Pitchfork pre-amplifier

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I dont think you can change bias current by changing D3 D4..... Q5 Q6 D3 D4 are current limiting cicuit .... short proof for the output ...

R1 & R4 are used to set output stage Q7 Q8 bias ... reduce the value you will reduce bias current ....

R2 R8 are used to set input circuit Q1 Q2 bias ...
 
Having built the preamp part to use it as a line preamp only,i was wondering if i could lower quiscent current bias to something lower like 16-20ma by changing resistors R4,R1 to 47 ohm.With current values of 220 or 330 ohm for R4,R1,output quiscent current is about 80-100ma.

Yes, you can do it in a few ways, for inst. you coud replace R1 and R4 with about 100 ohms and see what you'll get. Another way is to rise the value of output bjt emitter ressistors to about 33 ohms. And there is the third way.....
Try any of those, adjust the values you want and that is it. Will it sound differernt, I don't know, it's a "technical" answer ;)
 
Q5, Q6, D3 and D4 (D5) are CCS for the output stage, not current limiting.
They are current limiters, never operate unless there is an overload. Just run the DC .opt sim
There are 5 Si junctions involved, under steady state conditions there is 624nA flowing in the D3-5 path. Q5,6 are off.
You guys have to learn to use ltspice, it helps in understanding how a design works.
Pete posted the sim, in the 1st post, I download it at that time and played with it some. I just ran it again. To me it is a fantastic design, ltspice shows thd unmeasurable.
When I change R1,4 to 200 ohms, I get a ops bias I of 52mA and the ops bjts dissipate 751mW. the thd still shows unmeasurable. :)
What should this ops bias current be set for and why change it from what pete originally chose?
 
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