LM13600 VCA 3

LM13600 VCA 3

The same circuit as LM13600 VCA 2, except that the chip is driven a bit harder. The I_abcat 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 noise ratio.
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

Frequency response

Test results

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

Summary

Driving the chip this hard probably has more disadvantages than advantages.

• Very low signal bleedthrough

• Low noise

• High headroom

–

• Fairly low input inpedance

• CV bleedthrough slightly high