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3E Audio 260-2-29A : TPA3255 / HA3588 CoilCraft / PFFB Fully differential.

1) Input: none, Output: none -> no sound is generated (by any of the 3 boards)
2) Input: 1kHz sine, 1.97Vac rms, Output: none or dummy load -> audible 1kHz sine emitted (by any of the 3 boards if the input is present)
3) I don't have an analog scope, but if I connect a speaker to any output and play regular audio, the only noise issue is that the physical boards themselves are behaving like tiny speakers and emitting audio from anything that is above 1kHz
5) My only bus powered DAC is an old Behringer UMC204HD that is only capable of +3dBu output. Using it with my laptop or my phone will cause the issue, but it's quieter (as it's maxing out at about 1Vac rms)

My setup for these tests is very simple. MacBook Pro -> USB Audio Interface -> 1/4 TRS to XLR cable -> 3eaudio modules

(Note: I've tried with a MOTU 1248, MOTU Ultralite mk5, Behringer UMC204HD, and Behringer UMC1820 and all behave exactly the same)

Taking a suggestion from earlier in the thread, I tried poking around the boards to find which component was generating the audio. Pressing on the Coilcraft inductors lead to reduction in the noise (not fully, though). Next, I tried pressing on the bottom of the chassis right under where the boards are screwed down and that also led to a reduction. Out of curiosity, I unscrewed the amp module from the chassis and picked it up while it was connected and that reduced the noise even further. It appears that whatever is ringing on the board is made worse when it's physically attached to a larger chassis (which I chose to do for heat dissipation reasons).

Here's a video of this behavior. At first, I'm plugged into the middle amp module (that's firmly screwed down to the chassis). Then, I switch the input jack into the first amp module that's just resting on the chassis but isn't screwed down. Finally, I pick up the amp module as well as press on the inductors and the noise is reduced even further.

Is the humming/singing of the coils also present in real music at this volume?
Or only in the sine wave test signals?
 
It's present with real music as well. It basically acts like a tiny speaker with a low cutoff of around 700Hz. I can post a clip of it playing music if that's helpful to anyone
 
It's present with real music as well. It basically acts like a tiny speaker with a low cutoff of around 700Hz. I can post a clip of it playing music if that's helpful to anyone
Are you testing with an 8 ohm dummy load?
How high is the power you are testing with?
Does the humming/singing of the coils change when you play real music on a loudspeaker? Instead of the dummy load.

Please do not use silicone, bitum, other casting compounds or hot glue under any circumstances.
It is only sensible to use suitable epoxy resin in this case, not 5-minute epoxy or hobby glue.
 
Expensive...

Again, a problem in 3e Audio's quality control process:
* if a board sings, they should put it aside and send the customer a new (silent) one;
* latter pick the defective board(s) and do some more testing;
* do whatever it takes to make it stop singing.

Do not be quick to point the finger at the test procedure the customer is using to illustrate a problem.
The board should not have a problem in the first place, period.
this is not a quality control issue, these coilcraft(all inductors) without fully glued will ringing at higher power/current situation,that is cause by the magnetic reflection between the coil wire and the core,you can test other similar switching (class D)amplifier to see what happen with same condition.
@MicroAudio should has more experience on the SMPS transformer dipping paint(similar to glued) to avoid the audio-able noise,but most of supplier won't specify this parameter unless customer defined.
 
XS-3E Billet case design finalized....

IMG_20250123_155927.jpg
 
For now I glued the XLR connectors in and will get plated alloy XLR housings.
Doing some testing and it is Interesting that the Aiyima A04 32V 5A SMPS will NOT power this board up.
I tested the el-cheapo 36V 5A SMPS and it powers right up. What I can say is that the alloy case housing is definitely ridding the EMF/RFI from the unit just a foot away (Main design goal). The amp is DEAD silent unless I remove the billet cover, then I heard some errant noise with ear right to speaker (Testing on B&O C30's). I'll move this 3E amp back to the main rig when I add a bigger power supply to the new connector. For now, just gorgeous sounds on the bedroom rig...

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Doing some testing and it is Interesting that the Aiyima A04 32V 5A SMPS will NOT power this board up.
I tested the el-cheapo 36V 5A SMPS and it powers right up.
That doesn't surprise me, the board is specified for 36-51 V DC. The 12 V voltage conversion is probably designed for at least 36 V, or a little less.

Very nice build by the way.
 
Found a 48V 10A smps that will fit the case.
I've thoroughly tested and put the 3E PFFB board through it's paces with the el-cheapo 36V supply and the new Meanwell 48V (LOP 600-48) supply. Already excited about the XRK-3255 PFFB build using this 48V-10A SMPS as it is dead quiet, has ample bass punch at any listening level and most importantly fits my case design
XS-XRK Amp Case.png
 
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I can report back that the SMPS doesn't get hot either. I will not need to add an internal fan for my listening levels. After 3 hrs playing loud, I paused the track and put ear to tweeter. Was still dead silent.
 
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