The Groove Tubes

Glory Compressor
Reference Manual
Table of contents
Introduction
Safety Instructions
QUICK START guide
Front Panel Features and Controls
Other Recessed Controls
Rear Panel Features
Special Refinements Under the Hood
Unpacking and Inspection
Specifications
Obtaining Repair Service
Groove Tubes Limited Warranty

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INTRODUCTION:THANK YOU, for your purchase of the Groove Tubes Variable
Transconductance Glory Compressor.

- 1 -Please read over this manual carefully as it contains
information essential to the proper operation and maximum
enjoyment of this dynamics controller.
The Glory Compressor is designed to provide suitable
downstream dynamics processing when paired with the GT VIPRE,
or any other professional audio source, and furnish maximized
sonic performance coupled with a generous ability to wrap
itself around the dynamic content of any signal source you may
wish to transform.
With the Glory Compressor’s feature compliment, you no longer
have to settle for what a given audio signal sounds like witha low-headroom solid-state dynamics controller, or be boxed-inby limited side-chain control options.
The Glory Compressor is designed to be flexible, and to adapt
to accommodate your situation, rather then the other way‘round. To this end you will notice that it is the
anticipation of your compressor applications, which has driven
every detail of the Glory Compressor’s planning, engineering,
feature set, operating convenience and adaptability.

UNPACKING
Unpack the compressor carefully and make sure that all
supplied accessories are present. Examine all items for any
possibility of shipping damage. All seven tubes should bestanding at attention in their sockets. If the compressor isdamaged or fails to operate, notify the shipper and yourdealer or us immediately. Or if the compressor was shipped to
you directly, notify the shipping company without delay.
Your Glory Compressor was packed with the following
accessories:
A. 1 each rack-mount bracing kit.
L/R pair of rack mounting braces, which can be attached to thesides of the Glory chassis, and rack mounted I RU above theGlory front panel. This brace provides both rear chassis
support as well as insuring good ventilation for the top of
the Chassis.
B. 1 each 6 foot IEC 3-conductor power cable.
C. 1 each Owner’s manual.

- 2 -Note: It is prudent to retain the shipping materials
for future use, as these materials are custom formed for
the Glory Compressor and will greatly minimize thechance of shipping-related damage.

Important Safety
Instructions
Safety symbols used in this product:- 3 -This symbol alerts the user that there are important
operating and maintenance instructions in the literatureaccompanying this unit.
This symbol warns the user of un-insulated voltage
within the unit that can cause dangerous electric shocks.
This symbol warns the user that output connectors
contain voltages that can cause dangerous electricalshock.

Please follow these precautions when using 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 liquidcleaner onto the faceplate, as this may damage the front panel
controls or cause a dangerous condition.
7. Install in accordance with the manufacturer's
instructions.
8.Do not install near any heat sources such as radiators, heatregisters, stoves, or other apparatus (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 thirdprong is provided for your 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 on or pinched,particularly at plugs, convenience receptacles, and the point
where they exit from the apparatus.

- 4 -11.Use only attachments or accessories specified by the
manufacturer.
12.Use only with a cart, stand, bracket, or table designed foruse with professional audio or music equipment. In
any installation, make sure that injury or damage
will not result from cables pulling on theapparatus and it’s 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 whenunused for long periods of time.
14. Refer all servicing to qualified service personnel.
Servicing is required when the apparatus has beendamaged in any way, such as when the power-supply
cord or plug is 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 area with at least six inches ofclearance from peripheral equipment.
16. This product, in combination with an amplifier andheadphones or speakers, may be capable of producing soundlevels that could cause permanent hearing loss. Do not
operate for a long period of time at a high volume 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.
not place objects filled with liquids (flower vases, softdrink cans, coffee cups) on the apparatus.

Do

18. WARNING: To reduce the risk of fire or electric shock, do
not expose this apparatus to rain or moisture.

- 5 -CE Declaration of Conformity

Groove Tubes llc
1543 Truman Street
San Fernando, CA

Manufacturer’s Name:
Manufacturer’s Address:
91340

USA
declares, that the product:
Glory Comp
Variable

Product Name:
Model Type:Transconductance Tube Compressor

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

Quick Start Guide
Step 1: Preliminary inspection.

- 6 -Remove the Glory Compressor from the package and carefully
inspect the unit for outward signs of damage or distress. All
projecting controls and connectors should operate smoothly anduniformly, and the enclosure’s surfaces should be free of
irregularities. All seven tubes should be standing at
attention in their sockets. Contact your dealer, the shipper
or us without delay if there is evidence of damage to theunit.
Step 2: Park it.
Budget a suitable space to install the unit in an equipment
rack. Make sure there is at least 1U of breathing space aboveand below the compressor, and that the airflow in the rack is
not constricted, since there will be about 95 Watts of power
dissipated by the unit. Keep cables and other objects awayfrom the rear panel and heat-sink since this panel will get
rather warm during operation.
Step 3: Hook it up, front panel control initial start-up
positions.
A.
Route the target signal to either the INPUT XLR or TRS
jack. The TRS input jack will exhibit 6 dB more sensitivity
then the XLR input. Apply a 0 VU (+4 dBu, 1.23 Vrms) signal to
the XLR jack, or a -6 VU (-2 dBu, about 600 mVrms) signal to
the TRS jack. Using the TRS input jack will interrupt any
signal applied to the XLR input jack. Both jacks present
bridging loads to the line input signal, of about 10k and 20k
ohms respectively, and both are actively balanced.
B.
Route the processed signal from the unit via the PROGRAMOUTPUT XLR plug or TRS jack to suitable line-level monitoring
and/or recording gear. Be careful not to connect thecompressor outputs to any microphone-level inputs not capableof handling large line-level signal levels. Damage to the misconnected microphone preamp may result.
C.
Connect the compressor to the correct line voltage using
the supplied IEC power cable.
D.
Turn the power on. Power lamp blinks during 30 second
warm-up period, and COMP relays hard-bypass the compressor
audio path by tying the like-format PROGRAM INPUT and OUTPUT
connectors together. The green COMP LED remains unlit until
the warm-up period is completed.

