated when resuming
operation.

Vipre Reference Manual

3. Carefully raise the 1 dB GAIN control until thereceiver's CLIP LED (or the Vipre's SIGNAL
CLIP LED, whichever lights first) flashes
briefly on peaks.
4. Back off either or both of the controls to dial inexactly the headroom you want (for example,
one click back of the COARSE control andone click back of the FINE control would be 6
dB below clipping).
5. If the Vipre's VU meter is pegging, change the
VU METER RANGE to the +20 or +30
position.

Unlike solid-state microphone preamplifiers,
the Vipre exhibits a very gentle clipping
characteristic...which is to say that it’s OK todrive it into clipping if that’s what the artistic
situation calls for. Note, however, that theVipre is capable of extremely high output,
which may clip the following device; if therecorder or mixer has its own input level
control, make sure it's set low enough to avoid
clipping in that unit. In some situations, apassive attenuator may need to be inserted
between the Vipre and the recorder/mixer; orthe –10 dBV BALANCED OUT may need to
be used instead of the LINE OUT.

9

quick start guide • chapter 1

Rise TimePolarity

There is no “right” setting for the RISE TIME
control—just your artistic judgement. But generally
speaking, settings toward the FAST side will soundmore “modern”, while settings towards SLOW willbring out the more “vintage” aspects of the preamp.
See page 27 for more.

This reverses the “+” and “-“ of the input. Most of thetime, you’ll leave this set to NORM. It may not makean obvious difference, but ideally the polarity should
be set so that a positive pressure on the microphone
generates a positive pressure from the speaker. In
other words, if you’re miking a drum, the first transientof a drum hit should make the loudspeaker move
forward, not back. Polarity also makes a difference inmulti-microphone situations, or when miking opposite
sides of a diaphragm (above and below a pianosoundboard, a snare drum, etc.)

Impedance Selector
This switch is only active when the INPUT switch is in
the BALANCED XFMR position. When it is, you canexperiment with any of the four impedance selections,from 300 to 2400 ohms (W). How this affects thesound of a mic will vary upon the microphone’s actual
impedance and other characteristics, but again,
generally speaking, lower impedances are moresuited to older microphones.
The most “modern” or neutral setting of theVipre is to set the INPUT to Balanced Bridge(which bypasses the IMPEDANCESELECTOR entirely) and the RISE TIME to
FAST. This is the setting that is most similar
to contemporary solid-state console preamps,
but with a more pleasing warmth. But the funreally starts when you start to experiment withthe fifty or so combinations that use thedifferent transformer impedances and different
rise times.

The Vipre is wired according the modern
standard of “Pin 2 = Hot”. Some older
microphones were wired with Pin 3 hot (i.e., a
positive pressure on the diaphragm leads to a
positive voltage on Pin 3); if you’re using oneof these, set the POLARITY switch to REV.

Hi-Pass
This switch is another optional control; it rolls off thebass below 100 Hz at a gentle rate of 4 dB per octave.
It’s designed to get rid of undesirable low-frequency
rumbles and noises. Note, however, that many
microphones also feature high-pass filters of theirown; make sure the mic's filter is out if you want tohear the effect of the Vipre's Hi-Pass filter only.

10

Vipre Reference Manualchapter 1 • quick start guide

About the Instrument Input
The 1/4" input on the front panel labeled
INSTRUMENT INPUT is specially designed for guitar
and bass pickups. Instruments such as basses andguitars sound best if they “see” an extremely highinput impedance (1/2 megohm or greater). This input
feeds a special high-impedance circuit with its own
tube (a GT 6205), making the Vipre not only a great
mic preamp, but an incredible direct box for recording
basses and guitars.
If the instrument has active electronics internally, it
may be so loud that it clips even at low settings of the
GAIN controls, turn the INPUT switch to
INSTRUMENT –20 dB.
As you may be able to tell from looking at the INPUT
switch, the front-panel INSTRUMENT INPUT jackdoes not use the input transformer, so the
IMPEDANCE SELECTOR has no effect on it.
However, RISE TIME and all the other controls do
affect the Instrument Input.
Alternatively, instruments may be plugged into
the LINE IN jack on the back panel for aslightly different sound. The impedance andthe first preamp tubes are different in that
input.

Vipre Reference Manual

Step 3: ExperimentOnce you have experienced the difference that theVipre makes on one microphone, you’ll want to try
every other mic in your possession with it. You’ll findthat each mic reacts differently to the settings, and awhole new sonic palette will open up.
Finding the "right" setting
The Vipre's fundamental concept is different fromother kinds of studio equipment. Settings for
impedance and rise time will change the "flavor" of thesound, but will vary from case to case. The changesof each interact in very subtle ways…it's not nearly as
obvious as changing the settings on an equalizer orcompressor/limiter. So, this manual doesn't provide a
chart that lists the "right" settings for a particular
microphone, because the "right" setting can only be
determined by your ears.
However, knowledge is power. There is considerable
information about the Vipre in the following chaptersthat will help you understand the art and science of
why the Vipre affects your microphones the way it
does. Read on.

11chapter 2

Connections
Unpacking and Inspection
Your Groove Tubes Vipre was carefully packed at thefactory, and the shipping carton was designed toprotect the unit during shipping. Please retain thiscontainer in the unlikely event that you need to return
your Vipre for servicing.
The shipping carton should contain the following
items:•

Vipre Variable Impedance Preamp•

This instruction manual•

Power cable•

Groove Tubes Warranty card•

Rack mounting hardware (two pieces plus parts to
attach them to the Vipre when rack mounting).

J

12

It is important to register your purchase; if you
have not already filled out your warranty cardand mailed it back to Groove Tubes, pleasetake the time to do so now.

Installing in a Rack
The Vipre may be simply set on a table, or installed ina standard 19” audio equipment rack. While the rack
mounting holes are integral to the front panel, theVipre is unusually deep and heavy, so extra support
must be provided for the rear of the unit. Before theVipre is installed in a rack, we recommend that you
attach the reinforcing rack kit to handle the weight of
the unit and provide ventilation room. The rail kit
requires one free rack space above the Vipre.

J

Since the vacuum tubes in the Vipre generatea certain amount of heat, make sure adequate
ventilation is provided in the rack.

To attach the rack kit:
The reinforcing rails should be attached to the sides of
the unit. They are screwed to the sides of the preampand extend to above the front panel. Standard rackscrews are then used to fasten both the Front Paneland the Rack Kit to the Rack Rails panels.

Vipre Referencechapter 2 • connections

Power

Voltage conversion

Make sure you read the initial Important Safety
Instructions chapter at the front of this manual.
The Vipre works with a single standard line voltage
and comes with a detachable AC line cord suitable forthe destination to which the preamplifier is shipped.
Units sold in the United States are designed for use
with 110 to 120 volt AC power (nominal 60 Hz), butthere is a plug-in voltage selector in the power entry
module in the rear-panel switch allowing voltage
conversion to 100V or 220V–240V operation.
The line cable is an IEC-spec AC power cable
designed to be connected to a grounded 3-pin outlet,
with the third, round pin connected to ground. Do notsubstitute any other type of AC cord; IEC-spec cablesof various lengths may be purchased from electronics
stores or your Groove Tubes dealer.

If you need to use the Vipre in a country with adifferent voltage, contact Groove Tubes to locate aservice center in your area. Changing the voltage
requires internal adjustment on circuit boards that
operate at dangerous voltage levels. Again, refer to a
Groove Tubes service center for adjustment.

NEVER OPERATE THE VIPRE AT A
DIFFERENT VOLTAGE THAN THAT
MARKED ON THE UNIT. This will damage theunit.

The ground connection is an important safety featuredesigned to keep the chassis of electronic devices
such as the Vipre at ground potential. Unfortunately,
the presence of a third pin does not always indicatethat an outlet is properly grounded. You may use an
AC line tester to determine this. If the outlet is not
grounded, consult with a licensed electrician. WhenAC currents are suspected of being highly unstable in
VAC and Hz, a professional power conditioner should
be used.
To connect power to the Vipre, attach the female endof the AC power cord to the Vipre’s back panel andthe male end to a good quality, noise-free AC powersource of the proper rating.

