i'm on a roll... the kgsshv

[nopants]

I think the most I've seen within reason is a 600V-rated twisted pair floating around on navships ebay

[sorenb]

My KGSSHV onboard is begining to materialize ...

 

 

Will spend the evening populating the remainder of the AMP boards ...

[sorenb]

Starting the day powering up the AMPs ... light in all LEDs

No, strange noises ... no arcing ... only one board had 89V DC, while the other was at 2V or there abouts.

Turned out the the LSK389 was in fact the culprit, in fact the only transistor I didn't test before mounting

One side had odd behavior and forced the input stage out of balance

 

[eggil]

Congrats. That was pretty fast!

[FrankCooter]

I bought a few sets of the  industrial connectors from a local shop a few years back.  They are good for 1000V AC.  only 30 dollars per set.  

 

I could not find multi-conductor wire/cable for the job.  Most multi-conductors cable are good for low voltage only.  Can I use a bundle of teflon hook-up wires, bind them together to create an umbilical cord?

 

though I much prefer to use multi-conductor cable.

What you're looking for is called "SOOW cable". It's very flexible and is designed for equipment where there is a lot physical motion. I use 16 gauge 8 conductor. It's rated for 7A/600VAC. Try "Wire and Cable to Go". They sell it by the foot. If you can't get it anywhere else PM me and I'll cut you a piece off my (ever shrinking)

roll.

[dsavitsk]

McMaster has it by the foot, too.

[sorenb]

Well, so much for enjoyment ... after having tested my KGSSHV for about 1½ hours yesterday ....I did the same today ....after 2½ hours ....a very loud cracking sound ....

No smell, no apparent visuals to go after ....the PSU + was down to 1,2V ...

removed the amp boards ... checked the PSU ...+/-457V ...did it again with 10k load on both rails ...no prob ....

the I connected the amp boards one at a time .... to find that the one having the faulty LSK389 was the board having problems.

A closer inspection of every transistor/diodes revealed that the everything but the LSK389 seems to work .... the soldering joints of the two Sources seems to have experience excessive heat :

 

 

 

Any ideas to what might be causing this?

After replacing the LSK389 yesterday I had an offset of 18-15V ....I compared measurments between the two boards and got approx the same values when probing around the diodes and further down that stage, so I took that everything would be ok then ... apparently not

Testing the 389 itself directly on the legs, shows G(-) -> D/S(+) => OL, G(+) -> D/S(-) => 50ohms.

The board doesn't seem to have shorts in the vicinity of the 389.

I have tested all resistors to be measureing identical to the other board.

No caps seem to short either ....

 

Can it be the PCB itself causing this problem?

 

BTW all boards have been cleaned for flux before using. Also after doing replacement

 

Theres 16ohm between v+ and gnd ...

[spritzer]

The reason we use green boards is to easily spot any shorts so if you can't see any then the board isn't at fault. 

 

There isn't enough power in this circuit to cause anything like this so it has to be a short, bad part  or something like that. 

[sorenb]

OK, problem solved ... at least I think so - I might add, as my merrits fixing this beast isn't that glory.

 

Hunting down the 16ohm and ended up at the heatsink of the IXYS parts ...the one closest to the edge...shorted to ground ...although I did use 7721-10PPSG and aluminium oxide pads ... but I also did use ARCTIC SILVER   so I'm back to using white stuff only - so much for taking advice and not checking it thoroughly ...

No parts seems to be fried must be Kevins current limiter that saved the rest of my day ... its up and running again.....and seems stable at 17V offset .... each board pulls approx 2x17mA...I guess it's on the low side?

[sorenb]

@spritzer: thanks ...you were obviously right. Does it sound right that the boards are pulling 2x17mA each (the negative tends to bit a little lower) and is 15-18V DC acceptable or is it indicating that something is wrong somewhere? the other board is stable around +-1V.

[kevin gilmore]

absolutely no artic silver.  The stuff is electrically conductive.

[spritzer]

Yeah, that stuff should never be used. 

 

As for the 15-18V, are you talking about offset or balance?  The amp drifts a lot as it warms up but you might need to adjust the series resistor in the offset adjustment. 

