It still ends up being a Mechanical vibration. I would still try some sorbothane damping between transformer and the floor of the P15 by loosening centerbolt inserting sufficient sheet torquing center screw.
McIntosh places their transformer in a can and surrounds them with a tar like potting. Only heard of one amp they made with issues. They had not designed enough space between can and transformer. Iteration of design fixed that. Your going to have to improve the P15 design yourself or live with it or get rid of the equipment. Since tightening the bolt reduces vibration and noise. This remains an area to pursue. Stuff I have read about DC filters you often swap dynamics or soundstage for reducing DC hum.
James was kind as usual and Steve remotely monitored the P15 for a few days last week. We tried a lot of things together without success, just mitigating the noise a little bit. But after a few hours it tends to change for the worst or for the better.
VMax suggested also sorbothane under the transformer, I’m not yet tried.
Thanks for suggestions Vmax, yes I’m afraid I need to solve the issue by myself at this point.
A few experts assured me that the Toroidy DC Blocker - if the issue is due to incoming DC - is able to leave unaltered dynamics, acting only to block the DC without any other filters, unlike other similar products.
And Paul acknowledged that almost all PSA products, even DACs, have this issue and apparently it’s normal. Folks pointed out that other brands don’t have this issue and really this is just bad engineering on PSA part.
As owner of P15, BHK250 and BHK Pre and can confirm that they do emit hum, especially the BHK250 in my case. I switched to MC462 and dead silence, both from the speakers and from self. And imo sounds better too compared to the BHK250. I also have Luxman M10x and again dead silence both ways. I don’t recommend BHK250 if silence is your ultimate goal.
Luca I posted this in the thread. Check out Steve Huffs video on the Puritan device. Maybe swap out the P15 for one of those. Not what you want to hear more money and money lost on the P15, but he had very similar DC issues.
Hi Vmax, ended up that my P15 doesn’t work at all (problems over problems) and PSA sent me an oscillator board to try if replacing it could fix the issue.
Meanwhile (thank you @brian.fitterman) I purchased a Puritan PSM156 that I’m using right now for the very first hours. It’s able to bring back the magic (as per Steve Huff words) but in a different way compared to the P15.
Detail, unveiled, open, clean and with a huge soundstage, it recreates a bigger image, more oval shaped around the speakers and the side walls. The impact of attacks is solid and impressive. I miss something from the P15 due to a warm feeling and naturalness anyhow. Let it break in a few hours more, before judging. I don’t know if I like it but it changes remarkably the sound, for sure.
Just to give you a better idea: the Puritan sounds like the Purple, the P15 like the M-1. Don’t ask me about the SR Master, it’s in my drawer, still SEALED because its rate was right only for the MK II I sold even before installing it.
As soon as I can have the P15 in use again I’ll do some tests and comparisons, even trying to put the Puritan between the wall and the P15 for a while (I know it’s not recommended but I want to understand how/if it can mitigate the buzz).