Do not operate any electrical equipment with
ungrounded outlets. Plugging the Vipre into an
ungrounded outlet, or “lifting” the unit off
ground with a three-to-two wire adapter, cancreate a hazardous condition. Groove Tubes
cannot be responsible for problems caused byusing the Vipre or any associated equipmentwith improper AC wiring.

Vipre Reference Manual13connections • chapter 2

Avoiding ground loop noise
In today’s studio, where it seems every piece ofequipment has its own computer chip inside, there aremany opportunities for ground loop problems to occur.
These show up as hums, buzzes or sometimes radio
reception and can occur if a piece of equipment “sees”
two or more different paths to ground. While there aremethods to virtually eliminate ground loops and strayradio frequency interference, most of the professional
methods are expensive and involve installing aseparate power source just for the sound system.
Alternatively, here are some helpful hints thatprofessional studio installers use to keep those strayhums and buzzes to a minimum.

ÿC) Make sure that all of the audio cables are ingood working order. Cables with a detachedground wire will cause a very loud hum!!
D) Keep all cables as short as possible,
especially in unbalanced circuits.
If the basic experiments don’t uncover the source ofthe problem, consult your dealer or technician trainedin proper studio grounding techniques. In some cases,
a “star grounding” scheme must be used, with themixer at the center of the star providing the shield
ground on telescoping shields, which do NOT connect
to the chassis ground of other equipment in thesystem.

KEEP ALL ELECTRONICS OF THE SOUNDSYSTEM ON THE SAME AC ELECTRICAL
CIRCUIT.
Most stray hums and buzzes happen as a result ofdifferent parts of the sound system being plugged
into outlets of different AC circuits. If any noise
generating devices such as air conditioners,
refrigerators, neon lights, etc., are alreadyplugged into one of these circuits, you then have aperfect condition for stray buzzes. Since mostelectronic devices of a sound system don’t require
a lot of current (except for power amplifiers), it’susually safe to run a multi-outlet box or two from a
SINGLE wall outlet and plug in all of thecomponents of your system there.

ÿ

KEEP AUDIO WIRING AS FAR AWAY FROM ACWIRING AS POSSIBLE.
Many hums come from audio cabling being too
near AC wiring. If a hum occurs, try moving theaudio wiring around to see if the hum ceases ordiminishes. If it’s not possible to separate theaudio and AC wiring in some instances, makesure that the audio wires don’t run parallel to any
AC wire (they should only cross at right angles, if
possible).

ÿ

TO ELIMINATE HUM IF THE ABOVE HAS
FAILED:A) Disconnect the power from all outboard
devices and tape machines except for theVipre, the mixer and control room monitor
power amp.
B) Plug in each tape machine and outboard
effects device one at a time. If possible, flip
the polarity of the plug of each device (turn itaround in the socket) until the quietest
position is found.

14

Vipre Reference Manualchapter 2 • connections

Basic Connections
Output To a Mixing Console
Since the Vipre is a high-output preamplifier, its LINE
OUT (1/4” TRS Balanced +4dB) should be connected toa balanced line input of a console, not to themicrophone input whenever possible.
If the console's line input has an XLR input, you're inluck–simply connect a standard XLR-to-XLR cable fromthe Vipre's output to the line input of the console.

However, the line input of most modern consoles is athree-conductor TRS 1/4" phone jack, as shown below:

To maintain the benefit of fully-balanced operation, youwill need to get an XLR female to 1/4" male TRS
adapter or cable, like this:Sleeve (Ground)Pin 2 (+)

Pin 1 (Ground)

Tip (+)

Ring (-)

Pin 3 (-)
Important tip: Many XLR-to-1/4" adapters sold at electronics stores are NOT adapters, but transformers (and very
low quality transformers at that). Don't use these on the output of the Vipre—they're unnecessary andgenerally sound awful because they don't have the headroom to handle the Vipre's output. Get a hard-wired
adapter or cable from your professional audio dealer, or make one yourself from components.

Vipre Reference Manual15connections • chapter 2

If you must connect to a MIC IN jack:
Whenever possible, the output of the Vipre should beconnected to a balanced line input of a console,designed for a nominal input of +4 dBu (1.23 volts).
However, in some situations you may have no otherchoice than to connect to the XLR MIC IN of a console
or sound system. If this is the case, to avoid clippingof the console’s input:•

Set the console’s input gain (which may belabeled TRIM, ATT, GAIN, or MIC) to its lowest
setting.

Turn off any phantom power coming from theconsole if possible.
•

If there is an input pad switch (labeled PAD, ATT,
-20 DB, etc.), turn it on.

•

With the Vipre’s gain set for optimum, as
described in the first chapter, see if the console’s
input is clipping. If it is, you can either turn down
the Vipre’s GAIN controls, or insert a line
attenuator between the Vipre and the console.

•

Instead of using the Vipre's XLR LINE OUT jack,connect the Vipre's Lower Balanced 1/4" TRS
output to the unit. This cuts the output level of theVipre by 11.8 dB (the difference between a +4
dBu and –10 dBV nominal level).

Connecting directly to a +4 dBu recorder
Tip: For the cleanest possible recording, connect
the Vipre directly to the inputs of the recorderand avoid going through a mixing console
entirely while tracking.

Professional recorders typically feature balanced
3–pin XLR line-level balanced inputs. This allows you
to connect the LINE OUT of the Vipre directly to the
input of the track you plan to record on. The nominal
signal level of these units is +4 dBu (1.23 volts).
Balanced cables between the recorder and the Vipre
can be very long, if necessary, without adding noise.
Digital Recorders. Many Digital multitrack Recorders
feature a multipin ELCO or EDAC connector thatfeatures 8 balanced inputs and 8 balanced outputs ona single connector. To connect the Recorder directly
to the Vipre, obtain an ELCO-to- TRS multipair cable.
This will connect from the ELCO-type connector on
the Recorder on one end, fanning out to sixteen
connectors (labeled INPUT 1, OUTPUT 1 and so on)on the other end. Simply plug the 1/4" TRS Input on
the desired track of the Digital Recorder into theVipre's XLR output. Using a cable assembly with 1/4"
TRS plugs allows a choice of the +4dBm levelreferenced output jack on the Vipre, or the -10 dBV
output jack. Because the Vipre uses balanced
transformer outputs, an unbalanced plug may be usedwith either 1/4" output jack and will automaticallyconvert the jack from balanced to unbalanced
operation with no loss of signal level.
Note that some recorders with XLRs may not be truly
balanced, with pin 2 or 3 (depending on vintage) tied
to ground, which may cause a ground loop. Also,
depending on the characteristics of the deck, meteringlevels may not match between the deck and the Vipre.
Some multitracks have high/low level input switches;
follow the manufacturer’s instructions on setting theseproperly.

16

Vipre Reference Manualchapter 2 • connections

Connecting to an unbalanced device
Although it's not ideal, the Vipre may feed an
unbalanced input of a console or recorder and still
provide excellent results, particularly if the cable
lengths are short and the AC power system is notcomplicated.
The -10dBV 1/4" jack output of the Vipre can be used
for this purpose. If the receiving device has a 1/4"
input jack, obtain an 1/4"-to-1/4" (mono) cable oradapter. The nominal output of this output is –10 dBV(.316 volts), at the same time that the balanced
outputs on the XLR and upper 1/4" connectors are
putting out +4 dBu (1.23 volts).
If you want to use the 1/4" or XLR outputs:
It is possible to use the +4 dBm balanced 1/4" or XLR
output of the Vipre to feed an unbalanced device.
Note, however, that besides being balanced, thesedevices put out a hotter level that may overload the
input of the receiving device.
Use an adapter similar to the one shown on page 15.
The adapter may be an XLR-to-TRS or an XLR-to-1/4"
mono jack; in either case, pin 3 (-) must be connectedto the shield, preferably at the input to the device.
Alternatively, if there are noise problems, you may try
isolating the device by building or purchasing a
special cable that uses the balanced output on pins 2
and 3 of the Vipre to feed the + and – connectors of
the unbalanced receiver, leaving the ground floating(disconnected) at the receiver's end. (The shield muststill be connected at the Vipre to provide some path toground for interference.)

