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UAD Powered Plug-Ins Manual - 316 - History
CHAPTER 31
History
LA-2A
The LA-2A leveling amplifier, a tube unit with hand wired components and
three simple controls, was introduced in the mid-1960s. It utilized a system of
electro-luminescent optical gain control that was quite revolutionary. Gain re-
duction was controlled by applying the audio voltage to a luminescent driver
amplifier, with a second matched photoconductive cell used to control the me-
tering section. With its 0 to 40 dB of gain limiting, a balanced stereo inter-
connection, flat frequency response of 0.1 dB from 30-15,000Hz and a low
noise level (better than 70 dB below plus 10 dBm output), the LA-2A quickly
became a studio standard. Originally patented by Jim Lawrence, it was pro-
duced by Teletronix in Pasadena, California, which became a division of
Babcock Electronics Corporation. in 1965. In 1967 Babcock's broadcast di-
vision was acquired by the legendary Bill Putnam's company, Studio Electron-
ics Corporation shortly before he changed the company’s name to UREI®.
Three different versions of the LA-2A were produced under the auspices of
these different companies before production was discontinued around 1969.
1176LN
It was Bill Putnam himself who, in 1966, was responsible for the initial design
of the 1176. Its circuit was rooted in the 1108 preamplifier which was also
designed by Putnam. As is evident from entries and schematics in his design
notebook, he experimented with the recently developed Field Effect Transistor
(F.E.T.) in various configurations to control the gain reduction in the circuit. He
began using F.E.T.s as voltage variable resistors, in which the resistance be-
tween the drain and the source terminals is controlled by a voltage applied to
the gate. His greatest challenge was to ensure that distortion was minimized
by operating the F.E.T.s within a linear region of operation.