AW: Tempco Update

[gstopp at fibermux.com]

     Hey!!! My ASM-1 uses a unity gain CV summer with a 56K/1K divider 
     driving the base of the antilog transistor! Why didn't I think to try 
     that??? No feedback loop involved. Okay since the tempco samples I 
     have are 2K I can just make a 112K/2K divider... will this be a low 
     enough impedance to drive the transistor's base? Aw heck I'll try it 
     and let you guys know.
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: AW: Tempco Update
Author:  Haible_Juergen#Tel2743 <HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de>
at ccrelayout
Date:    5/9/96 7:20 PM
     
If you put too much inductance into the feedback loop of an opamp (as in 
the usual EN circuit, where the tempco resistor is placed there), you 
might get some trouble, as the opamp has incresaed gain at higher 
frequencies then, and it might not be internally compensated for this 
condition. Well, I said "might" - we'd have to calculate this. But
you could easily try if this problem also occurs when you use
a passive resistor divider with the tempco resistor! Just try to build 
the adder with a 100k in the feedback, and go with a passive divider 
to the base of the antilog transistor!
You could also try and use an externally compensated opamp with 
a rather oversized capacitor.
     
BTW, I asked Stefan where he got his tempcos for the Transistorbass-3, 
and he said they were manufactured to order in Japan. Well, I always 
was sure he would clone something as close as possible (;->), but
this is surely bad news as I expected to find another source for 
tempcos!
     
JH.