Class D amplifier with TPA 3250 board

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. 

You got low damping factor pretty much spot on.

Not modern (and no measurements available that I'm aware of), but I have a 20 year old Musical Fidelity X-A1 SS integrated amp that seems to have a very low damping factor as I've used it with many different types of speakers and it mimics the characteristics of a tube amp with "measured" very low damping.

I've had to open it, and the separate power supply, a few times to remedy what was basically shoddy assembly work and discovered that it had wire wound resisters on the speaker outputs (one per channel).

I also have an early 80's Carver SS receiver that also sounds as if the damping factor is quite low (Carver MXR130).

Anyway, hopefully switching to DC on your artisan amp will remedy the hum you are getting.

Also, definitely try the sub you own as doing so should give your single driver speakers a helping hand (making them richer/fuller sounding - more effortless) if the sub settings can attenuate the low frequency output of your single driver speakers.

DeKay

PS:

Couldn't resist and this is not a serious question, but does your amp builders demo/listening room look something like this?

DeKay

@dekay You’ll laugh but the artisan’s workshop had a bunch of noisy neon lights. The artisan told me that he couldn’t hear them anymore.

Thanks for the advice. Musical Fidelity sells the V90 amp new for 350€. The reviews seem kinda mixed. Everyone treats it like a cheap amp. Someone even says that it has a noise floor. 

There's no mention of low damping. I guess I'll give it a pass. I have to wait until Sunday anyways.

I own a very high sensitivity, fully horn loaded system (averaging 105dB sensitivity).

After many years swapping various "classic" amps, and being more or less happy, the death of the last pure class A amp I was using prompt me to try on a very low power class D amp, with a Tripath tA2024 chip. The amp is a heavily modded (all passive components) trends TA10.1

Let me tell you, it was a shock: the tiny cheap amp not only sounded very good, it was also more silent, and of course stays cold and doesn't draw much expensive electricity.

Since then, I've replaced most stuff in my system, and I'm now tri-amping, but the tiny class D amp stayed. I use another, even cheaper, class D amp on the 60 to 500Hz range, and only the subs still use class AB amps.

I'm thoroughly happy with how it sounds, in fact I think my system is at its best with those amps, they are completely devoid of noise and very lively and detailed, almost like a SET amp. The system stays on 24/7, the amps stay cold, they are completely fool proof, very transparent (you hear every upwards change immediately), for me there's no going back! No more headaches!!!

I encourage you to try one, but be aware that they are not all made equal, maybe start with something that has some "audiophile" pretentions like a Trends or a Charlize or an Amptastic. You will be VERY surprised (always with a good preamplifier in front! The Trends and Amptastic allow you to bypass their input level potentiometer, which gives even more transparency.

They are also very sensitive to the power supply and swapping the cheap SMPS for a higher current, very low noise linear PSU and good power cords and umbilical DC cables brings huge improvements and raise the sound quality of those amps from "suprisingly decent little toys" to truly audiophile. Really, I'm not lying.