February 10, 2016 Leave a comment
A few weeks ago I stumbled across a post on diyaudio mentioning the latest in (the long line of) ultra-mini class D chipamps offered on eBay/Aliexpress. The boards looked interesting and so I “splurged” for a pair which turned up this past weekend. Although in all honesty “splurged” probably isn’t the right term here as I paid a grand total of 12.50 EUR for the pair – including shipping (!!).
Like many of the other small amp boards, this one uses the TPA3118d2 class D IC from TI. The TPA3118 chip has a fairly good reputation on diyaudio and it will give a reasonably high power level when used as a mono amplifier (called PBTL-mode). The chip has a thermal pad on the underside and so uses the PCB copper as the heatsink surface. Unlike many other similar boards though, these boards are pure poweramps (no onboard volume pot) which is fine for me. They are also tiny at 35 by 46 mm – which means even two channels side-by-side are still visibly smaller than a credit card (!!)
So, very small, very cheap, quite powerful, and decent sound quality – what’s not to like? Not a lot actually. It would have been nice if the chip had been the TPA3116 which has the thermal pad facing upwards. Even through there isn’t a lot of space, it would still have been possible to fit a small heatsink on top of the chip and thereby (probably) improve the thermal performance and get a bit more output power.
Another slight negative is that the input capacitor is an X7R ceramic type which really isn’t the best choice for audio. Because it’s a 0603 SMD it’s also tiny and very difficult to replace/exchange with something better. The boards seem to be set to the highest gain (36 dB) which is good if the source is a smartphone or similar, but on the high side if it’s a typical hifi source like a DAC. Again, adjustment of the gain would require replacing 0603 resistors which is
not that fun a pain in the … but overall it’s a minor downside.
The boards in stock form don’t have any connectors for inputs and outputs, but I’ve added some to my pair to make testing a bit easier. I need to do a bit more listening with these “prototypes”, but if the sound quality is any good I do have a specific project in mind for them for later :-)