UREI continued making the tube-based LA-2A until 1969, but in the interim released several other versions LA-3A, LA-4 and LA-5. Two years later, Studio Electronics, the company owned by Bill Putnum (and soon to be renamed UREI) bought out Babcock. In 1965, a company called Babcock Electronics bought Teletronix from Lawrence. The LA-2A offered program- and frequency- dependent gain reduction (the latter through an adjustable sidechain), with a unique smooth and natural sound, and continued to gain popularity in the pro audio world. Then in 1962, the even-more-refined LA-2A was introduced, featuring a new wiring scheme and quieter operation. Lawrence continued to refine his design, subsequently releasing the LA-2, a unit that got picked up by large broadcast and recording companies like CBS and RCA. However, one of them found its way to Gene Autry, the famous singing cowboy and movie actor, who used it for recording sessions and radio broadcasts, and spread the word to industry colleagues about the product. Its first product was the LA-1 (LA, of course, stands for “Leveling Amplifier”), of which only about 100 were made.

Lawrence launched his own company, Teletronix, to implement his design. Photo resistors sensed the brightness and lowered the output gain proportionally. He developed his novel concept into the T4 optical attenuator, a component that featured an electroluminescent panel inside it that glowed more brightly as the input gain increased. It occurred to him that optical sensing circuitry could be used in the design of such a device, and the the idea for an optical compressor was born. While working at KMGM radio in Los Angeles, Lawrence realized that it would be a lot easier to control signal levels if it could be done automatically, rather than riding a fader or knob. Top to bottom: a mid-'60s gray-faced LA-2A, a late '60s “Silver” version, and an LA-2.

Uad fairchild 670 gain staging