· The tube Mic/DI Preamp from the MDP-1 with switchable
mic input transformers and mic loading
· The Delta-Mu tube Compressor/Limiter from the ES-8 with
five operating modes and sidechain filter.
· A new three band inductor-based Passive EQ with Aggressive
· A new Peak Limiter design with JFET and MOSFET modes
and accurate led metering.
· The Mic/DI, EQ, Delta-Mu compressor and Peak Limiter
can be patched out and used independently.
· The EQ can be placed before or after the compressor
· Transformerless or transformer output
· Short-signal path design with pure class A circuitry
· Gold-plated switch contacts, I/O connectors and tube
· Polypropylene caps and metal film resistors (pairs matched
· Fully regulated high voltage and filament power supplies
with soft-start warm-up and muting
· Custom toroidal power transformer with shield for minimum
· 120V or 240V ac voltage switch on the rear panel.
Thank you for purchasing the Pendulum Quartet II Mercenary
Edition, an all-purpose recording tool with attitude designed
to be the ultimate way to get your mic or source directly to
tape or hard disk. It is not an update nor a replacement
for our very popular Quartet. It is a complementary unit
that incorporates a substantially different combination of elements.
Designed with the input of Fletcher and the crew at Mercenary
Audio, many additional options have been provided to tailor the
texture of the audio character for maximum musical flexibility.
The tube Mic/DI preamp has the unique option of being able
to switch between two markedly different sounding input transformers
and loading options. The DI can handle pickups, keyboards, or
line-level signals. Independent gain and output controls permit
overdrive of the tube stage to vary the harmonic content.
The Delta -Mu (µ) tube compressor, derived from the
ES-8, has the classic compression profile of the Fairchild 660
and 670 limiters. It can be used in one of five modes: Fast,
Faster, Vintage (program-dependent), Average (rms), or full Manual
operation. It also features a switchable sidechain high pass
The new 3 band tube Passive/Aggressive Equalizer is a modern
take on the classic inductor-based passive EQ. It features simultaneous
Lo Shelf Boost and Cut, Mid Dip and Hi Peak bands. The Aggressive
mode increases the saturation of the EQ circuit to add harmonic
content. In addition, the EQ can be placed before or after the
compressor with the flip of a switch.
The new JFET/MOSFET Peak Limiter uses a novel approach to
brickwall analog limiting, with JFET and MOSFET modes for two
different characters of peak limiting, and accurate led metering.
Unlike other designs, distortion below threshold is negligible.
We have combined these four elements into a fully integrated
package that it makes it easy to track any source. The Quartet
II uses a modern tube, class A high voltage circuit topology
to deliver an open, intimate sound with a level of detail that
meets the requirements of the most demanding recording applications.
Our short signal path design excels in audio performance, delivering
extremely wide bandwidth, low noise, and high headroom.
The Quartet II also has a host of I/O options:
· Transformerless or transformer-coupled main outputs
· Post-Mic/DI loop for patching out the preamp separately
or for using an external mic preamp.
· Tube EQ In/Out
· Delta-Mu Compressor/Limiter In/Out with linking
· JFET/MOSFET Peak Limiter In/Out.
And all four elements can be patched out and used completely
The unit was carefully packed at the factory to protect against
damage in transit. Nevertheless, be sure to inspect the unit
and shipping carton for any signs of damage that may have occurred
during shipment. If there is any damage, notify us immediately
for further instructions. It's also a good idea to save the carton
and packing materials should you ever need to return the unit
for repair. The shipping carton should contain the following
items: the Quartet II Preamp/Processor, an IEC 3 prong power
cord, and this operating manual.
The Quartet II uses two EIA-standard rack spaces, and can be
mounted in any standard 19 inch (483mm) equipment rack. If the
Quartet II is mounted in a mobile rack or road case, it is important
that the rear of the chassis is supported to prevent possible
damage from mechanical shock and vibration. Excessive shock and
vibration can cause damage or premature failure of the vacuum
tubes, or cause them to shaken loose from their sockets. Please
avoid rough handling.
For proper operation, it is very important that adequate
ventilation is provided. Vacuum tubes produce a significant amount
of heat that must be removed from inside the chassis. The side
panel and top panel vents should never be blocked in any way.
Never mount the Quartet II below a rack unit with a depth greater
than 7 inches (178mm). Do not mount the Quartet II near other
heat-producing equipment such as power amplifiers or other vacuum
tube products. If possible, leave open at least one rack space
above the unit, and use a rack spacer with a ventilation grille.
Never operate the Quartet II inside a road case where the side
panels are cushioned in foam.
Preventing Ground Loop Hum
One of the reasons the Quartet II sounds so good is that unlike
many other vacuum tube products, it operates single-ended, Class
A and can be operated unbalanced without the output transformer
via the 1/4" output jack. However, when used unbalanced
it does not benefit from the galvanic isolation provided by the
output transformer. For this reason, a few precautions are necessary
to insure hum-free operation:
· Isolate the front panel from the rack rails. Use plastic
shoulder washers to prevent electrical contact between the rack
ears of the Quartet II and the metal rails of the equipment rack.
· Isolate the Quartet II from units mounted above or
below it in the rack. Make sure the front panels are not in electrical
contact and that the top or bottom cover screws of the Quartet
II are not touching those of any other units.
· Connect the 3 prong IEC power cord to the single-point
star grounded electrical source for your facility.