- 7 -Notice that the relay-bypass circuit can only connect
like style PROGRAM connectors together, i.e., XLR in
to XLR out, and TRS in to TRS out. For example, if the
XLR PGM input is being used and the bypass mode is asserted,no pass-through signal will be heard on the TRS PGM output
jack. In this case, the pass-through signal will be heard at
the XLR PGM output.
Step 4: front panel control initial start-up positions.
Position the front panel potentiometers and switches at thefollowing starting points:
INPUT = 0 Db,
THRESHOLD = -15 dB,
ATTACK = 35 ms,
RELEASE = 150 ms,
RELEASE MODE = LOGRATIO = 1:1 (compression disabled),
OUTPUT = 0 dB,
METER = IN,PGM position,
COMPressor (hard-wire bypass switch) = IN,
LINK = LOCAL,SIDE CHAIN SOURCE = INT,
SIDE CHAIN EQ LF = 0 dB, HF = 0 dB, and
GLORY = EARTH.
After the 30-second warm-up period, the compressor’s VU metershould show PGM IN activity derived from the signal hitting
the PROGRAM INPUT jacks, and, if the COMP switch is in the“IN” position, the green COMP LED will illuminate. Adjust the
INPUT control to get an average VU meter reading of 0 if needbe. It is OK if the meter gently hits the positive end-stops
on signal peaks; the compressor input circuitry has lots ofheadroom. The uncompressed signal should be audible at the
PROGRAM OUTPUT jacks. Then:
A. Rotate the METER switch to the OUT, +8 position, or
whichever position best suits your production plant’s
operating level. The soon-to-be processed (output) signal
level should be visible on the VU meter and audible on any
attached outboard monitoring gear.
Notice that the output meter indication reflects theactual signal present at the XLR PROGRAM OUTPUT plug, in
actual 600-ohm dBm units, when a 600 ohm load is present. The
reading will change somewhat depending on downstream load

- 8 -

conditions. If the load is light (say 10 k-ohms), the meter
will read at a somewhat higher level then if the load was
precisely 600 ohms. If the load is short-circuited, the meter
will read below -20 VU (no movement).
B. Rotate the METER switch to the GR, X1 position.
The meter should rest at the zero VU mark after 10 – 15
minutes of warm-up time (or you may adjust zero-trim at powerup if desired, but it may need to be touched up on the way totemp stabilization), and now indicates the amount of gain
reduction, in dB, which should be zero since the RATIO switch
is still at the 1:1 position. The 1:1 ratio is included inorder to allow an audition of the signal path without dynamics
processing.
Notice that the zero-trim interacts with the GR metercircuits only, and not the on-line audio signals.
The GR X2 position doubles the VU meter’s indicated amount ofGR, where a reading of -5 becomes -10 and so forth.
Rotate the RATIO switch slowly clockwise, stopping at 3:1.
The meter should deflect downward away from the zero mark,depending on the volume of signal exceeding the THRESHOLD
setting of -15 dB. Notice that the THRESHOLD switch
calibration marks are referred exclusively to the IN-PGM VU
meter zero mark. In this case, compression will begin for
signal levels that exceed -15 VU when the METER switch is in
the IN-PGM level-reading position.
Notice that the VU meter, in typical fashion, may notshow large amounts of downward deflection when
responding to compression of fast or staccato signals,
such as rim-shots and the like. Also, the total amount of GR
displayed will be reduced by long ATTACK or short RELEASE
time, since these types of settings reduce the magnitude of
the control voltage produced by the side-chain circuitry.
At this point, the compressor should be actively reducing theamplitude of the target signal. The user may now begin to
explore the various control settings, and arrive at thosewhich best suit the signal to be processed.

Note: Gain Reduction meter stabilization (GR x1 and x2)- 9 -Glory needs about 30 minutes of warming before the GR meter
will stabilize to read “0”. When turned on, the meter will
typically read a dB or so more than “0” until it fully warms
and stabilizes. Meanwhile, this temporary condition will notaffect Glory’s audio performance in any way OR affect theoperational mode of the meter when showing gain reduction. You
may wait for the meter to net itself in as the unit warms up,
or of course it is possible to continually trim the meter to“0” until fully warmed up. Unless time pressure prevents it,
we suggest that you trim the GR “0” setting when the Glory is
fully warmed up, and let the meter reach “0” during futuresessions.

Front Panel Features andControls
A brief description of the control functions follows. The
fundamental ideas will be well-known to those who have spenttime with dynamics controllers used for audio production, but- 10 -

there are a number of new twists and features that make an
examination of this section profitable.
The usual suspects
The Glory Compressor incorporates many familiarly labeledcontrols, as may be found when comparing the control familywith those appearing on recent models of solid-state dynamics
processors. Indeed, the attractive and flexible dynamicscontrol array found on modern and certain vintage compressors
did in part inspire the control complement for the Glory Comp.
The feature twist here is the objective of providing userselectable parametric time and level control flexibility in an
all-tube compressor. Tough, but do-able.
INPUT

potentiometer

and THRESHOLD rotary switch.

Do just what they say. The INPUT control
provides program signal input level scaling,from –20 dB of attenuation, to +10 dB ofgain. It is used to adjust the program input
level, until the average level provides
ample input INput-ProGraM VU meter
deflection with averages hovering about the
0 dB mark.
The THRESHOLD control may then be used to
set the level of the compression knee, withcompression effects commencing when input
signals exceed the chosen knee voltage. The
control’s calibration is referenced to the
PGM meter zero VU deflection mark. Unlike
most modern fixed-knee compressor designs,
the separate THRESHOLD compression knee control permits
flexibility over the indicated range, independent of the Input
control setting. Notice that the chosen compression ratio will
be reached at a signal level at about 2 dB over that indicatedby the THRESHOLD switch setting.
The independent RATIO and THRESHOLD controls permit
interesting and subtle application of the compressor, by, forexample, setting the knee at very low signal levels (-21 dB),and applying very shallow compression RATIOs of, say, 1.5:1.
The user may then reach deeply under the peak dynamic eventsin the program signal, and give subtle added thickness tomaterial starting at more than 20 dB BELOW the peak program- 11 -

operating level. Useful for raising foreground sound minutiae
and elevating room ambience details.
ATTACK and RELEASE rotary switches
ATTACK rotary switch

Each of these two controls function
conventionally, with separate time-constantcircuit stages dedicated to each control.
The ATTACK control sweeps through anapproximately 250:1 adjustable timeconstant range. The expanded 1 to 100 ms
mid-values correspond to the range of
average time intervals required for thehuman ear to respond to an impulsive signal.
Note however that a 1 millisecond transient willcorrespond to nearly 100 sound samples in a 96 kHz
digital system. Which means it will still be possible to clip
digital systems briefly, even with the ATTACK time set tominimum. Occasional slight clipping of a 1 ms interval ofprogram material in a well designed digital system will beinaudible, and may be avoided by modest drive level reduction
to the digital system.
The ATTACK and RELEASE controls are best set to values that
fit the particular musical situation. By “fit” it is meant
that, in general, faster A&R settings for percussive signals
where there is little sustain or ambient sound, and slower for
more ponderous acoustic events where there are long decay
intervals from an instrument or room reverberation. Initial
control-setting exploration will be necessary to fit the time
constant controls to the musical events at hand.
To minimize compression artifacts, it is best to keep the
ATTACK control set to time periods equal to ½ or less of the
RELEASE control setting, and both set to intervals longer then
the time period of whatever bass content might be present in
the signal.
Be aware that the wide time-constant control range provided isvery much a double-edged sword, where the most prominentelements in the program material may dominate the results. The
user may choose to apply these controls conventionally forsmooth results, or intentionally misapply them as an aid- 12 -

