How to Build Simple Bench Amplifier

This amplifier has an output of 325 mW with a gain of 200 which can be used as a bench amplifier, signal tracer, or universal amplifier. This amplifier is very easy to make with cheap components.

This circuit is based on IC LM386 which has the advantage of low power consumption. Based on the above circuit, the LM386 is assembled in a non-inverting manner which produces a gain of 200 times.

Circuit Diagram


R1: 22k Potentiometer
R2: 1R5
C1, C3: 330 uF
C2: 10 uF
IC1: LM386


You can download the LM386 IC datasheet from the national semiconductor site. This IC consists of 8 pins which are sold in several versions. The LM386N-1 has an output of 325mW with an 8-ohm loudspeaker load, while the LM386N-3 has an output of 700mW, and the last one is the LM386N-4 IC which offers 1 Watt output.

The gain value of LM386 is set with a capacitor that crosses pin 1 and pins 8. With a capacitor value of 10uF, the resulting gain is 200. However, if this capacitor is omitted, the resulting gain is 20.

IC LM386 can work well at a voltage of 4 to 12 VDC. Do not exceed 12 VDC so that the circuit is not damaged quickly and produces excessive noise.

In theory, the input impedance of this circuit is 50K. Capacitor C3 is useful for preventing DC voltage from flowing in the loudspeaker.

The example of finished circuit

Credit: Andy Collinson, [email protected]
circuit finished illustration from