Basic Audio Mixer Using Op-Amp
Audio mixer is used to mix several audio signal from many channel into one channel, in analog form. The basic requirement of an audio mixer is that the mixed signal is a product of simple addition. When connected to several source, each source should not interfere each other on each input line. If each sources has various DC offset level, this DC offset should not be transmitted to the output. Here is the schematic diagram of mixer circuit that satisfy above requirements:
The basic configuration of this circuit is potentiometer, DC decoupling capacitor, series resistor, and current amplifier. The potentiometer is used to adjust the volume of each channel. DC blocking capacitor is used to normalize the offset voltage, if exist on the input. The series resistor is used to limit the current, especially at maximum position of potentiometer. At the inverting input pin, the op-amp will keep this point to ground potential or zero volt. This make sure is all signal coming from series resistor will be zeroed, and the current will be summed. Zeroing the signal at this point makes sure that each signal won’t be propagated back to the input of different channels interfering them.