towards a particular artistic expression. For best results, it
is strongly recommended that the user spend a little time andacquaint themselves, if necessary, with the advantages andlimitations of the TC controls and their dynamic effects on
the processed signal.
Here’s an example of how short ATTACK control settings may
cause a conflict when processing a signal: The open E string
on a conventionally tuned string bass guitar will produce anote at about 41 Hz. This corresponds to about 25 milliseconds
per cycle.
There will be a cycle-by-cycle distortion induced into thesignal if the ATTACK and RELEASE controls
are set aggressively, to, say, 1 ms and 25
ms (LIN mode) respectively.
(Note figure at right: Output waveformwith ATTACK time period set longer thenthe bass note period, versus ATTACK set
shorter then bass note period. Each halfcycle of the bass will be individually
modulated in the latter case.)
The resulting induced artifacts should beinterpreted as normal and expected, since
the compressor’s time-constant controls
have been set in such a way as to force
the system to react to each bass note
cycle as if it were the bass signal’s
amplitude envelope. In this case, eachhalf-cycle will be subject to having abite taken out of it, which will be
audible. If these artifacts are deemed to be undesirable,
simply increasing the time-constant control settings a bit
will return the compressor to normal amplitude-envelope level
control mode.

In short order, the informed enthusiast/professional will get
the hang of it, and should have to endure no more than a briefteething period of compressor control exploration.
RELEASE rotary switch
The RELEASE control switch features a 40:1
adjustable time-constant range in two- 13 -

overlapping ranges. It is closely associated with the RELEASE
MODE switch, which splits the release mode time constants into
two largely overlapping ranges, yielding a maximum ratio of
80:1.
The first range, 50 – 2000 milliseconds, is covered by the LOG
release mode. The LOG (exponential) mode places the gaincell’s gain-reduction release profile under the control of atime-constant circuit comprised of a conventional “resistor
and capacitor control voltage network. The RELEASE control issimply the user-adjustable resistor in the R-C circuit. The
term “log” is used here because the curve shape is related to
the log family of curves, and it is easier to screen the term
“LOG” on the front panel of the equipment.

This kind of logarithmic (exponential)
release-control behavior, as derived froman R-C circuit, is available, if not
mandatory, in the vast majority of leveldynamics controllers that have everappeared on the market. In some designs, itcannot, for practical purposes, be avoided.
For example, the photo-resistors in
optically controlled compressors exhibit this logarithmic
attack and release response since it is native to the photoresistor’s behavior. In the past, many designers choose to use
photo-Rs that, in general, are somewhat quicker then 50
milliseconds, coupled to additional circuitry to stretch out
the time-constant values.
The second release mode range, 25-1000 milliseconds, isfurnished by the LINear release mode. This release mode
furnishes a crisp release profile, without the slow taper-tozero GR release characteristic of the LOG mode. Useful for
more aggressive dynamics control of dry signals, meaningsounds that do not have a long decay period associated withthem such as vibrating strings, or strong room reverberation.
RATIO rotary switch
The eleven-step RATIO control spanscompression ratios of 1:1 to 6:1, with theindicated ratio expressed in decibels. The
1:1 or “compression off” position lets
users audition (or use) any signal as it
flows through the all-tube audio path

- 14 -

without applying any compression, and without forcing the user
to engage the relay hard-bypass audio path. The 1:1 position
may be used as a convenient starting point for setting PGM and
OUTPUT levels if desired.

Notice that the RATIO control features an expanded
selection of values over the “shallow” compression
ratios of 1.25:1 through 3:1. The
shallow ratios may be used in a
subtle fashion by allowing the unit
to reach well below the audio
program’s zero dB PGM mark, and begin
lightly compressing material above
about -25 dB IN-PGM level for better
articulation of micro-dynamic program
details while at the same timelargely preserving macro-dynamic
events. The user should keep in mind that the full value ofthe selected RATIO setting will be reached when the signal isabout 2 dB above the THRESHOLD control setting, depending on
the nature of the signal being processed.
The shallow ratios are also useful when a track is to bepassed through the compressor two or more times. For example,
the first time during a live performance, and again during
playback, as some situations may demand. A high quality (lowartifact) recording medium is required for this kind of
application.
The compressor tops out at a ratio of 6:1, meaning, in thissituation, that the output level will rise by only 2 dB withan input rise of 12 dB over threshold. This is a fairly
drastic rate of compression for a single-stage discreet
component compressor, but may not be quite enough for thoseinterested in creating digital files whose average level isriding within a half dB of digital full-scale. Multiple passes
through the unit may be necessary, which effectively increases
the number of gain-varying stages the signal encounters. By
using two or more passes through the compressor, the control
settings may be optimized for peak events on the first pass,
and average events on the second. This approach mimics thechain-of-compressors/limiters technique used in many classic
recordings of the past. Of course, other additional analog ordigital dynamics processors may be brought to bear on thesignal, where the situation calls for it.

- 15 -

Side Chain Controls
Side CHAIN SOURCE switch

The SIDE CHAIN SOURCE switch’s INTernal
position directs a sample of the postcompressed audio signal to the front endof the side-chain circuitry, closing theside chain control loop. Any externalsignals present at the rear panel SIDECHAIN input jacks are ignored. In thisstate the compressor is running “closedloop” with all side-chain rotary switch settings conforming totheir stated values.
The EXTernal switch position routes any signal present at therear panel SIDE CHAIN jack directly to the front end of theside chain circuitry. In this state the compressor is running“open-loop” and, after passing through the side-chain Time
Constant circuitry, the control voltage is sent to the tube
variable gain cell. This approach provides a radicallydifferent gain-reduction control curve and shape, with a more
spread-out knee and a somewhat higher ultimate compression
ratio. Care must be taken to watch the amount of gain
reduction to prevent “bottoming out” as the GR approaches 20
dB. The amount of GR may be observed via the meter switch’s GR
X1 or X2 position.
SIDE CHAIN EQ rotary switches

