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Onyx Volume Swell

Based On
BOSS® SG-1 Slow Gear
Effect Type
Volume swell
Build Difficulty
Project Summary
One of the rarest BOSS effects, it acts as a sort of slow noise gate by gradually fading in the signal when it detects pick attack.
Onyx Volume Swell 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

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Project overview

The Onyx Volume Swell is an adaptation of the BOSS® SG-1 Slow Gear, first released in 1979. It’s one of the very first BOSS effects pedals and still among the rarest. It has notably been used by Adam Granduciel (The War on Drugs) and Billy Corgan among others.

The Slow Gear can be described as an attack delay, automatic volume swell, or reverse compressor. It mutes the signal normally, and once the signal level crosses a certain threshold it fades it in at a set rate.

The resulting effect is similar to using a volume pedal, providing a violin-like “attackless” onset of the notes. Internally, it’s more or less a tweaked noise gate—and in fact, the BOSS NS-1 Noise Suppressor is a nearly identical circuit, just tuned for more sensitivity and faster attack.

It’s a simple circuit, far from perfect in execution, but once you adapt your playing to its quirks, it’s a very unique effect that can add a new type of sound to your toolbox.

The Onyx is a direct adaptation of the SG-1 with one modification: we’ve added a Release switch that selects between two additional time constants that determine how quickly the trigger resets after it falls below the signal threshold. This offers a little extra flexibility to help accommodate different playing styles and speeds. It seems to impact the swell speed as well, which extends the usefulness. More on this in the build documentation if you’re curious.