Class D amplifier with TPA 3250 board

Confusing thread -- first hiss, now hum! Two distinctly different problems!

Appearance, evidence, and reports suggest this "artisan" is not an engineer, technician, or competent designer and probably lacks the proper tools to measure and evaluate the device to isolate, determine, and identify its inherent defects you should seek an immediate, full, and complete refund.

In summary, yeah. I would gladly spend 500€ or 1000€ on a good class A/B amplifier afterwards. Something without surprises. But the situation is hairy. This guy doesn't want to back down. He's insistent on his abilities which I don't care for anymore. Looking closely at the innards of the amplifier, his soldering is sloppy. Some tin was floating around in the casing. And I was driving as gently as possible with the anxiety that vibrations and bumps would desoldure components.

The artisan has a well equipped workshop and a great listening room. He has everything to succeed. That's why I stuck around for so long. I doubt that I'll ever get my money back. I don't want to deal with him anymore. The anxiety and amount of hours spent on driving is a burden on my life. But he'll be back next Sunday. 

Presently, the amplifier displays an audible "100 Hz hum". There was hiss prior to that, it is now resolved. 

Yeah the situation sucks but I'm in good health and my financials have never been better. I can afford to lose some cash (just not every month during the year like that). Heck! If only we lived in a world where we could mass produce good amplifiers for a few hundred bucks LOL 

I don’t often make a big mistakes, but when I do… I do what you are doing. Do the best to mitigate the problem… then sell it. Get what you can. Or throw it in the trash and caulk it up to experience. It was great of you to support a local artisan. Live and learn.

Unfortunately, if you do detailed research you get what you pay for. My amp cost $22K… and well worth it. Incredible performance, from a reputable company that has been around for 50 years. If I had a problem my dealer would come over, give me an interim replacement until he could deliver a fully functional replacement… but then, I am paying for that.

I understand what you're saying. You went to a reputable company, not some guy. Some guy convinced me that he could build a wonderful amplifier for me and that I could see him anytime if I have issues. In essence I paid for the same things you paid for. But the difference between you and I is the reputation and quality. 

In hindsight, I was lured by the prospect of finally experiencing tubes. My experience couldn't be worse and it's hilarious. I notice that my OGY speakers have more bass and fuller midrange with tubes compared to the Yamaha RN402 I regrettably sold. From memory, the differences are subtle but still there. It's like 20% better with tubes (listening to busy tracks where the hum disappears), and that's a huge improvement in audiophile terms. But the quality of the recording and my mood play a bigger part (IMHO).

Perhaps if I use the powered sub, the quality of the amplifier should matter less.

I researched low damping factor amplifiers briefly. It looks like today's transistor amplifiers are built for high damping factor by default. Low damping factor amplifiers are most commonly tubes. A high damping factor doesn't allow a woofer cone to vibrate much. So you get harder upper midrange and less bass with fullrange drivers. That's all theoretical and I'm probably out to lunch on the understanding.