LF and HF controls furnish up to 10 dB ofboost or cut to the internally sampled- 16 -

side-chain signal. The LF control shelves at 50 Hz, and the HF
control at 10 kHz. The EQ contours are low-Q in nature, andare similar to those found on consumer hi-fi preamps, much
like “Baxandall” style bass and treble curves. This helper EQ
is not intended to be of surgical precision, and is furnished
as a convenient aid in addressing musical signals overly richin low or high band-edge content.
The EQ controls are labeled in such a way as to reflect theresulting signal character exiting the compressor. Pushing the
LF EQ clockwise in the (+) direction will let more bass out of
the compressor, meaning the unit becomes less sensitive andreduces its reaction to bass content in the program material.
Conversely, rotating the HF control counterclockwise in the(-)
direction will make the compressor react more strongly to HF
content, such as cymbals, muted horns or vocal sibilance.
A typical application would be the application of the LF EQ
control when compressing bass-heavy material. This sort ofsignal can provoke a form of overreaction in the side-chain
circuitry, where gain reduction of the whole mix becomesdominated by the bass content. Rotating the LF control a few
steps clockwise can help tame the problem while permitting
more aggressive TC control settings then might otherwise be
possible.
Alternatively, the HF EQ control may be reduced, making thecompressor react more aggressively to the squeak of a mutedhorn, or to an overly sibilant vocal/microphone combination.
Notice that shorter ATTACK times may need to be selected
to help emphasize the side-chain’s reaction to fast or
high-frequency signals, and help shorten leading-edge chirp ofsuch signals. Set the ATTACK switch to the 1 or 10 ms setting
to aid in attaining fastest reaction to transient or othersignals rich in higher treble content.
The GLORY Control
This unique control adjusts the intensityof the Glory Effect as mixed into theprocessed signal. Specifically, the Effectis summed with the post-compressed audio
being fed to the compressor’s driver andpower output stage. But what exactly is
the Glory Control, and what does it do?

- 17 -

The Glory Effect essentially consists of special circuitrythat samples the program input signal, from which low-ordereven harmonics are generated, over a limited band of
frequencies, and intentionally added back to the compressedsignal in amounts deemed by the user to be appropriate for thesonic events at hand. The harmonic bandwidth is confined tooperate on signal fundamental frequencies from 40 to 700 Hz.
The program material is routed throughtwo parallel routes. This 1st
oscilloscope picture shows the signal
flowing through the side-chain signal
path is routed to the Glory effects
circuit. The Effects circuit thenmanipulates the signal so as to produce
even order harmonics ONLY, predominantly
2nd –order. These “close-in” signals, removed by only one
octave from the fundamental, are thenadded to the post-compressed signal inamounts to suit the tastes of theengineer / producer.
The next picture shows Enhancement of 2ndorder content as the GLORY control isadvanced towards fully clockwise
position. The last picture is somewhat
exaggerated for clarity.
The low-order harmonic content has thepotential to add thickness or palpability
to a single-voiced musical signal being
acted upon, provided it is used intasteful proportions. On certain sources,
such as upright bass or bass guitar, theapparent loudness and overall audibility
may be enhanced without noticeably
increasing the overall signal level. The effect on bass signal
content is somewhat reminiscent of the “synthetic bass”
circuits offered over the last 60 years, in that the bass
notes can be made more audible by putting harmonic energy
above the low-frequency pass-band limits of the monitor
loudspeakers or headphones. Used judiciously, the presence ofsmall amounts of 2nd order harmonic content in certain program
material is generally able to produce a pleasing consonantsonic sensation, versus the dissonant glary sensations
generally produced by higher-order harmonics.

- 18 -

Alternately, producing trace amounts of consonant phantom, or“Tartini” notes, as may be found in certain electric or
acoustical guitar playing styles for example, can bring forth
the “chimey” qualities of the sound source. The phenomenon
which produces the Tartini notes is called Intermodulation,
which exists in all electrical circuits, in loudspeakers, inmusical instruments, in the nonlinearities of the air itself,
and also within the human hearing mechanism. It is capable ofbeing produced in some quantity whenever one or more elements
in a (sound) system chain do not exhibit perfect linearity.
InterModulation products are comprised of the sum anddifference of two (or more) signal frequencies present in the
non-linear medium or signal path. In this case, the Glory
effect emphasizes the sum, or higher frequency components,
more then the difference frequencies. From an operational
standpoint, the Glory effect level may need to be increased
above those settings which produce tasteful amounts of 2nd
harmonic enhancement in order to produce appreciable amountsof IM.
As you might imagine, intermod creates both consonant anddissonant signals, many of which will not be musically related
to the fundamental. It can be a very aggressive sound spoiler,
or a suave and charming addition to the musical event being
processed. In general, as an effect, it is very much a wildcard in a wideband production chain, where you may expect
certain specific types of signals to be enhanced, while manyothers will be degraded. This is why the Glory effect is
intended primarily for use with individual voices or
instruments, rather then on finished mixes or other massed
sound sources. As always, quick auditioning will reveal
whether or not the Glory effect is appropriate for thesituation.
The Glory Circuit produces its effect in a new way, without
adding much in the way of DC-shift to the main signal,
partially due to the effect itself being free from muchfundamental signal content. There is no directly comparable
effect elsewhere on the market. Because of this, users areadvised to set aside a convenient exploratory period where thecareful application of harmonics to a variety of musicalsignals may be mapped out for best results for your particularapplications.

METER switch and GR ZERO trim.

- 19 -

The METER switch serves to point the VU
meter towards a variety of locations within
the compressor. The switch positions arearranged in four groups. Three of the four,
the OUTput, INput and the BAL OSC , aredirect audio level readings as measured at
the PGM XLR output connector.

The GR switch positions change the meter display to thecurrent level of compressor Gain Reduction, with the meteridle position of 0 VU rather then the mechanical rest positionat the far left of the meter scale. As thecompressor performs signal level reduction,
the VU meter will deflect towards the lefthand side of the scale, indicating theamount of gain reduction action in play.
Vacuum tubes being what they are, an amountof GR-zero drift will occur during theinitial few minutes after switching the unit on from a cold
start. The meter’s GR ZERO position may be trimmed to indicate
zero during this time if desired. Adjusting the zero trim
does not influence the amount of gain reduction the compressor
is providing; the change is confined to the meter drive
circuit only.
Notice that the meter’s ballistic behavior will remain
consistent with VU norms at all times and for all METER
switch settings. This means that the meter’s ability torespond to fast transient events is restricted, whether
directly reading an audio signal or the Gain Reduction signal.
Keep in mind that the amount of gain reduction may be muchhigher then indicated by the meter, especially when heavily
compressing transient-rich signals with ATTACK and RELEASE
time constants set to small values.

