I think he issue comes down to tolerances. It shouldn't hurt to lower the resistor though, for new builders I don't see why you couldn't just start with the lower value, doubtful any harm would ensue.

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?

If the adjustment of the batteries does not fix the problem, take a look around the J79 MOSFETs there should be around 50V between the drain and the source.

The above is only valid only if the batteries are correctly adjusted

I'm curious about current flow around the batteries.  I wanted to ask what the voltages are across R1, R2, R3, R42, R58 & R59.  Sounds like some dead transistors/LEDs for the current sources/sinks + something in the batteries as well.

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.

It's a T2... there will probably be a bit of noise.  Try to adjust the pots a bit to see if that cures most of it. 

you do have version 1.15 or later of the power supply board?

the first version of the board had a 1khz noise problem that required adding a cap and resistor (x4)

and I remember that knob

 

Edited September 20, 201510 yr by kevin gilmore

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.

Yes, adjust the trimpot for any noise. It may put the voltages off a smidge, but getting rid of the noise is key.

It's a T2... there will probably be a bit of noise.  Try to adjust the pots a bit to see if that cures most of it. 

Birgir, my T2 (Andy's second unit) is basically noise free.  

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?

Does the noise get audible? Meaning, you hear a squealing without using the headphones?

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.

Grounding is very important for noise. You should make sure there is continuity between the two cases, and you will need to scrape off some of the anodizing to make sure it doesn't insulate where you don't want it to. If you have continuity, then probably not grounding.

Was also wondering how close your resistors are to the board, especially the resistors in the batteries.

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.

Check continuity from a back plate screw on the amp chassis to a backplate screw on the psu.

And are those takman Rey or Rex (they look like Rey)?

Ahhh saw the batteries.  I bet that is the noise you are hearing, throw some Xicon's in there and it should work just fine.  

Birgir, my T2 (Andy's second unit) is basically noise free.  

Low noise maybe but not Carbon levels of utter dead silence.  Just can't be done with that T2 circuit. 

Ahhh saw the batteries.  I bet that is the noise you are hearing, throw some Xicon's in there and it should work just fine.  

Low noise maybe but not Carbon levels of utter dead silence.  Just can't be done with that T2 circuit. 

I think Inu used Takman Rey (metal film) without any issues, but I do seem to recall that he made a number of other modifications to deal with the noise... I have some 820k and 390k that I can send his way to see if that is the issue.

I will compare the Carbon to the T2 in November. The T2 does have a quad of input tubes that need to be as silent as possible - I suspect that everyone may have a different noise floor based on that alone.

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?

Did the noise change at all when adjusting the trimmers (all 4)? Noise is the same on both sides? 

Yea, the noise could very likely come from leaky resistors.  On mine, the leaky resistors not only caused noise, they also caused the active battery to be very unstable.

 

 

 

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.

Edited September 21, 201510 yr by s_r

Swap them out as the Xicon's are known good.  I might have a recording on the noise somewhere if I look hard enough... 

Edit:  Maybe this? 

Edited September 21, 201510 yr by spritzer

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.

Definitely sounds like the resistor issue, use Xicons...

/

 

Edited November 11, 201510 yr by JoaMat

Darn, I'm in the latter stages of my build and used Takman for the battery 390k/820k. And as things turned out (and a little help from my friends ) got Xicon 390k/820k. It would be easier to pull now rather than later, should I swap them? Or just give them a shot? 

 

Give them a shot. Help confirm for future builders