The Teletronix LA-2A is a hand-wired, tube-compressor. It uses an electroluminescent panel together with a cadmium-sulfide light dependent resistor to provide gain reduction, which is called the T4 cell. The properties of the T4 give the Teletronix LA-2A its unique character by making it an entirely program dependent design. The average attack time is 10 milliseconds, while the release time is about 60 ms for 50% release and 0.5 to 5 seconds for full release, depending on the previous program material.
The Teletronix LA-2A was originally produced in the early 1960s by Teletronix, which was later acquired by Babcock Electronics Corporation. Bill Putnam purchased the product rights and the name Teletronix from Babcock Engineering in 1967, folding it into his Studio Electronics Corporation, shortly before he changed the name to UREI. There were three different variations of the LA-2A during this period before production was discontinued around 1969.
Straightforward in its design, and initially intended for broadcast applications, the Teletronix LA-2A quickly became standard equipment in studios worldwide. Many have been painstakingly maintained for the 30 years that they have remained in use since production stopped. A tube-based compressor, the Teletronix LA-2A features hand-wired components and two simple controls.
At the time, its electro-luminescent optical gain reduction was quite revolutionary: applying the audio signal to an electro-luminescent light panel which shines on a photoelectric cell which in turn controls the gain. In contrast to the electro-optical devices which preceded it, the electro-luminescent light source provided the fast attack necessary for broadcast applications.
Additionally, the cadmium-sulfide photo-cells provided a very natural “two-stage” release which resulted in a compression characteristic more transparent than the other compressors of its day. To this day the Teletronix LA-2A delivers a trademark sound treasured by engineers worldwide.