The idea here is to make sure the Quartet II seeks ground
at only one point. For safety reasons, do not lift the ground
at the IEC power cord. Keep in mind that in a properly grounded
hookup, the Quartet II does not hum. Please, take the time to
do this right, and you will be rewarded with hum-free operation.
Contact us if you have any questions. Please note that pin 2
The Quartet II is equipped with a 3-prong IEC power connector
and detachable cord. Never operate the Quartet II with the ground
on the power cord defeated. Unless otherwise stated, this unit
operates from either 115-120V/60 Hz or 230-240V/50 Hz at 45W.
Before the unit is plugged in, select the correct ac voltage
using the switch adjacent to the IEC inlet on the rear panel.
The ac fuse is accessible within the rear panel IEC input jack
and is rated at 1.5A/250V (5x20mm) SLO-BLO. To check or replace
the fuse, unplug the power cable from the IEC input jack.
Other than changing the tubes, the user should not attempt to
service the Quartet II beyond that described in this manual.
Never remove the covers or attempt to replace the tubes until
the unit has been disconnected from the ac power source, and
all circuits inside have been allowed to discharge for a period
of at least 30 minutes. The vacuum tubes become very hot once
the unit has been turned on, and they should not be touched until
they have cooled to room temperature. To reduce the risk of fire
or electrical shock, do not expose to rain or moisture, or operate
it where it is exposed to water. Since potentially lethal voltages
are present inside the unit, it should only be opened by qualified
service personnel. Refer all servicing, or any questions about
servicing, to Pendulum Audio, Inc.
While the operation of the Quartet II may appear to be rather
straightforward, there are a few features which may differ from
what you're accustomed to seeing on other stand-alone preamp/processors.
You may find it useful to refer to the Condensed Operating Instructions
at the beginning of this manual to quickly identify the operation
of the front panel controls. However, we suggest you read through
this section to take advantage of all its features, and to make
sure you are operating the Quartet II in the way most appropriate
for the type of recording you're doing.
Please refer to the rear panel layout (see the Condensed Operating
Instructions) for the location of the inputs, outputs, ac power
inlet and power switch. Make all connections to the Quartet II
and select the proper ac voltage before applying power.
· On the right hand side of the rear panel are the input
jacks for the Mic/DI preamp. The female XLR connector on top
is the transformer-balanced mic input. Connect microphones to
this input using standard balanced XLR mic cables. Pin 1 = ground.
Pin 2 = + (positive phase), pin 3 = - (negative phase). Note:
this input may be +48v phantom powered, as selected by the '+48'
switches on the front panel. Do not use phantom power on a microphone
that does not require it! (e.g. dynamic, ribbon, or tube microphones).
Make all mic connections before applying phantom power!
· The 1/4" jack below the XLR connector is the
unbalanced DI input. The input impedance of this jack is 1M when
the DI input switch on the front panel is set to Instrument,
or 100K with a 20dB pad when the DI input switch is set to Line.
This input can be used for connecting an instrument directly
to the rear panel, or for connecting the Quartet II to an unbalanced
patch bay. The 1/4" input on the front panel can be used
for either instrument (10M) or line level (100k/-20dB) signals.
Individual I/O, Patching, and Link
There are nine 1/4" jacks on the rear panel located between
the input and output jacks. These are used to patch out the Mic/DI
preamp, EQ, Compressor and peak limiter, or to patch other equipment
into the signal chain.
Mic/DI Insert (Send): Use this jack to obtain a direct
output from the Mic/DI preamp, or to send the Mic/DI preamp signal
out of the Quartet II for outboard processing. This jack is normalled
to the Mic/DI Insert Return.
Mic/DI Insert (Return): Use this jack to patch an external
preamp into the Quartet II, or to return the Mic/DI preamp signal
into the Quartet II after outboard processing. This jack is normalled
to the Mic/DI Insert Send.
EQ In/Out: Use these jacks to patch the tube EQ out for external
processing. Make sure the IN/BYPASS switch on the front panel
is in BYPASS.
Compressor In/Out: Use these jacks to patch the Delta-Mu
compressor out for external processing. Make sure the IN/BYPASS
switch on the front panel is in BYPASS.
Link: A TRS jack for linking two Quartet II compressors for
stereo operation. Linking requires a TRS 'crossover' cable, in
which the tip and ring connections are inverted on the opposite
side of the cable. It is wired as follows: Tip 1 to Ring 2, Ring
1 to Tip 2, Ground 1 to Ground 2. Set the Threshold, Output and
dynamics controls on each unit to the same settings.
· To the far left of the input jacks are the main output
jacks. The male XLR connector on top is a 3 pin transformer-balanced
output, with Pin = ground, Pin 2 = + phase, Pin 3 = - phase.
Connect this output to 3 pin balanced console, converter, or
tape input. When connecting to a balanced patch bay, be sure
that Pin 2 = Tip. If you encounter ground loop hum when connecting
to active-balanced or transformer-balanced inputs, lift the ground
at the end of the XLR connecting cable opposite from the Quartet
· The 1/4" jack below the XLR connector is unbalanced
output connector with Tip = + phase,
Ring + Sleeve = ground. Use it for connecting the Quartet II
to an unbalanced input, or to a balanced input with Tip = pin
2, Ring = pin 3, Sleeve = ground.
