Monday, July 27, 2009

Mini Audio Mixer circuit

This is simple mini audio mixer. This circuit consume low current due to the simple design. Also featuring three inputs with switchable high/low sensitivity and unusual level-control circuits, providing high overload margins and low-noise figures, proportional to gain-level settings.
Mini Audio Mixer circuit diagram

Component parts:
P1,P2,P3_________5K  Linear Potentiometers

R3,R13,R17_____750R (See Notes)

C1,C6,C8_________1µF 63V Polyester or Electrolytic Capacitors
C2,C4,C7,C9____100µF 25V Electrolytic Capacitors
C3,C5__________220µF 25V Electrolytic Capacitors

Q1,Q4,Q5______BC550C 45V 100mA Low noise High gain NPN Transistors
Q2____________BC547 45V 100mA General purpose NPN Transistor
Q3____________BC557 45V 100mA General purpose PNP Transistor

J1,J2,J3________3mm or 6mm Mono Jack sockets
SW1,2,3,4______SPST Toggle or Slider Switches
B1_______________9V PP3 Battery
Clip for PP3 Battery


  • When SW1, SW2 or SW3 are open the input sensitivity is suited to high-output devices like CD players, tuners, tape recorders, iPods, miniDisc players, computer audio outputs etc.
  • When SW1, SW2 or SW3 are closed the input sensitivity is suited to low-output, low-impedance moving coil or electret microphones.
  • Sometimes, the 750 Ohm value for R3, R13 and R17 resistors could be not easy to find. In this case, two 1K5 resistors wired in parallel can be used to replace each item.
  • To make a stereo mixer, all the parts must be doubled excepting R6, C3, C5, SW4 and B1.

About Audio Amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 - 20 000 Hz, the human range of hearing) to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.

The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification, equalization, tone control, mixing/effects, or audio sources like record players, CD players, and cassette players. Most audio amplifiers require these low-level inputs to adhere to line levels.

While the input signal to an audio amplifier may measure only a few hundred microwatts, its output may be tens, hundreds, or thousands of watts. More explanation about power audio amplifier can be found at

This is a video tutorial about how to a very simple audio amplifier based on the LM386 amplifier chip. It can be built for less than $20 (or might be less than $8 in some countries) and used to amplify any low level audio signal including a guitar, bass or mp3 player.

Watch the video:

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