Audio Mixer Circuit

The circuit schematic below represents one method for the design on an audio mixer. The active component is an LM318, although basically any operational amplifier would work in its place. The circuit is the classic design for an Op Amp summing amplifier. Four individual audio channels are shown and may be mixed together. Channel D is really intend
Audio Mixer Circuit - schematic

ed to show the addition of more channels and not used in the equation to calculate gain. The capacitors [C] are not used in the mixing function, but are there to DC block one channel from effecting another channel. The value of the capacitor should be selected so that it passes the signal of interest will little or no attenuation. In the case of an audio mixer the value should be selected so that it passes the audio frequency range. The value of each capacitor should be identical for each channel, otherwise an off-set in gain will occur between the channels. A common value found in one data sheet indicates a 1uF capacitor would work. Refer to Companies making Capacitors. A 0. 01uF capacitor is connected between the minus input and ground. The value of the potentiometer or adjustable resistor depends on the range of mixing desired and the values used for the other resistors in the circuit. Common potentiometer values include 100k and 500k ohms. A data sheet used 500k ohm values for each potentiometer. A decision also has to made regarding the style of tapper; a linear tapper or audio tapper. Refer to the Audio Amplifier topic for more information of using an audio tapper. The value and style of potentiometer should be same for each channel. Refer to Companies making Potentiometers. Note that most commercial mixing boards use a linear potentiometer which moves back and worth in a straight line, which is not the same thing as...

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