Available as an assembled Module and as a DIY project.
This Module is currently available.
4-input dc coupled mixer
This module is a DC Coupled mixer with four inputs, attenuators, unity gain and an output attenuator.
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.