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need help with adding active mixer? Answered

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Hello .i need help with adding a active mixer before the "MXR headphone amp" .

The images bellow are the original schematic and my new schematic

my question is :
1.will this circuit work properly ?
2.i need the gain of mixer = 1 , so Ra=Rb=Rc=Rd , but what value should i use ?
3.What value should i use for Ca,Cb,Cc ?
4.What value should i use for Rx

Thanks in advance!
sorry for my bad English!

1 Replies

steveastroukBest Answer (author)2012-05-19

I'd say try 10K for the resistors and 0.47uF for the caps - but use something like polyesters. Basically, you want the impedance of the caps to be << input impedance of the amp, which is set by the resistors you use. The impedance of the caps is 1/2 pi x f x C - guess at the lowest frequency you're expecting a response at.

Rx should ~4.7K (Ra // Rd) , but I hate that biasing network - you WILL insist on using it, despite the fact its output impedance is very high. You really should use a unity gain buffer instead.


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