Other Recessed Controls
BALANCE potentiometers
The two BALANCE controls trim the counterphase or “push-pull” balanced signal levels
developed by the matched pair of variabletransconductance tubes within thecompressor. They are used at the factory- 20 -

for initial set-up, and, as the control tubes age, foroccasional slight touch-up as needed. They are also used when
the sad time comes to replace the variable-gain tubes with newones.
The gain-changing capability of the Glory Compressor rests
upon the behavior of the selected pair of 5749 variabletransconductance tubes in the push-pull program audio signal
path. Because of this, every compressor is fitted with aclosely matched pair of these tubes, and the BALANCE
potentiometers are trimmed for best counter-phase balancelevel-matching before leaving the factory.
Each potentiometer influences different parts of the tube
pair’s variable gain curves, and by careful adjustment a very
good mirror-image signal match may be obtained as the tubes
sweep over their variable-gain operating range.
The CATHODE trim pot pushes the tube’s variable-gain curves
about over their entire operating range, and is a somewhat
more critical control. The PLATE pot has influence over thehigh-gain part of the gain curves, where the compressor is at
idle, at or near zero GR. Both potentiometers respectively
control the balance of the cathode and plate loads seen by thepair of 5749s. A rough indication of the relative matching of
the tubes can be made by observing how well electrically
centered these controls are when the unit is in operation. By
centered it is meant that the control is at or near mid-spanin mechanical and electrical location. Each potentiometer’smechanical rotation range covers about 300 degrees.
Note that it is a good practice to leave these controls
undisturbed except when a quick test indicates the needfor slight adjustments. The need for adjustment may beascertained by an increase in audible artifacts during heavycompression and release of sharp percussive sounds, or as
indicated by a large increase in the relative level of theresidual signal heard when the internal BALance OSCillator isput into action.
BALANCE OSCILLATORAs an aid in correctly setting the PLATE and CATHODE trim
pots, the compressor is equipped with a built-in 330 Hz testbalance oscillator. The BAL OSC is asserted, and a balanceindicating signal becomes audible through the PROGRAM outputs,- 21 -

when the METER switch is rotated to the BAL OSC position atfull clockwise rotation.
The balance test of the variable transconductance tubes isdone by impressing upon them a common mode (not push-pull)signal. When the balance is ideal, there will be zero outputof the test signal at the program output jack.
In practice, this is rarely the case, therefore the PLATE and
CATHODE trim pots are slowly rocked back and forth to produce
the deepest null of the test tone. There will be several test
tone null pair settings of these controls, and the deepest
null should be chosen as representing the best setting. This
null should occur near the center of the trim pot rotation(+/- 20% of center). If not, the variable transconductancetubes may need replacement with better matched devices.
NOTE: Allow the unit to fully warm up before
interpreting any test results. Otherwise the results
will not be valid.
SLaVe CAL control
The SLV CAL control permits GR line-up with other linked Glory
Compressors and is discussed below.

Rear Panel Features
LINK switch and STEREO LINK TRS jacks
Each Glory Compressor is equipped with a pair of three-circuit(TRS) Control Voltage jacks on the rear panel. The two areelectrically identical for easy daisy-chaining arrangements.
The jack’s tip contact is the CV send voltage, and the ring is
the CV receiver circuit. The sleeve is circuit ground. A
program-level and control-setting dependent control voltage isdeveloped within each unit, and may be sent (by daisychaining) to a maximum of 6 neighboring Glory Compressors via
the rear panel jacks.
Be careful not to inadvertently connect an audio signal tothese control jacks, or to wire these jacks to otheraudio inputs on other gear. Doing so may result indamage to the compressor or other equipment. Be careful not touse 2 circuit TS cables with the LINK jacks.

- 22 -

Using the LINK switch, each Glory Compressor within a local
linked group may be set to one of three control modes.
The MASTER position asserts the chosen unit to be the mastertime constant control source for the remaining units.
Essentially, the master unit’s side-chain controls represent
the “dashboard” for itself and the other units in the linked
chain. In this mode, all control voltages, including themaster’s, are fed through the master side-chain through analog“diode-OR”ing of the control signal. This means that whichever
compressor is being hit with the loudest signal (or producing
the highest control voltage) will be the dominant device inthe chain, with all others following the GR commands of thatparticular unit, including the master.

Note: Be careful not to set two or more linked units
into the MASTER mode, since this jams control amplifier
outputs together, and may overheat components inside theaffected compressors.
*When starting out with a linked set of compressors, it isrecommended that each unit’s THRESHOLD, ATTACK, RELEASE,RELEASE MODE and RATIO controls be set alike as a starting
point.
Any single unit in the chain may be designated as the MASTER,
as convenience dictates.
The SLV position switches the unit into the control voltage
listening mode, where the gain reduction is under the commandof the master or external control voltage. If no external
voltage is detected, the compressor will return to zero GR andthe local side-chain controls will be offline.
As an aid in lining up the compressor with its neighbor(s), a
SLV CAL control is furnished above the LINK switch. This
control will slew the GR control signal by about +/- 50%, withthe mid-rotation position corresponding to a zero-trim state.
*Typical alignment procedure, for two (or more) linked units:
1. Send a 0 VU (+4 dB) signal to the MASTER compressor input
jack.
2. Adjust the MASTER unit’s INPUT, THRESHOLD and RATIO
controls to produce a -6 dB (50%) reading on the X1 GR
meter scale.

- 23 -

3. Observe the SLAVE unit’s X1 GR meter reading; adjust trim
to reach -6 dB reading as necessary.
The LINK switch’s LOCAL switch position removes the unit fromthe chained set without removing the LINK cabling on the rear
panel. In this stand-alone mode, the selected unit will not
send any control signal to the master, or respond to any
outside control voltages. Useful for setup of an individual
unit in a set of chained units, by getting the local
compressor into the ballpark before restoring it to the linked
group.

Special Refinements Under the Hood
The heart of the matter:
Variable transconductance tube gain stage.
The Groove Tubes Glory Compressor is, first and foremost, an
all-tube compressor. Inside, the program audio is multiplied
by nothing but tubes, as the Program signal propagates fromthe main input jacks to the main output plugs and jacks.

- 24 -

Each stage, and there are four distinct amplifier stages,
consists of pairs of carefully balanced and self-balancing
push-pull class-A vacuum-tube circuits. This includes theelectronically controlled vacuum-tube-based variable gainstage.
Very much the exception in what
are today generically referred
to as “all-tube” compressors,
the Glory Comp makes use of thespectacularly linear andspecially selected remote-cutoff 5749 pentode operating in
the triode mode. These variabletransconductance tubes handle
the delicate task of modulating
the program signal level. The
most important of the desirable
characteristics that this tube provides are a superbly wide
dynamic control range approaching 20 dB (near a 10-to-1
voltage reduction), coupled with freedom from undesirable
artifacts. Twenty dB of clean gain reduction represents thegreatest practical limit for a factory-built audio production
compressor based on a single balanced stage of variable-gain
tube circuitry.
The sonic bonus of using this tube type is a delightfullysmooth and suave gain-change characteristic as the variable
gain stage sweeps through its control range. Being more linear
and more “invisible” than alternative 6386-based designs,
users will find that only the most extreme control settings
produce audible compression phenomenon.
In the spirit of high-linearity, the Glory Compressor’s
variable gain stage is carefully devised in order to secure
optimum gain reduction behavior from the stage’s pair ofvariable transconductance tubes. The stage design includes
calibration trim controls mounted on the front panel for easy
accessibility. The controls serve a dual purpose by helping
the user touch up slight drift over time, if needed, and help
swamp out the inevitable production tolerance differences that
may be found between various specimens of the same GT-VMU-101
tube type.
Happily, each half of the variable gain stage circuit, and its
pair of tubes, is individually accessible, with each tube

