Nuts and Volts - March 2015

higher than the theoretical specs say it should. However, at such a low price ($11.80), it's easy to imagine there were some design trade-offs to keep the price down while still delivering reasonable audio quality.

In total, the distortion started just over 1% THD+N at 0.25W into any load and rose to over 10% THD+N at about 9W, capping out at a total of 19.2% THD+N into a four ohm load at a maximum output of 10W. Oddly, neither sample of this module I was sent would deliver above 5W into an eight ohm load. I did experience some odd cut-in/cut-out behavior at bass frequencies and when running it very hard; Rory mentioned he'd encountered similar behavior on our call.

We determined it occurs when the amplifier exhausts its current reserve in the onboard electrolytic capacitor. It would be pretty easy to change out the stock 470 µF capacitor for a much larger one to improve the low end performance (Photo 13).

My live listening test confirmed what the meter measured: a fair amount of background hiss, although not oo bad at low volume; and distortion growing quickly but still delivering quite an intelligible signal. Due to the noise and distortion on this module, I couldn't recommend it for a hi-fi musical application, but in a project where audio quality isn't a huge factor it could certainly get the job done. Guitar amplifiers often have a fairly high distortion figure anyway, so the self-powered guitar project is still on the table. Other applications where you need some volume but won't be playing much recorded music would also be great — maybe a DIY intercom or pager project, or built into a small kiosk or pop-up display to play interface noises and sound effects. Several forum posts on diyAudio and other Web communities also report similar performance with modules based on this chip, and speculate that performance might be improved by swapping out some of the surface-mount components for other values and adding better cooling.

If you're into experimenting, it might be a fun exercise to get this little module to perform better. The price is low enough it wouldn't break the bank to try. The underlying chip has great specs, so if you've got a set of hot tweezers and don't mind working under a magnifying glass, modifying the module would probably be an interesting project unto itself.

Headers Only

Moving up a bit, the model TA2024 amplifier module (its stock number happens to be the same as the chip) takes up quite a bit more space, but really does offer a lot of flexibility — all that extra space means bigger, better components. There are a set of film input capacitors, plus an actual sharp-cutoff low pass filter on the output to remove any residual RF left over after the switching.