[EFM] Re: all tranny vca+

[tomg]

I fixed the labels too...It's great having the pc back on the bench
where it belongs...;-)

http://www.xavax.com/efm/pdf/vca-t2.pdf

Tom


> 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
> > 
> > 
> 
>