Vipre Reference Manual17connections • chapter 2

Connecting Microphones
The balanced female XLR connector on the rear panel
is intended for use by low-impedance microphones
needing preamplification. It is wired in the standard
configuration (Pin 1 shield, Pin 2 “hot”, Pin 3 “cold”)
and will receive 48-volt phantom power when the 48V
PHANTOM switch is on. (WARNING-DO NOT USE
PHANTOM
POWER
WITH
RIBBONMICROPHONES-SERIOUS DAMAGE MAY RESULT)
When the GAIN switches are both set to maximum,
the signal at the XLR jack will be amplified 75 dB.
When both GAINs are at minimum, it will be amplified
15 dB.

Warning about connecting line-level sources
to the XLR input:
Though the XLR IN may be used with a balanced linelevel source such as the output of a VCR, headroom
will be limited; even with the GAIN at minimum, theinput will clip when the input level rises above +10
dBu. For this reason, it’s better to connect balanced
line sources to the 1/4" LINE IN jack on the rear panel
using an XLR-to-1/4” TRS adapter or cable.

Never connect an electronic line input to the
XLR IN jack if phantom power will be turned
on. Doing this could damage the equipment
and the Vipre.

Connecting microphones with outboard
power supplies
Many high-quality microphones, such as the Groove
Tubes microphone systems, feature outboard power
supply boxes that connect directly to the microphoneusing a multipin cable. The power supply usually has
a standard 3-pin XLR output, which should beconnected to the XLR input of the Vipre using ashielded microphone cable.

Connecting Instruments
The Vipre has a 1/4" jack on the front panel labeled
INSTRUMENT INPUT. This is intended for inputs that"like" extremely high impedances, such as electricguitars and basses. Simply plug an unbalanced 1/4"
cable into the jack, and set the INPUT switch to
INSTRUMENT.
This jack has a nominal impedance of 470 kohms,
more than twice that of a typical line input on aconsole. This keeps the pickups of the instrumentfrom being loaded down and improves high frequency
response.
For that reason, it is not necessary to use a "directbox", either passive or active, between a guitar andthe Vipre. The Vipre is, itself, an extremely highquality direct box.
If the CLIP light goes on when the instrument isplayed even though the gains are turned down tominimum, set the INPUT switch to INSTRUMENT –20
dB. You may need to increase the GAIN controls of
the Vipre to compensate a little for this attenuation.

Connecting Line Inputs
On the rear panel is a 1/4" jack labeled "BALANCED
LINE INPUT". This jack is in parallel with the XLR
microphone input, but has a 20 dB lower sensitivity.
When the front panel gain controls are at +30 (5 dB
Gain Switch)and +1(1 dB Gain Switch), a +4 dBm
input to the LINE IN jack will be equivalent to unity
gain (+4 dBm output). If you need to connect theoutput of a line-level device such as a signal
processor, synthesizer, or recording device throughthe Vipre, connect it here.
The 1/4" BALANCED LINE IN jack does NOT connect
to the input transformer, but directly to the
BALANCED BRIDGE position of the INPUT switch.
Set the INPUT SWITCH to that position to hear signal
at the LINE IN jack. Disconnect any connection to the
MIC IN jack when using the LINE IN jack.

This type of microphone doesn't require phantom
power from the Vipre, so leave the 48V PHANTOM
switch on the front panel OFF.

18

Vipre Reference Manualchapter 3

About the Vipre
Why is the microphone preamplifier so important?
In today's era of high-resolution digital recording, thesonic characteristics of the microphone preamplifier
have become crucial in determining the overall soundquality. Most of the gain in the recording signal pathis provided by the mic preamp, and accordingly the
dynamic range of the recording is set by the noise
floor of the preamp. The wider availability of largediaphragm condenser microphones, coupled with thescarcity of vintage equipment properly designed foruse with those microphones, has been another trendthat focused attention on the preamp. Many recording
studios own large assortments of mics and preamps
in order to be better prepared for the needs of various
artists and groups. And for good reason: the more
tonal variations a facility can provide, the more diverseand desirable their clientele.
The choice of
microphone and preamp are primarily responsible forthese variations.

the Vipre has NO semiconductors, transistors,
integrated circuit chips, or electrolytic capacitors
anywhere in the signal path.

The 20-bit and 24-bit digital recorders now commonly
available allow engineers to capture subtleties thatused to be lost in tape noise or covered up by
irregular frequency response. Early complaints aboutthe "harshness of digital" have been recognized forwhat they are: complaints about inferior microphonepreamps that are only now being revealed by theaccuracy of digital recording. The engineers at
Groove set out to build an authentic, no-compromise
mic preamp that utilizes the best of vintage technology
to fulfill the potential of today's digital technology.
They have achieved that goal with the Vipre (Variable
Impedance Preamp), an all-tube variable impedance
microphone preamplifier with selectable rise time andVU meter range. It's a premium single-channel device
designed for critical recording applications demanding
the ultimate in mic preamplification. It features
extremely wide frequency response, low inter-stage
feedback, very high gain, enormous dynamic range,and graceful overload characteristics.
Each component in the signal path was carefully
chosen for its sonic purity. When components were
not available "off the shelf", they were custommanufactured to Groove Tubes' exacting
specifications. Even the phenolic knobs on the front
panel were custom-molded. But as you will read in
the rest of this chapter, the attention to detail goes
well beyond the appearance of the front panel. Most
importantly, unlike other "tube preamps" that feature asingle vacuum tube in a largely transistorized circuit,

19

Vipre Reference

about the Vipre • chapter 3

The Input Section
About the Input Transformer
The Vipre features an exclusive input transformer
custom-made in California to the highest industry
standards. A key feature is that it's a multitaptransformer, allowing a selection from four different
load impedances for a microphone. (Some other"variable impedance" products on the market simply
switch in additional resistors, which actually makes
them "variable resistance"–—a subtle but potentiallyaudible difference because of the insertion losses that
resistors cause.)
Benefits of transformers, generally
While modern solid-state input circuitry can deliver
excellent results at very low cost, input transformers
deliver several significant advantages:•

Greater CMRR (common mode rejection ratio):
this means that noise from the cable that appears
on both the + and – leads simultaneously is more
likely to be rejected. Solid-state differentiallybalanced circuits may have a good CMRR spec at
1 kHz, but often aren't as good at otherfrequencies.

•

More resistance to RF (radio frequency
interference): the windings of a transformer,
being naturally inductive, reject ultra-high radio
frequencies without requiring a capacitor in theaudio path as electronically-balanced circuits do.

•

Lower impedance: it is easier to build a lowimpedance input transformer than a lowimpedance transistor input (which is one of thereasons the industry went to bridging impedancesin the last few decades).

•A transformer is fully floating, isolating the circuitfrom DC offsets, and to a certain extent fromsurges and stray signals. You could think of it asa magnetic link that keeps the circuits free frommutual contamination.

For these and other reasons, the highest-level audio
consoles, especially those used by touring soundcompanies, have always used input transformers. But
good quality input transformers are expensive, andcheap input transformers used in affordable consoles
several decades ago gave transformers a bad namewith some engineers due to their irregular frequency
response and distortion.
The input transformer used in the Vipre is a totallydifferent story. Special care is taken to shield thetransformer windings from noise: a high-quality
double Mu-metal can surrounds the transformer. The
transformer itself is a "humbucking" type, withspecially-wound oppositional coils that cancel out

20

induced noise from the environment or nearby
circuitry.
Impedance: Matching vs. bridging
In early audio devices, circuits were designed tomaximize power transfer between units. This meantthat input and output impedances should be matched,e.g. a 150-ohm source would be terminated by a 150ohm load. This impedance matching maximized thecurrent in the load, at a time when every bit of current
was necessary due to primitive amplification methods.
One obvious down side to impedance matching wasthat a single source couldn't easily feed several inputs
at once.
After the advent of high-impedance solid-state
circuitry, the era of maximum power transfer was overand the focus shifted to conveying signals throughvoltage, not current. The microphone or other source
generates a varying voltage, but very little current isdrawn in the circuit because the load it "sees" is sohigh that it may as well be connected to nothing at all.
Most modern audio equipment is designed to present
a very high impedance load to the source. The typicalinput impedance of a load is designed to be 10 to 20
times the output impedance of a typical source. Thisis called a bridging input. (For a more in-depth
explanation of the importance of impedance, see page31.)
But what is the actual impedance of the microphone
you're plugging in? And what kind of circuit was thatmicrophone designed to "see" for optimum
performance? Particularly in the case of vintage
condenser and ribbon microphones, the original
design usually were set up for impedance matching ,not bridging. When these microphones are plugged
into the MIC IN jacks of today's solid-state mic
preamps or consoles, they're seeing a very different
load than they were designed for. When they'replugged into the input of the Vipre and the impedanceis set to lower values, they exhibit the more open
sound heard on classic recordings. Yet, othermicrophones may need to see a higher, bridging load
for best performance. In any case, altering the load
against which the microphone has to pushfundamentally alters the tone and character of theoutput signal. The Vipre gives you the best of bothworlds. A key to this flexibility is the input transformer,
which is the first component the microphone "sees"
when the INPUT SELECT switch is in the XFMR
positions.

