No NFB line amp (GainWire mk2)

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I think that I mentioned that in this thread, I am not sure. Yes it is possible to make R17 a volume attenuator, let say if you use 2k potentiometer instead R17, but remember this is possible only in NGNFB only, so forget CFA part. There is not easy to find good quality 2k log pot or stepped volume attenuator.

According to simulations, the lower the value of R17, the lower the distortion.

The quality of the pot is determinant off course but it is not worst than it's effect in the input I guess.

As usual I would like to take this build as a lesson because I feel it is not a very good idea to just build things without fully understanding the concept.

Can you please describe the circuit using plain English language ?

What is the purpose of the building block Q6 Q8 Q9 Q10... and why is there a zobel (C2 R39) ?
 
According to simulations, the lower the value of R17, the lower the distortion.

The quality of the pot is determinant off course but it is not worst than it's effect in the input I guess.

As usual I would like to take this build as a lesson because I feel it is not a very good idea to just build things without fully understanding the concept.

Can you please describe the circuit using plain English language ?

What is the purpose of the building block Q6 Q8 Q9 Q10... and why is there a zobel (C2 R39) ?

My first GainWire preamp with a current conveyor as a building block was described here http://www.diyaudio.com/forums/analog-line-level/223835-current-conveyor-voltage-amplifier.html and maybe you could find your answers there, but I think I described a current conveyor principle here too.
C2 and R39 are not a Zobel but shunt compensation.
Regarding the pot if used instead R17 it's passing higher current then if in input, so ordinary pot could deteriorate fast.
 
Today I measured 100 BC550C and 100BC560C.

Unfortunately I found only
20 x BC550 matched to 680Hfe and
20 x BC560 matched to 640Hfe

Hope this Beta differences do not create difficulties in the mirrors, the input or the output buffer.
 
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