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audio mixer board

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adam12

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hi, i am trying to build an audio mixer board to record/mix a small number of tracks. i have been looking around for schematics and have found many different opinions and methods. i want to start with a few microphone and line inputs with preamps, then mixed together with a final summing amplifier. i have seen schematics using either op amps or transistors for the amplifiers. is one kind better the other (lower noise)? any schematics or any other links or ideas would be greatly appreciated.

adam
 

crust

Member
I would use the op-amps with as high a rail-to-rail voltage as possible. The op-amps are simpler to use, you can find them with countless parameters and it will make your circuit smaller. Using high rail-to-rail voltages will allow lots of dynamic range. Commercial mixers sometimes use rail voltages of +/- 30 or so to get lots of clean signal.
 

adam12

New Member
thanks for the quick reply crust

i have seen many different op amp designs including using the inverting and non-inverting inputs, grounding the inverting input etc. do these different configurations affect the quality of the amplification? (i am trying for the cleanest, low-noise configuration) or is it the quality of the op amp that will determine the quality? any recommendations for the best low-noise op amps or any other schematics of good configurations would really help

thanks

adam
 

crust

Member
An op-amp can be used in many configurations, two of them you mentioned were inverting and non-inverting. Depending on the gain you desire phase inversion may or may not matter. The issues that come into play are stability, gain, and bandwidth. For instance if you want a unity-gain circuit, the non-inverting version will require no resistors whereas the inverting version requires 2 resistors. You also get more bandwidth out of the non-inverting unity gain configuration. Perhaps somebody else can suggest suitable amps though it is probably not too difficult to find them designed specifically for audio (for video they definately exist and are labeled as such).
 
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