MLA

So, presumably 1.5A per GRLV then (i.e. 3.0A for a bipolar one). That said, Sören’s suggestion above is very interesting! I’ll think about rebuilding my Dynahi Psu that way, just to try it out.

So around 2A in total (pos and neg rail combined)? If I remember correctly, Dynahi pulls about 2.4A in total (600mA per rail per board), so you'll be close to Dynahi levels with your next step Btw, can GRLV deliver that much current? I thought it maxed out at 1.5A, but maybe that was per rail, not total?

Nice! What’s the max current through the Sigma? Nevermind, ten seconds of research later I see it doesn’t have a current limiter Are you planning for dual GRLVs when running it at 30V, or is one enough currentwise?

@mdr30 arranged for a prototype to pass by Gothenburg for evaluation a few months ago. Transient response was very good but the frequency voicing was quite off; at that time they claimed to have voiced it for vocals which translated into a big upper mid hump that made it difficult to listen to. Mid-bass was also lacking. They claimed they would address that right away; apparently we were not alone in giving this feedback... They do however give a whole new meaning to the concept of open headphones Very different, but in a good way. At HD-800 price levels, it would be a contender. At 4K, not so much I think.

I agree. Built a 360-ish volt version before, so will do a 400V next time. For the record, as good as Dynahi and Dynalo are, the CFA2 is where I plug my dynamic cans in most often. Guess I have a personal preference for current feedback. Or perhaps more adequately, Kevin's current feedback designs are awesome

It is a great amp, fairly independent of price range I think (though 37K obviously is the Best Ever...) When I build mine, I only had it for a couple of weeks and really liked it a lot. Then a friend asked to borrow an e-stat setup so it went to him for further opinion. A month later he declared he’s not giving it back unless I force him to do so. Have to build another one I guess

Well, just checked mine and they are SZ2 - 2253. I purchased them on site in Tokyo in November last year from a music store. They were not in stock at the store, so these were delivered straight from Stax the next day. Unless someone kept yours in storage for a couple of years before selling, I'd assume it's new stock.

Can check mine when I get home. Bought them a little less than a year ago in Tokyo.

So, you are someone who actually needs a preamp To continue your DIY journey, this would be the time to build the KG ubal/bal board (check the thread). Gain of 2 into balanced, but can be set to taste by changing a couple of resistors.

Sören's guide is excellent! Should get you on the right track. Also, I'd suggest checking the status of the BC557; they can handle max 45-50V across, so if the whole circuit has seen 360x 1.414 = 509V while something else is out of place they may be toast...

It's no so much contradictions as the manufacturer specifying thresholds the component is tested to meet under various standards for operation. http://www.ni.com/white-paper/2827/en/ Assuming you're powering your amp from a wall outlet in your house rather than straight from the distribution lines :), I think the 630V rating applies.

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...