Rocket Drive


This is our take on a classic CMOS overdrive circuit.

A bit of history:

In 1975, Craig Anderton wrote one of the coolest books ever - “Electronics Projects for Musicians”. I found my copy as a kid in a secondhand bookshop in the 1990’s on a family road trip to country NSW. Project No. 24 in the book was a dirt box called the “Tube-Sound Fuzz”. This funky little circuit is designed around something called a CMOS chip. CMOS chips are the basic building blocks of old-school computers form the 70’s… We’re talking about ‘Pong’ consoles and that sort of thing.

You see, CMOS chips are full of FETs and with pretty clever design tricks, you can get these things to push though guitar signals instead of 1’s and 0’s. What you get is some really dynamic, warm and very 70’s sounding overdrive. We thought we better have a play with this circuit before they stop making these chips - yep, these chips still made from the exact same recipe that was developed over 40 years ago.

We’re not the first to take on this circuit. There are some huge names in pedal building that have CMOS overdrives, all based on the basic “tube-sound fuzz” style circuit… So we took the concept, respected its roots and added a few tasty Red Sun tweaks.

We took a close look at the gain and filtering of each stage and tweaked to really enhance the natural warmth and dynamics of the CMOS circuit. While ‘tube-sound’ is probably a bridge too far, it has a great sound signature all of its own, and really does react to playing dynamics in a similar way to a triode front end. The Rocket Drive gain control lets you go from adding a bit of warmth and compression all the way to a nice fat overdrive sound - I kind of picture plugging a cherry red SG into this thing.

The tone control (an unusual thing for a CMOS drive) is a simple low pass filter circuit. This seems to work best for this circuit as it lets you taper off some of that top-end harmonic if you need to. If you really want to, you can take the tone all the way down to get those nice muddy old -school rhythm tones.

A couple of last notes; as usual, the circuit is true bypass, and we’ve added a low noise active buffer to the output to stop any tone sucking.