Groove Tubes Vipre
TM

www.groovetubes.com

Vipre
White Paper
The benefits of variable impedance,rise-times and component-level engineering

GROOVE TUBES CUSTOM SHOP PRODUCTS

VariableImpedancePreampTM

The Groove Tubes

GROOVE TUBES LLC

Vipre

A general description

The Groove Tubes Vipre is an all-tube, variableimpedance microphone preamplifier with selectablerise-time and VU meter ranges. It features extremely
high bandwidth, low inter-stage feedback, very highgain, enormous dynamic range and graceful overload
characteristics.
• All-tube audio path – NO semiconductors, transistors,ICs or electrolytic caps anywhere in the signal path.
• Eight Groove Tube compliment:
4 x 6922 (6DJ8) – preamp and rise-time circuitr y
1 x 12AT7 – output driver and rise-time circuitr y
1 x GT6205 – instrument input preamplification
2 x 6AQ5 – Class A push/pull output• Switch-selectable fully-floating differential input andfully-floating differential output.
• Switch-selectable variable-impedance input, stepped
between 300-, 600-, 1200- and 2400-ohm taps offhigh-performance, custom-wound input transformers.
• Switch-selectable rise-times.
• Precise and repeatable gain settings, in 5dB and 1dB
increments from 15dB to 75dB.
• Precision audio metering facilities with expanded andpeak views on a true VU meter.
• Robust one watt (+30dBm) output.
• Massive energy storage (>60 joules) in the hightension power supply.
• DC-to-daylight bandwidth (4Hz >100kHz).
• Hand-wired point-to-point connections using highest
possible quality components and wires.
• Custom-built ceramic deck attenuators.
• Superior and stable audio performance under thewidest range of preamplifier applications.
• Classic design – inside and out.

Multiple personalities
Experienced recordists know about the wide variety ofsound character and “personality” found in the criticalselection of both microphones and preamps.
Many recording facilities own large assortmentsof mics and preamps in order to be better prepared forthe needs of various artists and groups. And for goodreason. The more tonal variations a facility can provide,the more diverse and desirable their clientele. The
choice of microphone and preamp are primarily
responsible for these variations.
Experience has shown that most of these sonicdifferences can be attributed to slight variations inequalization, speed of response, available bandwidthand residual distortion. These changes have, until now,
been addressed in quite heavy-handed ways, such asproviding EQ in a preamplifer, or resorting to ‘tube
distortion’ as a desired effect. The Groove Tubes Vipre,
however, provides an unparalleled means of controllingthe interaction and responsiveness of both themicrophone and preamp.

Ohm-mazing discoveries!
Early in the annals of professional audio, microphones
and microphone preamplifiers were often made by thesame company, and the output and input impedance
between the mic and preamp were matched to provide
the best possible audio quality. Those days are longgone now, and most condenser microphones send a
200-250-ohm load into an input about ten times theimpedance – roughly 2000-3000 ohms.

Altering the load against which the microphone
has to push fundamentally alters the tone and characterof the output signal.
At the core of the Vipre is a multi-tap highperformance input transformer, with four distinct
positions: 300-, 600-, 1200- and 2400-ohms. Thischanges the working impedance or loading of a given
microphone and can strongly influence the soundqualities by the cumulative effects of small differences.
These differences vary from microphone tomicrophone, but all mics respond quite audibly when thepreamplifier input impedance is altered. This control
feature opens a much larger sonic window to eachmicrophone, and provides the ability to magnify certain
attractive tonal shifts in the way it responds toimpedance changes.
Vintage microphones are especially sensitive toload terminations, as impedance matching was thenorm in early broadcast and recording facilities.
Ribbon microphones, for example, are sought
after for their smooth tonal properties. When properly
terminated or loaded with 300-ohms, the tonal
characteristics change, and the sound seems to“bloom” in a way most people have never heard.
The equalization changes slightly as well, withthe entire spectrum from about 100Hz to 15kHz taking
on a very slight tilt, typically around -1dB at the low end,
and around +1dB at the upper registers. Very slightwhen looking at individual frequencies, but thecumulative effect over the whole spectrum isunmistakable.
This kind of variation would be almost
impossible to recreate with any kind of equalizer, unlessthe principle of a simple, uncluttered signal path isabandoned altogether.
Moreover, a balanced-bridged or transformerless
input is provided, bypassing the variable-impedance
input transformer altogether for a completely different
sonic character.
An instrument input is also provided on the front
panel for easy access, and can be padded by -20dB toaccommodate the stronger output signals from activeinstrument electronics.

