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previous: Morris After thinking about it for a bit I... -- 3/8/2000 3:20 AM View Thread

Re: Aiken "Long-Tailed-Pair" Article A's

3/8/2000 3:31 AM
Randall Aiken
Re: Aiken "Long-Tailed-Pair" Article A's
(1) Yes, I suggested matching the two resistors in case you want to use the second input, such as for a reverb summing point, or a second channel input. If you aren't going to use it, and are just grounding the 0.1uF cap, making the first side (the inverting output) plate resistor smaller than the other side will match the gains a bit more tightly.  
(2) The feedback balances the outputs a bit better, and doesn't require as large a tail resistor. Once again, I assumed you might want to use both inputs (I like to!). The larger tail resistor contributes to better balance and better common-mode rejection, because it better simulates a current source, which has a very high impedance.  
Note also, that the required drive level to the non-feedback PI input will be approximately half that of the feedback PI for the same output clipping level. This of course varies depending upon how much feedback you are using.  
Randall Aiken