Schematics / Serge VCA As Suggested By Serge Tchernepnin In An Old Issue Of Electronotes
Serge VCA as suggested by Serge Tchernepnin in an old issue of Electronotes . Schematic shared by Jörgen Bergfors ,visit http://hem.bredband.net/bersyn/VCA/vca_shootout.htm Jörgen's DIY VCA shootout for in detailed analysis on various VCA's . On this LM13700 based circuit Jörgen wrote :
It has the resistors on the inputs connected to -15V instead of ground. The theory was that the linearizing diodes would be more effective that way. The output stage is like LM13600 VCA 1. The contol caracteristics are the same as the other LM13600 VCAs. Whatever the theory behind ths circuit was, it seems to be wrong. This circuit performs terrible, compared to the one from the National Semiconductor application notes. The distortion is very high regardless of signal level. It seems the linearizing diodes overcompensate the linearity error in the amplifier. Another problem is that the signal bleedthrough is alarmingly high. Only 59 dB attenuation at 10 kHz is not enough.
make sure you visit http://hem.bredband.net/bersyn/VCA/lm13600%20vca%20Serge.htm for details on the performance of this circuit .