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kevin gilmore

i'm on a roll... the kgsshv

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I'd use kapton tape to provide an extra layer of insulation between the 450v caps and the PCB itself as one of the guys here had there's short to ground. 

 

Yes caps blowing up is a spectacle to behold. 

 

Btw that toroidy looks pretty big, what's the dimensions?

Edited by DefQon

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The ground plane on the newer pcbs has been removed from under the caps.

I don’t see having the caps hard up against the pcb would be a problem now as the clearance is at least 3mm.

Edited by johnwmclean
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I'd use kapton tape to provide an extra layer of insulation between the 450v caps and the PCB itself as one of the guys here had there's short to ground. 

 

Yes caps blowing up is a spectacle to behold. 

 

Btw that toroidy looks pretty big, what's the dimensions?

 

15cm in diameter, close to 8cm tall. About 4.2 kg in weight. Problem is, the leads come out from the bottom of it, so I have to get some nuts or some padding under it, unless I want to screw the transformer to the top of the chassis.

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For the 16V-0-16V, there's a 0V lead from the transformer, do I connect it to ground?

 

For the low voltage 16V, do I leave the CT unconnected too?

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The transformer could have a shield tap and that is connected to ground.  If you don't connect the low voltage CT then you have just a single 32V winding and that won't work. 

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If I can't get the pro bias to exactly 580V, is it better to stray towards 570+ V, or 590+ V?

Edited by kh90123

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Doesn't matter in the slightest.  No other amp has a regulated bias supply. 

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I meant more in the "not some crazy idea Kevin and I had" sense.  :)  There are others too and even the old BH supply (as in found in all the Headamp units) was just updated and modernized with new parts and a regulated bias supply. 

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How do I match the IXTP01N100D? I am only using it as the current source.

 

Do I need to like apply some 24V across the drain and source, put for eg a 1kohm resistor on drain, and 0V to gate, then measure the current?

Edited by kh90123

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Are the high wattage resistors supposed to get pretty hot? I use an infrared thermometer and it's showing one of the 240kohm resistor at close to 80 Celcius.

 

Also, the 2sa1486 and the KSC5026M gets pretty warm too, in the range of 60-70+ Celcius. My ambient is very high though, at about 30 Celcius. That's about 50C delta. And I haven't even connected the amp boards to the power board yet.

 

I measure 2.5mV of AC noise on the -500V output, and 0mV of on the +500V output, is it supposed to have a bit of AC noise? The caps should filter them isn't it.

 

After swapping a 150V zener to 130V, my bias now stabilizes at 577V, not bad at all. It was 598V, -20, should be about 578V.

Edited by kh90123

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Any ideas what could be potential causes of intermittent noise & distortion on a 500V onboard KGSShv in a single channel? This unit uses boards from Lil Knight. 

 

The issue first reared its head with SR-009 a few weeks ago; I shut it down for the night, and then the amp continued playing clean until 2 days ago. It's a noticeable hash/grunge type distortion to the signal that has occurred while playing moderate-to-loud levels, and is readily apparent when I switch the source signal to mono to confirm the distortion's presence in the R channel. When I pause the source after this starts, there's a "rustling leaves" type noise floor in the R channel that sounds a lot like when a small-signal tube goes noisy/bad (this noise is very audible, but would be masked by the signal, so I believe it's 2 separate artifacts). The amp had been on for several hours each time it's occurred; the last 2 times it appeared very quickly after I switched from Lambda Pros at a moderate level to SR-007 at a higher level.

 

I've verified with a rock-solid 400V offboard KGSShv that the issue is isolated to this 500V amp. Would love to know whether anyone else knows what this might be just from my meager description, though I realize that may not be possible. Hopefully more along the lines of "dance this jig" or "replace this part" rather than "rebuild the board". Possibly unrelated, the Alpha pot on this unit isn't very smooth and consistent on this unit, unlike the very smooth Alpha pot on the 400V amp. 

 

The damn thing sounds pretty amazing when clean, too -- almost on par with a BHSE. 

