i'm on a roll... the kgsshv

[johnwmclean]

Yes that’s completely wrong, slaps head, it’s 130VA for the two 450V windings, apologies.

Edited September 8, 2012 by johnwmclean

[livewire]

I shoehorned a 400VA monster toroid into my KGSSHV after the SumR blew. Complete overkill.

Was dirt cheap and does the job well. Runs cool too!

[jwzhan]

±15V and Bias are working. -497V is giving me around -496V for now. but +497V is just plain wrong.

The +497V measured +486V just before dramatically dropping to +30V. When it was still 30V, I measured the reference which is still at 10V.

Then I left it there for the whole labor day weekend. When turning it back on, the output gave me 80V. Measuring before the lt1021 gave me 80V and measuring the reference voltage also gave me 80V, which means lt1021 is fried.

so here are what I did today:

pulled lt1021 out and I thought 10m90s, 2sa1486, and 2sc3840 are also fried so I pulled those out too, but they all measured fine (BJT with hfe and 10m90s with a simple testing circuit.)

I then went on measuring the resistors, which are all within tolerance.

I also pulled out the 100uF output caps which are again fine (pulled out so I can actually measure the resistor ladder.)

I then measured the resistance between the GDS of the fqpf8n80c in circuit, which are consistant to the ones in the -500V.

I also measured the bridge with diode test in circuit again, which are also consistant to the ones in the -500V.

The rest of the diodes still conduct fine unidirectionally.

Massive confusion and headache.

probably going to put everything back and put a good lt1021 in there to see what happens...

[spritzer]

400VA is indeed utter overkill and could cause issues with the unregulated voltage and thus causing the PSU to overheat. 200VA is plenty big.

One thing would make the job a lot easier is paralleling over 180 ohm resistors, would this be a problem Kevin or Spritzer?

That should work just fine.

[jwzhan]

stuffed every part back in for the Positive rail, replaced the reference today and fired it up. Everything worked for.... 20min. There was a violent explosion under the 680uF input cap of Negative rail (the arc also left a mark on the wima.) I pulled the cap out and, sure enough there was a short between the ground and the rail.

basically it blew through the plastic cover of the cap and shorted via the metal container of the cap on the top (red) trace.

this PSU is not being kind to me.... First it was a reference chip that got fried by nothing, and I had to take all the transistors out to confirm that. Then it's this... will i ever get it up and running...

[Victor Chew]

Are you saying that the board is defective? If not, have you found any reason for the short yet?

[jwzhan]

Are you saying that the board is defective? If not, have you found any reason for the short yet?

I can't find anything wrong with the board. This is a pretty simple two sided board. For some reason it's just not working for me... the short that happened yesterday was just out of no where... it just decided to blow through the silkscreen of the board and to have a short...

[spritzer]

It's not likely that the PCB is at fault but ever relying on the slikscreen for insulation is a bad call IMO. I always raise those caps just 1mm to make sure they can never short. Same goes for any and all top mounted traces and parts that pass over them. This is why we go to such great lengths of tracing everything at the bottom of the board.

[livewire]

Sorry to hear of your PSU woes, I can relate. I thought my PSU would never see the light of day.

Mine blew twice due to my bumbling with the multimeter while testing the PSU under power.

Spritzer once mentioned that heatsinks placed on top of traces could short them

because the soldermask paint on the pcb isnt the best insulator.

They should be "stood off" above the pcb, not in physical contact.

I havent forgot that and now I always check for potential short paths before assembly.

My KGSSHV PSU doesnt have the same potential for shorting as your's did.

The HV traces run underneath the board, with only the groundplane under the caps.

It is a much older revision, a different circuit entirely.

I am currently building a KGBH. The PSU has HV rail traces under the caps like your PSU does.

I will be insulating these traces additionally with a strip of kapton tape between them and the electrolytic caps.

Slight overkill, but cheap insurance nonetheless. One can never be too careful when dealing with high voltage.

That shit can jump like a rabbit!

It would be nice to see a pic of the underside of your damaged cap.

I know nothing about the insulating properties of the plastic they use to wrap those caps,

although in the past i have seen caps where the plastic does not wrap over the edge of the metal can

or there are perforations in the seam of the plastic.

I'm wishing you the best of luck on getting your PSU sorted. Third time's a charm?

Edited September 11, 2012 by livewire

[spritzer]

One has to remember that PCB's are nothing more than painted slabs of copper on a FR4 substrate. To rely on that paint for insulation wouldn't be the greatest idea.

[TMoney]

In boosting the current up to 10mA, how much more power draw is that going to equate to? Something in the vicinity of 20% more?

I think it'd probably be ok to push my SumR trafo that far, but if it ends up being in the vicinity of 50% or more I'm not sure I want to risk it.

Edited September 11, 2012 by TMoney

[deepak]

I think it'd probably be ok to push my SumR trafo that far,

Just curious why you say that, what do you have your transformer spec'd at?

[TMoney]

Its 100VA.

With all the talk about transformer issues going around recently I'm just not sure how far I want to push things given that the amp is currently functioning perfectly.

