[time-nuts] Isolation amp transistors

[ed breya]

Thanks Gerhard, for putting up the schematic. After a quick look, I'd 
recommend trying the following changes. Of course, I don't know the fine 
details, so this is just from a general circuit perspective - could be 
all wrong versus the actual situation.

1. Delete the Q7 circuitry including R10 and R11, and take +2.7 V bias 
from D2, bypassed by a good cap. Around 220 to 1k ohm (depending on Q2's 
gain and final emitter current needed) from there to the B2 node may be 
about right. This puts Q2's emitter around 2 V, and the R8, R1 and C9 
combo can set the DC bias and AC gain somewhat separately.

BTW, if Q7 and its circuitry are as shown, it appears that the DC base 
bias loop provides positive feedback rather than negative. Unless I'm 
missing something, I don't think this is what you want. It may be moot 
anyway, if a simpler scheme is used.

2. Change the base resistors R3, R4, and R16 to something around 2.7 to 
10 ohms range, and optionally delete C3.

3. Consider deleting R14 or raising its value, and just let L1 terminate 
the DC. This can reduce the DC bias needed, or get you up to 3 dB more 
gain. You can make a matching network if needed, depending on the output 
cable driving situation.

Ed