Stereo Mixer

With this circuit you can mix four separate audio inputs. Each input will accept high or low impedance microphones, phonograph, tape or aux signals. You can adjust the gain of each input by adjusting each respective pot. With the Stereo/Mono switch you can combine just inputs 1,2 and 3,4 or in the Mono position combine all four inputs. Signal response is 20 Hz. to 20kHz. with very high input impedance and very low distortion with complete output short circuit protection. This circuit will drive any power amp with an input impedance of 2,000 ohms.
And you can read more about LF353 here.
From : http://home.maine.rr.com/randylinscott/may20.htm

2-INPUT AUDIO MIXER by 2N3904
As simple as it gets. The mixer consists of two transistor-based preamplifiers. The first one (designated "Mike in") offers higher gain. it works well with a regular dynamic microphone. The second one can be used to control audio input from a tape recorder/CD player. Source:http://www.geo ...
6 Input Mixer by IC 741 , LF351 ,TL071
Description: A simple mixer with 3 line inputs and 3 mic inputs using commonly available parts. Notes: The mixer circuit below has 3 line inputs and 3 mic inputs. The mic inputs are suitable for low impedance 200-1000R dynamic microphones. An ECM or condenser mic can also be used, but must ...
Easy Audio Mixer by LM837
The mixer itself is a fixed-gain summing amplifier based on an LM837. It sums up all the six microphone preamp signals into a single output. This is called the MIX OUT, and is a rear-panel socket. The single output is split into two outputs, to allow easy connection to external stereo equipm ...
Microphone Mixer by 741
This relatively simple mixer was designed for three dynamic microphones, but can be re-designed for more or less. Level and tone controls are available to tailor the sound to your needs. Part R1, R2, R3 3 1K 1/4W Resistor R4, R5, R6 3 10K Logarithmic Pot R7 1 1Meg 1/4W Resistor R8, R1 ...
Audio Mixer by 2N3819 Junction FET
This simple circuit mixes two or more channels into one channel (eg. stereo into mono). The circuit can mix as many or as few channels as you like and consumes very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "sections" which ...