CorvusDistortion / Sustainer

From the vendor

The 1978 redesign of the classic Big Muff Pi, using op-amps instead of transistors. Famously used by Billy Corgan on the Smashing Pumpkins album Siamese Dream.

The Corvus Distortion / Sustainer is a clone of the 1977-1980 “op-amp” EHX Big Muff Pi, a redesign of the classic Big Muff circuit using op-amps instead of transistor gain stages. It was designed by Howard Davis, a brilliant EHX engineer who also invented the Memory Man delay and Electric Mistress flanger as well as the Deluxe Big Muff Pi.

He was tasked in the redesign with getting a similar sound to the Big Muff, but the circuit itself bears no resemblance to the earlier 4-transistor circuit apart from the tone control. Therefore, while it was the only commercially-available version of the Big Muff for several years, today it’s seen as a fully separate circuit. (In 2017, EHX reissued this version of the Big Muff, formally adopting its formerly unofficial name, the “Op-Amp Big Muff Pi”.)

The Corvus is more specifically based on the 1978 revision, which added a “Tone Bypass” switch. As inferred by the name, this switch fully bypasses the tone stack for a more raw and aggressive sound.

The Corvus is a direct adaptation of the 1978 circuit except for the inclusion of an optional modification to the gain control, originally conceived by Analogguru. This converts the op-amp configuration into a variable gain stage, whereas the stock unit uses a fixed gain boost followed by a volume control. With this modification, the op-amp isn’t amplifying the signal any more than it needs to. However, the original version can also be built if preferred (see build notes for details).

Note: The PCB-only version of this project uses a type of capacitor that has been temporarily discontinued by WIMA. Please see our news article about the issue and the substitution spreadsheet for project-specific recommendations. We are stocking a limited supply in the mean time. The build document has not yet been updated to reflect this. It does not impact the kits.