Easily one of the most cloned pieces of audio hardware ever produced, the legendary 1176 Limiting Amplifier has been widely used in the recording industry since its introduction.
Built in 1967, the 1176 marked the end of the vacuum-tube era, as the design evolved from the Universal Audio 176. This was a tube-based variable-mu compressor with four selectable ratios and variable attack and release controls.
It was then replaced by the 1176, which at the time was the first transistor-based compressor produced in the USA.
The design of the 1176 Limiting Amplifier
An input level-dependent feedback compressor by design, the 1176 uses a line input transformer and a variable resistor in the form of an FET (Field Effect Transistor), which controls the gain reduction.
In some of the revisions, the FET directs a portion of the input signal to ground, while others use it as the top leg of a voltage divider which is placed in parallel to the preamp stage input.
As the design evolved, the overall gain of the circuit was directly affected by the relationship between fixed resistances and the dynamic resistance of the FET.
The 1176 revisions
The 1176 underwent many revisions over the years, from cosmetic changes to using different input and output transformers and overall efficiency improvements. It’s important to note that the sound does differ between revisions, so let’s find out why.
Blueface (Rev A/AB/B)
The first Blueface 1176 was built in 1967 and became the foundation for all the revisions that would follow. Compared to others, the initial Rev A model has some differences in that it uses an FET in both the preamp and the line amp.
In addition, the Rev A does not have low-noise circuitry. This means you get far more harmonic distortion with an increased noise floor. With only 25 Rev A units ever produced, this makes it one of the rarest vintage compressors ever.
Rev AB tweaked a few resistors and a bypass capacitor was added to the circuit feeding the gain-reduction FET. As a result, the limiter performed in a slightly more predictable way and could be controlled more precisely.
Blackface (Rev C/D/E)
From Rev C onwards, all of the improvements in circuitry were intended to reduce noise and distortion. So apart from the black front panel, the model now bore the LN (Low Noise) designation.
The gain-reduction FET now functioned in a more linear fashion, as its voltage intake was decreased. In addition, a Q-bias pot was added to the circuit to reduce distortion.
This LN circuitry was only patented in Rev D, so Rev C used a specially designed epoxy module to protect it. Meanwhile, Rev E brought in 220v operation, to the joy of users in the UK, Europe, and the rest of the world.
Revision F still retained the formidable-looking black faceplate, but the 1108 class-A preamplifier that was used in the output gain circuit up until that point was replaced with a push-pull amplifier based on the 1109 preamp.
With this addition, Rev F could produce more output gain. However, the overall sound is characteristically different from the previous versions, as it produces the lowest distortion readings of any revision.
Both Revs F and G used integrated circuitry for the first time. While F altered the metering circuit from discrete to an opamp-based design, Rev G then swapped out the input transformer with an NE5532 IC.
Silverface (Rev H)
Some 1176 enthusiasts may claim it’s the most aesthetically pleasing version, but the improvements introduced in Rev H were precisely that – aesthetic.
All the key circuitry changes from Revs F and G were maintained, but there were a few minor tweaks.
Apart from the silver faceplate, these included a red “off” button, a blue UREI logo, and a new Modutec “lightbox” type VU meter with two internal lamps.
Universal Audio Reissue and Anniversary Edition
In 2000, the newly re-established Universal Audio brand launched the 1176 LN as its first offering. This reissue was closely based on the revisions from the C, D, and E era but as it was 220v compatible, it’s closest to the Rev E design.
This reissue proved immensely popular and is still available today. Moreover, the classic tracking channel strip pairing of the Neve 1073 preamp and the 1176 remains one of the standards for vocal recording.
Universal Audio later released a special Aniversary Edition in 2008 with a return to the character of the Rev A. There were many more incredible features added, but only 500 units were ever produced.
Which is your favourite version of the 1176? Please let us know in the comments below!
More about the 1176 Limiting Amplifier:
- 1176 Revision History
- Building an 1176
- 1176 History at Universal Audio
- All about compressors
- Leveling amplifiers
- Thomann’s guide to compressors
- Everything vintage
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- Blueface: Universal Audio
- Blackface: Vintage King
- Silverface: BAKU Pru Audio