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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 24th November 2017, 06:47 PM   #97671
hhoyt is offline hhoyt  United States
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John Curl's Blowtorch preamplifier part II
Default New Amp Testing Methodology

I hope I am not double posting, but as we all know, no existing tests quantify amplifier sound quality (ducks).

Here is a Master's thesis proposing an alternate method:
https://goo.gl/M6FpVu

...and he makes some interesting points, although I disagree with his conclusions in general. Of course being that the listening tests were conducted using a pair of 1960's Radio Shack 16 ohm PA monitors, skepticism is perhaps called for.

I just figured after all of that turkey you US audio dudes ate, some rousing theological conflict could stir you out of your torpor!

Happy Thanksgiving!
Howie
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Old 24th November 2017, 07:00 PM   #97672
scott wurcer is offline scott wurcer  United States
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There have been regular bashing sessions on Cheever's thesis here over the years.
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Old 24th November 2017, 07:30 PM   #97673
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Originally Posted by scott wurcer View Post
Face it Jan at least one of your builds on this will really let some spectacular smoke out. Make sure the 2KV supplies have a very low output impedance and lots of energy storage. We had an ADSL customer in China that called and said our parts were "holeing" we thought it was a mistranslation. It turned out one of their tests was shorting to the rail on the near side of the transformer, and the die was vaporizing and blowing a hole in the SMT power package.
Mosfets can do strange stuff. I managed to blow holes through the tops of some TO-3's. They looked like they'd been hit with a laser or somesuch.
The manufacturer's engineer blamed it on ' plasma '
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Old 24th November 2017, 09:28 PM   #97674
anatech is offline anatech  Canada
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John Curl's Blowtorch preamplifier part II
I've seen Carver amps that did the same to MJ15024 and MJ15025 transistors, and also burned through the cover on the PM-1.5t amps. Customer plugged them into 550 VAC by mistake.

Yes, those were the last electrons those amps ever saw. The damage was more than severe!

-Chris
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Old 24th November 2017, 09:29 PM   #97675
jan.didden is offline jan.didden  Europe
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Originally Posted by Nelson Pass View Post
It appears that they do know something about it.
Nelson thanks for that, indeed this seems like they are aware and trying to solve. My communication was with support in Germany and this was never mentioned.

Jan
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Old 24th November 2017, 09:34 PM   #97676
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by scott wurcer View Post
Face it Jan at least one of your builds on this will really let some spectacular smoke out. Make sure the 2KV supplies have a very low output impedance and lots of energy storage. We had an ADSL customer in China that called and said our parts were "holeing" we thought it was a mistranslation. It turned out one of their tests was shorting to the rail on the near side of the transformer, and the die was vaporizing and blowing a hole in the SMT power package.
The 2.1kV supplies are regulated and current limited. So far no device has been lost, but I know it probably will happen one of these days. No reason to stop trying to finish it, of course.
I am planning to switch to 4.5kV IGBTs for the output stage, as these have more robust SOAs.
But for the Vas they have too much interelectrode capacitances. I can handle that in the output stage as a (sizeable) fraction of the load, but not in the Vas.

Then again, I really wonder if a class A quiescent of just 6mA would ever trigger this behaviour, even at +/-2kV - but eventually I'll have to prove the pudding. Haven't run it over +/-1kV so far.

Jan
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Old 25th November 2017, 09:34 AM   #97677
marce is offline marce  United Kingdom
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John Curl's Blowtorch preamplifier part II
This may be of interest Jan.
http://www.magazines007.com/pdf/High...e-PCDesign.pdf

If you are having PCB's made I would recommend a high voltage laminate once you get over 2K. AT home so haven't got access to my work notes, but from memory there can be issues with normal PCB laminate. One problem is micro bubbles within the material that can cause micro arcs. I'll dig the stuff out it was interesting. It was for Ion containment electrodes so high voltage but low current, but reasonable switching speeds, . Nightmare for spacing so multi-layer PCBs are best with ALL high voltage tracks on inner layers, then you only have to worry about pads and component legs for external spacing's. Multi layer boards also give you the ability to add screening layers if required.
For your thermal stuff have you thought of looking at Avvid or similar, had some fun with thermal pipes and thermal ribbon pipes, allowing a good thermal pathway from hard to reach areas or devices to a thermal radiator.
On these designs when it goes wrong it can be spectacular, I once had some diodes put in the wrong way on a PCB, in a prototype high voltage (35kV, 10-15KV 2X2.5kV and 6x1kV) all shorted together for one illuminating instance, for some reason I did not get the employer of the month award but a verbal a*** kicking.
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Old 25th November 2017, 09:55 AM   #97678
jan.didden is offline jan.didden  Europe
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Nice, thanks. According to this paper my design rates as 'medium high voltage' as my max is +/-2.1kV.
Still worthwhile to review. I have tried to take care of creeping distances and avoiding sharp bends and such but didn't think about the material itself.

Jan
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Old 25th November 2017, 11:04 AM   #97679
marce is offline marce  United Kingdom
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John Curl's Blowtorch preamplifier part II
Medium high voltage Its all relative I suppose.
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Old 25th November 2017, 11:22 AM   #97680
jan.didden is offline jan.didden  Europe
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Originally Posted by marce View Post
Medium high voltage Its all relative I suppose.
Al least since 1916 ;-)
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