This is plain mixer, may be used also for DC signals, like control voltages. OP249 fast precision opamps were used for their low ofset and good dynamic parameters, but mostly because they are my opamps of choice at the moment. Master gain pot simply changes summer gain, so by adjusting it at appropriate levels it's impossible to overdrive even with all inputs fully open and active. Little helper - clip indicator lights up when output amplitude reaches limits of linear operation, i.e. when output dangerously reaches power rails causing distortion.
In my modular I use +/-12V power, but this circuit can work with any voltage from +/-5 to +/-15V. Master gain pot, not shown in the schematic is a 200k linear taper with shunt resistor selected to achieve unity gain when input and master pots are fully open.
- MASTER knob:
- master volume
- IN1-IN6 knobs:
- individual inputs attenuators
- PEAK lamp:
- clip indicator
- OUT, INVERTED OUT