Cirrus (Legacy)

From the vendor

The Cirrus Overdrive project is a clone of the Ibanez ST-9 Super Tube Screamer, an incredibly rare Tube Screamer variant from the early 1980s. It’s a stock Tube Screamer with an added stage, a semi-parametric midrange control that delivers a fixed 24dB boost at a variable frequency. In this project, you can choose whether the boost is placed before (ST-9) or after (STL) the clipping stage, or even omitted altogether if you want to build a classic Tube Screamer. There is also a clipping diode switch so you can set up a second set of diodes, and if you use a center-off switch, you can lift the diodes entirely in the middle position.

The original ST-9 uses a 20kC dual pot for the midrange control. This value is not available to the DIY scene as of right now. Accordingly, for this project, the surrounding values in the parametric filter have been modified so you can instead use a 100kC dual pot (which is much easier to find).