Although the modular Portable Mixer design available on these web pages has become a hit for many amateurs, some correspondents required a much simpler device, mainly for mixing mono signals. This design should fulfil their needs, 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. Low current consumption due to a simple, five-transistor circuitry, allows the Mini Mixer to be powered by a common 9V PP3 battery for many hours. Parts:P1 = 5K P2 = 5K P3 = 5K R1 = 180K R2 = 2M2 R3 = 750R R4 = 1K R5 = 15K R6 = 220R R7 = 1.5K R8 = 820R R9 = 150R R10 = 100K R11 = 180K R12 = 2.2M R13 = 750R R14 = 1K R15 = 180K R16 = 2M2 R17 = 750R R18 = 1K Capacitors:C1 = 1µF-63V C2 = 100µF-25V C3 = 220µF-25V C4 = 100µF-25V C5 = 220µF-25V C6 = 1µF-63V C7 = 100µF-25V C8 = 1µF-63V C9 = 100µF-25V Transistors: Q1 = BC550C Q2 = BC547 Q3 = BC557 Q4 = BC550C Q5 = BC550C Misc. Components B1 = 9V PP3 Battery J1,J2,J3 = 3mm Mono Jack sockets SW1,2,3,4 = SPST Toggle or Slider Switches Notes:* 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.