MLA

I think the Rane note is spot on and you've done that part right. However, since it sounds like the hum travels from left to right channel depending on pot position (though much less audible in the left channel due to high attenuation when pot is at low volume) something else seems amiss. Have you tried either @Laowei's suggestion (amps directly to star ground rather than to PSUs) or first tying PSU grounds together and then use a single connection rather than two from PSU to star ground? Also, I would probably go for pot to either floating as per Laowei or to star ground, rather than amp boards.

I usually attach pot ground to star ground directly. Is that one of the options you already tried? Also, are your inputs tied to star ground as well, or to the pot?

Somehow I knew you were going to say exactly that

Very cool! Which part of the spectrum benefits most?

The DragonFly? You may be in for some device generated problems that may or may not have to do with the power supply: http://archimago.blogspot.se/2017/06/measurements-audioquest-dragonfly-black.html Rather than dropping 200 on an isolator, you might want to try a different device first: http://archimago.blogspot.se/2017/05/measurements-smsl-idea-usb-dac.html That said, some quick cable surgery will probably give you the answers you need right away.

Assuming what you want to do is find out if cutting the computer power line reduces noise, it's just like bomb dismantling in the movies Get two identical USB-cables that meet USB 2.0 standards (assuming audio is focus). Make a small incision in one of them with a sharp knife and cut the red wire. Voila, you now have two identical USB cables exept one does not carry computer power. A/B test away....

^this

Yes, across any of the 2 ohm resistors, that's correct.

It's in the thread.

So, there seems to be competition in the market; behold the TKD-401. This looks like stereo only, but I bet between channel tracking is very precise, as long as you keep going straight.

Just basic JJ El34's. From what I understand, different tubes should have limited sonic inpact in this curcuit, but I got the GB BH boards for a later build and there I think changes may be more audible. Apart from looking for exotic, I also intend to try the JJ EL-34L which the guitar crowd claims had more bottom end than the regular JJ EL-34. Fun times ahead

Well, vacation is over and my GG lives. Turned out to be a partially dead lsk389 on one channel and a cold solder joint on the other, combined with too high tail resistor values on both. Obviously not my finest hour stuffing those boards . Anyway, the amp sounds really really good, so many thanks to KG and all other contributors for this great circuit! Now to find some exotic and good looking EL-34's to top it off...

If that's the board from page 2 of this thread, I don't think it has a servo on board...

Very good guide. I'm away vacationing for a few days, so this will be next sunday's mental exercise. Whatever the error is it's symmetrical, cause both amp boards are acting up identically. I'll post back once I've investigated a bit more...

Looks excellent! Trying to sort mine out as well, was suspecting the lsk389 are dead because while voltages are fine with inputs shorted they go crazy when fed a signal, but a cold solder joint on the nfb might explain that as well. Where did you find the rings for the top lid? They look great!