Handy-Amp
Approx construction cost US$30
A simple multi-purpose amplifier with built-in-speaker and headphone output.
Until recently, the author’s household hi-fi system had a piece of screened cable hanging down the back. This was left connected to the amplifier’s high-level (auxiliary) input. When some piece of experimental audio equipment needed to be tested, the cable could be retrieved and connected to the circuit. It was then possible to listen to the result.
This method was far from satisfactory, so the small battery-operated "bench" amplifier forming this project was designed for such purposes. As well as having an in-built loudspeaker, it has the facility for connecting personal stereo type headphones or an external loudspeaker. Also, it will accept both high-level and low-level input devices.
Magnetic record player cartridges and dynamic microphones provide a low-level output while the "line output’’ socket fitted to many pieces of consumer equipment (such as CD players and video recorders) provide a high level.
Many readers will, no doubt, wish to construct the amplifier for experimental purposes. However, it could have a variety of other applications. Examples include a small practice amplifier for electronic musical instruments and as the basis for an intercom, or toys and games.
Being battery-operated it may be set up outdoors and, with just a microphone (possibly with an extension lead) and a pair of headphones connected, it could be used to listen to wildlife.
Readers should note that the amplifier has been designed to be small and relatively inexpensive to construct. Although the maximum output power (one watt approximately) and sound quality are perfectly adequate for the applications suggested earlier, it is not suitable for critical applications such as serious music listening.
More details on this construction project can be found in the August 2000 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
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