General Purpose Bench/Utility Amplifier

Figure 1 

The design of the circuit was intended to produce a signal tracer, bench amplifier, or output amplifier of personal radios.

• Amplifier – any device that changes, usually increases, the amplitude of a signal
• LM386 – a low voltage audio power amplifier with features such as battery operated, minimum external parts, wide supply voltage range, low quiescent current drain, high voltage gain, ground referenced input, self centering output quiescent voltage, low distortion, and available in 8 pin MSOP package

The power output of the circuit can range from around 325 mW (LM386N-1), 700 mW (LM386N-3), or 1000 mW (LM386N-4), provided that the supply voltage is in the range of 4 to 12 Volts and does not exceed the recommended DC range. These versions of amplifiers are packaged in an 8-pin dual in-line (DIL) package. This electronic package includes two parallel rows of connecting pins with a rectangular casing. The pins are pointed downward with an extension of the pins enough to fit, be mounted and soldered on the other side of a printed circuit board (PCB). With a supply of 9V, the overall gain of the circuit is 200 with the LM386 functioning as a non-inverting amplifier.

The capacitor across pin 1 and pin 8 manipulates the gain of the circuit using LM386. It is a high power op-amp used to drive the 8 ohm loudspeaker. Without this 10 uF capacitor would turn the voltage gain from 200 to 20. The potentiometer handles the volume control of the circuit to vary the output from the loudspeaker while it shunts the internal input impedance of the amplifier that is producing 50K ohm. With a value 22K ohm, the input impedance can be limited to a lower value of about 15K ohms. To prevent the loudspeaker from getting damaged, a coupling capacitor may be connected in series with the potentiometer because the input is DC coupled.

LM386 may be used in several applications such as power converters, small servo drivers, ultrasonic drivers, line drivers, TV sound systems, portable tape player amplifiers, AM-FM radio amplifiers and intercoms. The bench amplifier is suitable for testing audio and tone circuits. In amplifiers, the audio stages are tested such as the front end of FM bugs.

Source:www.zen22142.zen.co.uk/Circuits/Testgear/benchamp.htm