Slow – curves ahead
By providing a rise-time control, the recording engineer
has the ability to slow down the signal path electronics
as he sees fit. FAST preserves the full percussive andforward qualities of the source, while SLOW helps tameoverly aggressive sound qualities and "rounds out" or"smooths" the material.
No less than five distinct rise-time settings
ranging from a quick six volts per microsecond, to atame .75 volts per microsecond (reminiscent of moreclassic preamps) are instantly available from any input
selected.
While subtle, these settings can significantly
influence the tonal characteristics of the recording.

All-tube – not “also-tube”
Only a few of the mic preamplifiers on the market today
can be described as all-tube from input to output. Cost
constraints almost invariably lead to hybridized designs
and certain sonic compromises.
However, experience has shown that a lowparts-count simple circuit can produce sonically pleasing
results. Creating a symmetrically arranged mirror-image
circuit configuration further enhances thisuncomplicated approach.
By employing a fully-differential, Class A
push/pull design, the Vipre keeps its inherently simple
circuit philosophy and performance while significantly
increasing signal-to-noise ratio and dynamic range.
This approach both reduces power supply
induced noise and lowers distortion. The result is a
microphone preamplifier which has "DC-to-daylight"
performance characteristics – with the ability to convey
great detail while remaining nearly free of typicallyunwanted sonic imprints.

No pain in the gain
In order to maintain a fully floated and balanced signal
path throughout the entire circuit, there are nopotentiometers on the front panel. Instead, gain
controls consist of ceramic deck rotary switch
assemblies arranged for discrete step attenuation,
providing repeatability, economy, ultra-wide control range
and superior accuracy.
The Vipre's step attenuators are built to havegreater than 1.0% interstage matching at any and all
chosen settings, and extra effort has been expended tofrequency-compensate the 5dB coarse gain attenuator,
eliminating the typical bandwidth-robbing effects ofparasitic circuit and wiring capacitance.
The Groove Tubes Vipre boasts an impressive
75dB of available gain, with 5dB COARSE (20dB to70dB) and 1dB FINE (+/- 5dB, centered at 0) step
attenuators. These very-high-accuracy step attenuatorspreserve the balanced integrity of the signal path, which
ultimately translates to better noise, distortion anddynamic range specifications.

A preamp with a VU
To watch over all of this signal manipulation capability,
the Vipre has been fitted with a genuine VU meter for
signal observation.
The VU meter has been in use for over 60years, and has that “old comfortable pair of shoes” feelfor many users. However, its principal limitation has
been its inability to show any signal information below-20dB, and the deleterious effects of placing a rectifier
feeding a meter movement across the output signalline.
Both of these obstacles have been overcome by
the employment of an amplified VU meter driver circuit,with five separate types of VU response.
In addition to the standard view of -20dB to+4dB, the meter driver gives the user the ability toswitch to an "expanded view," allowing for -60dB to+9dB response.
Three additional settings place 0dB VU at+10dB, +20dB and +30dB, giving more of a “peakresponse” for higher gain applications. These custom
settings provide metering far beyond a conventional VU,
allowing observation of weak acoustic signals (such as
traffic or air conditioning rumble) to be spotted andeliminated before recording.

an afterthought in audio equipment, the Vipre's power
supply is designed with massive energy storage in mind.
Over 60 joules of energy reserve ensure that the highlevel stages get adequate power, while filtering rectifier
hum down to inaudible levels.
Note that most 100-watt hi-fi stereo power
amplifiers have less energy storage than does the onewatt-output Vipre. This high energy reserve gives anunshakeable foundation to the low-frequency end of theaudio spectrum, while keeping the supply design very
simple and robust – and far less costly and complicatedthan an actively regulated power supply.

