The Universal Audio 1176 – A Timeless Compressor

1966 was a significant year in the pro audio world, as it saw significant shifts in recording and processing technology. Tubes sounded great, but were difficult to maintain, and wore out, or melted, and had to be replaced fairly often. Bill Putnam, through his experiments with solid state technology, developed preamps and compressors that relied on transistors, rather than vacuum tubes. As a result of this, his 175 and 176 tube compressors were redesigned and rebranded as the Urei 1176 FET (Field-Effect Transistor) based compressor, which was released in 1968, as a peak limiter and leveling amplifier.

The attack time of the 1176, at the time of release, was previously unheard of, and it remains one of the fastest attack compressors till date, with an attack time of 20 microseconds, a mere 0.0002 seconds. At this almost instant speed, it is capable of catching almost 100% of the transients in fast attack instruments like drums and acoustic guitars, and it handled heavy vocal compression without even breaking a sweat. This turned out to become one of the major selling points for the 1176, and the units began to gain popularity all over the world. Another unique feature of this compressor was that it liked to be hit hard in terms of signal level. On average, the 1176 sounded best when it was carrying out 5-7dB of gain reduction, rather than 3dB on average for most compressors. The FET circuitry would generously lend the audio source a characteristic harmonic colouration, even when compression was not being used, and these harmonics would become more and more apparent as the compressor was made to work harder. The effect was so pleasant, in fact, that an auxiliary use for the 1176 was as an audio colouring device, with the attack control of the compressor set to ‘Off’. The preamp had about 45dB of clean headroom, as well, which made the compressor useable as a mic preamp too.

How the 1176 Works

The 1176 has become possibly the most famous example of a feedback compressor (as opposed to a feed forward style). Every compressor has a detection circuit that tells the compression circuit when to adjust the level of the incoming signal. Feed forward compressors have the detector placed before the compression circuit, but feedback compressors have them after the compression circuit. This results in a very slight delay in attack time, and the detector circuit spending most of its time listening to an already compressed signal, which makes the compression itself sound smoother, and more musical. In the case of the 1176, the first thing the audio signal hits is a line input transformer, which colours the sound and makes it harmonically rich. The next part of the circuit involves the FET (the transistor), which acts as a variable voltage control, sending varied signals to the compression and detection circuits. The signal then travels through an output transformer, which applies another layer of colouration to the signal on its way out of the processor. Having so many ‘non-transparent’ components in the circuit meant that the FET had to operate in a very narrow, linear range, and measures had to be taken to enclose the negative feedback of the output amplifier, in order to limit the colouration to musical and useful harmonics, rather than full-blown, heavy-handed distortion.

The compressor has a variable (but not controllable) threshold, which depends on the ratio selected. 4:1 and 8:1 ratios were meant to be used for compression, and 12:1 and 20:1 for limiting. The higher the ratio needed to be, the higher the threshold for compression became, as well. The lowest ratio also had the softest compression curve, or knee, which got steeper and more plateau-like, as the ratio was increased. The input gain control is used to drive the signal to the required amount to meet the threshold, and the output control made up for any gain lost during compression, though driving the input hard also meant having to turn the output control down, in order to maintain constant peak levels through the process. A very unique feature of the compressor at the time of release, was the fact that attack and release time were continuously variable, and not variable in steps. This gave the engineer a lot of precise control over the time constants of the compressor, and allowed them to shape the envelopes more accurately and musically.

Each of the ratio buttons on the 1176 are meant to be used exclusively, but it was discovered that pushing all four buttons in together led to a completely different sound being produced by the unit. Not only did significantly increase the harmonic content of the unit, but it also made noticeable differences to the attack and release characteristics as well. The 1176 has always been a program dependent compressor, that reacts uniquely to the material that is fed into it. This program dependency increases when all buttons are pushed in, and though the reaction to transients remains consistent and faithful, the release characteristics become even more sensitive than usual to the material being fed into the compressor. The ratio of this mode lies somewhere between 12:1 and 20:1, and the compression curve develops a very hard knee, and becomes like a plateau, edging very close to limiting territory. A combination of all this gives the all-buttons-in mode its characteristic over-driven, saturated sound, and has arguably become the compressor’s party piece.

Conclusion

It is safe to say that thousands of brands have created 1176 replicas or tributes, since the compressor gained cult status, and pretty much every plug-in manufacturer has a plug-in that is meant to sound like, and sometimes look like the 1176 as well. The first manufacturer to create an 1176 clone was Purple Audio, with their MC77. Modern revisions and improvements have turned it into an ‘original’, unique compressor in its own right, and there is even a plug-in version of the unit available for purchase now. Black Lion Audio, notably, has recreated famous mix engineer Chris Lord-Alge’s ‘unicorn’ blue stripe 1176, and has dubbed it the Bluey. Warm Audio also makes a fairly faithful 1176 clone.