Golden Age Project COMP-2A User manual
Vintage Style Tube Compressor / Leveler
COMP-2A
Congratulations on choosing the Golden Age Project COMP-2A Compressor / Leveler!
The COMP-2A is a one channel vintage style Compressor / Leveler using vacuum tubes in the signal and
side-chain path. The input and output is transformer balanced, using two different transformers, each one
optimized for its purpose. This is the way audio components were built before transistors and integrated
circuits became available.
Integrated circuits are small and cheap and widely used in most modern designs. The drawback is that audio
components built with modern technology doesn´t always provide the best perceived sound quality or the type
of character that the modern user desires.
The subjective sound quality delivered by vintage equipment is often prefered over the one delivered by
modern units, a situation that is even more obvious now when music is recorded with clean-sounding digital
audio equipment.
This is the reason why so many vintage audio components are cloned and produced again and also why the
vintage originals are often very expensive on the second hand market.
The circuit used in the COMP-2A is based on a classic design that was originally produced in the early 1960s
and it was initially intended for broadcast applications. It uses an electro-luminescent panel and a photoelectric cell to control gain. This gives it a unique, program dependent compression characteristic. In addition, the
all tube signal path and the transformers adds a wonderful and musical character to the sound.
The ease of use with only two main controls makes it very simple to achieve the desired sound. These attributes has made the original units a favourite of engineers and musicians worldwide. This classic sound is
now available at a very affordable price point with the COMP-2A.
FEATURES
- Vintage style all tube signal path. The tubes are fitted with grounded shields.
- Transformer balanced input and output. Can drive almost any load, balanced or unbalanced.
- Golden Age Project’s version of the classic optical unit using a long life electroluminescent panel and two carefully matched Silonex NSL5910
photoresistors for T4B-style electro-optical gain control with program dependent attack and release times.
- Very simple to operate with only two main controls, Gain and Peak Reduction.
- HF control can make the side-chain circuit more sensitive to mid and high frequency content.
- Linear regulated low noise filament and high voltage power supply.
- A big meter selectable to show gain reduction or output level at two different reference levels.
- Hardwire bypass switch for easy comparisons.
- XLR and TRS input and output jacks for flexible connections.
- Link jack and switch for connecting to another unit for stereo operation.
- All external controls located on the front panel.
- Compact 2RU half rack format. Two units can be mounted with our 19-inch rack kit, the UNITE BIG.
- A solid build quality that will last many years of normal use.
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CIRCUIT DESCRIPTION
The signal first enters the input
transformer that balances the input
signal and increase the level, it is
then fed into both the side-chain
circuit and the gain reduction
circuit.
The gain reduction circuit consists
of a resistor in series with the
photo resistor in the T4B module. The signal then goes to
the GAIN potentiometer and to the output stage that consists of two double-triode tubes, a 12AX7 which operates
as a voltage amplifier followed by a 6N6 which operates as
a cathode-follower. The final component in the main signal
path is the output transformer which provides impedance
matching and a balanced output.
The side-chain section uses a12AX7 double-triode and a
6P1 power penthode tube that drives the electro-luminescent panel in the T4B. The higher the voltage the more light
is emitted on the photocells, their resistance decreases
as the light intensity increases, thereby bringing the audio
signal closer to ground in a R1/R2 resistor attenuator
resulting in a lower signal level (the photocell is the “R2”).
Engaging the HF control, ie turning it clockwise, increases
the side-chain signal level in the mid- and high frequencies
which will increase compression of frequencies above 1
kHz.
USING THE COMP-2A
The best way to explore the possibilities of any compres-
sor and how different settings affects the sound of different
sound sources is to experiment. You can also find a lot of
information on the www helping you to understand how
compressors work and how to use them.
To get started with using the COMP-2A:
- The components in the COMP-2A generates heat, it is very
important that it gets adequate ventilation. Do not cover the
top, back or the side panels of the unit. Make sure that air
can circulate freely through all ventilations slots. Do not use
it in hot surroundings.
- Since audio transformers are sensitive to external electromagnetic fields, try to keep a distance to mains power
transformers in other units as big possible.
- Make sure that the AC voltage selector (above the mains
power socket) is set to the correct mains voltage, 115 or
230V, change the setting if needed.
- Connect the mains power cable. Power on the unit with
the switch on the front panel.
- Connect your line level audio source to one of the input
jacks at the back panel and one of the output jacks to a line
input on the next unit in the signal chain. The TRS and XLR
jacks are connected in parallel so they carry exactly the
same signal, both can be used at the same time in most
cases.
Since the output is transformer balanced and fully floating
towards ground, it doesn’t matter if it feeds a balanced or
an unbalanced input.
- The GAIN control sets the output level. A setting of around
1,5 will result in an output level that is similar to the input
level (= 0 dB of gain) with no compression applied, ie PEAK
REDUCTION set fully counter clockwise.
- Set the BYPASS switch to the IN position, turn PEAK
REDUCTION clockwise until you get the desired amount of
compression, The output level will decrease as compression increases, compensate that by increasing GAIN.
- The approximate amount of gain reduction can be
diplayed by selecting GR on the meter switch. The normal
reading is 0 VU with no compression applied. You can trim
this reading using the ZERO adjustment potentiometer that
is accessed through a hole in the front panel.
The output level can be displayed by selecting +4 or +10 on
the meter switch. The numbers corresponds to the reference level when the meter shows 0 VU. The +10 position is
useful for avoiding the meter needle hitting its end stop at
high output levels,
- You can easily check the effect of the processing in the
COMP-2A by using the BYPASS switch, the unit is completely removed from the signal path in the BYPASS position.
- Setting the LIMIT/COMPRESS switch in the LIMIT position
will increase the compression ratio, resulting in a higher
compression, especially when the unit compresses heavily.
The COMPRESS position is the standard mode.
- Turning the HF control clockwise will make the compressor more sensitive to mid and high frequency content.
- For stereo operation, the side-chain of two COMP-2A units
can be linked together through the LINK jack at the back
panel, using a TRS cable. The MONO adjustment potentiometer can be used to balance the units. An instruction of
the procedure can be found on our web site.
TUBE SUBSTITUTION
There are a number of tubes available from different brands
that can be used in the COMP-2A.
- The 12A7X´s (tube socket “U1” and “U4”) can be replaced
with any equivalent from your favourite brand.
- The 6N6 in socket “U2” can be replaced with a 12BH7.
Please note that you must then move the jumper “TX1”
close to the socket from the “6N6” to the “12BH7” position.
- The 6P1 in socket “U3-6P1” and be removed if a 6AQ5 or
an equivalent is placed in socket “U3-6AQ5”.
DO NOT POPULATE BOTH THE 6P1 AND THE 6AQ5 SOCKETS AT THE SAME TIME!
WARRANTY
The COMP-2A is built to last. But as in any electronic device,
components can break down.
There is a fuse located at the bottom of the mains power
input socket. If the unit dies, please check this fuse. If it has
blown, replace it with a new one.
If this doesn´t help, or if the unit has another problem, it will
need repair and you should then contact the reseller where
you bought the unit.
The warranty terms are decided by the Distributor for your
country. The Distributor will support Golden Age Project
resellers and end users with repairs and spare parts.
REGISTRATION
You are welcome to register your unit at our website:
www.goldenageproject.com
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I would like to thank you for chosing the COMP-2A!
I hope it will serve you well and that it will help you
in making many great sounding recordings.
Yours,
Bo Medin
Vintage character for modern ideas!
WWW.GOLDENAGEPROJECT.COM
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