· On the left side of the rear panel is the IEC input
socket. Connect to a 120V/60Hz or 230V/50Hz receptacle with the
3 prong IEC power cable supplied with the Quartet II. Set the
ac voltage switch for the correct line voltage before connecting
the Quartet II to the ac line. For safety reasons, do not lift
the ground on the power plug by using a 3-to-2 ground lift adapter.
· Turn on the power to the unit using the ac power
switch located on the lower right-had side of the front panel.
The meters will illuminate immediately. The blue 'ON" LED
will illuminate after the power-up sequence is completed (see
· If necessary, replace the 1.5A/250V (5x20mm) SLO-BLO
fuse (inside the IEC input socket) only with the same type and
· To prolong tube life, the Quartet II goes through
a soft-start sequence for gently applying power to the tubes
and stabilizing the circuit before engaging the outputs. When
the power switch is turned on, the outputs are relay-muted to
ground and the dc voltage on the tube filaments is ramped up
to 6.3 and 12.6Vdc. Next, the high voltage supplies are slowly
increased to 250 and 300V and the circuit is allowed to stabilize
for about 2 minutes. Finally, the relay lifts the outputs from
ground and the blue 'on' led on the front panel is illuminated.
For best results, please allow the Quartet II to warm up for
10 minutes or longer before using it.
Using the Quartet II Mic/DI as a Mic Preamp
Please refer to the front panel layout (see the Condensed
Operating Instructions) for the location of all switches and
controls discussed below. The Mic/DI preamp features an all-tube
This switch allows you to choose between two very different-sounding
input transformers. The 'Full' transformer is a Jensen 13K7A,
which has a 1:5 turns ratio (13 dB of voltage gain) and has a
very open sound with extended high and low end response. It's
the ideal choice for recording many instrumental and vocal sources,
particularly if you're looking for 'truer' reproduction.
The 'Focused' transformer is custom-wound for us, with a (1:10)
turns ratio (+20 dB of voltage gain) and has a 'push' or emphasis
in the midrange that can make some sources, especially vocals
and electric guitar, sit easily in a busy mix with greater definition.
The additional gain also makes it the ideal choice for low output
mics such as passive ribbon microphones.
This switch allows you to select the load impedance presented
to the microphone by the input transformer. Depending on the
mic, the amount of loading can alter the tone and overload characteristics
of the mic. This is especially true with microphones that have
an output transformer, including vintage (or vintage-style) tube
condenser mics, dynamic mics, and ribbon mics. Active mics, particularly
phantom-powered condenser mics, may be less sensitive to loading.
The standard load specified by most mic manufacturers is 1500
ohms. Our experience is that loading the mic more lightly, at
10kohms, can open up the top end and may also increase the output
level. The mic signal is muted for about 1 second when switching
between Full and Focused transformers, to eliminate any 'popping'
when the phantom power is engaged.
Input Mode: MIC
With the input switch in the 'MIC' position, the Quartet II is
configured as a mic preamp, with the XLR input connector enabled
and the DI inputs on both the front and rear panels disabled.
In this mode the signal path consists of the input transformer
followed by a Class A tube gain stage with a transformerless
Phantom Power: +48V/0
In the +48V position, 48 volts is supplied to pins 2 and 3 of
the XLR input. The phantom voltage is applied via two 6.81k metal-film
resistors that are hand-matched to better than 0.1%.
Mic Input Pad: 0/-20
In the -20 position, a 20dB impedance-matched resistive pad is
inserted in front of the input transformer to prevent overload.
To optimize common-mode rejection, the metal-film resistors are
hand-matched to better than 0.1%. Use this position when recording
with mics placed on sources with high sound pressure levels such
as drums, guitar amps, or when close-micing a singer with a high
output mic. Use if distortion is heard, or if the output level
of the preamp is too high with the GAIN selector switch at its
lowest setting (+33dB/Full or +40dB/focused). For the best noise
performance, use only when necessary. The input pad may limit
the effectiveness of the Loading switch. Use the pad when the
XLR input is used with +4dBu line-level balanced sources.
Note: with the DI input in LINE position, the Mic input pad is
increased to 40dB.
In the - position, the phase of the mic signal is inverted at
the secondary of the input transformer. Configured this way,
the phase of the mic can be switched without interrupting the
dc voltage to a mic requiring phantom power. Positive phase is
Pin 2 hot.
Lo Cut: Off, 75 Hz and 150 Hz
The LO CUT is an 3 position toggle switch that provides a 12dB
per octave rolloff for the Mic input at 75 or 150Hz. In the center
'Off' position, the filter circuit is removed from the signal
path. Flip the switch 'up' for 75Hz rolloff, and down for 150Hz
rolloff. Note that the Lo Cut filter affects only the mic input,
and not the DI input.
GAIN: +33 to +63dB (Full), or +40 to +70dB (Focused)
The GAIN Control is an 11 position rotary switch that adjusts
the gain of the tube stage from +33dB to +63dB (Full) or +40dB
to +70dB (Focused) in 3dB steps. The 1% metal-film resistors
that determine gain are selected for precise 3dB increments.
At low gain settings, there is more global feedback in the tube
circuit, which offers a more 'accurate' and 'controlled' sound.
At higher gain settings, the sound is a little more 'open' and
'harmonically rich'. Used in conjunction with the OUTPUT control
(discussed below), subtle variations in the character of sound
can be achieved.
