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Problem with "upgraded" mini amp PSU

Posted by KanedaK (A) on August 31, 2020 at 01:32:05

Some of you might remember that I'm active bi-amping my horns with some tiny class D amps.
On the high pass (400 > 20KHz) I have a 8watt Trends TA10.1 highly modded; on the low pass (60 > 400Hz I have a stock SMSL SA50 (25W). Subs are driven by higher power class AB amp.

Well, I've very recently bought an upgraded, low noise, "audio" SMPS supply for my Trends amp.
The PSU is sold by the British company Amptastic, who makes the Mini1 amp. Both the Mini1 and my Trends amp share the same Tripath chip, and compatibility shouldn't be an issue even tho the upgraded PSU outputs 13.5V 7.5A and the stock one outputs 12V 3A.

And indeed, when using the Amptastic psu the sound is more organic and composed, less "in your face", and much less "class D".

HOWEVER, when using it, there's a faint high pitched noise coming from the horns, it's not like hiss, it's more like a faint tonality. It modulates if I touch the umbilical cable that links the PSU to the amp.
I contacted Amptastic who told me that failures where extremely rare and that I was probably experiencing some feedback.

But, what causes it? how can I prevent it? how come I don't experience it with the stock PSU?... I'm a bit lost here. It wasn't an expensive upgrade, of course, so it's not really a big deal financially, BUT besides that faint noise (which is very irritating through horns), it sounded great and I'd like to use it.

Any help welcome! :-)

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