CalypsoCMOS Drive

From the vendor

An overdrive using cascaded CMOS inverters in an amp-like topology, with a result that lands somewhere between Marshall and Orange in tone.

The Calypso CMOS Drive is based on the Catalinbread Supercharged Overdrive, a hex-inverter drive circuit first released in 2004 and traced by Aion FX in 2021.

Catalinbread was known for tweaking circuits along the way, especially in the early years, with no allegiance to a particular schematic. The SCOD appeared in a few different editions, starting life as a horizontal layout similar to ZVEX pedals before moving to the more traditional vertical format. So while it had been traced once in the past, we thought it’d be worthwhile to get a definitive trace of the most recent version before it was discontinued, both to verify the original trace and to get a record of circuit changes that may have been made along the way.

The SCOD is unique in its use of the CD4007 CMOS chip, compared to other similar circuits such as the Way Huge Red Llama or EHX Hot Tubes that use the CD4049 and CD4069. The 4007 provides direct access to the complementary MOSFET pairs on the chip, which in theory makes it more flexible. However, in this application the three MOSFET pairs are wired as inverters, meaning they should perform basically the same as the 4049/4069.

Despite this, the SCOD is still a very unique circuit that stands apart from the others, with an amp-inspired global feedback that serves as the tone control. It’s voiced similarly to Marshall “Plexi” or Orange amps, and fills a space not otherwise occupied by the rest of Catalinbread’s amp-drive lineup.

The Calypso is a direct adaptation of the SCOD with no mods or changes other than increasing the amount of power filtering.

Note: 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.