OUTPUT: 0 to 10
The OUTPUT Control is a passive attenuator positioned between
the mic preamp tube stage and the other elements of the Quartet
II. It can be used in conjunction with the GAIN control to adjust
the level that is sent to the EQ, Compressor or Peak Limiter
(or a tape machine or hard disk recorder, if the other elements
are bypassed). For the cleanest sound, set the OUTPUT control
fully clockwise (completely out of the signal path) and use the
GAIN control to set the overall signal level. To add more 'harmonic
content' by driving the tubes at a higher signal level, set the
GAIN control to a higher gain setting and use the OUTPUT attenuator
to bring the output level down to a more useable range. Or, use
the OUTPUT control to make fine adjustments (within the 3dB range
of the GAIN switch settings) to the level sent to a tape machine.
Used sparingly, this gentle tube 'overdrive' can create subtle
changes in the harmonic balance of the source. Used to excess,
it will cause audible distortion. Proceed with caution. With
the OUTPUT attenuator set to mid-range, the level of attenuation
is 20dB for load impedances greater than 10k.
Using the Mic Preamp Without the Input Transformer
Here's another thing that's fun to try. The Quartet II can
be used with high output tube microphones as a fully transformerless
mic preamp. Simply connect the mic to the rear panel DI input
using an XLR to 1/4" adapter, and switch the input mode
to DI (in instrument mode). Increase the GAIN about 18dB to compensate
for the lack of transformer gain and the 6dB loss when running
the mic unbalanced. The noise performance suffers a bit, but
when used for recording vocals with a high output microphone
(e.g. Neumann M149), the results are superb. Keep the mic cable
as short as possible. The output transformer of many tube mics
(e.g. Neumann U47, U67, etc.) sound best when terminated into
a 1500 load impedance. To do this, place a 1500 resistor across
pin 2 and 3 of the XLR to 1/4" adapter.
Using the Quartet II as a DI Preamp
The Quartet II features a full-function, short-signal path
DI. Please refer to the front panel layout (see the Condensed
Operating Instructions) for the location of the switches and
inputs discussed below.
Input Mode: DI
With the input switch in the 'DI' position, the Quartet II is
configured as a line-level DI preamp, with the DI inputs on both
the front and rear panels enabled and the XLR mic input connector
disabled. In this mode the signal path of the DI preamp consists
of a Class A tube line stage with a transformerless output at
the Mic/DI Send output, and a transformerless or transformer-balanced
output at the main outputs. The input impedance is 100k for line
level inputs, or 1M and 10M for instrument inputs. The front
and rear panel jacks are wired so that the rear jack is disabled
when a 1/4" plug is inserted into the front jack.
DI Input: Instrument
With the DI INPUT switch on the front panel in the INSTRUMENT
position, the 1/4" input jacks on the front and rear panels
are configured to accept unbalanced high impedance sources. The
GAIN range is +20 to +50dB in 3dB increments.
· The front panel jack has an input impedance of 10M,
which ideal for very high impedance sources such as piezo transducers.
Use this input when minimum loading of the source is desired.
· The rear panel jack has an input impedance of 1M,
which is ideal for moderate impedance sources such as passive
magnetic guitar or bass pickups. Use this input when light loading
of the source is desired. Loading the magnetic coil of a (passive)
bass guitar pickup with 1M can sometimes tighten
up the low end, adding definition. Since this effect depends
on the inductance any given pickup, try it both ways and see
which sounds the best.
DI Input: Line
With the DI INPUT switch on the front panel in the LINE position,
the 1/4" input jacks on the front and rear panels are configured
to accept unbalanced high level sources.
· The input impedance is 100k for both front and rear
input jacks, with a -20dB resistive pad inserted between the
input and the tube line stage.
· The range of the GAIN control is 0 to +30dB, which
is ideal for line-level sources such as -10dBV unbalanced consumer
audio equipment or keyboard outputs.
· Use the rear panel jacks to connect the DI inputs
to an unbalanced patch bay.
· Note: For balanced line-level signals, use the Mic
input with the 20dB pad engaged. With the DI input in LINE position,
the Mic input pad is increased to 40dB.
Gain and Output Controls
See 'Using the Quartet II as a Mic Preamp' for a discussion of
how to use the GAIN and OUTPUT controls to achieve subtle changes
in the character of the sound of the DI. Note that while the
Quartet II can in principle be softly 'overdriven' like an guitar
preamp, it doesn't have the same radical tone-shaping EQ. However,
the Quartet II can be used to overdrive the front end of a tube
Using the Passive/Aggressive Tube EQ
The three band tube EQ in the Quartet II is a passive, inductor-based
EQ network followed by an all-tube class A line stage. The 'Aggressive'
mode increases the saturation of the EQ circuit to add harmonic
content. It combines the features most often need when tracking
a wide variety of sources. Please refer to the front panel layout
(see the Condensed Operating Instructions) for the location of
all switches and controls discussed below.
With the switch in the 'IN' position, the equalizer is placed
in the Quartet II's signal path, and the blue LED near the switch
is illuminated. The 'BYPASS' position removes the EQ from the
signal path entirely (a 'hard' bypass). When patching the EQ
out to use it separately on another source (see "Individual
I/O Patching and Link" above), be sure this switch is set
EQ -> µ / µ->EQ
With the switch in the EQ -> µ position, the EQ stage
is placed before the Delta-Mu Compressor/Limiter in the Quartet
II's signal path. Use this position to contour the frequency
response of the source material before compression. In the µ
-> EQ position, the EQ stage is placed after the Delta-Mu
Compressor/Limiter in the Quartet II's signal path. Use this
position to contour the frequency response of the source material
after compression. It is common, especially for vocal tracking,
to use the 75 or 150Hz LO CUT filter on the Mic/DI preamp to
reduce 'over-compression' on low frequencies due to proximity
effect and breath noise ('popping'). Then, the EQ can be used
to add more low end after compression, if desired. Or, use the
Sidechain Lo Cut filter (described below) to reduce the compressor's
sensitivity to low frequency content.