Edited by mulveling

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VR1 1K pot

 

Is that the 1K trimpot labeled "Offset", and do you think the problem is that the adjustment is out of whack?

 

Edit: Ah, VR="variable resistor"? I am not a DIY'er obviously, but I'd like to pick up bits where I can.

Edited by mulveling

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A sound like that is almost always due to a noisy trimpot. 

 

Some of the first Alpha pots weren't as smooth as the latter ones.  A bit of screaming at the company fixed that...

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A sound like that is almost always due to a noisy trimpot. 

 

Some of the first Alpha pots weren't as smooth as the latter ones.  A bit of screaming at the company fixed that...

Cool, so if the R channel trimpots get replaced, then there's at least a chance it will resolve the issue? Also, is the KGSShv trimpot adjustment procedure anything at all like this:

 

HeadAmp Blue Hawaii SE (BHSE) Electrostatic Amp Bias Adjustment

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It's exactly the same unless it's one of the new HV's which have a servo.  Then the procedure is the same but the servo has to be defeated first. 

 

Only make adjustments after the amp has warmed up.  For a 500V unit that can be an hour or more. 

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Thanks Spritzer -- 30 mins into warmup (not to adjust, just to check), and the balance and offset Voltages for both channels look fairly reasonable and stable (biggest number I saw was a touch over 5V for an offset and 3V for balance). I'll check again after 2 hours; maybe try to adjust them a bit closer to 0 if possible. I can eventually give trimpot replacement a shot if the noise proves problematic with continued use -- I read about how to adjust each of the 1K/2K before installation.

 

Is there any potential danger to headphones from something like this, if the noisy part gets worse? I thought the only real danger to headphones was if the bias got way higher than 580V for some reason -- is that correct?

Edited by mulveling

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So the offset for both R and L kept creeping up and up and up as the amp warmed up for over 2 hours -- but otherwise it seems relatively stable and symmetric between the R and L. I adjusted them for full warmup conditions, then re-tweaked the balances and let them settle. This is a Prod Rev 0.2 board, so no offset servo.

 

What's not so stable and symmetric is the R channel balance when driving higher signals. I can now pretty reliably reproduce the following: play music fairly loud (but not beyond listenable) on the SR-007, and about a minute or 2 in the distortion will appear (fairly abruptly, too) on the R channel. When I pause the input signal, remove headphones, and measure balance at this point, it can read up to 24V or so (!!), while the L channel is still in its reasonable range (under 2V). The R channel will start to drop back down to a reasonable value over the next few/several minutes as the signal is paused, but this seems to indicate a problem. It kind of seems like there's signal level at which the distortion/instability is triggered.

 

I'm pushing 4-6dB more signal into the 007 vs. 009 and Lambda Pro for comparable volumes -- which I guess is why this has never occurred yet with Lambda Pros. And only once being stupid with the 009. 

Edited by mulveling

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The volume level should have nothing to do with this.  The amp always burns relatively the same amount of power regardless of how hard you drive it. 

 

If the offset pot failes then yes, the phones could be damaged.  We have protection built in should it happen though. 

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It's exactly the same unless it's one of the new HV's which have a servo.  Then the procedure is the same but the servo has to be defeated first. 

 

Only make adjustments after the amp has warmed up.  For a 500V unit that can be an hour or more. 

 

Do you mean I should disable the servo when adjusting the offset?

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I think the worst case scenario is one of the outputs is stuck at negative rail. Other than that I am not sure what could really happen catastrophic...

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Do you mean I should disable the servo when adjusting the offset?

 

Yes, the amp should be zero'd out when running at full temp and then powered off and the servo engaged. 

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Thanks, interesting. Is it at all possible that the source (NAD M51 via XLR) could be pushing the extra DC into one channel at these times -- I could try to swap input channels (I realize many of my questions, probably this one, are going to be stupid)?

 

If it still sounds like trimpot replacement time to you guys, I'll proceed with that. The problematic board uses Bourns 3299 (Costa Rica) which are slightly bigger than the L board's 3296 (Taiwan).

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