Published in issue 312, July 2002
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.
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Please note. In view of the complexity of international markets, Elektor cannot guarantee the availability of components for this project.