When the switch in the 'Aggressive' position, a custom-designed
transformer is inserted into the EQ circuit, which adds harmonic
content to the source. By varying degrees, it fattens the bottom
end, pushes the midrange forward, and adds sizzle to the high
end. The degree of 'aggression' depends on how hard the EQ is
driven, and how much boost is applied.
The LO band (shelving response) has separate BOOST and CUT controls,
and a rotary switch for frequency selection. The controls are
continuously variable with up to 20dB of boost or cut (full counter-clockwise
rotation) at one of five turnover frequencies: 20, 30, 50, 100,
120 Hz. The controls can be used simultaneously, to create unusual
contours in the low frequency response.
The MID Cut band (peaking inductor response) has a CUT control,
a 5-position rotary switch for frequency selection, and a Bandwidth
control. The CUT control is continuously variable with up to
25dB ('Sharp') or 10dB ('Broad') of attenuation at one of six
frequencies: 200, 350, 500, 650 or 800 Hz. The range of the Bandwidth
control is 0.7 (Sharp) to 3.7 (Broad).
The HI band (Peaking inductor response) has a BOOST control,
an 11-position rotary switch for frequency selection, and a Bandwidth
control.. The BOOST control is continuously variable with up
to 20dB ('Sharp') or 10dB ('Broad') of boost at one of 11 turnover
frequencies: 0.8, 1.4, 2, 3, 4, 5, 8, 10, 12, 15 or 18 kHz. The
range of the Bandwidth control is 0.7 (Sharp) to 3.0 (Broad).
Using the Delta/Mu Compressor/Limiter
The Delta-Mu Compressor, derived from the popular ES-8, has
a sound all its own. It can be used in one of five modes: Fast
, Faster, Vintage (with program-dependent response), Average
(rms responding), or full manual operation. Please refer to the
front panel layout (see the Condensed Operating Instructions)
for the location of all switches and controls discussed below.
With the switch in the 'IN' position, the Delta-Mu Compressor
is placed in the Quartet II's signal path, and the blue LED near
the switch is illuminated. The 'BYPASS' position removes the
compressor from the signal path entirely (a 'hard' bypass). When
patching the compressor out to use it separately on another source
(see "Individual I/O Patching and Link" above), be
sure this switch is set to BYPASS.
Threshold: Off to Max
The THRESHOLD control determines how much gain reduction is applied
to the source material. A maximum of 15dB of gain reduction is
available from the remote cutoff gain control tube. The range
of the THRESHOLD control is off to -20dB, which permits a steady-state
input level as low as -5dBu to achieve the full 15 dB of gain
Output: Off to Max
Use the OUTPUT control to increase the signal level after compression.
Up to 15dB above the level of the input signal is possible. The
unity-gain setting (0dB) is 12:00. The OUTPUT control is a 20%
audio taper potentiometer, which permits finer adjustment of
output level in the critical 0-15dB range.
Sidechain Lo Cut Filter
This switch inserts a 150 Hz high pass filter (12dB/Octave) into
the sidechain detector. This is useful for reducing the sensitivity
of the compressor to low frequency content. It prevents the compressor
from over-responding to low frequency content, like that generated
from microphone proximity effect and plosives in a vocal track.
It may also be used creatively on sources like kick drum, bass,
or program material.
The Quartet incorporates a solid-state sidechain circuit to provide
a wide range of dynamic control. For maximum versatility, there
are five distinctly different modes of operation.
In the FAST mode, the gain control tube operates with fast attack
and release times (1 ms and 50ms respectively). This mode is
remarkably free of pumping artifacts even at high compression
levels. It's the ideal choice for tracking or tight program compression.
Use it whenever you don't want to hear it working, particularly
on vocal tracks.
In the FASTER mode, the gain control tube operates with very
fast attack and release times (0.1 ms and 50ms respectively).
This mode grabs the signal very aggressively, like an hot-rodded
Fairchild. It's definitely a sound you can hear and feel. However
it should be used with caution, since the amount of control voltage
artifacts impressed on your audio are maximized in his mode.
In addition, it can add considerable distortion to signals with
lots of low frequency content, like bass guitar. Listen and judge
The Vintage mode emulates program-dependent action of vintage
compressors. Early opto-style units had a built-in 'memory effect',
where the attack and release times were dependent on previous
levels of gain reduction. Here we use a three-stage program-dependent
time constant, where there is initially a quick release, followed
by a slower decay times approaching zero gain reduction. Think
of these settings as a 'gated' release time, where the compressor
operates more rapidly at the average program level, but takes
much longer to return back to zero gain reduction. In other words,
the compressor does not immediately 'suck back to zero' when
there is a brief pause in the program, e.g. between words in
a vocal track.
