From Designer Tim Caswell’s own hand:

The amplifier (AMP) is a 2 stage Class A discrete design using 3 pairs of hand matched transistors. Envelope is usually applied to ST1/1. ST1/2 goes thru an attenuverter and can be used for envelope or modulation. ST2/1 goes to the 2nd stage, and is typically used for volume control. ST2/2 goes thru an attenuverter and is typically used for modulation.

The AMP, the 5089, and the 3003 are Class A circuits. They draw more current from the +12 rail than from the -12 volt rail. If the system power supply is under-sized, hum or buzz may be heard. In that case, larger filter capacitors and/or a larger power transformer will be needed. The 4075 draws equally from both rails, and is more immune to hum. Like our filters Boomstar Modular AMPs are hand-built entirely in the U. S. of A—just ask Rachael Herbison!

Two attenuverters and two attenuation pots control the INPUT, ST1 CV2, ST2 CV2, and OUTPUT, delivering smooth, detailed, and complex expression.

Uber useful continuous hypnotic DRONE for endless sustain/release, and DRIVE—the overdrive circuit from the Boomstar desktop—for last stage energy, bite, soft clipping, and gonzo ’70’s era “Distortion +” crunchy fuzz.

Six patch points: INPUT, ST1 CV1, ST1 CV2, ST2 CV1, ST2 CV2, OUTPUT direct the deepest manipulation.

INPUT – Adjusts the audio input.
ST1 CV2 – Adjusts stage 1, control voltage 2.
ST2 CV2 – Adjusts stage 2, control voltage 2.
DRONE – Sustains the last note received.
DRIVE – Final output stage overdirve/saturation.
OUTPUT – Adjusts the audio output.
INPUT – Audio input.
ST1 CV1 – Stage 1, control voltage 1 input.
ST1 CV2 – Stage 1, control voltage 2 input.
ST2 CV1 – Stage 2, control voltage 1 input.
ST2 CV2 – Stage 2, control voltage 2 input.
OUTPUT – Audio output.

Size – 8hp
Depth – 39.7mm with ribbon cable attached
Power Usage – 35mA, 12mA (+12 / -12)