Audio Combiner

This circuit arose from the need to couple the outputs of two CDROM drives to the input of a single sound card. Simply ‘stacking’ the connectors is possible but not particularly elegant, and the result is somewhat unpredictable due to mutual interference between the two drives. Using a quad opamp and handful of passive components, it is possible to quickly put together a mixer that first buffers the signals before adding them together. This completely eliminates any possibility of feedback or mutual interference.

A 4.7-µF electrolytic capacitor should be connected between R17 and ground. The + terminal of the capacitor is connected to R17. The same applies to R18, R19 and R20.