What’s the best input impedance?
There is no best one. Like EQ or effects, the “right”
setting is the one that sounds best in a particularsituation. However, it might help you to choose a
Vipre Reference Manualchapter 3 • about the Vipre
setting if you understand what’s going onelectronically. The choice of impedance between
300W, 600W, 1200W and 2400W on the front panel will
make slight variations in equalization and residual
distortion, depending upon the individual mic.
For example, an early broadcast microphone like the
RCA 77 will sound smoother when terminated at
300W. The tonal characteristics change, and thesound seems to "bloom" in a way most people havenever heard. The equalization changes slightly as
well, with the entire spectrum from about 100 Hz to 15
kHz taking on a very slight tilt, typically around –1 dB
at the low end, and around +1 dB at the upper
registers. This is very slight when looking at individual
frequencies, but the cumulative effect over the whole
spectrum is unmistakable. This kind of variation
would be almost impossible to recreate with any kindof equalizer, unless the principle of an simple,
uncluttered signal path is abandoned altogether.
Tip: Try matching the era with the impedance:
Generally speaking, the older the microphone,
the lower the impedance. Microphones fromthe 1940s and '50s can handle 300W quite
well. Mics from the '60s tend to "like" 1200W
while those from the '70s and '80s prefer
2400W. New mics, since they were designed
in an era when almost all consoles have highimpedance bridging inputs, will sound the way
the designers intended when the Vipre's
INPUT is in BALANCED BRIDGE mode. But,
this is just a starting point. The IMPEDANCESELECTOR switch is an "audio timemachine", and can make new mics sound likevintage mics. Remember: you can't hurt amicrophone by setting the input impedance
incorrectly.

Vipre Reference ManualFrequently-Asked Questions
If I set the impedance too low, will it hurt the
microphone?
No. Even microphones with their own power supplies
are protected against a dead short.
Is there a special setting for ribbon microphones?
Vintage ribbon mics like the RCA 77 were designed inan era when impedances were supposed to bematched to give maximum power transfer. Thesemics are particularly suited for the Vipre’s 300-ohm
setting. (Note: DO NOT USE PHANTOM POWER
WITH RIBBON MICROPHONES. SERIOUS
DAMAGE CAN RESULT)
But modern ribbon mics (like those from Beyer andRoyer) tend to be designed for higher impedances,although you can try them at any setting.
How come it sounds so different in bridged mode?
Because it’s bypassing the transformer, with its many
complex impedance and inductance characteristics,
and using a purely electronic input with a much higher
impedance.
Aren’t electronic inputs cleaner than transformer
inputs?
Input transformers got a bum rap several decadesago, mostly because of the sound of the cheap
versions used in popular consoles. But a high-quality,
custom-wound transformer such as that used in theVipre doesn’t have that kind of degradation. In
addition, the common-mode rejection of noise of atransformer, especially at high frequencies, is superior
to that of an electronic circuit.
Having said that, a transformer does have certain
nonlinearities that may not be suited to certain
applications. That’s why the Vipre gives you a choice.
The BALANCED BRIDGE position, the input
transformer is bypassed, giving you a modern
electronically-balanced, 12 kW impedance input.

21

about the Vipre • chapter 3

About Vacuum Tubes
TheoryTubes are the original devices for amplifying signals.
Although solid-state (transistor/ semiconductor)
circuitry has replaced them in general use, there arestill applications where vacuum tubes (or “valves”, inthe UK) demonstrate their superior characteristics.
Only a few of the mic preamplifiers on the market
today are truly all-tube from input to output; most ofthem are "also-tube" circuits with significant parts ofthe signal path consisting of semiconductors. Cost
constraints almost invariably lead to hybridized
designs and sonic compromise.
The engineers at Groove Tubes, drawing on theiryears of experience as providers of high-quality
vacuum tubes, set out to build a state-of-the-art true
tube preamp. The result is both uncomplicated anduncompromising, utilizing a symmetrically arranged
mirror-image circuit configuration that is a fully
differential Class A push-pull design, balanced andfloated throughout the entire signal path.

Impedance of tubes
An important fact about tube circuitry is that its
impedance can be much lower than most solid-state
circuitry. In the business of amplifying a microphone,this is a distinct advantage. While the input
transformer provides the load impedance seen by the
microphone (if switched to that position), the low
impedance of the following stages helps maintain theVipre's inherently simple circuit philosophy andperformance while significantly increasing signal-tonoise ratio and dynamic range. This approach both
reduces power supply induced noise and lowers
distortion. The result is a preamplifier with a 7 Hz to
100 kHz frequency range, and the ability to convey
great detail while remaining nearly free of unwanted
sonic imprints.

the entire swing of the signal, positive and negative,
goes through a single device. By comparison, othertypes of amplifiers such as Class B and Class AB
switch the positive and negative halves of the
waveform between different drivers (in other words,
one tube goes only positive, and one tube goes only
negative). Class B designs are more efficient at using
power, but they are inherently less linear. Since theVipre's main requirement is to amplify the signal as
accurately as possible, Class A was the only way to
go. This led to the requirement for a massive hightension power supply, with over 60 Joules of energy
storage. For a device that only needs to put out 1
watt of power, this may seem high, but it guarantees
that the Vipre can follow the input waveform wherever
it may lead.
The term "fully differential" may need some
explanation as well. In essence, it means that from
input to output, there are two identical signal paths,
each of opposite polarity from the other. While mostengineers understand the benefits of balanced
connections between separate pieces of equipment,
some may not be aware that in most devices(especially mixing consoles) the signal becomes
unbalanced right after the input circuit and stays
unbalanced until just before the output circuit. In
contrast, the Vipre is balanced all through its signal
path, providing common-mode rejection of noise ininternal circuitry as well as externally.

The Vipre employs eight different tubes, seven of
those tubes are rubber shock-mounted on the main
PCB to avoid transmission of mechanical noise to thecircuit:•

6922 (6DJ8)(4): preamplification, rise time circuitry•

12AT7 (1): output driver•

GT6205 (1): Instrument Input preamp tube•

6AQ5 (2): Class A push/pull output

About Class A circuitry
The Vipre uses fully differential, push-pull Class A
topology throughout. The term "Class A" refers to aparticular method of utilizing amplification devices(tubes or transistors) in an amplifier. Class A designs
are the most linear (i.e., the lowest distortion) because

22

Vipre Reference Manualchapter 3 • about the Vipre

Care and feeding of vacuum tubes

Tube Replacements

Unlike the tubes found in guitar amplifiers, the tubes inthe Vipre should not “burn out” very often in normal
use. Nor will their sonic characteristics change
dramatically over time. This is because the tubes are
not being operated at the extremely high plate
voltages and currents typical of that required for a
100-watt amplifier connected to a loudspeaker. Whenthey do fail in normal use, it is usually a gradualprocess rather than a sudden stop. The gain will be
noticeably lower, or the noise floor will rise.

The tubes used in the Vipre are special, he cream of
the crop. They have each been individually tested by
Groove Tubes before being used in your Vipre, andfurther burned in for many hours before we shipped it
to you. While replacements are available fromelectronics supply stores, for the highest quality
replacement tubes please contact Groove Tubes.
This will assure you of receiving a premium-selected
tube that will give you the same performance as theoriginal.

It is also possible for tubes to experience filament
failure. Vacuum tubes have small glowing heating
filaments inside them similar to those in light bulbs,
except their job is to make heat instead of light. Whenthey are hot, they are more susceptible to physicalstress.

