4 Channel Portable Audio Mixer

       High-quality modular design, 9V Battery powered - Very low current drawing

Input Amplifier Module: a low noise circuit equipped with a variable voltage-gain (10 - 100) preset, primarily intended as high quality microphone input, also suitable for low-level line input.

Tone Control Module: a three-band (Bass, Middle, Treble) tone control circuit providing unity-gain when its controls are set to flat frequency response. It can be inserted after one or more Input Amplifier Modules and/or after the Main Mixer Amplifiers.

Main Mixer Amplifier Module: a stereo circuit incorporating two virtual-earth mixers and showing the connection of one Main Fader and one Pan-Pot.

The image below shows a Block diagram of the entire mixer featuring four Input Amplifier Modules followed by four in-out switchable Tone Control 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 further Tone Control Modules switchable in and out for each channel, inserted before the main Left and Right outputs. 

Block diagram: it gives only the arrangement 

Input Amplifier Module

parts:-

R1 = 22K - 1/4W Resistor
R2 = 22K - 1/4W Resistor
R3 = 47K - 1/4W Resistor
R4 = 47K - 1/4W Resistor
R5 = 47K - 1/4W Resistor
R6 = 4K7 - 1/4W Resistor
R7 = 22K - 1/4W Resistor
R8 = 220R - 1/4W Resistor
R9 = 2K - 1/2W Trimmer Cermet (See Notes)
R10 = 470K - 1/4W Resistor
R11 = 560R - 1/4W Resistor
R12 = 100K - 1/4W Resistor
R13 = 220R - 1/4W Resistor

C1 = 470nF - 63V Polyester Capacitor
C2 = 100µF - 25V Electrolytic Capacitor
C3 = 2µ2 - 63V Electrolytic Capacitor
C4 = 2µ2 - 63V Electrolytic Capacitor
C5 = 2µ2 - 63V Electrolytic Capacitor
C6 = 47pF - 63V Ceramic Capacitor
C7 = 4µ7 - 63V Electrolytic Capacitor
C8 = 100µF - 25V Electrolytic Capacitor
Q1 = BC560C - 45V 100mA Low noise High gain PNP Transistor
Q2 = BC550C - 45V 100mA Low noise High gain NPN Transistor
IC1 = TL061 - Low current BIFET Op-Amp

Tone Control Module

parts :-

P1 = 100K - Linear Potentiometer
P2 = 100K - Linear Potentiometer
P3 = 470K - Linear Potentiometer

R1 = 12K - 1/4W Resistor
R2 = 12K - 1/4W Resistor
R3 = 12K - 1/4W Resistor
R4 = 3K9 - 1/4W Resistor
R5 = 3K9 - 1/4W Resistor
R6 = 1K8 - 1/4W Resistor
R7 = 1K8 - 1/4W Resistor
R8 = 22K - 1/4W Resistor
R9 = 22K - 1/4W Resistor
R10 = 560R - 1/4W Resistor
R11 = 100K - 1/4W Resistor
R12 = 220R - 1/4W Resistor

C1 = 1µF - 63V Polyester Capacitor
C2 = 47nF - 63V Polyester Capacitor
C3 = 4n7 - 63V Polyester Capacitor
C4 = 22nF - 63V Polyester Capacitor
C5 = 4n7 - 63V Polyester Capacitors
C6 = 100µF - 25V Electrolytic Capacitor
C7 = 4µ7 - 63V Electrolytic Capacitor
C8 = 100µF - 25V Electrolytic Capacitor
IC1 = TL061 - Low current BIFET Op-Amp

Main Mixer Amplifier Module

Parts:
P1 = 100K - Linear Potentiometer
P2 = 10K - Linear Potentiometer
R1 = 15K - 1/4W Resistor
R2 = 15K - 1/4W Resistor
R3 = 100K - 1/4W Resistor
R4 = 100K - 1/4W Resistor
R5 = 22K - 1/4W Resistors
R6 = 22K - 1/4W Resistors
R7 = 390K - 1/4W Resistor
R8 = 390K - 1/4W Resistor
R9 = 560R - 1/4W Resistor
R10 = 560R - 1/4W Resistor
R11 = 100K - 1/4W Resistor
R12 = 100K - 1/4W Resistor
R13 = 220R - 1/4W Resistor

C1 = 330nF - 63V Polyester Capacitors
C2 = 330nF - 63V Polyester Capacitors
C3 = 100µF - 25V Electrolytic Capacitors
C4 = 10pF - 63V Ceramic Capacitors
C5 = 10pF - 63V Ceramic Capacitors
C6 = 4µ7 - 63V Electrolytic Capacitors
C7 = 4µ7 - 63V Electrolytic Capacitors
C8 = 100µF - 25V Electrolytic Capacitors
IC1 = TL062 - Low current BIFET Dual Op-Amp

Notes:

• Current drawing for one stereo Main Mixer Amplifier Module is 800µA.
• Frequency response is 20Hz to 20KHz - 0.5dB.
• Total Harmonic Distortion measured @ 2V RMS output = <0.008%>
• THD is 0.005% @ 1V RMS output.
• Maximum undistorted output voltage: 2.8V RMS