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1176 Compressor: From Birth to Benchmark in Audio History

1176 Compressor: From Birth to Benchmark in Audio History

Discover how Bill Putnam created the world's most famous limiter.

In 1966, Bill Putnam started using new solid-state technology in his Universal Audio preamps and compressors, replacing the "old" technology of vacuum tubes.

The legendary engineer and equipment manufacturer had previously redesigned his original 108 tube microphone preamp (taken from his UA/United Recording consoles in Chicago and Hollywood), into the new 1108 — using the recently invented Field Effect Transistor (FET).

Subsequently, he redesigned his successful 175B/176 tube compressor using FETs, and thus was born the 1176.

The Introduction of the 1176

Billed in the 1968 release as a “true peak limiter with all transistor circuitry and superior performance on all types of program material," the 1176’s major selling point was its ultra-fast attack time — 20 µS (.00002 seconds) at its fastest setting.

It also offered contemporary design, featuring knobs with clear surrounds, pushbuttons, and a brushed aluminum face panel with a blue stripe near the VU meter — none of those then-typical big Bakelite knobs in sight. The initial price — $489.

The Rev A Bluestripe 1176 compressor is known for its aggressive sound.
The Rev A Bluestripe 1176 compressor is known for its aggressive sound.

Similar to the 176, the 1176 featured no threshold control — just input and output controls — and included a continuously variable attack and release, which was a novelty at the time. The amount of compression was determined by setting the input level — the hotter the signal reaching the detection circuits, the greater the resulting compression.

Another unique feature was the selectable ratios of 4:1 and 8:1 for compression, and 12:1 and 20:1 for limiting.

The 1176 became an instant favorite with producers and engineers because of its unique lightning-fast attack and release times (20 µS to 800 µS Attack, 50 mS to 1.1 seconds for Release), its Class A output stage, and its wide range of sounds, ranging from a very subtle, near-transparent compression at 4:1, to its most notable setting, the “All Buttons In” mode, where all the ratio buttons are depressed simultaneously.

This allowed the 1176 to make a sound unlike any other processor ever heard before. Distortion increased, along with a plateaued slope and a lag time in response to initial transients, creating an explosive sound on drum room mics, making an incredible grungy bass or electric guitar sound, or squeezing a vocal so it sat right in your face.

What does an 1176 Compressor Sound Like?

The characteristic that most 1176 lovers agree on is that what comes out is better than what went in.

Bruce Swedien used his 1176 on all the Michael Jackson vocals he recorded. Some even use the 1176 with the compression turned off, just for the distinctive tone it imparts.

The amplifiers and transformers all by themselves give a desirable “hot” quality to anything passing through them.

Other famous examples of the 1176 are found on Led Zeppelin IV, with the legendary drum intro to "When the Levee Breaks" where engineer Andy Johns used "all buttons" mode to crush the room mics.

The album also features a "non-traditional" use of the 1176 on "Black Dog," where Jimmy Page used two 1176s for some gnarly fuzz.

How the 1176 Works

The 1176 is a “feedback” compressor. The signal goes through the input stage, via the line input transformer, which has a big impact on the sound. From there, the signal is routed to the top of a FET, which is being used as a variable voltage resistor.

Depending on the revision of the unit, the FET is either used to shunt some of the input signal to ground, or as the top leg of a voltage divider in parallel to the input of a pre-amplifier stage. The resistance between the Drain and Source leads of the FET will change in response to voltage applied to the Gate lead.

In the later revisions, the relationship between fixed resistances and the FET’s dynamic resistance affects the gain of the circuit. As the signal flows to the output stage, it is tapped and also sent to a sidechain detector circuit. This sidechain develops a Gate control voltage for the FET based on the dynamics and level of the input signal, as well as the front panel control settings.

Universal Audio engineers bench testing the 1176.
Universal Audio engineers bench testing the 1176.

For minimal distortion, careful circuit design was required to make the FET operate within a narrow linear range. The output stage is an all-Class A line level amplifier, designed to drive the 1960s standard load of 600 ohms.

The output transformer is an integral part of the sound of the 1176, balancing the impedance matching for the output. By enclosing the negative feedback of the output amplifier, its nonlinearities were compensated and corrected for, producing very low output distortion.

Because of the input and output transformers, and the Class A output circuitry, the 1176 has a very distinctive sound even when it is not compressing. By turning the Attack knob fully counterclockwise to the OFF position, the unit can be used as a straight line amp just for its unique sound.

The 1176 also offers a whopping 45 dB of gain at .5% THD — as much gain as some mic preamps, and far more than most compressors.

The input knob controls the threshold, but the threshold is also dependent on the ratio selected — the higher the ratio, the higher the threshold. As the input level is turned up, a corresponding decrease in output level may be required.

The front-panel meter will indicate GR (Gain Reduction) or output level at either +4 or +8 dBm. Output metering (as opposed to GR) will introduce additional distortion.

Brochure for the Brad Plunkett-designed 1176LN.
Brochure for the Brad Plunkett-designed 1176LN.

One of the most popular features of the 1176 is its ability to vary its release time based on program material. After a transient, it releases quickly to avoid level drops, but if there is a continued state of heavy compression, the 1176 will exhibit a longer release to reduce pumping.

Revisions of the 1176

One thing any 1176 devotee knows is that not all 1176s are created equal.

The initial units released in 1967 were A’s, followed within months by AB revisions, and B revs in 1968. Rev C came in 1970, and sported the familiar all-black face panel. These were badged 1176LN, after a redesign by Brad Plunkett lowered the noise and increased linearity.

The D and E revs from 1970 to 1973 are widely considered to be the best-sounding units. Additional gradual design changes were made to the audio circuitry from 1973 onward.

There is often a debate that rages about which revision sounds best, but aging components and the different calibrations of older units can dramatically impact the sound regardless of which revision it is. Universal Audio actually has a full revision history of the 1176 and LA-2A, which you can find here.

In 2000, Universal Audio began reissuing the 1176LN. These units are still handmade today in Santa Cruz, California.
In 2000, Universal Audio began reissuing the 1176LN. These units are still handmade today in Santa Cruz, California.

The Next-Generation of 1176

In 1999, when Bill Putnam, Jr. relaunched Universal Audio, a reproduction of the black 1176LN was the company’s first product. Reissued in 2000, it was based on the circuit designs of the C, D, and E revs.

One of the most critical aspects of recreating the sound of the original 1176 was faithfully reproducing the original output transformer, complete with the additional windings that provided the feedback signal to the final line output amplifier circuit. Bill Jr. found extensive design notes that enabled him to recreate and improve on the original design.

All these factors combine to make the 1176 one of the most unique and beloved compressors of all time with a huge devoted fan base. Still manufactured today, 45 years since its introduction, it is truly a studio legend.

— Lynn Fuston

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