- 25 -

fitted to its own socket. Through this arrangement, thechronic problem of matching each tube’s gain characteristics
to one another is effectively addressed! This is especiallyrelevant when the 5749 is compared to some historically
popular, but now scarce and very expensive alternatives thatconsist of two triode sections trapped within one bottle.
Indeed, when examining the issue of scarcity, the 5749 isavailable in deep supply from Groove Tubes for about $20 USD
each, as compared to the 6386 which is now in short supply andtypically sell for over $100 each IF you can find anyone who
is willing to part with them.
Glory owners will find that keeping spares around or buying
any replacement tube types for the compressor is not now, norwill it soon become a bank-account-breaking frustration in the
future. Low cost-of-ownership is intended by design.
Polyphase rectifier for smoooother control of bass dynamics.
Special attention was lavished on the traditionally underserved side-chain circuitry found in compressors, which isused to derive the gain-varying DC control voltage from thesignal being processed.
One of the historically difficult areas of signal-dynamics
control has been that of handling bass-rich signal content.
Specifically, it was and is difficult to cleanly control, say,upright bass or bass guitar when the compressor’s Attack andRelease controls are set to very short time periods. Strong
compression artifacts can arise when a compressor’s dynamiccontrol time constants are increased to periods approaching,or equal to, the time period of the wave it is trying todynamically control (which is generally a bad practice). The
severity of these artifacts depends somewhat on thecompressor’s signal rectifier and control loop design, and thesettings of the ATTACK and RELEASE controls.
Difficulties with conflicting “signal-vs-settings” time
constants seldom arise with, say, electro-optical compressors.
Primarily because the compression (attack and release) time
constants reach a ceiling imposed by the relatively slow
electro-optical resistive cells used for that kind ofcompressor, even though specific user “attack” and “release”
controls are provided. The trade-off between the two variablegain techniques becomes that of cost and complexity versus
loss of dynamics-control range. In the end, due to the limited
time-constant control range available, the optical- 26 -

compressor’s usefulness is ultimately restricted to a smaller
number of possible compressor applications, and virtually no
hard limiter applications since the optical elements tend to
be a bit too slow for instantaneous level control.
The Glory Compressor’s dynamics-control circuitry has been
specially designed to bridge the gap between electronic andoptical gain-reduction characteristics. The Glory Compfeatures special low-frequency phase-splitting circuitry which
is applied to the varying program signal voltage sample,
before being presented to the compressor’s rectifier circuit.
The LF signal content is then full-wave-rectified by two
separate peak rectifier circuits. The result is up to fourpeak events per cycle of bass signal content (versus two),creating a far smoother DC control voltage for modulating thevariable gain circuitry at low frequencies. This yields anelectronic gain control with the smoothness of opticallimiting, but without the ultimate speed and control
restrictions of the optical approach! Plus, the Attack/Release
controls may be positioned at faster, more aggressive settings
for bass signals before noticeable sonic conflict sets in.
Note, however that the compressor’s front panel time-constantcontrols have enough short time-period range for a user tooverwhelm the advantages of the rectified 4-phase bass
signals, which will produce audible artifacts.
Transformerless inter-stage coupling to the make-up-gainstage!
Designers of vintage variable-mu tube compressors had very few
options when contemplating how to cleanly get the processedsignal off the plates of the variable-gain tubes. In the pastthis was traditionally accomplished by using inter-stagetransformers, with balanced primary windings connected to thevariable-transconductance tubes, and isolated secondaries
connected to downstream amplifier stages. The transformer
served to work around two important problems.
First, it removed the wildly varying DC bias voltage component
from the audio signal on the plates of the variabletransconductance tubes, leaving only the audio voltage present
on the secondary winding.
Second, the signal balance of the recovered audio signal
voltage could be maintained in near-perfect push-pullcomplementary symmetry by virtue of constructing a pair ofidentical coils for the inter-stage transformer secondary. The- 27 -

signals on the secondary would then be fed to the make-up gainstage, or, as in the case of the good old Fairchild 660 /670,
directly out to the line-matching output transformer.
But this approach was not and is not without compromise. Wideband high-performance inter-stage transformers, then as now,
are complex and expensive components, which, at best, impose
rather severe bandwidth and phase limitations on the audio
signals passing through them. This especially true whenconnecting a transformer with fixed characteristics to tubes
whose output characteristics are intentionally changing oncommand. Basically, as the variable transconductance tubes arebiased into heavy gain reduction, their ability to push thetransformer is reduced. This can and does induce a certain
amount of degradation in the audio path. One may expect, forstarters, elevated levels of distortion at the band edges, andan overall drop in bandwidth (dulling of high frequencies,
thinning of deep bass notes) during compression.
The Glory Compressor features a novel hybrid servo system,
which cancels the fluctuating DC control voltage in therecovered audio from the variable transconductance tubes in an
active all-electronic manner. This leaves only the balanced
audio signal, without resorting to inter-stage transformers.
The variable transconductance tubes are loaded only withforgiving, purely resistive loads. This provides the user withan all-tube variable gain cell whose high bandwidth remains
constant during compression! Remarkable! Fun is waiting for
the user, as the Glory Comp throws open new tonal territory inhigh-bandwidth vacuum-tube based dynamics processing.
The Output Stage (Too loud, man.)
The Glory Compressor follows in the footsteps of the venerable
VIPRE microphone preamplifier in its internal all-balanced
signal path architecture, and in its prodigious output signal
level capabilities. In the spirit of professional production
gear from the past, and in light of current new 24-bit digitalrecording developments, the output stage has been designed toprovide up to +36 dBm, or 4 Watts into 600 ohms, or 120 V
peak-to-peak across 600 ohms! What this means is that thecompressor will never be the weak link in so far as headroom
or voltage drive capabilities are concerned.
Ironically, the latest developments in some of the newest“high-definition” digital audio production workstations have a
direct bearing on why the high voltage / high power capability- 28 -

