Mini Mixer

Small portable device - 9V battery operation

Three high/low-sensitivity switchable inputs

Circuit diagram:

Mini Mixer


P1,P2,P3_________5K  Linear Potentiometers

R1,R11,R15_____180K  1/4W Resistors
R2,R12,R16_______2M2 1/4W Resistors
R3,R13,R17_____750R  1/4W Resistors (See Notes)
R4,R14,R18_______1K  1/4W Resistors
R5______________15K  1/4W Resistor
R6_____________220R  1/4W Resistor
R7_______________1K5 1/4W Resistor
R8_____________820R  1/4W Resistor
R9_____________150R  1/4W Resistor
R10____________100K  1/4W Resistor

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


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.


Technical data (Level controls in mid position)


Low level inputs:
2mV RMS for 316mV RMS output [-10dB(V)]
6mV RMS for 0.775V RMS output [0dB(V)]
High level inputs:
130mV RMS for 316mV RMS output [-10dB(V)]
400mV RMS for 0.775V RMS output [0dB(V)]

Maximum Input sensitivity: 1.3mV RMS for 0.775V RMS output [0dB(V)]

Maximum undistorted output: 2.4V RMS [+10dB(V)]

Frequency response: flat from 20Hz to 20KHz

Total harmonic distortion @ 1KHz: <0.1% @ -10dB(V); <0.3% @ 0dB(V)

Total harmonic distortion @10KHz: <0.08% @ -10dB(V); <0.24% @ 0dB(V)

Current drawing: 7mA @ 9V supply