Discrete Transistor VCA

A Voltage-Controlled Amplifier (VCA) made from three BC549 NPN transistors and three BC214 PNP transistors. It's a Gm Cell with variable current followed by a simple op-amp.

 

The four traces shown on the Tek 5440 are the input (1kHz), the two intermediate signals and the output. The control or modulation voltage was a sinewave in this case.

Done