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Golden Age Audio Project Comp-2A
The Golden Age Audio Project 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 preferred 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 favorite of engineers and musicians worldwide. This classic sound is now available at a very affordable price point with the COMP-2A.
Image: Golden Age Audio Project Comp-2A
Teletronix LA-2A
The Comp2-A is based on the vintage LA-2A, which was designed and released in the early 1960s by James F Lawrence II under the Teletronix brand, and employed valve gain stages.
Image: Teletronix LA-2A
In the signal path, the Comp-2A employs two tubes: a 12AX7 dual-triode amplifier, and a 6N6 cathode-follower, both of which are dual-triode types. In the side-chain circuitry are two more tubes — another 12AX7 and a 6P1 tetrode, the latter driving the T4B’s EL panel. Golden Age have included an additional tube socket which can accommodate the 6AQ5 pentode used in the UREI/Teletronix version — you can remove the factory 6P1 tube and install one of those. And the 6N6 can, if you wish, be replaced with a 12BH7 too, as in the Teletronix unit
Image: Built with mods in mind: in addition to the four vacuum tubes, there’s a spare socket to accommodate the 6AQ5 used in the original. Copied from SoundOnSound
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.
Operation of the COMP-2A
- 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 displayed 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!
Video
Setup in Skippy Studio
