LM13600 VCA 2

This circuit is identical to LM13600 VCA 1, with the exception of the output stage. Here, the load resistor is in the feedback loop of an inverting amplifier, instead of connected to ground. The effect this has on performance turned out to be neglible. Signal bledthrough seems to be very slightly better, which makes this circuit to the overall winner.

Noise & signal attenuation

Red = signal bleedthtrough at 0V CV. Blue = 10V CV, no signal. Green = 0V CV, no signal.

Distortion (THD+N) vs. input level

Frequency response

Test results

Dynamic range 10 V CV, no signal  82 dBr A
  0 V CV, no signal 109 dBr A
  0 V CV, 1kHz 10 V p-p in 98 dBr A
  0 V CV, 2 kHz 10 V p-pin  93 dBr A
  0 V CV, 10 kHz 10 V p-pin  85 dBr A
  Headroom (over 10V p-p)  8 dB
CV bleedthrough after careful trimming  20 mV



A good, low cost VCA


Low signal bleedthrough

Low distortion

High headroom

Rather low input inpedance