is part of the design. It seems that some of the new 24-bit
digital systems demand rather high input voltage in order toreach full-scale modulation. Evidently, in order to make thesignal-to-noise improvements inherent in the new 24 bit
systems meaningful, some converter hardware suppliers haveraised the A-to-D input drive voltage requirements to levels
beyond the capabilities of what most popular op-amp basedoutboard gear can provide. This was foreseeable, since, atpresent and practically speaking, there will always be about ½
to 2 micro-volts of noise present across a 20 kHz audio
bandwidth at the input of the new 24-bit high-bandwidth
converters, unless exotic and expensive (and impractical)
cryogenic methods are used to reduce it. The noise origins are
a combination of the real-world effective signal source
impedance being presented to the converter’s analog inputs,
and nearby spurious digital or analog noise sources, which may
be leaking into the converter inputs due to circuit layout
issues, or proximity to other noisy system elements, and soforth.
When 1 microvolt of input noise is multiplied by about 16.8
million, which is the approximate number of steps in a 24-bit
system, the resulting number is 16.8 volts. This implies aminimum drive voltage requirement of 16.8 volts RMS (sinewave) or about 48 volts peak-to peak for meaningful 24-bit
full-scale modulation under ideal circumstances, not counting
dither. Many real world converter systems will generally needmore drive than 16 Vrms. Surprise! You’re out of drive
headroom when hitting your 24-bit converter with a signal fromoutboard gear using monolithic op-amps running off of +/- 15
to 18 volt supply rails!
Here’s some numbers from a field report received recently
regarding the new HD workstation systems and theircompatibility with a lot of existing gear:
When most solid-state gear is hooked up to the new 24 bit
inputs, the signal can only get up to “-6 or –12” (dB BELOW
full-scale) on a given track before wholesale clipping of thesource gear sets in, depending on the design of the source.
When faced with this awful situation brought on by limited
voltage drive capabilities, the recording engineer must decide
whether to use the less sensitive “+4” inputs on his new 24bit digital equipment, and throw away the top 2 or 4 or 5 bitsof resolution in order to keep from clipping his source gear.
Or, equally unattractive, choose to use the more sensitive “10” A/D converter inputs, and throw away the BOTTOM 2 or 4 or

- 29 -

5 bits to noise, ON TOP of whatever the dithering algorithm isdoing to the low-level data. Either way, some of the extra
resolution provided by the 24 bit systems, and much of thepoint and effort to provide new high-resolution digital
mediums, is simply discarded by such compromise.
The Glory Compressor itself will never force the recording
engineer into a no-win drive-level trade-off, since thecompressor’s audio path electronics are very far removed fromthe paltry +/-15 volt power-supply voltage-rail limitations
found in nearly all of the popular op-amp-laden audio
production gear. Here again the tried-and-true vacuum tube,
and it’s purpose-designed application in audio production, ismore then up to the task of providing plenty of clean
attractive audio for the latest and greatest digital gear. No
stock (unmodified) audio production equipment pieces currently
in production and on the American market can casually provide
abundant headroom for the 24-bit systems, by furnishing 120Vpp
across 600 ohms (more when lightly loaded!). Output
capabilities like this are realizable in transistorized
designs, but with much greater circuit complexity and expense,
along with lower reliability, not to mention the sonicpenalties.
Power Supply Highlights
The Glory Compressor uses all-triode circuitry throughout thesignal path. This includes all of the pentode tubes, which areelectronically configured as triodes. In this way theattractive characteristics of the triode are made available
without the high cost and general unavailability of othergeneric triodes, which might otherwise be suitable for the job
at hand.
In order to keep the chain of triodes confined to operatingover the specific working range intended, the high-voltage
supply must be held at a constant value. Since the compressor
is a dynamics or signal-level processor, it becomes mandatory
to hold the high-voltage rail to within a few percent of thetarget voltage at all times. In this spirit, the Glory
Compressor features a special high-voltage regulator thatserves to keep the high-voltage at a stable value, and,through an unusual synthetic-inductor function, provides
smoothing or ripple filtering as well. All of this regulator
activity is located “upstream” of the high-tension supply’s
large filter capacitor, zeroing out any small wide-band noise
components which the regulator may generate.

- 30 -

The power supply features a warm-up high-voltage hold-off
circuit, which keeps the B+ on hold until the tube filaments
are sufficiently warmed up. In this case, the hard-wire signal
bypass relays electrically link the program input and output
connectors together until the warm-up cycle is complete. This
prevents any large warm-up-related signal transients fromappearing at the program output connectors.
Power supply energy storage is ample in the Glory Compressor.
Over 50 joules of potential energy in the large high-voltage
filter cap alone! This level of reserve energy helps give thesignal path and output stage immunity from perturbation by
loud or highly dynamic signals. Put another way, the program
audio will have that completely un-strained quality that only
abundant power reserves and signal headroom will provide.

Unpacking and Inspection
Your Groove Tubes Glory Compressor was carefully packed at thefactory, and the shipping carton was designed to protect theunit during shipping. Please retain this container in theunlikely event that you need to return your Glory forservicing.
The shipping carton should contain the following items:- 31 -

• Glory Variable Transconductance Compressor• This instruction manual• Power cable• Groove Tubes Warranty card
• Rack mounting hardware (two pieces plus parts to attach themto the Glory when rack mounting).
NOTE: It is important to register your purchase; if you
have not already filled out your warranty card andmailed it back to Groove Tubes, please take the time todo so now.
Installing in a Rack
The Glory may be simply set on a table, or installed in astandard 19” audio equipment rack. While the rack mounting
holes are integral to the front panel, the Glory is unusually
deep and heavy, so extra support must be provided for the rearof the unit. Before the Glory 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 Glory.
NOTE Since the vacuum tubes in the Glory generate acertain 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 theunit. They are screwed to the sides of the preamp and extend
to above the front panel. Standard rack screws are then used
to fasten both the Front Panel and the Rack Kit to the Rack
Rails panels.

Specifications
Size: 19”W x 18”D x 5.2” (3RU) H, including projecting
controls and parts. Budget 5 RU for proper ventilation andheat dissipation, with 1 RU above and below the enclosure.
Exceptions being other equipment housed in shallow enclosuresthat will not block the compressor’s ventilation slots.
Weight: 37 lbs, not including rack brace kit. Kit requires 1
RU of vertical clearance, which makes good use of the- 32 -

ventilation spacing required by the unit, and must be
installed if the compressor is to be used in a mobile ortransportable production application.
Mains requirements: 120 VAC, 60~, 130 Watts warm-up interval,
100 Watts during operation.
Warm-up delay: Approximately 30 seconds from cold start to
COMP relay engagement (green comp lamp is lit). Note thatabout 5 minutes of additional warm-up time is recommended topermit the tubes to reach thermal equilibrium before use
begins.
Fuse Complement (120 VAC): 5x20 mm 1.6 A, 250 V SLO-BLO forthe mains, 5x20 mm 0.125 A, 250 VAC standard speed for B+.
Maximum PROGRAM input signal level, PROGRAM XLR input: +32
dBu, or 30 Vrms, 87 Vp-p.
PROGRAM input impedance: XLR= 35 k-ohm bridging balanced, TRS= 18 k-ohm bridging balanced. Always ground the ¼ inch plug’s
RING to SLEEVE when feeding UNbalanced signals into the
PROGRAM input TRS jack.
Maximum PROGRAM output signal level, PROGRAM XLR output: +34
dBu, or 38 Vrms, 109 Vp-p across 600 ohms (2.5 watts), add
about 5 dB for 10k-ohm loads (Caution! High voltage!).
Subtract 6 dB (50%) for the PROGRAM TRS output jack.
PROGRAM output impedance: XLR = 600 ohm balanced floatingtransformer coil, TRS = 150 ohm balanced floating transformer
coil. Always ground the ¼ inch plug’s RING to SLEEVE whenconverting BALanced signals from the TRS jack into UNbalanced
signals.

