I've been designing a 2-channel TAA4100 based amp in the last couple of months and I just finished the first prototype. It's almost interely based on the application schematic provided in the datasheet. The only changes are the input capacitors (1.5 F foil instead of 0.47F elco) and the input are clamped with 5.2V zeners. The power supply is a 20V 120W SMPS.
Upon first testing I discovered a few problems. First of all: the transition from mute to unmute is not quiet at all. I get a pretty large "thump" followed by +/- 0.5 seconds of white noise (oscillations?).
The little amp sounds very nice at low power, but once I ask for more than a few watts of output power I get some strange sounds: at a certain power output level you can hear a slight "ticking" sound through the speaker..when you raise the volume some more this "ticking" goes over in white noise (again: oscillations?). When the heatsink and chip is warm (let's say 45C) this noise will be more prominent and sometimes won't stop even when you turn down the volume. If you play, for example, a pure 25hz sinus tone, there is a ticking or crackling sound even at lower power output (speakers are ok, I tested this with a few different pairs). At higher frequencies (80-100hz) I can get a low more power out of the amp. The problem seems to be concentrated at lower freqs....
I triple checked all soldering, schematic and board layout...and everything seems to be ok. I have the feeling this has something to do with a grounding issue...or maybe something at the inputs: when I touch the RCA jacks (metal, signal carrying part), the amp stays quiet, as it should. However, when I touch the input pins on the tripath chip (or anything after the input caps) there's a loud hum. Even stranger: if I touch input nr. 3: 50hz hum + white noise. The other inputs: just a 50hz hum.
FYI: Power ground (= - pole of the SMPS input jack) and signal ground are connected at 1 point on the PCB.
Any ideas what this could be? Maybe a faulty component? Or a major design fault?
Please have a look at the schematic, board layout and pics of the board.