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Quartz Optical Compressor

Based On
Diamond Compressor
Effect Type
Build Difficulty
Project Summary
A vintage-inspired optical compressor with an EQ adapted from hi-fi consoles of the 1970s and 80s.
Quartz Optical Compressor printed circuit board

Printed Circuit Board

What's included?
PCB only. Build instructions and parts list can be viewed or downloaded from this page.


In stock

Complete Kit

Not yet available.
Kits are developed based on interest, so if you’d like to see one for this project, let us know.
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Project overview

The Quartz Optical Compressor is based on the Diamond CPR-1 Compressor and BCP-1 Bass Compressor, two vintage-inspired optical compressor pedals that share the same overall schematic.

The original Diamond Compressor was released in 2005. Like other optical compressors, it used an optocoupler for dynamic gain reduction. But the tone control was something never seen before in a pedal: an adaptation of the “Tilt” control from the Quad Model 34 hi-fi preamps of the 1980s, which is similar in usage to the bass/treble pivot of the Big Muff tone control, but refined so that it has a truly flat frequency response in the middle.

The Bass Compressor followed in 2009 after many requests for a bass-specific variant. While the original compressor worked fine on bass, the tone control’s pivot frequency was not optimized for the bass guitar’s sweet spots. A toggle switch was added to switch between 900 Hz (the value of the original Diamond Compressor) and 250 Hz. The envelope detector circuit was also made more sensitive so it reacts better to bass-specific styles of playing.

In 2020, Diamond Pedals ceased operations and all pedals were discontinued. The brand was later sold to SolidGoldFX, who relaunched new compact versions of Diamond’s most popular circuits in 2023. These have been very well received, but are not identical circuits to the original versions.

The Quartz is an adaptation of the original Diamond circuits that allows either the standard or bass version to be built. Our version also adds a third position to the frequency selector, which is a feature in the 2023 compact pedals but not the originals.