AW: Re: AW: Re: PCB for MAT-04 VCA

[gstopp at fibermux.com]

     I did look at CV rejection, which was not real good (no input, sine 
     wave to CV input, monitor output) somehwere on the order of tenths of 
     a volt). However I did not try to correct for it, nor did I examine it 
     during the heat-gun test.
     
     I was able to make a "real" exponential VCA by re-creating the 
     3080-type tri-square VCO exponential converter, and just using the 
     3080 part as a VCA rather than as an integrator. This worked great, 
     although when the gain was unity at CV = 5V, adding to this CV just a 
     little causes the VCA gain to increase very rapidly (exponentially, 
     even!) into distortion. Maybe a zener to limit the CV?
     
     - Gene
     gstopp at fibermux.com


______________________________ Reply Separator _________________________________
Subject: AW: Re: AW: Re: PCB for MAT-04 VCA
Author:  Haible Juergen <Juergen.Haible at nbgm.siemens.de> at ccrelayout
Date:    2/27/97 2:33 AM
     .
     .
     .
How about CV rejection? I think this would be the most critical point. 
The opamp at the output calculates the difference of the two branches 
and thus eliminates the DC offset currents.
But if the transistors which control the current distribution in each 
branch have different gain (due to mismatch or temperature),
I'd expect a serious CV feedthru.