# 1176 Peak Limiter

The 1176 Peak Limiter is a dynamic range compressor introduced by UREI in 1967. Derived from the 175 and 176 tube compressors, it marked the transition from vacuum tubes to solid-state technology.
With its distinctive tone and its wide range of sounds, deriving from the Class A amplifiers, its input and output transformers, the uncommonly fast attack and release times and their program dependence, and different compression ratios and modes, the 1176 was immediately appreciated by engineers and producers and established as a studio standard through the years. At the time of its introduction, it was the first true peak limiter with all solid-state circuitry.
The 1176LN was inducted into the TECnology Hall of Fame in 2008.

## History

In 1966, the engineer Bill Putnam, founder of Universal Audio, began to employ the recently invented field-effect transistors (FET), replacing vacuum tubes in his equipment designs. After successfully adapting the 108 tube microphone preamplifier into the new FET-based 1108, he redesigned the 175 and 176 variable-mu tube compressors into the new 1176 compressor.
The initial units (A and AB revisions) were available in 1967 and were informally referred as "blue stripe" for their blue-colored meter section. Revision C, designed in 1970, saw one of the major design evolutions, with less noise and harmonic distortion. It was renamed to 1176LN and the face color changed to the now familiar solid black.
Bill Putnam sold UREI in 1985 and Revision H was the last series produced by the original company. However, the company was re-established as Universal Audio in 1999 by the sons Bill Putnam, Jr. and Jim Putnam, and re-issued the 1176LN as its first product. The original design was reproduced and revised thanks to the extensive design notes left by Bill Putnam.

## Design

The 1176 uses a field-effect transistor (FET) to obtain gain reduction arranged in a feedback configuration. As its predecessor, the 1176 utilizes soft knee compression and fixed threshold: compression amount is controlled through the input control. The compression character is handled by attack and release times and four selectable compression ratios. The release time is program-dependent: it is quicker after transients to obtain a more consistent level, but it slows down after sustained and heavy compression to reduce pumping effects. The threshold is set higher on higher ratios.
* Four different compression ratios are available: 4:1, 8:1, 12:1, and 20:1
* Attack time is adjustable from 20 μs to 800 μs (0.00002–0.0008 seconds)
* Release times are adjustable from 50 ms to 1100 ms (0.05–1.1 seconds)
* Two units can be linked for proper stereo operation (not just dual mono)

### "All-button" or British mode

The ratio buttons are designed to be mutually exclusive, so that pressing one ratio button deselects the others. However, British engineers discovered it was possible to push all four buttons in at once, an unexpected use case that led to unintended behaviour, with a substantial increase of harmonic distortion. This became known as "All-button" mode or British mode, and is popular enough to be explicitly supported by modern clones of the 1176.
   The way the 1176 sounds, and specifically, the way all-button mode sounds, is partially due to its being a program dependent compressor. The attack and release are program dependent, as is the ratio.
   The 1176 will faithfully compress or limit at the selected ratio for transients, but the ratio will always increase a bit after the transient. To what degree is once again material dependent. This is true for any of the 1176's ratio settings, and is part of the 1176's sound.
   But in all-button mode, a few more things are happening; the ratio goes to somewhere between 12:1 and 20:1, and the bias points change all over the circuit. As a result, the attack and release times change. This change in attack and release times and the compression curve that results is the main contributor to the all-button sound. This is what gives way to the trademark overdriven tone. The shape of the compression curve changes dramatically in all-button. Where 4:1 is a gentle slope, all-button is more like severe plateau! Furthermore, in all-button mode there is a lag time on the attack of initial transients. This strange phenomenon might be described as a "reverse look-ahead".

## Revisions

The 1176 underwent a number of revisions; one notable change in the early revisions was the addition of Brad Plunkett's circuitry, which reduced noise by 6 dB and redistributed the noise spectrum, producing even more noise reduction in the sensitive mid-range; linearity was also increased by reducing harmonic distortion. These revisions, easily distinguishable for their solid black face panel, were labelled 1176LN.
Revisions D and E are reputed to sound the best.
| Revision | Design date | Serial numbers | Notes |
| Revision A | June 20, 1967 | 101–125 | The original design by Bill Putnam; it had a brushed aluminium faceplate with a blue meter section. The output transformer was the UA-5002. |
| Revision AB | November 20, 1967 | 126–216 | Several resistor values changes in signal pre-amp stages improved stability and noise. |
| Revision B | Not indicated | 217–1078 | FETs in the signal pre-amp were replaced with bipolar transistors (2N3391A). |
| Revision C | January 9, 1970 | 1079–1238 | Low noise ("LN") circuitry was added in the signal preamp, reducing DS voltage on the gain reduction FET and keeping the FET within its linear range. The FET feedback circuit was revised to minimize distortion. Program dependency behavior was re-tuned. The faceplate was changed to anodized black. |
| Revision D | Not indicated | 1239–2331 | This revision had no circuit changes, but the additional low-noise circuitry was incorporated into a new main circuit board. "UREI" branding was added to the original "Universal Audio" branding. |
| Revision E | Not indicated | 2332–2611 | New power transformer, now switchable between 110 V and 220 V. |
| Revision F | March 15, 1973 | 2612–7052 | The output amplifier was changed from a class A to a push-pull (class AB) design, based on the 1109 preamplifier, providing more output drive. The output transformer was changed to the B11148 type (already used in UREI LA-3A). Metering circuit now uses an op-amp. |
| Revision G | Not indicated | 7053–7651 | The input transformer was removed and replaced with a differential amplifier. Program dependency behavior was removed. |
| Revision H | Not indicated | 7652–8000+ | The faceplate was changed to the original silver faceplate and included a red "Off" button. The only version with a blue "UREI" logo and without "Universal Audio" branding. |
| Re-issue | 4 January 2000 | 101–1959 | Reproduction based on C, D and E revisions; most resembling the E model, due to the use of the switchable power transformer. |
| Re-issue | 4 January 2000 | 1960–2946 | Input attenuator and transformer changed, since the original Precision Electronics T-pad attenuator and 012 Magnetika transformer became unavailable. |
| Re-issue | 4 January 2000 | 2947– | Production were resumed with T-pad attenuators and 012 Magnetika input transformers. |
| Revision AE | June 4, 2008 | 001–500 | The "Anniversary Edition", limited to 500 units worldwide and resembling the first revisions with a black faceplate and a blue painted stripe, introduced a more moderate compression ratio of 2:1, a slow 10 ms attack and reintroduced revision A program dependency. |

## Reputation

Mike Shipley says "The 1176 absolutely adds a bright character to a sound, and you can set the attack so it's got a nice bite to it. I usually use them on four to one, with quite a lot of gain reduction. I like how variable the attack and release is; there's a sound on the attack and release which I don't think you can get with any other compressor. I listen for how it affects the vocal, and depending on the song I set the attack or release—faster attack if I want a bit more bite. My preference is for the black face model, the 4000 series—I think the top end is especially clean."
Jim Scott says "They have an equalizer kind of effect, adding a coloration that's bright and clear. Not only do they give you a little more impact from the compression, they also sort of clear things up; maybe a little bottom end gets squeezed out or maybe they are just sort of excitingly solid state or whatever they are. The big thing for me is the clarity, and the improvement in the top end."