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The Headcase Stax thread


thrice
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Go for a Blue Hawaii Nate. Tubes man. Tubes.

I don't see this happening any time soon. I haven't even managed to get the 950s working off the SRD7 yet. :-X

Then I'm in, dagummit! But, er, how much, y'know, like electricity am I gonna be exposed to? If there's one thing I like less than unlean hands, it's getting zapped.

I believe we're talking on the order of 600V or so. :eek:
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I don't see this happening any time soon. I haven't even managed to get the 950s working off the SRD7 yet. :-XI believe we're talking on the order of 600V or so. :eek:

try 700v for the psu and 1.2kv peak-to-peak output. That's the stock output, you can easily double the current / power if you have heatsinking. It's fun, just pray that the exit wound will be *very* near the entrance wound for any electrocutions.

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please at least give an option for external heat sinking. This amp really improves with extra biasing and it's stupid simple to do...

Having a dual purpose board shouldn't be that hard with an angle bracket or a second set of traces.

I'm not sure if it would be worth the trouble pulling them apart to replace the cable. The problem is that the ear cups are glued in place (bad idea I know) and would have to be removed.

Good point. I don't see why they are built like that as I've yet to come across a stat which doesn't have a removable baffle of some sorts.

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What are the required specifications for the KGSS trafo again? I was going to contact a trafo-man'f today anyway regarding a custom transformer so I might as well ask them about this project as well.

Colin mentioned the following: 100VA R-core transformer with 300v-0-300v at 80mA,0-6.3v at 2A, 0-18v*2 at 1.2A, and 0-12.6v at 1A.

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What are the required specifications for the KGSS trafo again? I was going to contact a trafo-man'f today anyway regarding a custom transformer so I might as well ask them about this project as well.

Colin mentioned the following: 100VA R-core transformer with 300v-0-300v at 80mA,0-6.3v at 2A, 0-18v*2 at 1.2A, and 0-12.6v at 1A.

The first KGSS psu called for a 800VAC CT @ 0.2A (Thordarson 24R22U) plus a

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use 500v caps then.

If that's all it takes for it to be sufficient, great.

Also, I'd love to see the required mods to raise the bias up a bit from the stock 580VDC. I know that some of you have already done this and have specific thoughts about what bias the 950s really like to run at (above 600V). I'm sure this is just a matter of tweaking a few part values.

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I know, but then Colin said this:

Colin is a bright guy so I assign a good deal of weight to what he has to say. Dr. Gilmore's thoughts would be greatly appreciated.

Bright guy, hah. All I was looking at was that 800VAC*1.41/2 = ~564VDC, with a whole lotta ripple. I dont really feel that the R-Core I am looking at is perfect, but it seems pretty close, and still capable of providing significantly more current than is needed by the KGSS (which would allow one to bump up the output transistors' bias. I would use a bit different values if I were to get something custom wound though, though I am also planning to use different voltage regulators for all supplies. I would probably go for something like two windings of 280-0-280 at 100mA, and 18-0-18 at 250mA. The current ratings are kinda arbitrary.

2sa1968's not needed for kgss. Think KGBH power supply.

Front end fets can be matched from single devices if necessary, but

lsk389 is a wonderful part.

I am sure you are aware of this, but the KGBH power supply has double the 2sa1968 count of the KGSS supply, seen in the CCS biasing the zener string. Would be easy enough to change though. I dont have much experience in HV regulator design, but do you feel 500v parts gives sufficient margin. I am thinking parts like FQP4N50 and FQP3P50.

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My original board layout is pathetic compared to the stuff justin did

afterwards. Someone would need to do a new layout complete with

ground plane and all that other modern good stuff.

Don't try and build the original power supply. Go with a BH supply

set for + and -350 volts. Which requires dual high voltage secondaries.

Oops forgot about the 2sa1968 as the current source. I'm using something

else for current sources these days. That is a 900 volt part anyway.

The pass fets can be anything rated at 600 volts or more. Pretty much

anything works...

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cetoole:

I'm using the Fairchild FQPF2N60C in a HV regulator design. Pretty nice specs.

I buy my heatsinks from R-Theta these days and absolutely love their service, but for the price this guy cannot be beat:

http://search.ebay.com/_W0QQsassZbarrredboss

Plus, he will custom cut the extrusion to whatever you'd like. Great guy to work with.

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I've found that the mosfet as a pass device doesn't sound as good with the KGSS. I'm guessing it's due to the behavior of a vertical mosfet (BUZ90, IRFBC30, etc.) under (relatively) low current conditions. Does anyone have an opinion on this? There has been some stuff written on this, but obviously not in terms of audio...

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cetoole:

I'm using the Fairchild FQPF2N60C in a HV regulator design. Pretty nice specs.

I buy my heatsinks from R-Theta these days and absolutely love their service, but for the price this guy cannot be beat:

http://search.ebay.com/_W0QQsassZbarrredboss

Plus, he will custom cut the extrusion to whatever you'd like. Great guy to work with.

Prices on those heatsinks looks good, but they are the wrong profile for efficient operation. I guess if he will cut them to around 3", they could work pretty well, though I dont know how you would go about mounting one of those. Anything that is not board mounted means more casework for me, and casework is the bane of my (DIY) existence, almost as bad as packing group buy stuff.

I did look at that Fairchild part, but it doesnt have a P-Channel near equivalent.

I've found that the mosfet as a pass device doesn't sound as good with the KGSS. I'm guessing it's due to the behavior of a vertical mosfet (BUZ90, IRFBC30, etc.) under (relatively) low current conditions. Does anyone have an opinion on this? There has been some stuff written on this, but obviously not in terms of audio...

Lower transconductance maybe, giving higher output z? Are you using it as a simple source follower, open loop?

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The 2sa1968 is the ONLY p type device i have found that has a voltage

greater than 600 volts. It is not a high power device. Its use is primarily

focus applications for high-resolution CRT tubes, and we all know where

that is going. So expect that devices to disappear soon.

A fully dual tracking shunt regulated power supply with only n type devices

is definitely very possible. But you need an isolation amplifier and a second

set of +/-15 power supplies to drive the negative supply.

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Sounds like a great price for the system. I bet you'll be able to sell it for around 500$ on Head-fi when you upgrade to OII. >:D

Cool thing is that I can pick it up in person, too. I'm beginning to understand that in addition to the sweet sound, part of the fun of this Stax business is the thrill of the chase.

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