Mixer 4 Input Circuit
The input levels able to set by potentiometers P1 or P3. Furthermore, which each input level able to trimmed with support of trimmers pots P4 to P6 to adapt each input to the source. The resistors at the non-inverting inputs of the opamps work as DC bias and set DC output at 50% of the power supply for this powered audio mixer.
All 4 inputs signals are summed by the 4 opamp A4 through the resistors R3, R7 and R11. The commom volume level is cotrolled through the potentiometer P7.
You able switch an input channel on or off through the switches S1 and S3. An input channel is turn off that its switch is closing. It is also possible to replace these mechanical switches with transistor gates. with doing so, you can build an analog multiplexer circuit that can be easily expanded by several inputs.
