Wiring Schematic Diagram

LM3900 Audio Mixer Circuit

Audio mixer circuit consists of 4 four-channel amplifier (LM3900) two microphone inputs and two audio inputs are available directly online at this circuit. By adding the parallel with this circuit, you can increase the number of entries according to applications. Each input is connected to the inverting terminal of the LM3900.

The amplifier built in each section amplifies each audio input separately and fed to the output terminals. The output terminal of each channel is connected to a single output line with a resistance no greater than 680 and produces a mixture of audio output with low noise. This audio mixer circuit does not use a low impedance input sources to the mix of ideals. Capacitors C1 to C4 are decoupling capacitors corresponding channels. C5 is the decoupling capacitor production.

The image below shows a Block diagram of the entire mixer that includes four Input Amplifier Modules followed by four in-out switchable Tone management Modules, one stereo Line input, four mono Main Faders, one stereo dual-ganged Main Fader, four Pan-Pots, a stereo Main Mixer Amplifier Module and two additional Tone management Modules switchable in and out for every channel, inserted before the main Left and Right outputs.

The basic arrangement of this circuit comes from the recent Quad magnetic pick-up cartridge module. The circuit was rearranged to address microphone input and a single-rail low voltage provide.

This low-noise, absolutely symmetrical, two-transistor head amplifier layout, allows the utilization of a traditional FET input Op-Amp as the second gain stage, even for terribly sensitive microphone inputs.

The voltage-gain of this amplifier is varied by suggests that of R9 from 10 to one hundred, i.e. 20 to 40dB.