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The first Q&D compressor was first posted back in the late 1990s on the AMZ site and is an adaptation of the basic datasheet circuit to make it compatible with guitar use. The circuit was built and used successfully by a large number of pedal builders.

The new S-Comp version is an updated and expanded circuit design that includes some extra features for better interfacing with guitars and pedals. It can also be used with bass guitar without having to make any mods or changes to the circuit.

These pc boards were originally made several years ago but the project was dropped when the DIP version of the compressor chip was discontinued by the manufacturer. I recently secured a handful of these rare chips and decided to make the project available for DIY use.

The Analog Devices SSM2165 is a compressor on a chip, which has an internal voltage controlled amplifier and an RMS detector circuit. I have found that the action of this circuit on the guitar signal seems to be smoother and less like a hard limiter than the common circuits based on the 3080 OTA. Also, the more modern VCA in this chip results in less distortion and a full range response, which gives a more transparent sound to the compressed signal.

The S-Comp also has an internal noise gate that shuts off annoying background hiss than can be a problem with many compressors. The 2165 chip does not allow adjustment of the noise gate threshold. The signal level is also limited to -9.8dBu (250mv rms) so it cannot overload the devices following it in the signal chain.

The layout, parts list, schematic and instructions for assembly with mods is provided to everyone who buys the pcb.

The SSM2165 compressor chip is included with the pcb purchase and you must provide the remainder of the parts, enclosure, jacks, switch, knobs, etc. I do not have enough SSM chips to sell them separately at this time.


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