LM13600 VCA 3
The same circuit as LM13600 VCA 2, except that
the chip is driven a bit harder. The Iabcat 10V CV is
increased to 1 mA and the input signal is increased slightly. To
maintain unity gain, the load resistor is reduced accordingly.
The effect of these changes is that the signal bleedthrough is
somewhat reduced. There is very little improvement in signal to
Unfortunately the control voltage bleedthrough goes up when the chip is driven harder. This circuit has the lowest signal bleedthrough of the lot, but with higher CV bleedthrough it is probably not preferrable to LM13600 VCA 2.
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
|Dynamic range||10 V CV, no signal||83 dBr A|
|0 V CV, no signal||110 dBr A|
|0 V CV, 1kHz 10 V p-p in||105 dBr A|
|0 V CV, 2 kHz 10 V p-pin||101 dBr A|
|0 V CV, 10 kHz 10 V p-pin||86 dBr A|
|Headroom (over 10V p-p)||7 dB|
|CV bleedthrough||after careful trimming||40 mV|
Driving the chip this hard probably has more disadvantages than advantages.
Very low signal bleedthrough
Fairly low input inpedance
CV bleedthrough slightly high