The output stage of the 1176 is a carefully crafted class A line level amplifier, designed to work with
the (then) standard load of 600
Ω
. The heart of this stage is the output transformer, whose design
and performance is critical. Its primary function is to convert the unbalanced nature of the 1176
circuit to a balanced line output, and to provide the proper impedance matching to drive the line
impedance of 600
Ω
. This transformer is critical due to the fact that it uses several additional sets of
windings to provide feedback, which makes it an integral component in the operation of the output
amplifier. Putnam spent a great deal of time perfecting the design of this tricky transformer and
carefully qualified the few vendors capable of producing it.
The first major modification to the 1176 circuit was designed by Brad Plunkett in an effort to reduce
noise--hence the birth of the 1176LN, whose LN stands for low noise. Numerous design improvements
followed, resulting in at least 13 revisions of the 1176. The D and E 'black-face' LN revisions are
widely considered to be the best-sounding models; therefore Universal Audio modeled our reissue after
these two models.
The LA-2A
The LA-2A leveling amplifier, a tube unit with hand wired components and three simple controls, was
introduced in the early 1960s. It utilized a system of electro-luminescent optical gain control that was
quite revolutionary; gain reduction was controlled by applying the audio voltage to a luminescent
driver amplifier, with a second matched photoconductive cell used to control the metering section.
With its 0 to 40 dB of gain limiting, flat frequency response of 0.1 dB from 30-15,000 Hz 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 produced by Teletronix in Pasadena, California,
which became a division of Babcock Electronics Corp. in 1965. In 1967 Babcock's broadcast division
was acquired by Bill Putnam Sr.’s company, Studio Electronics 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.
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