J

Avoid shaking the Vipre when power is turned
on, even in standby mode. If you’re going tomove the Vipre, let the unit cool off for fiveminutes before moving it. A hot tube filamentthat is shaken is more likely to fail.

There are four Groove Tubes 6922 (aka: 6DJ8or
ECC88) in the first two stages of Vipre. The
instrument input Gains stage is powered by aGroove Tubes 6205. The output section uses
a single Groove Tubes selected 12AT7 todrive a Matched Pair of GT6005's (A.K.A.
6AQ5)
The 6922/6DJ8 tubes in your Vipre can be
replaced with the consumer-grade 6DJ8, but it
is possible that sonic performance will beslightly degraded, and tube life will not be as
long.

Field replacement of tubes should only be performedby qualified electronic service technicians. For more
information, see page 34.

Vipre Reference Manual

23

about the Vipre • chapter 3

The VU Meter
VU (for Volume Unit) meters are one of the oldest,
and perhaps still the best, tools for displaying the levelof an audio signal. The meter for the Vipre wascustom-built to match the characteristics of classic
meters, right down to the ivory color of the
background. Compared to less-expensive LED
meters, the VU meter by its nature averages out thepeaks to display the RMS (root-mean-square) value ofa signal, which is what most people perceive as
loudness. A VU meter's ballistics are intentionallydesigned to respond to a newly-applied signal within
3/10ths of a second.

Clip LEDs
However, while the VU meter accurately models what
the human ear perceives as level, it does not respondquickly enough to show very short peaks which candistort the signal, particularly on digital devices. For
this reason, the Vipre supplements the VU meter with
two SIGNAL LEDs (“-3 dB” and “CLIP”) located underthe meter. These respond instantly to any audio
signal approaching the maximum output level of theVipre.

VU Meter Range Control
Another limitation of the classic VU meter is its 23 dB
range. If you're recording audio with a very low level,
the meter won't move at all at its standard setting.
Similarly, if you're sending very high-level signals (to adigital recorder that peaks at +19 dBu, for example),the VU meter will be "pegged" most of the time.
The Vipre overcomes this by a separate meter drivercircuit and the VU METER RANGE switch. Thischanges the voltage reference of the meter as follows:

0 VU: 0 VU = +4 dBm output, range -20 to +3 dB(–16 dBm to +7 dBm)
EXPAND: 0 VU = +4 dBm, range –60 to +9 dB+10 dB: 0 VU = +10 dBm, range –10 to +13 dBm+20 dB: 0 VU = +20 dBm, range –0 to +23 dBm+30 dB: 0 VU = +30 dBm, range +10 to +33 dBm

Note that these are still average values, however. If
the VU RANGE switch is set to +20, and the meter isreading around "0", there still may be peaks of 10–12
dB that will not be shown on the meter. Those will becaught by the SIGNAL LEDs.

24

Vipre Reference Manualchapter 3 • about the Vipre

Gain Controls
Proper setting of microphone gain is one of the most
crucial aspects of recording. If there's not enoughgain at the preamp and you try to make up for it laterby adding gain at the console, you will be amplifying
noise. If there's too much gain, the sudden transients
common to many types of music will drive the system
into distortion. The dynamic range and clarity of theentire recording are determined at this critical stage.
Yet, most mixing consoles relegate this important task
to a single carbon-track potentiometer covering a 40
to 60 dB range. Worse still, in most cases the taper ofthe control puts most of the gain in a few degrees ofrotation at the very top of the control. On many
consoles, the difference between 40 dB and 50 dB ofgain (the most common range for many applications)
may be covered in as little as 1/8th of a turn. This
makes setting the gain correctly almost impossible.
And if you want to recreate the exact gain structure ata later time after the control has been moved, you'reout of luck.
The Vipre's GAIN controls, prominently located at thecenter of the front panel surrounding the VU meterand signal LEDs, are a vast improvement on
potentiometer gain controls. They are ceramic deckrotary switches attached to individual precisionresistors. This discrete-step attenuation provides
repeatability, economy, ultra-wide control range andsuperior accuracy. The 5 dB control sets the gainfrom 20 to 70 dB in 5 dB steps, and the 1 dB control
sets the gain ±5 dB in 1 dB steps. If you see on themeter of a digital recorder that you have exactly 4 dBof headroom left, you can add exactly 4 dB of gain at
the Vipre before the next take if you wish.
Besides their usefulness in operation, the GAIN
controls add to the sonic integrity of the Vipre.
Continuous potentiometers in a balanced circuit must
be of the double-pot type, and precisely matching
resistances between the two carbon tracks is
impossible. The Vipre's step attenuators are built tohave greater than 1% interstage matching at any andall chosen settings, maintaining a fully floated andbalanced signal path throughout the entire circuit.
Extra effort has been expended to frequencycompensate the 5 dB coarse gain attenuator,
eliminating the typical bandwidth-robbing effects ofparasitic circuit and wiring capacitance.
While most consoles have 60 dB of mic preamp gainat best, the Vipre boasts an impressive 75 dB ofavailable gain. This extra 15 dB of gain is particularly
valuable when miking classical instruments from a
distance.

Vipre Reference Manual

GAIN Setting Procedures
The best method for setting the gain will varydepending on what the output of the Vipre isconnected to, but here are some general guidelines.
See page 8 for the basic gain setting procedure.

Start low and work up
The Vipre has an incredible amount of potential output
gain, much more than most mic preamps. For thisreason, use caution with the GAIN control. Start withthe 5 dB control at its minimum setting, and increase it
step by step until the level is correct as shown on themeter of the receiving device (mixer, recorder etc.).

Check the sensitivity of the receiving device
Digital recorders
Since most professional digital recorders don’t have
input level controls, if you're plugging the output of theVipre directly into them the GAIN settings must be set
while watching the recorder’s meter, not the Vipre’s.
For example, some popular digital recorders arecalibrated for 15 dB of headroom over a nominal +4
dBu input, which means the maximum signal therecorder can accept at its balanced input connector
without clipping is +19 dBu, about 11 dB less than the
maximum output of the Vipre. Most other digitalrecording systems have similar amounts of headroom,from 12 to 18 dB. In this case, the CLIP and –3 dB
SIGNAL LEDs of the Vipre should obviously nevercome on. Set the Vipre's GAIN controls while
watching the digital recorder's meter, adjusting to get
the hottest level possible while never exceeding 0
dBFS (MAX), perhaps allowing several dB of extra
headroom to allow for unexpected transients. Whenusing digital recorders with -10dBv "0" reference use
the -10dBv Referenced Output 1/4" TRS jack on theVipre.
Mixer/signal processor
If the output of the Vipre is feeding a mixer or othersignal processor, your options are more varied. A
mixer with its own input trim controls or attenuatorswitches may be set up in different ways dependingon the effect desired.
For the best signal-to-noise ratio, or to intentionally
overdrive the Vipre for a particular effect, you willneed to decrease the input sensitivity of the mixer toavoid clipping the input section of the mixer.
For maximum dynamic range, set the mixer's input
trim to its lowest level, and increase the GAIN controlsof the Vipre until the Vipre's –3 dB and/or CLIP LEDs
barely flash on the loudest peaks. Check to see if themixer's input meter is clipping; if so, you'll have to25

about the Vipre • chapter 3
back off the GAIN. If not, you may raise the mixer's
input gain to get the desired recording level, in mostcases with the channel fader and output faders set to
the nominal 0 dB position.

If the Vipre's output is too loud:In cases where the mixer or signal processor's input
doesn't have enough attenuation to handle the Vipre's
output at maximum, you may try the following:

26•

Insert a passive attenuator between the Vipre andthe input of the device, or•

Use the lower level -10dBv balanced 1/4” LINEOUT of the Vipre instead of the XLR output. This
output has approximately 12 dB less level.

Overload characteristic
The soft-clipping characteristic of an all-Class A tube
design leads to a much gentler transition to clipping
than that of a solid-state circuit. The onset of clipping
is slow and its characteristics are soft. Low-feedback
amp stages keep clipping recovery times short, as
there is very little loss-of-feedback overdrive induced
by soft clipping at any given stage.
Furthermore, the clipping maintains its moderate
behavior due to the fact that all gain stages operate inpush-pull Class A mode. The sum of the bias andaudio currents that flow through each push-pull stage
is held constant at all times. None of the audio
currents can escape, meaning the balanced design isfree from undesirable bilateral interaction with otherstages or the power supply.

