Analog Tremolo (Guitar) Sound Effect

Tremolo effect produce an amplitude modulated signal. Unlike vibrato effect that produce frequency modulated, this tremolo effect will produce the same effect as quickly turning up-ad-down your volume control repeatedly. Here is the schematic diagram of the circuit:

Q1 is general small signal audio transistor, you can use almost any type of NPN small signal transistors. MFC3304P is a voltage controlled amplifier  IC with negative control, it might be difficult to find these days,  but I think you can replace with general OTA (operational transconductance amplifier), with the appropriate biasing circuit off course. Just bias the current control of an OTA through a resistor, and add the C4 modulator signal at the control pin of the OTA. [Circuit’s schematic diagram source: eleccircuit.com]