[sdiy] Re: Resistor war and 22K

[Lincoln Fong]

On the subject of noise Im sure someone can answer this: I notice that
virtual earth mixing amps almost always use 22K input resistors from the mix
busses. When using a simple opamp circuit the feedback resistor will be 22K
also. But suppose you try and squeeze some gain out of this circuit by
increasing the feedback resistor to 100K or try and increase the input
impedance because you want to make a mixer that can accept (non buss)
signals of a higher impedance and what happens: A lot more noise than you
bargained for in my experience.
For some reason mixer circuits prefer unity gain and additional gain stages
are added elsewhere. Can someone explain this please? What's magic about
22K?
Lincoln