[sorenb]

Yes sir, I am already busy being 'the clean up guy' removing the stuff

[sorenb]

I have balance and trim in the middle for now.

One board is +-1V and the other is +18-15V ...approching 15 after an hour or so ....the latter board are +1V (-O) and -15V (+O)

[mwl168]

I have the off-board version of the KGSSHV amp boards.

To share my experience of the offset adjustment (measured between O+ and GND and without the servo); the offset can drift as much as 30V from cold start to when the amp is fully warm up.

After I adjust the balance and offset to within a few hundred mV when the amp is fully warm up. If I then power down the amp and restart it a few hours later, the initial offset is often in the - 20 something V and gradually decrease to a few hundred mV and then drift back and forth a bit afterwards. The balance usually is within a few volt difference from cold start to warm up - much less drift compares to the offset.

Your offset figure does not look out of ordinary to me.

Edited May 11, 2015 by mwl168

[sorenb]

@mwl168: Thanks for sharing your experience ... I have spent the evening listning to music from the amp, I'll adjust balance and offset and see if I experience likewise  ;o)

[DefQon]

You know they did a test with the arctic silver paste and turns out it is not electrically conductive. Assuming its the same one we are talking about used in computers.

 

Surprised myself when I found out it wasn't. 

Edited May 12, 2015 by DefQon

[n_maher]

You should read more, like the company's own website.

 

While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.

 

I'd also wager (although admittedly I didn't bother looking for the source you are sighting) that the designers didn't test conductivity at the voltages that we're talking about in these amps.  

[nopants]

What nate said, also similar line of reasoning when people tell you flux isn't conductive

 

I had to learn that one the hard way

[sorenb]

Here's some pics of the situation yesterday, first the board itself, after removing the two IXYS parts, and a mark to where the short took place

 

A close up of the actual scene of crime

 

A pic of the insulation/screw etc ....the left parts was carrying the short, whereas the right didn't ....the washer is the 10PPSG so I guess only the "Arctic Silver 5" can be the suspect here, maybe it should be "Arc-ing Silver 5" would be the proper name for it

 

 

Both amp boards has been cleaned and is back in business. Had a listen for some hours yesterday and it sounds very similar to the one very very well build edition I bought from Spritzer. It may sound less sweet, perhaps a little cold in direct comparison to the Spritzer build.

There are a few apparent differences between the two:

 

Current Sources:

Mine: IXYS

Spritzer: A1968

 

Input FETs

Mine: LSK389

Spritzer: separate fets

 

Heat:

Mine: warm to the touch

Spritzer: hot to the touch

 

 ... judging from the heat I guess Spritzers run at higher current than mine

 

@DefQon: if the Arcing Silver isn't conductive I don't see how that short should ever be possible ... maybe something from the screw penetrating the washer ... but that would require some force and I don't tighten the screws that much ...just a rather soft grib and stop when the screwdriver slips my fingers

 

@n_maher + nopants: I guess the Arcing Silver is meant to be used in PCs. I took advice and didn't check it out before hand ... I've checked everything else for this amp but the LSK389 and the Arcing Silver.learning the hard way seems to very true when fiddeling with HV.

Edited May 12, 2015 by sorenb

[johnwmclean]

Sorenb, congrats on your progressing build.

I appreciate your detailed follow up post above, that is really helpful!

[JoaMat]

Congrats to success and thank you for informative posts.

[nopants]

thanks for the breakdown

 

if the lsk389 is giving you trouble 2sk170s seem to work pretty well (also listed on the board iirc). I've used matched pairs and typically I don't experience issues, even when I forget to bond them for thermal tracking purposes. ymmv though

Edited May 12, 2015 by nopants

[JimL]

Re Arctic silver 5 - from the website:  "Made with 99.9% pure silver:  Arctic Silver 5 uses three unique shapes and sizes of pure silver particles..."  Siver is definitely conductive.  Maybe not mixed in a non-conductive paste for heatsinking in a computer where the highest voltage is 12 volts, but definitely possible when the voltage is 450 volts and up!  Air isn't conductive either - but shuffle across a rug and touch a metal doorknob...and air doesn't contain micronized silver.

[spritzer]

The heatsink is grounded so it doesn't make any sense that it shorts there.  Also no traces too close to that spot...   Weird...