I wouldn't be surprised if they are not stepping the tube B+ up beyond the 24 volts of the supply rail. It would be interesting to measure it but that's my suspicion.

Will glad to see you making a full tube amp

Throwing in a couple of valves, is like adding a red racing stripe to your car - makes it go faster.  yeah right

Douk ST-01 Pro TUBE tip: If your amp came with Chinese 6k4 tubes (has a red star printed on the glass), mine caused distortion.  I upgraded to much better sound for $17 with GE JAN 5654W matched pair tubes.  6k4 tubes can be replaced by 6J1, 6J2, 6J3, 6J4, 6J5, 6"1N, 64N, 65N, 5654/5654W, 5725, 6AK5, EF95, 6BA6, 403B, etc.  Your tubes may be ok.  Just an FYI free tip.

Nice

Really professional looks

I have the same one powering my Yamaha Ns45 towers, and I love it. It sounds perfect to me, but it might get a bit hot after a few hours of normal usage. Also, I had some minor issues with bluetooth having micro-cuts

Approximately, what watt output do you get if you switch to a 32-volt power supply? Thanks.

I do think some of these tube buffer pre amps do add to the sound tbh. I think they add a warmth to the sound which i like with some music. Not to everyones taste obviously.

Dear John lets face it. My everyday driver is a hamble CD7379 + "AD828" (fake I think  from Aliexpress) powered by a 220 VAC / 12 VAC 4,5A  transformer for halogen spot lights. I can't hear even the slightest  back-ground noise  and I'm very satisfied from the audio quality  (not for "critical listening) in conjunction with a pair of full-range speakers (open faffle) . In contrast  OVER A FEW MONTHS  I'm  trying to make a class-D amplifier to drive the same speakers with a descent "quality" (not screaming highs) and  S/N  ratio, BUT IN VAIN !

Might throw a thermal pad on the bottom of the pcb to makes some kind of useful contact with the case where the chip is.

thank you for this
Do you know what is the amp's input impedance (resistance)?  thank you

So this VU meter show the point when amplifier started to clipping?
Thank you

Will this be good with my r41m speakers

Are the tubes just for choreography or do they really work?

I think they have added a valve (a RF valve) for looks only. With all those 5532s the circuit offers more than enough gain. So, the valve can only really contribute to noise and harmonic distortion.
Remove the valve and all its associated circuitry and you probably get less noise, lower THD. Less issues with impedance matching. Overall, it will sound better and cost probably 50% less. With such poor filter design your chosen speakers should be a very close 8 ohms with no impedance drops towards the 4 ohm area or it will sound dull.
Using an RF valve for audio is not a good idea. Thats why audio valves like EF86 etc were made just for audio. Such valves do not really exist in the Chinese surplice market. so they throw in any cheap and unsuitable valve knowing the public just see a valve and get super excited.

Great review. Use of tubes I find dubious.

1:03 Brings me back to my student days..  2:20 Ah yes, I've got AYIMA version of this, tried using as a preamp only into an Arcam Alpha 9 power amp, not particularly impressive; tube rolling won't help it's the fundamental design of the circuit which ultimately dictates how good the sound is.

What do you think about the integrated DAC of this model? Its usable or an external DAC would be a nice upgrade?

@JohnAudioTech did you ever discern what the pot on the bottom was for? i have been scouring the internet and your the only one who even mentioned it.