Vipre Reference Manualchapter 3 • about the Vipre

Rise Time
A voltage cannot instantly change from nothing tosomething, or from 0 volts to 2 volts. There is always
some transition time. Technically, this is called theslew rate, measured in volts per microsecond. This isoften shown by how “square” a square wave is on an
oscilloscope. Since slew rate or rise time has arelationship to extended high frequency response andtransient response, the faster a circuit can go fromone voltage to another one, the better...or so the logic
has been.
In fact, classic circuitry used to process audio in
decades past often did not have the fast rise times ofmodern integrated circuits, and that was part of its
sound. Digital recorders are sometimes blamed forhaving an "edgy" sound, when in fact all they are
doing is accurately recording a very fast-risingpreamp.

The Output Transformer
Even though the Vipre is a line-level device (1 wattmaximum output), its output transformer iscomparable in size to those used in 30-watt guitar
amplifiers. This overcapacity ensures that thenonlinearities that plague less-expensive transformers
are diminished, while the classic sound and otherbenefits of transformer coupling (already covered on
page 20) are gained.

If the output sees phantom power:
The transformer output by nature is balanced, so acommon 48 volt phantom voltage received on eachside (pin 2 and 3) will not harm the Vipre. However,avoid plugging the LINE OUT of the Vipre into a MIC
IN whose phantom power is on. The output should be
plugged into a line-level input, in any case.

The Vipre features special tube circuitry that allows
the user to adjust the rise time from slow to fast, infive steps. The FAST setting corresponds to the slew
rates of modern preamplifiers (6 volts per
microsecond), while the SLOW setting is more typicalof vintage equipment (.75 volts per microsecond).
The effect, especially on a large-diaphragm vocal
microphone, is like that of a time machine—the slower
the rise time, the more it will sound like 1950.
Another way of looking at it is that FAST preserves
the full percussive and forward qualities of the source,
while SLOW helps tame overly aggressive soundqualities and "rounds out" or "smoothes" the material.
As with the IMPEDANCE SELECTOR switch, there isno "best" setting for the RISE TIME control. You
simply experiment to find the right setting for aparticular sound. Rise Time is a very subtle effect, butwith critical material the settings can significantly
affect the tonal characteristics of the recording.

Vipre Reference Manual27

about the Vipre • chapter 3

Mute Switch
The MUTE switch is designed to cut off all output
signal from the Vipre when you're changing
microphones, making connections, or drasticallychanging settings. The output is muted (off) when theyellow light is ON. Use MUTE to avoid potentiallydamaging pops and clicks in the system.

ÿTurn MUTE ON when:•

you're plugging in a microphone•

the unit is in STANDBY mode•

you’re switching to a different input source(INSTRUMENT INPUT) and aren’t sure of the
level

•

you need to set the GAIN before the recorder ormixer is ready•when the drummer trips over a mic cable sending
your best overhead drum mics crashing into thecymbols and beyond.

•when in doubt….
NOTE: The MUTE switch is connected to asealed multipole double-throw mechanicalrelay that switches the signal on and off
between the output transformer and the LINE
OUT jacks.

StandbyThe STANDBY switch turns off the plate voltage (alsocalled “B+”) to the amplifier tubes, but leaves the tube
filaments on. There are several reasons for a standby
switch in tube gear:
1. It extends tube life. If you allow the filaments towarm up the tube cathodes before the B+ voltage
is applied across the tube, the cathodes will not
be “stripped” of molecules before the cathode is
fully charged.
2. It lowers the unit's power consumption when it's
temporarily not being used, and
3. It saves you from having to wait for the tubes towarm up when you want to use the Vipre again.

ÿTurn STANDBY ON:•

before turning the POWER switch on; leave theunit in STANDBY for at least 30 seconds after
power has been turned on•a few seconds before turning the POWER switch
off (this is less important than during power-up,
but it’s still a good practice)•whenever the Vipre is not going to be used for ashort period, up to an hour or two

Do not leave the Vipre unattended for long
periods of time with the POWER switch on,even in STANDBY mode. Turn off the
POWER switch whenever you leave the studioat the end of the day.

28

Vipre Reference Manualchapter 3 • about the Vipre

Block Diagram

Vipre Reference Manual

29

about the Vipre • chapter 330

Vipre Reference Manualchapter 4

Microphone & Preamp
TheoryAbout Impedance
The importance of impedance
Understanding what we mean by "variable impedance
preamp" is crucial to getting the most from your Vipre.
A quick review of some basic electronic theory, often
taken for granted in today's studio, may help.
A microphone is essentially a small electrical generator
trying to push voltage to its output. The input
impedance of the microphone preamp is what it’s
pushing against. When you think of it this way, it’s
clear that the input impedance of a preamp can have asignificant effect on the sonic characteristics of a
microphone.
Let's look at three different situations between thesource and its load. When sound strikes the diaphragmof a microphone, it translates that mechanical energy
into electrical energy. In a dynamic microphone, a coilof fine wire is pushed back and forth in a magnetic field.
Similarly, in an AC generator, several coils of wire arerotated around through magnetic fields, and the result
is also a voltage potential across the output. In aschematic diagram, the symbol for a generator and its
outputs is this:This is a source of voltage, but it is not yet a circuit. In
audio terms, this "unplugged microphone" isunterminated. Note that even an unplugged dynamic
microphone still generates a voltage when it "hears"
audio. But since it's not in a circuit, it's not generating acurrent. To be useful, a voltage source must be
terminated in a load, which is symbolized by the signal
for a resistor like this:

31

Rs

RL

where RL is the impedance of the load in ohms.
But remember those coils of wire inside thegenerator/microphone? They also have an
impedance. This source impedance is a crucial
factor in the design of the circuit. As current flows
in a circle from the source to the load and backagain, it expends power; some in the load, andsome in the source. The symbol Rs above
represents the source impedance in ohms. And if
the goal is to get maximum transfer of power, Rs
should equal RL.
Consider what would happen if, instead of loading
the generator/microphone with a resistor, we
simply placed a straight wire across the outputs,
shorting it out:

When the load impedance is zero, all the power
has to be expended in the source itself. If it wasa generator, this would obviously cause
overheating and failure. The consequences ofshorting out a microphone aren't so drastic, but
between the first example of an unterminatedsource, and the last example of a source that's
entirely shorted out, you can see the simple but
crucial way the load and source interact.
In the case of the Vipre, which is the load that the
microphone or other input source "sees", a great
deal of care was taken to allow for the many
subtle variations between different sources, byallowing the user to set a specific load impedance
that the mic will see. As explained earlier in thismanual, the need for different impedances is a
result of the history of the development of theaudio industry, as the circuitry and capabilities ofpreamplifiers and consoles changed. Microphone
Vipre Referencemic preamp theory • chapter 4
designers usually (although not always) manufactured
and tested their microphones using the circuitry of theperiod. Most people thought that a higher load
impedance than an original design would have noeffect, or even improve performance. But the slight “tilt”
in frequency response when a microphone seesdifferent impedances, coupled with other factors likedistortion and small damping effects can have subtle
effects that no other device in the studio can truly
replicate.

About NoiseOne of the primary questions people have about a mic
preamp is how quiet it is. Any noise that's generated in
the preamp will persist through the rest of the chain,and can't be eliminated. But when you crank up thegain of any mic preamp and hear hiss, it's usually amistake to think that the noise is coming from thepreamp. In most cases, the preamp is merely
amplifying noise that's already there. And frankly, since
the Vipre has 15 to 25 dB more gain than otherpreamps you may have used, this noise will be louder
when you crank the gain up. Simply setting twocompeting preamps side-by-side will lead to misleading
results unless you control the test very carefully. So,
where does the noise come from?

Thermal Noise32

Microphone Self-Noise
Beyond this thermal input noise, the picturechanges dramatically when you plug in an actual
microphone.
Even the best microphones
generate noise signals considerably above thistheoretical thermal minimum, called self-noise.
Since the microphone has to be tested in an
absolutely silent space for this (with 0 dB SPL or
better), the measurement is very difficult to make.
Typical figures are in the 9 to 14 dB range above
the thermal noise floor, which means that in mostcases, the microphone generates more noise
than the preamp does.

