mini-amplifier

elektor july/august 1985 This little amplifier, operating from 3...9 V, and providing 1 W output into a 4 Q loudspeaker, is one of those circuits of which you never have enough. The amplifier is based on one 8-pin DIL IC type LM1895N. Electrolytic capacitors C2and C6decouple the supply lines; C7 prevents d.c. reaching the loudspeaker; and C3and C5 provide a low-impedance path to earth for audio frequencies. The input signal is applied to pin 4 of the LM1895N via P1and C4. Resistor B4and capacitor C8 suppress any tendency to oscillation, i.e., improve the stability. The amplification is determined by R1 and /33: it is of the order of 50. Capacitor C1, in parallel with RI, ensures that the amplification drops off for frequencies above about 20 kHz. If the amplifier is intended for use with a small AM receiver, it is desirable that the amplification starts falling off at a lower frequency. This is brought about by enlarging C1; for instance, if its value is doubled, the amplification...