hi-fi headphone amplifier

This 1-watt amplifier lends itself par excellence for use as driver for a low impedance headphone or as output stage in a hi-fi preamplifier driving an active loudspeaker. Many preampli- fiers do not permit long, unscreened leads to be connected to them, but the present amplifier accepts these happily. The circuit — figure 1 — consists of an opamp type LF 356 and a push-pull transistor output stage. Low-pass filter 81/C2at the input limits the slew rate of the input signal. In conjuction with the relatively fast LF 356, this results in very low delay distortion. The fixed quiescent current of 30 mA drawn by the output transistors, and set by diodes D1... D4 in conjunction with emitter resistors R7and R8, ensures very low crossover distortion. Feedback resistors /?3 and R 4 fix the gain at about 15 dB. The consequent overall distortion with a —3 dB band- width from 10 Hz to 30 kHz is only 0.1 per cent. • 7-78 1 hi-fi headphone amplifier E CB • SOO toot 6 . 10 V elektor ...