Not only is this a gutsy little amplifier, it is an ideal learn-while-you-build-it project for high school and tech college students. It all fits onto a single largish PC board with no 240VAC mains voltages present – that’s taken care of by the 16VAC plugpack.

The new amplifier is built into a low-profile ABS instrument case measuring just 225 x 165 x 40mm. Construction is straightforward, since all the parts except for the loudspeaker terminals are mounted on a single PC board. Power comes from an external 16VAC 1.25A plugpack supply.

The TwinTen has inputs for three stereo program sources such as CD player, MP3 player and FM/AM tuner and has front-panel LEDs to indicate which source has been selected. The other controls are Bass, Treble, Volume and Balance. At the rear, there are RCA line inputs, binding posts for the speaker connections, a finned heatsink and a socket for the plugpack supply jack.

As part of the final checking of this amplifier, one of our staff members took it home for a blast on his large stereo system. His daughter was so impressed with the performance from such a tiny package that she wanted it straight away. We thought that was a pretty good endorsement.

The reason why it packs such a punch is that it can deliver around 17 watts music power per channel into 4-ohm loudspeakers. In a typical room with reasonably efficient speakers, that’s enough to blast you out of your seat. And did we say it’s tiny? It measures just 225mm wide, 40mm high and 165mm deep, including the knobs and rear heatsink.

It’s also pretty quiet and its other performance parameters are pretty good as well, considering that we have kept a very tight rein on the overall cost of the design.

One reason it performs so well is that it is based on the same National Semiconductor LM1875T 20W audio amplifier IC used in the Schoolies’ Amplifier, published in the December 2004 issue. This IC has inbuilt thermal protection so that even if you abuse it or short out its output, it won’t be damaged. The power amplifier circuits are very close to the Schoolies’ Amplifier circuit but inevitably there are component differences to provide different gain and so on.