The Cirrus Dynamic Overdrive project is a clone of the rare Ibanez ST-9 Super Tube Screamer, which was produced from 1983-84. It features a frequency-adjustable midrange boost, which is a unique addition to the Tube Screamer circuit.

The ST-9 was part of the original run of the 9-series, but it was quickly discontinued along with the rest of the series. However, the circuit reappeared the following year as part of the Master Series, called the STL Super Tube. The STL version had broader distribution and is easier to find.

The main difference between the ST-9 and STL versions is the placement of the mid-boost stage. The ST-9 placed it before the clipping, while the STL version placed it after the clipping. This results in a noticeable difference in the mid-boost effect.

The Cirrus project incorporates both versions of the mid-boost stage, allowing the user to toggle between placing it before or after the clipping using an on-board slide switch. This is an update from the original 1590B version of the Cirrus, which used on-board jumpers to set the mid-boost location but couldn’t be toggled.

Additionally, the Cirrus includes a clipping diode switch, which allows the user to select between three different sets of diodes. This provides further versatility and customization options for the overdrive sound.

Summary created by AI from the original source.