all tranny vca+

[tomg]

Juergen said I that I should explain that this is the basic circuit
and that a compensation capacitors and offset trimmers would
be a good idea....Well what he really asked was if it was stable.
LOL.....anyway have fun...

oh....wait....I should really explain huh.....ok..... The fist pair need 
a comp cap. Place a 47pF between the 100K resistors connected
to the collectors.  For offset adjustment, lift the base of the second 
transistor with a 1K resistor to gnd and connect a 100K resistor 
from the base to a 50K trimmer that goes to +/-V.  Maybe change
both resistors to 2.2K......More?? Ok...

The other two NPN pairs could also use a comp cap. You can
put a 1K resistor between +V and the collectors going directly
to +V now. Then place a 22pF to 100pF cap between the 
collectors. Try a 47pF here too. The idea is to kill distortion
without changing frequency response.... 

Compensation capacitors help prevent crossover distortion 
between the diff-pairs. I'm using those 2SC1583s and I'm not
having any problems but hand matched pairs will show some
distortion without  the caps. The offset trim allows you to 
compensate for any voltage shift the circuit imposes on the 
original signal.

Does that cover it all ??

Tom..;-)


> As you guys know I've been working to put together a pile of
> all tranny stuff  because frankly I'm tired searching for 13600s
> and other DIY parts that are harder and harder to get.
> 
> BTW - From what I understand if you need CA3096s you
> better get 'em while you can...anyway.......
> 
> This is an all tranny VCA. Here is another way to build VCFs 
> opamps and VCOs too if you were determined. (I built one 
> of each for fun). NPN pairs are 2SC1583s but the pairs can 
> be hand matched. 
> 
> http://www.xavax.com/efm/pdf/vca-t2.pdf
> 
> Happy DIY
> 
> Tom
> 
>