In the AVERAGE mode, the detector operates with RMS (root-mean-square)
response. Rather than triggering on peak information, RMS detection
more accurately reflects the average energy content of the waveform,
which better approximates the loudness perceived by the human
ear. The compressor responds more slowly than the FAST setting
and can sound more 'open' on highly transient material such as
electric bass and percussion. This setting can also work well
The MANUAL mode offers total control over the attack and release
times. The range of the attack and release controls is 1ms to
100ms and 0.1s to 2s respectively. Manual control is particularly
useful for creative compression effects or for processing bass
guitar. Quite often, a greater level of compression can be applied
to program material if a very long attack time and a short release
time are used. In this instance, the compressor is responding
to the average program level, does not 'over-compress' on short
peaks, and recovers quickly. In other words, it doesn't 'pump'
JFET/MOSFET Peak Limiter
The new JFET/MOSFET Peak Limiter uses a novel approach to
brickwall analog limiting, with JFET and MOSFET modes for two
different characters of peak limiting, and accurate led metering.
Unlike other designs, distortion below threshold is negligible.
When not triggered, the Peak Limiter is out of the signal path
entirely. The peak limiter uses a class A, solid-state signal
A Few General Comments About Peak Limiting
· All peak limiters add distortion when limiting. By
their very nature, they change the shape of the waveform, which
is, by definition, distortion. However, some peak limiters begin
distorting well below threshold. The active devices doing the
peak limiting in the JFET/MOSFET Peak Limiter are entirely out
of the circuit until the threshold for limiting is achieved,
and switched out again after limiting. This keeps distortion
negligible when no limiting is occurring.
· The amount of distortion depends on how the peak
limiting is accomplished. The trick is to do it in a way that
sounds inaudible. In the JFET/MOSFET Peak Limiter, a certain
amount of 'compliance' is built-in to the limiting action. This
means that instead of chopping off the peaks and losing all dynamic
information, some 'wiggle' is left at the top. This makes the
limiting more inaudible. The JFET and MOSFET devices have differing
amounts of compliance, which results in differences in the character
of limiting. The JFET tends to produce 'harder' limiting, with
less compliance, while the MOSFET produces 'softer' limiting,
or more compliance.
· Peak limiting should be used to avoid a worse-sounding
alternative. For example, clipping distortion from digital 'overs'
will always sound worse than a good peak limiter.
· Peak limiting does not take the place of a compressor.
Use the Delta-Mu compressor to raise the average program level,
and the peak limiter to catch transients. Any peak limiter will
be audible when trying to act on steady-state program material
(e.g. bass guitar). The LED display can serve as a guide to how
audible the peak limiting might be. If the leds are lit continuously,
you can be certain that significant distortion is occurring.
· Ignore all of the above when using the peak limiter
as an effect. Heavy limiting of an acoustic guitar might sound
nasty, but heavy limiting of distorted tracks, like electric
guitar, can be a beautiful thing. Same goes for percussion tracks.
With the switch in the 'IN' position, the Peak Limiter activated,
and the blue LED near the switch is illuminated. When in 'BYPASS',
the Peak Limiter is entirely out of the signal path.
The CEILING control determines the reference output level at
which the peak limiter is activated. It can be set from +22dBu
to + 12dBu. This encompasses the range of 'digital zero' most
often encountered with typical A/D converters, as well as having
additional 'margin' for using the peak limiter creatively.
The JFET/MOSFET switch determines which type of device is doing
the peak limiting. As discussed above, the JFET gives a stiffer
form of limiting, while the MOSFET is more forgiving. Due to
the differing nature of the JFET and MOSFET devices, slight re-adjustment
of the CEILING control may be necessary when switching between
the two modes.
The 9 segment LED display gives a true indication of the amount
of peak limiting applied to the signal. It is obtained by continuously
comparing the input and output levels, and scaling this difference
in dB relative to the CEILING reference level. It displays the
amount of peak reduction in
1 dB increments from 0 to greater than -8 dB. The LED ladder
uses a 3 color scheme to indicate how audible the peak limiting
might be on transient source material. Green (0 to -4) is the
'safe' region of operation, with yellow (-5) and red (-6 to >-8)
indicating caution is required.
The illuminated ANSI VU meter is electronically isolated from
the signal path, and can be switched to measure output or compression.
Keep in mind that a VU meter is a mechanical device, designed
in accordance with a with a well-accepted ballistic standard,
to indicate an average loudness level. On the other hand, the
led meters on your mixer or digital recorder are reading a peak
program level, and faithfully register all those short transient
spikes that add little to the perceived loudness of the program
material. The ratio of the peak to average levels can be 20dB
or greater depending on the source (e.g. drums). So, if you're
wondering why the led meter on your recorder is flashing near
zero, but the output level on the VU meters of the Quartet II
are hovering at or below -10, you're simply seeing the difference
between the peak and average program level.
When the METER switch is in the COMPRESSION position, the VU
meter indicates the amount of gain reduction applied to the input
source. Keep in mind that the meter is indicating an average
gain reduction, and does not reflect how the Delta-Mu compressor
is responding to peaks faster than the meter's response time.
This is particularly true when using the FAST and FASTER modes.
When the peak to average ratio is high (e.g. drums), trust your
ears to be the ultimate judge.
A screwdriver - adjustable trim control, located below the METER
switch, is used for zeroing the meter when it is set to read
COMPRESSION. Use a small, flat-bladed screwdriver, and adjust
the meter to indicate 0VU with the THRESHOLD control set to OFF.
Let the unit warm up at least 20 minutes before making any adjustment.
