User Manual

UAD Powered Plug-Ins Manual - 260 - History
After several unsuccessful attempts at using F.E.T.s in gain reduction circuits,
Putnam settled upon the straightforward approach of using the F.E.T. as the
bottom leg in a voltage divider circuit, which is placed ahead of a preamp
stage.
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 ohms. 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 ohms. These two jobs are accomplished by the pri-
mary and secondary windings whose turns' ratio defines the impedance ra-
tio.
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 ca-
pable 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. Legend has it that the D and E blackface revisions
sound the most “authentic”.
The original Universal Audio 1176LN designed by Bill Putnam was a major
breakthrough in limiter technology – the first true peak limiter with all transis-
tor circuitry offering superior performance and a signature sound. Evolved
from the popular Universal Audio 175 and 176 vacuum tube limiters, the
1176LN retained the proven qualities of these industry leaders, and set the
standard for all limiters to follow.