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Yea, that noise is similar. But it's less crackly/more like white noise on mine. Guess the next step is to try swapping the takmans for xicons. For what it's worth, even despite the noise I can tell this amp will be something truly special.

The 390k/820k resistors are takman metal films (REYs). Would be slightly annoying if they turned out to be the culprit, given their price. Anyway here's a pic showing their height off the board. I get continuity between the ground screw of the amp and the backplate screws of the PSU. Not between the two sets of backplate screws though. The noise didn't seem to change at all when adjusting the trimpots. It's also close to identical on both channels, but not quite. If it helps the input tubes are JAN Philips 'low noise' 6922s.

Well I've managed to solve the hum at least (noise still remains). There's continuity between the two chassis, between pin K & IEC ground, and between circuit ground & IEC ground. Essentially I've done the grounding the same way you have. The resistors are all lifted off the board by a few mm. I'll take a picture later that shows that height.

Nope, not while the batteries are within proper range. Gonna try cleaning the pins of the input 6922s in case that cures it. If it doesn't I'll probably look at the grounding in the PSU, since I do hear a faint hum (which I think might be 60Hz) among the noise.

Well after fiddling with the trimpots for a while the noise doesn't want to disappear. I'd run out of adjustment range (as in the LEDs would turn off) in either direction before any change in the noise happened. Any ideas?

Yep, the boards are the later version. The noise is also not a solid tone but a wider (white?) noise. Will try adjusting the pots in a bit.

Good news: George's suggestion worked. Things just sort of fell into place once the 22k resistor was adjusted to ~6.55V. Then all the batteries could adjust to +200/-541V. Offset and balance are also nice and low. Unfortunately now that I've actually plugged in a pair of headphones, I'm hearing a constant noise. Doesn't change at any position of the volume pot either.

So I've gotten to the point in my build where I can fire up the amp itself. Unfortunately some LEDs are unlit and the batteries don't want to change their voltage (+250V/-559V) with the trimpots. Specifically D1, D6/D7, D10/D11 and D24 are unlit. Aside from those the LEDs outside of the batteries are dim. The PSU voltages measure dead on. Any obvious culprits I should check?

Just to add, the HV900 boards should be the single type. So it'd be 4 HV900 boards per amp that way. Also, could you offer the 450V fat/split PSU boards as well?

Won't it need the output boards, driver boards, and the HV900 boards? The driver board is different from the regular carbon amp board last I checked. It might make more sense to offer the boards as a full set, but either way I'm interested.

For the new fat/split carbon PSUs, what wattage should the two 249kOhm resistors be? Would 1/2W suffice?

That was fast. Looks good Kerry.

Paid. Thanks for running this.

I'll switch to the FT caps as well then. From 20x mundorf caps to 50x of the FT ones.

Paid. Thanks again for running this.

I'm interested, depending on how much a matched quad totals in the end.

Correct me if I'm wrong, but aren't the v2 attenuators capable of balanced stereo on one board? Also just to check, all that's required to use this is the attentuator(s), an uno, a separate +5V supply, and either a pot or rotary encoder?

Correct quantities for me as well. Gift payment is fine. Thanks for organizing this

I'm assuming only one value will be ordered then? Either way I'm in for at least 20.

Is that for 680uF or 470uF?

I'd be in for 20x 680uF/550V caps if you're going to order 100+. Right now those 20 caps take up a large sum of cash on my mouser cart.

Was answered I believe Kerry also mentioned to use AC325 for 400V output and AC360 for 450V output.

The data sheet off mouser for the kemets I have selected say it's 2 lead (since A is the termination code right after ALC10).

How about mounting the driver/output boards vertically & the PSU boards horizontally? Should put less stress on the caps & leave enough space for toroids on the bottom plate (this is assuming 500mm depth). I can include a rudimentary sketch if needed.

Already edited my first post, but I'll take all v3 amp boards.