When the METER switch is in the OUTPUT position, the VU meter
indicates the signal level at the XLR and 1/4" output connectors.
The meter is calibrated to 0dB = +4dBu (1.23vrms). Use this setting
to monitor the average program level sent to a recorder, mixer
input or channel insert.
Replacing the Tubes
All vacuum tubes have a limited life due to reduced electron
emission from the oxide coating on the cathode and/or a buildup
of impurity gases is the bulb. The life of the preamp tubes in
the Quartet II is estimated to be several years. If you notice
the sound quality deteriorating - higher distortion, muddiness,
or microphonic behavior - it's time to change the tubes. If you
are uncomfortable with replacing the tubes yourself, please have
it done by qualified service personnel. Replacement tubes are
available directly from us.
1. Unplug Quartet II and wait at least 30 minutes for the
high voltage in the unit to discharge and for the tubes to cool
to room temperature.
2. Remove the top cover by removing the nine #6-32 Phillips-head
DO NOT remove the bottom cover.
3. Note the position of the five tubes (V1-V5) in the porcelain
· The input tubes are 12AX7A/ECC83 (V1, V3)
· The output tubes are 6922/6DJ8 (V2, V4)
· The gain control tube is a 6ES8/ECC189 (V5)
NOTE: THERE ARE NO SUBSTITUTES FOR THE 6ES8/ECC189!
ONLY THE EXACT REPLACEMENT WILL WORK!
4. Remove each tube and replace with the same type removed from
the each socket.
DO NOT install the tubes in the wrong positions!
5. Reinstall the top cover and screws.
There are a large variety of ECC83/12AX7s available. Each
type has slightly different internal structure and design. Consequently,
each type has its own sonic signature. Sometimes the differences
are subtle - sometime not. You are encouraged to sample the different
varieties and pick the one that sounds the best to you.
The 6922 is a rugged, military style 6DJ8. Since it is used
as a high current output driver, we recommend replacing it with
the same type and rating. The 6922 used in this fashion has much
less influence on the sound of the Quartet II than the 12AX7A
Note: In most cases, tube DC and AC rebalancing and gain calibration
and will be required when replacing the 6ES8/ECC189. Although
this not a difficult process, it should be performed only by
qualified service personnel that are familiar with servicing
vacuum tube equipment. Potentially lethal voltages are present
inside the unit. Detailed instructions for performing these procedures
will be provided on request.
There are several adjustments to the Quartet II that are only
accessible by removing the top cover:
· Adjustment of the EQ output level..
· Calibration of the meter when measuring gain reduction
· AC and DC balance of the gain control tube for control
· Adjustment of symmetry, detector gain and reference
voltage of the Peak Limiter (THESE SHOULD NEVER NEED ADJUSTMENT).
These adjustments are required only if one of the tubes are
replaced, or if they drift out of calibration with age. Since
these adjustments must be made with the ac power on, and potentially
lethal voltages are present inside the chassis, we recommend
that they be made only by qualified service personnel who are
familiar with working around high voltage tube circuitry.
For your safety, we strongly recommend that you contact us
for servicing. On request, detailed instructions for performing
these procedures will be provided to qualified service personnel.
Quartet II Specifications
Circuit Type: Class A vacuum tube design with transformerless
or transformer-balanced output
Input Gain:+33 to +63dB (Full) or +40 to +70dB (Focused) in 3dB
Input Impedance:1500 or 10K (switchable), transformer balanced
Full: -1.0dB 12Hz and 65kHz with 10K load, +45dB gain, unbalanced
-1.0dB 24Hz and 60kHz with 600 load, +45dB gain, unbalanced or
Focused: -1.0dB 30Hz and 40kHz with 600 or 10K load,
+45dB gain, unbalanced or transformer-balanced output
Noise:EIN less than -124dBu with 150 input load (> 85dB below
+4dBu), 0-30Khz bandwidth
Distortion:Full: THD+N less than 0.03%, +45dB gain, unbalanced
less than 0.06% from 200Hz-20kHz (< 0.2% at 20Hz), transformer-balanced
Focused: THD+N less than 0.07%, +52dB gain, 200Hz-20kHz, 1.5%
less than 0.08% from 200Hz-20kHz (<1.7% at 20Hz), transformer-balanced
Input Gain:+20 to +50dB (Instrument), 0 to +20dB (Line) in 3dB
Input Impedance:10M or 1M (Instrument), 100k with 20dB pad (Line)
Frequency Response:-1.0dB 12Hz and 110kHz, with 10K load, + 20dB
gain, unbalanced or
-1.0dB 20Hz and 95kHz, with 600 load, + 20dB gain, unbalanced
Noise:EIN less than -116dBu with input shorted (> 87dB below
Distortion:THD+N less than 0.015%, 20Hz-20kHz, +20dB gain, unbalanced
less than 0.05% from 200Hz-20kHz (< 0.5% at 20Hz), transformer-balanced
Max. Output Level:+34dBu into 10k load, Output control at maximum,
+25dBu into 600 load, Output control at maximum, unbalanced or
Phantom Power:+48Vdc applied to pins 2 and 3
Mic Pad:-20dB pad at the primary of the mic input transformer
(-40dB with DI input switched to 'Line').
