I recently got a YuanJing brand low cost TDA8920 based board from ebay. This is a fairly basic low frills build but worth documenting for those interested.

I’d already wired up the case for my second ConnexElectronics TDA8920 board when I managed to fry the board. Out of curiousity I decided to check out this lower cost board that was going cheap cheap ($19USD + $9USD postage), as I could use the transformer I’d already mounted in the case as they are similar units.

This is the board on ebay:
TDA8920 Class D Amplifier board/ audio Power AMP 2X100W – eBay Power Amplifiers, Amplifiers, Home Audio, Electronics. (end time 19-Jul-10 02:14:45 AEST)

It has a smaller heatsink than the connex module, and smaller PSU 4700uF caps.

Initially it sounded OK, but not as good as the Connex module, quite a bit more grainy.. also interestingly it uses 5W power even when silent, and hence (with the smaller heatsink) runs a lot hotter.

Tracing out the circuit it appears it is pretty much the reference implementation of the TDA8920 circuit, with a volume control tacked on. Though the PCB mentions 0.680uF caps, they have used values 0.470 as per the reference circuit

Some minor tweaks I have made to the unit include:

• remove the input capacitors, and put the inputs where the capacitors were. This cuts out the 0.47 coupling caps, the volume control, and some 5.6K resistors. Also means I have to make sure anything I plug into it doesn’t have any DC offset! This has really cleared up the amps sound quality a lot.
• took the 10000uF caps from the connex amp and wired them in parallel with the existing 4700uF caps. Seems to have more solid bass… but hard to say.
• took the 11uH inductors from the Connex amp and replaced the 33uH inductors (which are in metal cans). After comparing the circuits and discussing with Col also replaced the 0.470 caps output filter caps with 2 in parallel (0.95uF) to match the values as per the Connex amp. Hard to tell if this helped either.

The overall result now sounds better. Not incredible but quite OK for a modded cheapy. Interestingly this unit doesn’t seem to have what I call the “Diana Krall” bug (faint fizz audible on very soft piano notes) thats been noted on other TDA8920 based modules.

Other parts used for the build (besides the parts stripped from the Connex TDA8920 module) include:

• 160VA 18+18 toroidal transformer from Altronics for $52.50.
• ABS plastic instrument case from Altronics for $14.95.
• gold RCA sockets from Altronics for $3.45 each.
• heavy duty banana sockets from Rockby

The the ESP groundloop protection has been added to the circuit to ensure quiet operation.