4 Channel Mixer

 In this post I'll document the making of a 4 channel mixer for audio purposes.


CONCEPT


The mixer is a simple build. It has a volume control and a kill switch per channel and offers two standards for audio input (P2 and P10).


The only difference from the circuit shown above to the one in the mixer is the operational amplifier. The one used was a LM741 which is still not ideal. The best choice would have been a TL071 due to it's low noise feature.

As for the theory behind it, the overwall circuit is an opamp adder. The potentiometers are for volume control and the capacitors offer DC blocking. 
Adding another DC blocking cap at the end creates a high pass filter which is not desirable.

CONSTRUCTION

The components were assembled in a perf. board.


The 'X'ed components were removed from the final circuit. The opamp was mounted in an IC socket for maitenance reasons. The connection to components meant for the pannel are through the pin headers.

The panel was made from a salvaged steel sheet, later painted black and the holes for the components were drilled.


In this picture, the connections from the board to the pannel can be seen. 



The finished mixer mounted on the rack.



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