Acoustic Noise
On top of all of this, the room the microphone isplaced in is almost always noisier than either the
mic or the preamp. Air conditioning fans, traffic
rumbling nearby, and audience noises usually
make up the true noise floor of a typical live
recording. Even in recording studios, very few
facilities are soundproofed well enough to haveambient sound pressure levels much below 40 dB
SPL. Audio control rooms, now with computer
cooling fans, hard drives and other motorized
equipment, often have an ambient SPL (soundpressure level) of 50 dB or higher.

Thermal noise is always present in audio circuitry.
Molecules rubbing against each other in any piece ofwire produce random electronic signals. In a resistor of
150 ohms at 70 degrees Fahrenheit, these random
voltages are equivalent to –132.88 dBu. This, for allpractical purposes, is the noise floor of the audio
universe. The only way to get equipment that has nothermal noise is to freeze the circuit to absolute zero(–459° F.)...an expensive proposition.

For this reason, the most effective way to improve
the signal-to-noise ratio of a recording is to movethe microphone closer to the source. A loudsinger can generate 100 dB at 3", which in a 40
dB SPL environment gives a dynamic range of 60
dB…still notably less than the range of 16-bit
digital recording, but a vast improvement overwhat happens if the singer is ten feet from themicrophone.

The Equivalent Input Noise (EIN) spec of a microphonepreamp is determined by plugging in a pure resistive
load (or in some cases, shorting out the input), cranking
up the gain to its maximum, measuring the noisevoltage, and subtracting the gain. The EIN of the Vipreis –129 dBu, which is only 3.88 dB above thetheoretical minimum. However, even this small figure,when you amplify it by the 75 dB gain available in theVipre, becomes a signal of –54 dBu which may be
audible in the control room, depending on masking byother factors.

Since classical music is usually recorded using
microphones placed at a distance from thesource, careful attention has to be paid tominimizing noise from all parts of the system.
Setting gain to optimize the performance of thepreamp, selecting a microphone with low selfnoise, and recording in a room that has been
carefully soundproofed should all be considered.
Only with all three will you get the quietest
recording possible.

Vipre Reference Manualchapter 5

Troubleshooting
Troubleshooting Index
If you experience problems while operating your Vipre, please use the following table to locate possible causes andsolutions before contacting Groove Tubes Product Support for assistance.
Symptom
No audio from outputs

Cause
No input audio

Solution
Test with a known good
input.
Bad cables
Replace the cables.
Destination is turned Check the connections anddown
the level of the mixer or
amp that the Vipre isconnected to.
MUTEswitcho r Turn the switch on.
STANDBY switch is on.
Power is not connected
Time for a coffee break.
Buzz from outputs
Cables are crossing a Make sure that the Vipre
power cableand its audio cables are
kept away from power
cables, other powertransformers and wall
warts.
Bad cables
Replace the cable with anew, high-quality cable.
Problem with the source Try bypassing the Vipre, byconnecting the input cables
to the output cables orusing another preamp, andsee if the problem remains.
Power LED won't go on.
Blown fuse
Correct any problem that
may have caused the fuse
to blow, and replace thefuse with the proper type.
Lights are low, erratic Voltage set to 240 V on Turn off unit and reset theoperation
rear panel when AC is voltage switch to 120 volts.
120-volt
Fuse blows immediately on Voltage set to 120 V on Turn off unit, replace thepower-uprear panel where AC is fuse, reset the voltage
240-volt
switch to 240 V
Unit is becoming noisy, or Tubes are wearing out Replace the tubes withgain is less(typically after several high-quality selected pairs
years of use)from Groove Tubes
AC humGround loop
Use
onlybalancedconnections in the studioPlace all equipment in thestudio on a common
ground (see p. 14)

Care and Maintenance
Cleaning
Disconnect the AC cord, then use a damp cloth to clean
the Vipre’s metal and plastic surfaces. For heavy dirt,
use a non-abrasive household cleaner such as Formula

33

409™ or Fantastik™. DO NOT SPRAY THE
CLEANER DIRECTLY ONTO THE FRONT OF
THE UNIT AS IT MAY DESTROY THE
LUBRICANTS USED IN THE SWITCHES AND
Vipre Referencetroubleshooting • chapter 5
CONTROLS! Spray onto a cloth, then use cloth toclean the unit.

How to replace tubes

Refer All Servicing to Groove Tubes

While tubes will rarely if ever need replacement, it
is possible to replace them in the field ifnecessary.

We believe that the Vipre is one of the best microphonepreamplifiers that can be made using current
technology, and should provide years of trouble-freeuse. However, should problems occur, DO NOT
attempt to service the unit yourself unless you havetraining and experience. Service on this product shouldbe performed only by qualified technicians. NO USERSERVICEABLE PARTS INSIDE.

The unit must be totally disconnected from all
sources of AC power before the unit is opened.
HAZARDOUS VOLTAGES EXIST WITHIN THE
CHASSIS THAT MAY BE FATAL.
The
following instructions are intended only for
professionals with experience and training inservicing electronic equipment. IF YOU DON'T
KNOW WHAT YOU'RE DOING, DO NOTATTEMPT TO REPLACE TUBES YOURSELF.
HAVE THE UNIT PROFESSIONALLYSERVICED!

Remove the cover
INSERT STEP-BY-STEP INSTRUCTIONS HERE

Test the tubes
Familiarize yourself with the location of the tubes
on the circuit card suspended in the center of theVipre. Then carefully remove the tubes, noting
which tube type goes to which socket. Tube
types are written on the circuit board, but it ispossible that the designation on the tube itself
may have burned off. (Note: one tube, theminiature 6205, is soldered in place; it should
only be replaced if the INSTRUMENT INPUT is
noticeably noisy or inoperative.)
Test the tubes on a standard testing device,setting the parameters carefully before applying
voltage. If a defective tube is found, replace it(and its pair, if applicable) with a new, militaryspecification replacement. Contact Groove
Tubes for hand-selected and tested equivalents.
Reassemble the unit
Replace the tubes in their sockets and carefully
reassemble the unit. Make sure nothing has
fallen into the unit which could cause a short!

34

Vipre Reference Manualchapter 4 • troubleshooting

Obtaining Repair Service
Before contacting Groove Tubes, check over all yourconnections, and make sure you’ve read the manual.
Customers in the USA and Canada: If the problem
persists, call Groove Tubes 818-361-4500 and request
the Customer Service department. Make sure you
have the unit’s serial number with you. Talk the
problem over with one of our technicians; if necessary,
you will be given a return order (RO) number andinstructions on how to return the unit. All units must be
shipped prepaid and COD shipments will not be
accepted.
For prompt service, indicate the RO number on the
shipping label. Units without an RO will not be
accepted. If you do not have the original packing, ship
the unit in a sturdy carton, with shock-absorbing
materials such as Styrofoam pellets (the kind without
CFCs, please) or “bubble-pack” surrounding the unit.
Shipping damage caused by inadequate packing is notcovered by the Groove Tubes warranty.

Customers outside the USA and Canada:
Contact your local Groove Tubes distributor for
any warranty assistance. The Groove Tubes
Limited Warranty applies only to products sold tousers in the USA and Canada. Customers
outside of the USA and Canada are not coveredby this Limited Warranty and may or may not becovered by an independent distributor warranty inthe country of sale. Do not return products to thefactory unless you have been given specificinstructions to do so.
Internet Address: Important information andadvice is available on our web site:
WEB SITE: http://www.groovetubes.com
Email may be addressed to:
SALES: sales@groovetubes.com
TECHNICAL: lab@groovetubes.com

Tape a note to the top of the unit describing the
problem, include your name and a phone number
where Groove Tubes can contact you if necessary, as
well as instructions on where you want the productreturned. Groove Tubes will pay for standard one-way
shipping back to you on any repair covered under theterms of this warranty. Next day service is available fora surcharge. Field repairs are not authorized during thewarranty period, and repair attempts by unqualified
personnel may invalidate the warranty.
Service address for customers in the USA:
Groove Tubes Service Department
1543 Truman Street
San Fernando, CA 91340

Vipre Reference Manual35Specifications
Subject to change without notice
Inputs:MIC IN (balanced XLR, Pin 2 Hot)
LINE IN (balanced 1/4”)
INSTRUMENT IN (front panel, unbalanced 1/4”)

