Dual Balanced Modulator

The balanced modulator or four quadrant multiplier, is a great classical module. it provides the same functions as those of a ring modulator.

Its main purpose is to generate sounds with a complex overtone content such as bell sounds and other klang tones !
The principle of this circuit is based on a Gilbert cell (see references at the end of this page) contained in the classical LM1496 IC.

Basically, if one feeds the A input with a sinewave with frequency f1, that is sin(2?f1), and the B input with a sinewave with frequenc f2, that is sin(2?f2), one gets at the output the product these two signals, that is sin(2?f1) x sin(2?f2).

Due to trigonomic properties it reads :

sin(2?f1) x sin(2?f2) = sin(2?(f1+f2)) + sin(2?(f1-f2))

in other words the output is a mixture of two sinewaves, one with frequency f1+f2 and the other with frequency f1-f2.