Mic Phase:inverts the phase at the secondary of the mic input
Mic Lo Cut:12dB/octave rolloff at 75 or 150Hz
Polarity:input and output XLR connectors are pin 2 hot
Circuit Type:Inductor-based passive EQ network with all-tube
gain makeup stage ,with 'aggressive' mode
Hi Peak: +10 to +20dB peaking at 0.8, 1.4, 2, 3, 4, 5, 8, 10,
12, 15 or 18 kHz, BW = 0.7 to 3.0
Mid Dip:-10 to -25dB notching at 200, 350, 500, 650, or 800 Hz,
BW = 0.7 to 3.7
Lo Boost/Cut: ±20dB shelving Boost or Cut at 20, 30, 50,
100, or 120 Hz
Freq. Response:-1.0dB 5Hz and 200kHz with 10K output load, unbalanced
-1.0dB 20Hz and 370kHz with 600 output load, unbalanced or transformer-balanced
Noise:> 87dB below +4dBu
Distortion:THD+N less than 0.015% from 20Hz-20kHz, +20dB gain,
less than 0.06% from 100Hz-20kHz (< 0.2% at 20Hz), transformer-balanced
Passive/Aggressive: THD+N less than 1% @ 20Hz at +4 dBu, EQ controls
Max. Output Level:+34dBu into 10k load, +24dBu into 600 load,
Circuit Type:Remote-cutoff gain control tube with class A
solid-state gain makeup stage
Input Impedance:10k (nominal) with 1:1 input transformer
Freq. Response: -1.0dB 16Hz and 56kHz with 600 output load
Noise:>89dB below +4dBu output level
with Output control at unity gain (12:00)
Distortion:less than 0.1% THD+N, 20Hz to 20kHz, below threshold
Output: +22 dBu into 10k load
Max. Gain Reduction:greater than 15dB
Threshold: up to 15dB of gain reduction at -5dBu input level
Ratio:1:1 to limiting, program-dependent
Output: off to +15dB
Modes: fast, faster, vintage, average or manual operation
Fast: 1.0 ms attack, 50ms release
Faster: 0.1 ms attack, 50ms release
Average: rms responding
Vintage multi-stage attack and release times, program dependent
Manual: attack time varaible from 1.0ms to 100ms
release time varaible from 0.1s to 2s
Circuit Type: Class A solid-state line amp with JFET or MOSFET
Freq. Response: -1.0dB 10Hz and 50kHz with 600 output load
Noise: >90dB below +4dBu
Distortion:less than 0.01% THD+N, 20Hz to 20kHz, with limiter
Output: +22dBu into 10k load
Display:9 segment led ladder in 1 dB intervals from 0 to -8dB
Vacuum Tubes: (2) ECC83/12AX7A, (2) 6922/6DJ8, (1) 6ES8/ECC189
Power: 120V or 240Vac, 45W
Power Supplies: +300Vdc, + 250Vdc, +6.3Vdc, +12.6Vdc , ±
18Vdc, +15Vdc, +10Vdc, fully regulated with soft-start warm-up
and output muting
Dimensions:2U enclosure, 19" x 3.5" x 12.5" (48.2
x 8.8 x 31.8 cm)
Weight: 15.8 lb. (7.2kg)
Note: Operating level is +4dBu = 0VU = 1.228v
Unless otherwise stated, all measurements are referenced to +4dBu,
0-80 kHz bandwidth.
All specifications are subject to change without notice.
As with all tube circuits, specifications will vary with tube
brand, age or differences in internal structure.
Pendulum Audio, Inc. warrants to the first purchaser of a
new Pendulum Quartet II Tube Recording Channel that the unit
is free of manufacturing defects in materials and workmanship
for a period of one (1) year from the date of purchase. Pendulum
Audio, Inc.'s sole obligation under this warranty shall be to
provide, without charge, parts and labor necessary to remedy
defects, if any, which appear within one (1) year from the date
of purchase. All warranties expressed or implied made by Pendulum
Audio, Inc., including warranties of merchantability and fitness,
are limited to the period of this warranty. Pendulum Audio, Inc.
is not responsible for indirect, incidental or consequential
damages arising from the use or failure of this product, including
injury to persons or property.
This warranty does not cover damage due to: misuse, abuse,
modification, accident or negligence. The warranty does not apply
if the unit is repaired or altered by persons unauthorized by
Pendulum Audio, Inc. in such a manner as to injure, in Pendulum's
sole judgment, the performance, stability or reliability of the
unit. The warranty does not apply if the unit is connected, installed
or used otherwise than in accordance with the instructions furnished
by Pendulum Audio, Inc. There is no warranty on vacuum tubes
or meter lights.
If the equipment requires warranty repair, return authorization
must be obtained from Pendulum Audio, Inc. prior to shipment.
Equipment should not be shipped to Pendulum Audio, Inc. until
return authorization and the proper shipping address is obtained
from us. The equipment (with all its components parts and connecting
cables) must be suitably packaged, including a note with the
owner's name, address, telephone number and a description of
the reason for return. The owner pays two-way shipping (we recommend
UPS or Fed Ex, not US postal service), and we suggest that the
shipment be insured for its full value.
This limited warranty is in lieu of all other warranties,
expressed or implied, and no representative or person is authorized
to represent or assume for us any liability in connection with
the sale of our products than set forth herein. This limited
warranty gives you specific legal rights, and you may also have
other rights which vary from state to state.
Pendulum Audio, Inc., P.O. Box 339, Gillette, NJ 07933.·
(908) 665-9333 · www.pendulumaudio.com