This module is a DC Coupled mixer circuit similar to CGS04 or AI002. Mixers are important for summing oscillators to make more complex sound, summing control voltages for making more complex modulation, or summing audio to combine cables at the output. Level shifting is important in all these applications, so this module lets you control the input levels of 4 signals and the output level after that. Five knobs in 6HP can be a little tight, so you might want smaller knobs.
| Price | Note | |
| PCB/Panel | $20 | |
| Full Kit (incl pcb/panel) | $60 | |
| Built & Tested | $110 |
Power Draw is about 4mA on each power rail, just the one TL072.
Module size is 6HP wide, 3U tall, and about 25 millimeters deep, very skiff friendly.
BOM – Build Guide for v101
BOM – Build Guide for v111 and an ibom.
All parts are through-hole, and use 1/4 watt resistors.
Troubleshooting
I’ll add tips here for building, as problems arise.
The electrolytic caps are marked to go on the inside(top/front) between the faceplate components, just to use some space there and have fewer big things hanging off the rear. It’s very tight in there on the v1.0 edition, so you should click in the potentiometers and fold over the electros before soldering them. Then unfold to continue with all the resistor soldering. You could carefully put the electros on the outside back, respecting original polarity.
Options
In V1.0 R7 and R3 set the maximum output gain, they’re equal by default, for a 100% unity, but some alteration could give you a 2x final output gain. Subject to the quality of your opamp choice. In V1.1 they’re called R7 and R9.
It can me easily modded to have various output gain. If R7 is 100K then it’s unity gain, if R7 is 200K it’s a 2x max output, and the final knob would be unity at 12 o’clock. If for some reason you wanted the output to drop a 10Vpp synth level signal to a 1Vpp line level, put a 10K in for R7. I like the idea of more than unity gain, but to be wary of clipping, I might recommend going to 150K on R7.