CA3080 VCA 1

The trusty old CA3080 is used here in a logarithmic VCA. The circuit is similar to the one in Elektor Formant, except that the FET buffer is replaced by a FET input op-amp. The load resistor is connected to ground and the op-amp is a voltage follower. This chip is frowned upon by some people. It has a reputation for being very noisy. In reality it is only slightly noisier than the alternatives. The noise is only present at full gain, which makes it a problem only if the VCA is fed with very weak signals.
What can be more of a problem is that the signal bleedthrough at higher frequencies is rather high. But even at low frequencies the signal attenuation is not as good as with the LM13600 or the SSM2024. The CA3080 has very low CV bleedthrough if it is carefully trimmed.

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  77 dBr A
  0 V CV, no signal 117 dBr A
  0 V CV, 1kHz 10 V p-p in 83 dBr A
  0 V CV, 2 kHz 10 V p-pin  76 dBr A
  0 V CV, 10 kHz 10 V p-pin  65 dBr A
  Headroom (over 10V p-p)  5 dB
CV bleedthrough with careful trimming 6 mV



This was expected to be a poor performer but turned out to be quite respectable. It is a little noisier but the difference is surprisingly small.


Very low CV bleedthrough

High signal bleedthrough at higher frequencies

Yes, it is the noisiest of the lot