Other goodies
The Groove Tubes Vipre also features accoutrements
and ergonomic touches like polarity reverse – a truehigh-pass filter (which gently reduces gain below 100Hz
at 4dB per octave, rather than a harsh 12dB curve
often used for low cut) – +48V phantom power – arelayed mute switch for silent starts and mic changes –a B+ standby switch – and ample lamps for status
reading even in dimly-lit studio environments.
The classic knobs and vintage appearance
further underscore the Vipre's design as a deliberate
throwback to the days when the focus was on quality ofoperation, durability and functionality.

Caution! High voltage!
The use of high voltage at high speed is pushed to fulladvantage in the Vipre amplifier stages. Equivalent input
noise is below -129dBm (“A”-weighted, 600-ohm input
shorted), while maximum output level at onset of soft
clipping is +30dBm (one watt into 600 ohms). Clipping
is noted by two lamps just below the VU meter, amber
at -3dB below clipping, and red upon CLIP.
In the unlikely event that the Vipre should be
driven into clipping, its onset is slow and thecharacteristics 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 all gain stages operating inpush/pull Class A mode. The sum of the bias and audio
currents that flow though each push-pull stage is held
constant at all times. None of the audio currents canescape, meaning the balanced design is free fromundesirable bilateral interaction with other stages or thepower supply.
Presiding over the delivery of energy to theGroove Tubes Vipre's circuitry is the power supply. Often

It’s like having 50 of
the world’s finest all-tube
preamps...
With three distinct audio inputs (XLR, TRS andinstrument), four impedance selections, atransformerless bridging input setting, and five rise-time
variations, the Vipre can be set for over 50 different
tonal variations - all without ever requiring EQ or othersignal-degrading devices to achieve them.
Imagine having 50 of the world's finest ALLTUBE preamplifiers available to you at any time, all in
one unit!
For the discriminating collector of microphones,or the serious recordist, the Groove Tubes Vipre
represents huge leaps in subtle tonal sculpturing basedon proven, accepted and reliable methods - all without
resorting to electronic trickery.

Technology that won’t goout-of-date
Moreover, the Vipre is mature technology, meaning thatits design will never be outdated as the digital format
wars rage on.
No matter what the industry accepts as thenext recording standard in the next five, 10 or 20 years,
rest assured Vipre will remain as a functional analog
anachronism in the digital age.

Groove Tubes Vipre
Tech specs
Rear panel inputs

Distortion – THD at 1kHzXLR In – Balanced
600 ohms +8dBm max in

Input with transformer at +4dBM
output at XLR<.025% at 45dB gain

XLR TRS – Balanced
Nominal 25K +28dBm max inEquivalent input noise (EIN)
Front panel instrument input-129dBu(600-ohm source, "A"-weighted)

XLR – Unbalanced
47K
200mv at +75 dB gain (max gain)

Frequency response

Rear panel outputs

4Hz - >100kHz( -1.5dB at 100kHz)XLR Out – Balanced
600 ohms +30 dBM, 1khz max
XLR TRS – Balanced
600 ohms +30dBM
RCA-10dbV = +4dBM at XLR Out
1K ohms

GROOVE TUBES LLC
Groove Tubes LLC
Custom Shop Products
1543 Truman Street
San Fernando, California 91340 USA
Tel 818 361 4500
Fax 818 365 9884
www.groovetubes.com©2001 Groove Tubes LLC. All rights reserved. Groove Tubes, the GT in a circle logomark, Groove Tubes Custom Shop,
Groove Tubes Custom Shop Products and Vipre are trademarks and service marks created and owned by Groove Tubes LLC.
All specifications subject to change without notice.