HI-FI HEADPHONE AMPLIFIER

This l-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 preamplifiers do not permit long, unscreened leads to be connected to them, but the present amplifier accepts these happily.

The amplifier delivers a maximum power of 1 watt into 8 Q for an input signal of about 500 mVrms.

High-impedance headphones and 4 Q loudspeakers may also be connected without detriment. the two transistors should be mounted on heat sinks - do not forget the insulating washers and the heat conducting paste.

The power supply need not be more than a simple affair, consisting of a mains transformer with a centre-tapped, 6 ... 8 V, 0.5 A secondary, a suitable bridge rectifier, and two 1000uF 16V electrolytic capacitors in a conventional arrangement. To drive high-impedance headphones at high volume, you need a ± 15V regulated power supply: in some cases, this may be derived from the preamplifier supply. In this arrangement, care must be taken not to short-circuit the output terminals.