Thanks for an awesome review Amir.
A few notes based on the 3e audio thread I have been following:
https://www.audiosciencereview.com/...-dapx002-tpa3250-tpa3255-dsp-amplifier.14315/
Quite robust discussion of this line of products in there.
1. Changing op-amp reduces noise - this seems to be a design flaw in the initially released product which was missing some capacitors in the op-amp circuit. This is outlined
here. @3eaudio mentioned that with the capacitor fix, noise can be reduced to 200-300uV. Only replacing op-amp (what Amir did) reduces it to 500-600uV. This matches quite well with Amir's measurement of 490uV. So its expected that doing the capacitor modification will net another 6dB (?) improvement in noise performance. 3e audio has confirmed that 2021 versions of the amp will have the capacitor fix implemented.
2. Power limit: Looks like the amp has built in power limiter which clamps output voltage to 22Vrms which corresponds to 60.5W into 8 Ohms. This again matches Amir's measurement of 65W. The DSP can be reprogrammed to remove this limitation - alluded to in
this post. With the limitation relaxed, looks like the amp will make 80W into 8 Ohms.
3. There have been
reports of capacitors installed in wrong polarity. 3e audio has acknowledged and (hopefully) fixed.
4. Input sensitivity is 1V. This means amp will clip when signal is above this level. Most DAC's with fixed output voltages will not work as such since their output is typically 2V. Well I guess they will work but may sound horrible if you digital source volume is turned up (as it should be). 3e audio has DIY fix to change sensitivity to 2V - outlined
here.
Overall seems a good product for folks not afraid to open up electronics and muck around a bit. If you are new to DIY electronics though, I would advice an abundance of caution for reasons Amir has already outlined - this device is direct mains powered and that will mean voltages approaching 200V inside. I personally wouldn't leave it powered on unattended for long periods of time until after I've had it and used it a while.