Nominal Input Voltage:(to obtain +4 dBm out,)(with 45 dB of Gain)MIC IN, XFMR -41 dBm
MIC IN, BRIDGED, -30 dBm
LINE IN -10 dBm
INSTRUMENT INPUT –12 dBm
INSTRUMENT INPUT (20 dB pad) +8dBm

Maximum Input Level (both GAIN switches set to minimum):MIC IN, Balanced Transformer +10 dBm
MIC IN, Balanced Bridged , _+14 dBm LINE IN +30 dBm
INSTRUMENT INPUT +26 dBm (Both Instrument positions)
Input impedance:
MIC IN
LINE IN
INSTRUMENT IN

Switchable from 300-600-1200-2400 ohms (BALANCEDXFMR position); 2.4K ohms (BALANCED BRIDGE position)
24K ohms
470K ohms

Outputs:

LINE OUT (XLR & 1/4" TRS) +4 dBm nominal
LINE OUT (1/4" TRS) –10 dBV nominal

Output impedance

600 ohms LINE OUT XLR & 1/4" TRS (+4dBm referenced)
10,000 ohms LINE OUT 1/4” TRS ( -10 dBV referenced)

Maximum Output Level:+30 dBu ( 24.4 rms volts) at XLR LINE OUT+18 dBm (6.13 vrms volts) at balanced LINE OUT

MAX Available Gain:

75 dB (MIC IN, XFMRto XLR LINE OUT)
64 dB (MIC IN, BRIDGED to XLR LINE OUT
44 dB (LINE IN to XLR LINE OUT)
46 dB (INSTRUMENT IN to XLR LINE OUT)
26 dB (INSTRUMENT IN, -20 dB to XLR LINE OUT)

Equivalent Input Noise (EIN): -129 dBu (600W source, "A" Weighted)

36

THD+N:<0.06% (RISE TIME at FAST, BALANCED XFMR INPUT,
600 ohms, -45 dBm input)

Slew rate:

Varies according to setting of RISE TIME control, from0.75 V/µsecond to 6 V/µsecond

Frequency Response:

20-20,000Hz +/- 1.5 dB any input to any output;
Vipre ReferenceSpecifications

total range 4Hz–20K, -1.5 dB@ 100 kHz (BALANCEDXFMR position)
4Hz–20K, -1.5dB@100kHz (BALANCED BRIDGE position)
20Hz-20K, -1.5 db@100K (INSTRUMENT INPUT)
HI PASS filter (switchable):-4 dB per octave below 100 Hz

Power consumption:

90 watts Max

Size:

5.25”H x 19”W x 14.75”D (without rack kit)

Rack spaces:

3 spaces without rack reinforcing kit
4 spaces with rack reinforcing kit

Weight:28 lbs w/rack kit

All measurements done over a 20Hz-20,000Hz range with a nominal 1KHz sine wave
Impedances are measured at 1 kHz.

Dimensional drawing

FRONT: 5.25”H by 19”W

TOP: 14.75”D by 19”W

Allow 4”
additional
clearance forrear connectors

Allow extra
1–7/8” height for
rack
reinforcement kit

Note: rack holes
are in middle of
top and bottom
space (U.S.style spacing)

Vipre Reference Manual37IndexAC powerand noise, 14
ADAT, 16, 26
BALANCED BRIDGE, 8
BALANCED XFMR, 8
Block Diagram, 30
Class A, 23, 27
Clip LEDs, 25
clipping, 9Connections, 15
direct box, 18
EIN, 33
ELCO, 16
filament, 24
fuse, 34
GAIN, 8, 18
Gain Controls, 26
Ground Loops, 14
grounding, 3, 13
headroom, 26
Hi-Pass, 10
impedance, 22, 32
of tubes, 23
source and load, definition, 32
Impedance Selector, 10
INSTRUMENT INPUT, 11, 18
Instruments, 18LINE IN jack, 18
Maintenance, 35
MIC INconnecting Vipre output to, 16
microphoneribbon, low impedance, 22
Microphones, 18
mixer
gain setting with, 26
Mute, 8, 29
noise, 14, 33
PHANTOM, 8, 18
phantom power, 28
Polarity, 10
potentiometer, 26Power, 13
Power cable, 3
rack mounting, 12
Rise Time, 10, 28
Safety, 3
shock, 3slew rate, 28Specifications, 37
STANDBY, 29
Transformer
input, 2138

output, 28
Tubes, 23
replacing, 24, 35
unbalanced output, 17
ventilation, 12
voltage, 34
Voltage conversion, 13
VU Meter, 25
XLR, 16
input, 18
to TRS adapter, 15
XLR output
feeding unbalanced device, 17Vipre ReferenceGroove Tubes Limited
Warranty
GROOVE TUBES llc ("GROOVE TUBES") warrants this product to be free of defects in material and workmanship fora period of one (1) year for parts and for a period of one (1) year for labor from the date of original retail purchase. This warranty
is enforceable only by the original retail purchaser and cannot be transferred or assigned.
The purchaser should complete and return the enclosed warranty card within 14 days of purchase.
During the warranty period GROOVE TUBES shall, at its sole and absolute option, either repair or replace free ofcharge any product that proves to be defective on inspection by GROOVE TUBES or its authorized service representative. In allcases disputes concerning this warranty shall be resolved as prescribed by law.
To obtain warranty service, the purchaser must first call or write GROOVE TUBES at the address and telephone
number printed below to obtain a Return Authorization Number and instructions concerning where to return the unit for service.
All inquiries must be accompanied by a description of the problem. All authorized returns must be sent to GROOVE TUBES or
an authorized GROOVE TUBES repair facility postage prepaid, insured and properly packaged. Proof of purchase must bepresented in the form of a bill of sale, canceled check or some other positive proof that the product is within the warranty period.
GROOVE TUBES reserves the right to update any unit returned for repair. GROOVE TUBES reserves the right to change or
improve design of the product at any time without prior notice.
This warranty does not cover claims for damage due to abuse, neglect, alteration or attempted repair by unauthorized
personnel, and is limited to failures arising during normal use that are due to defects in material or workmanship in the product.
THE ABOVE WARRANTIES ARE IN LIEU OF ANY OTHER WARRANTIES OR REPRESENTATIONS WHETHER
EXPRESS OR IMPLIED OR OTHERWISE, WITH RESPECT TO THE PRODUCT, AND SPECIFICALLY EXCLUDE ANYIMPLIED WARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY OR OTHER IMPLIEDWARRANTIES. Some states do not allow limitations on how long an implied warranty lasts, so the above limitation may not
apply to you.
IN NO EVENT WILL GROOVE TUBES BE LIABLE FOR INCIDENTAL, CONSEQUENTIAL, INDIRECT OR OTHERDAMAGES RESULTING FROM THE BREACH OF ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING, AMONG OTHER
THINGS, DAMAGE TO PROPERTY, DAMAGE BASED ON INCONVENIENCE OR ON LOSS OF USE OF THE PRODUCT,
AND, TO THE EXTENT PERMITTED BY LAW, DAMAGES FOR PERSONAL INJURY. Some states do not allow the exclusion
or limitation of incidental or consequential damages, so the above limitation or exclusion may not apply to you.
THIS CONTRACT SHALL BE GOVERNED BY THE INTERNAL LAWS OF THE STATE OF CALIFORNIA WITHOUTREFERENCE TO CONFLICTS OF LAWS. This warranty gives you specific legal rights, and you may also have other rights
required by law which vary from state to state.
This warranty only applies to products sold to purchasers in the United States of America or Canada. The terms ofthis warranty and any obligations of Groove Tubes under this warranty shall apply only within the country of sale. Without
limiting the foregoing, repairs under this warranty shall be made only by a duly authorized Groove Tubes service representativein the country of sale. For warranty information in all other countries please refer to your local distributor.

GROOVE TUBES llc
1543 Truman Street
San Fernando, CA91340
818-361-4500
www.groovetubes.com

PLEASE SEND IN YOUR WARRANTY CARD
for more effective service and product update notices
Groove Tubes llc 1543 Truman Street, San Fernando, CA91340

39

Vipre ReferenceWarranty© 2001 Groove Tubes Specifications Subject To Change Without Notice40

Vipre Reference Manual