System PROGRAM THD, IM at:
Input and Output Gain = 0 dB, operating level = 1.23 V rms @440 Hz (+4 dBm output), no gain reduction, Glory effect at
minimum, Program XLR output, 600 ohm load, Bandwidth 22 – 22kHz.
THD = 0.09 %, IMD = 0.06%.
System PROGRAM THD, IM at:- 33 -

Input and Output Gain = 0 dB, operating level = 12.3 V rms(+24 dBm output), no gain reduction, Glory effect at minimum,
Program XLR output, 600 ohm load, Bandwidth 22 – 22 kHz.
THD = 0.6%, IMD = 0.6% .
System PROGRAM THD, IM at:
Input and Output Gain = 0 dB, input level = 7.75 V rms (+20
dBu input, +20 dBm output), 10 dB of gain reduction, Glory
effect at minimum,Program XLR output, 600 ohm load, Bandwidth
22 – 22 kHz.
THD = 1.1 %, IMD = 0.6% .
System PROGRAM hum+noise, IN/OUT controls @ unity, input jacks
open, A weighted = -68 dBm.
System PROGRAM dynamic range = 103 dB, ref +35 dBm out or 3%
THD.
Maximum PROGRAM path gain = 20 dB.
Maximum PROGRAM gain reduction = 18 dB, single-stage balanced
variable transconductance vacuum tubes.
Maximum SIDE CHAIN input signal level, SIDE CHAIN XLR input:+24 dBu, or 12.3 Vrms, 35 Vp-p.
Note that the XLR and SIDE CHAIN TRS input jack sets are
furnished hard-wired in parallel, as a convenience tothe operator. Be careful not to drive both XLR and TRS jacks
with separate line input signals, use one input at a time.
Maximum SIDE CHAIN output signal level, SIDE CHAIN XLR output:+24 dBu, or 12.3 Vrms, 35 Vp-p. Subtract 6 dB (50%) for the
SIDE CHAIN TRS output jack.

Note that the SC output level is between 10 and 15 dB
lower then the program input signal, due to dynamic
range limitations of the op-amp based side-chain circuitry.
The side chain signals are not intended to be used as a sourceof on-line production quality audio.

- 34 -

SIDE CHAIN EQualisation: Shelving, +/- 10 dB @ 50 Hz, and +/10 dB @10 kHz. Operates on INTernal SIDE CHAIN SOURCE mode
only.
GLORY EFFECT: 0 – 50% THD, mostly 2nd order, injection ratio
depending on instantaneous Gain Reduction, input signal andoutput signal drive levels. Effect limited to 60 – 800 Hz
window; intended primarily for operation on fundamental signal
content of single or small groups of instruments or voices.
Operating temperature: 10 – 40 degrees C, 50 – 104 degrees F.
Operating humidity: 0 – 90 percent relative humidity, noncondensing.

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 withyou. Talk the problem over with one of our technicians; ifnecessary, you will be given a return order (RO) number and- 35 -

instructions 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 shippinglabel. 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 Styrofoampellets (the kind without CFCs, please) or “bubble-pack”
surrounding the unit. Shipping damage caused by inadequate
packing is not covered by the Groove Tubes warranty.
Tape a note to the top of the unit describing the problem,
include your name and a phone number where Groove Tubes cancontact you if necessary, as well as instructions on where youwant the product returned. 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 for asurcharge. 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
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 to users in the USA and Canada. Customers
outside of the USA and Canada are not covered by this Limited
Warranty and may or may not be covered by an independent
distributor warranty in the country of sale. Do not return
products to the factory unless you have been given specificinstructions to do so.
Internet Address: Important information and advice isavailable on our web site:
WEB SITE: http://www.groovetubes.com
Email may be addressed to:
SALES: sales@groovetubes.com
TECHNICAL: lab@groovetubes.com- 36 -

Groove Tubes Limited Warranty
GROOVE TUBES llc ("GROOVE TUBES") warrants this product to be
free of defects in material and workmanship for a period ofone (1) year for parts and for a period of one (1) year forlabor from the date of original retail purchase. This warranty
is enforceable only by the original retail purchaser andcannot 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 andabsolute option, either repair or replace free of charge any
product that proves to be defective on inspection by GROOVE
TUBES or its authorized service representative. In all cases
disputes concerning this warranty shall be resolved asprescribed 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 orsome other positive proof that the product is within thewarranty period. GROOVE TUBES reserves the right to update
any unit returned for repair. GROOVE TUBES reserves the rightto 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, WITHRESPECT TO THE PRODUCT, AND SPECIFICALLY EXCLUDE ANY IMPLIEDWARRANTIES OF FITNESS FOR A PARTICULAR PURPOSE OR
MERCHANTABILITY OR OTHER IMPLIED WARRANTIES.
Some states do not allow limitations on how long an implied
warranty lasts, so the above limitation may not apply to you.

- 37 -

IN NO EVENT WILL GROOVE TUBES BE LIABLE FOR INCIDENTAL,CONSEQUENTIAL, INDIRECT OR OTHER DAMAGES RESULTING FROM THE
BREACH OF ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING, AMONGOTHER 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. Somestates do not allow the exclusion or limitation of incidental
or consequential damages, so the above limitation or exclusion
may not apply to you.
THE INTERNAL LAWS OF THE STATE OF CALIFORNIA SHALL GOVERN THISCONTRACT WITHOUT REFERENCE 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 tostate.
This warranty only applies to products sold to purchasers in
the United States of America or Canada. The terms of thiswarranty and any obligations of Groove Tubes under thiswarranty shall apply only within the country of sale. Without
limiting the foregoing, repairs under this warranty shall bemade only by a duly authorized Groove Tubes service
representative in the country of sale. For warranty
information in all other countries please refer to your local
distributor.
PLEASE SEND IN YOUR WARRANTY CARD for more effective service andproduct update notices

GROOVE TUBES llc
1543 Truman Street, San Fernando, CA 91340
818-361-4500

www.groovetubes.com© 2006 Groove Tubes llc.

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