As per the name of the circuit, it is clear that this circuit connects four different audio signals as one. So, it is call four channel audio mixer. Here is that simple circuit; “four channel audio mixer“ using op-amplifier 741. It is to be noted in the circuit that the op-amplifier 741 works here as an inverting amplifier.
Circuit Description of four channel audio mixture:
The circuit of four channel audio mixers is wired around op-amp IC 741 followed by few other active as well as passive components. The IC 741 as previously mentioned works in inverting mode with extra resistor for every single input channel. When a single audio signal is fed as input in the circuit, it starts working as an inverting amplifier, where R1 and R7 are combined for voltage gain. Capacitor C1 behaves as a blocking capacitor whereas variable resistor VR1 as signal controller for channel 1.
In the circuit four channel audio mixture, when two or more audio signals are fed in the input terminal, then the input circuit combines all input signals as one and connects the input pin of audio signals with inverting pin of the IC-741. As a result, the voltage in the output pin is equal to the total sum of every individual input signal.
This circuit is used as a high quality audio mixer.
For stereo effect, two different circuits can be used to obtain the desired output.
We have tested four channel audio mixture in lab of BEP with three different input signals.
PARTS LIST OF FOUR CHANNER AUDIO MIXTURE
Resistor (all ¼-watt, ± 5% Carbon)
R1 – R4, R7 = 100 KΩ
R5, R6 = 39 KΩ
R8 = 220 KΩ
R9, R10 = 22 KΩ
R11 = 150 KΩ
R12 = 330 KΩ
R13 = 4.7 KΩ
VR1 – VR4 = 100 KΩ
VR5 = 1 KΩ
C1 – C4 = 0.22 µF (Ceramic Disc)
C5 = 100 µF/12V (Electrolytic capacitor)
C6, C7 = 10 µF/16V (Electrolytic capacitor)
C8, C10, C12, C15 = 100 µF/25V (Electrolytic capacitor)
C9 = 10 µF/25V (Electrolytic capacitor)
C11, C13 = 2000 µF/25V (Electrolytic capacitor)
C14 = 100 KpF (Ceramic Disc)
IC1 = 741 (operational amplifier)
T1 = BC148B (NPN transistor)
D1 – D4 = 1N4001 (rectifier diode)
X1 = 220V/50 Hz or 110V/60Hz primary to 9V – 0 – 9V secondary step down centre tap transformer