The Complete Guide to UREI/Universal Audio 1176 Revisions April 18, 2011 08:56 3 Comments
1176 Revison History
Revisions A/AB June 20, 1967: Wild transients tremble in fear of the enigmatic "Blue-Striped Terror."
Bill Putnam created the first 1176 compressor in 1967. Although it was the basis for all 1176 revisions, the rev A has numerous peculiarities that set it apart from the others. It is the only revision to use FETs rather than bipolar transistors in the preamp and line amps. It is also cosmetically unique, sporting a distinctive blue stripe through the meter. Finally, the rev A does not have the low-noise circuitry of later revisions, which means it imparts more harmonic distortion at the expense of a higher noise floor. The Universal Audio website tells us that there were only 25 of this revision made (serial no. #101-125), which makes them about as rare as a piece of gear can be.
Mnats' Rev A PCB is actually based on what UA calls "rev AB," which changed some resistor values and added a bypass cap for the resistor feeding the gain-reduction FET. So, for all intents and purposes it is a rev A 1176, but with a more stable and controllable limiter.
Revisions C/D/E 1970: A clean up, a suffix, and a dark new look.
Most 1176 fetishists reading this have already noticed two conspicuous differences between the rev A and the compressor most of us know today: the black front panel and the "LN" signification. These were both introduced with rev C and codified with the rev D. "LN" stands for "Low Noise," and all of the circuit changes in rev C were intended to reduce noise and distortion. These include reducing the voltage going to the gain-reduction FET to make its operation more linear, and incorporating a Q-bias pot to minimize distortion. Mnats reported that his rev D build tested 3.4dB quieter than the rev A.
Revisions C, D, and E are all in fact the same circuit with some superficial differences. For rev C, the LN circuitry was kept in its own epoxy module to protect the not-yet-patented design, but was added directly to the main PCB for rev D. Rev E merely added 220v operation in order to aggravate transients on both sides of the pond.
Universal Audio's current reproductions are based on these revisions, so if you are looking to DIY an 1176 rather than buying a new one, rev D is the way to go.
Revisions F/G 1973: Pulling out of class A / Integrating integrated circuits.
From the beginning the 1176 had used the class-A 1108 preamp for output gain. Rev F replaced this with a push-pull amplifier based on the 1109 preamp. This gives the rev F more output gain and a slightly different sonic character than previous revisions. In spite of this, this revision measures the lowest harmonic distortion of any revision, making it the best choice for those looking for 1176-style compression with less coloration.
Rev F replaced the UA-5002 output transformer with a Bournes B11148 which, according once again to the estimable Mr. Mnats, adds a small boost in the extreme high and low frequencies.
Revs F and G were also the first to incorporate integrated circuits. First, the rev F switched from a discreet to an opamp-based metering circuit, while the rev G replaced the input transformer with an NE5532 IC. This gives the rev G the potential to be the cleanest 1176 yet.
The Gyraf G1176 is based on rev F, but does not accept Ed Andersons B11148 transformer clone. Both revs F and G can be built on Mnats' rev F PCB.
Revision H The final frontier?
Silver faceplate, red "Off" button, blue UREI logo. That's it. Not much of a revision, really, and to my knowledge it has never been DIYed. Who wants to be the first to clone the front panel of the elusive revision H?
So, which one should I build?Odds are you probably know by now which revision appeals most to you. But in case you are still trying to sort out which one is right for you, let's do a 10-second, over-simplified takeaway:
Rev A: Juiciest, noisiest, vintagey-ist.
Rev D: Lower-noise, classic character. Closest to the modern repros from UA.
Rev F/G: Cleanest, unique output transformer.
Rev H: Snazzy faceplate.
All revisions use the UTC-012 input transformer, except for G, which has no input transformer.
All use the UA-5002 output transformer, except for F/G which uses the Bournes B11148.