A differential amp using a BJT pair often uses current mirror as its load to boost gain. I was interested in applying the idea to a long-tail-pair VCA, so tried it. I first ran a simulation with the circuit as follows to ensure it works as a VCA properly.
Then built the circuit on a breadboard. But the result was not good. The offset at 5V CV with no input is too large.
That’s it for this topic. I would not pursue this issue further. Well, it’s really hard to design a VCA.