[gustavo.skn]

Well, I'm waiting for the next board production to get the pcb and start building mine, since It's kinda difficult to get one now... Any prediction on when another board run happens?

Thanks

[spritzer]

I'm too tired to make any sense now but I believe the stock configuration runs at 6mA so it's a significant jump in current draw.

There isn't another board run planned but the Gerber files have been posted in the thread and it's easy to just drop any fabhouse and email for a quote. Just ask how much a pair of amp boards and a PSU board would run you. Larger yields are cheaper though.

[jwzhan]

It's not likely that the PCB is at fault but ever relying on the slikscreen for insulation is a bad call IMO. I always raise those caps just 1mm to make sure they can never short. Same goes for any and all top mounted traces and parts that pass over them. This is why we go to such great lengths of tracing everything at the bottom of the board.

lesson learned

I am currently building a KGBH. The PSU has HV rail traces under the caps like your PSU does.

I will be insulating these traces additionally with a strip of kapton tape between them and the electrolytic caps.

Slight overkill, but cheap insurance nonetheless. One can never be too careful when dealing with high voltage.

That shit can jump like a rabbit!

note taken, just bought some kapton

I'm too tired to make any sense now but I believe the stock configuration runs at 6mA so it's a significant jump in current draw.

From a thread posted by KG on headfi, it's 5.5mA

[gustavo.skn]

I'm too tired to make any sense now but I believe the stock configuration runs at 6mA so it's a significant jump in current draw.

There isn't another board run planned but the Gerber files have been posted in the thread and it's easy to just drop any fabhouse and email for a quote. Just ask how much a pair of amp boards and a PSU board would run you. Larger yields are cheaper though.

Thanks spritzer, will send the Gerber to some fabhouses to see how much it would be! Hope that they make small quantities of the board...

Can someone confirm if this are the last gerber avaliable?

http://gilmore.chem....gsshvampv7s.zip

http://gilmore.chem..../kgsshvps8e.zip

I need two of the kgsshvampv7s and one of the kgsshvps8e right? Is it better to use onboard heatsink or pesante?

Thanks

[livewire]

kgsshvampv7s.zip is the off-board heatsink style amp from the last board run.

kgsshvps8e.zip is the PSU from the last board run. I believe these are the latest revision.

Keep in mind the PSU uses on-board heatsinks and will require a 3 to 4 inch tall case.

On-board heatsinks for the amp is cheaper, but off-board sinks can yield a very low height slimline unit, if done as a two case build.

I do not know where to find the zip file for the latest amp boards that use the on-board heatsinks.

Keep looking and please note that there were some trace errors in the early revision amp boards.

[jwzhan]

To my knowledge the V6 onboard version doesn't have trace error and is easier to build. The V7 offboard on the other hand has trace error, but it's fixed in the latest version (REV 0.5).

From a prior post, there is a revised PSU, but there is no change in performance.

I don't know about the size thing... offboard builds need one 3U400 or two 2U whereas the onboard can be tightly fitted into one 2U..

[gustavo.skn]

Thanks guys,

I'm quite lucky since an user from a brazilian forum sent me a pm willing to sell me his pcb from Lil Knight board run, offboard version rev0.6 - so probably no trace error? I got the FCE from johnwmclean, who was very kind to share it with me. Things are going well, let's hope it continue like this until the end!

[jwzhan]

Thanks guys,

I'm quite lucky since an user from a brazilian forum sent me a pm willing to sell me his pcb from Lil Knight board run, offboard version rev0.6 - so probably no trace error? I got the FCE from johnwmclean, who was very kind to share it with me. Things are going well, let's hope it continue like this until the end!

Schematic is available. It can be easily checked by comparing. The trace error of the previous version is mentioned somewhere in this thread.. you probably should take your time and go through the thread even if you got the correct board. You can never be careful enough... even the slightest error can lead to violent explosion...

Edited September 13, 2012 by jwzhan

[johnwmclean]

Its 100VA.

With all the talk about transformer issues going around recently I'm just not sure how far I want to push things given that the amp is currently functioning perfectly.

Richard has worked out a spec for a new build I'm toying with. Based on running ~10mA for the fourth stage the secondaries have been increased to handle 250mA @ continuous. The core is essentially the same size as the 100VA model with increased gauge for extra current handling, plus added insulation to help with surge.

Edited September 13, 2012 by johnwmclean

[Victor Chew]

John, will this change be for existing amp or are you building a completely new one? Grateful if you could let us know your procedures and being our first to experiment. Infact, I had earlier asked Kerry about it but then decided not to proceed with it as I did not want to screw around with a working amp. I have a second one, off board, I am working on so I might be tempted to do it though.

Edited September 13, 2012 by Victor Chew

[johnwmclean]

Victor, I’m undecided, I will most likely modify the existing amp.

Edited September 14, 2012 by johnwmclean

[jwzhan]

PSU is finally done.... positive is stable at 505V, negative at -505V, and bias at 396V. I didn't use the Fluke 113 due to the low impedance input, so the measurement might be off by one percent; however, as long as they are matching I'm satisfied.

My friend made a LTspice file for the positive and negatic rail. If anyone is interested, just send me a PM with email.