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DIY Electrostatic Headphone Amp

M

MartinC

pfm Member
Toying with the idea of building a DIY headphone amp for my Stax SR-007's. Not too many choices out there, Stax fanatics are drooling over the Kevin Gilmore KGSSHV Carbon design that used SiC devices, but apparently is a bit of a bear to build, plus information is scattered all over the place and there are apparently quite a few variants. A second option is the regular KGSSHV, one big advantage is that a partial kit (boards, transformer, and difficult to source parts are available from mjolnir-audio, and there is plenty of information on building.

It's impossible to audition these amps to see if the improvement over Stax's own SRM-727 will be large, but is does sound like an interesting project!

Anyone tried a similar build?

Cheers
 
Doede Douma Auridux? Remember reading about this some years ago but a bit too technical for me. Supposed to be very good and measures exceptionally well.
AP
 
I've got quite a few leftover PCBs for various Gilmore designs (KGSSHV, KGSSHV-mini, KGST, PSUs etc.) that I had made over the years. Happy to let you have some for not much more than the cost of postage (from Denmark). I should have some BoMs etc as well, but of course you'll have to source sourcing parts etc. yourself. Not quite as easy as the Mjolnir kit, but could be a bit cheaper.

The only thing I've really finished is a small KGSSHV and honestly it sounds like it's well worth the hassle, but of course I don't really have a lot to compare with.

Send me a PM if you're interested and I'll dig a bit to see what's hiding in the boxes :D
 
I built one of these a while ago. Sounds great with my SR407s and not that complicated to build. Despite the talk about the circuit's ability to cancel power supply noise, I found that the +-300v supply had to be very clean for good results. Good layout and star grounding are essential to avoid hum.
 
Thank you for all the suggestions. I have decided on the KGSSHV Carbon, parts availability is pretty good, and by all accounts it is a step up from the older KGSSHV.
 
Progress so far... One PSU board powered up fine, with such high voltages I am being very cautious! (1200v linesmans gloves, rubber soles, checking all caps are discharged etc.). Cranking the Variac up is pretty daunting as the circuit output creeps up to just over 400v!

Second PSU board got to around 150v output and poof... sparks and burning. Found out I had mistakenly but a 50ohm resistor in a critical spot as opposed to a 50k resistor. This took a series of semiconductors out as well. Replacing the resistors and the transistors and now a nice stable 407 volt output.

Next step the amp boards. This is not the most technically challenging build but certainly the scariest, plus there is no real documentation other than bulletin board discussions.
 
Designing a high voltage but low power amplifier that is safe for headphone use without spoiling the sound is hard to get right, so some of these haphazard projects concern me.
How that Stax headphone socket passes any regulation I don't know.
 
Remover "it's the volts that jolts but the mils that kills".

The current output from Stax amps and energisers is tiny. An agricultural electric fence runs at high voltage but low current.
 
Making sure that the current is tiny, even under single fault conditions is the hard part.
As headphones are firmly on your head, I would aim for the medical device touch current limit, just 500uA
 
cctaylor said:
An agricultural electric fence runs at high voltage but low current.
Click to expand...

But when you step over one (that you had definitely switched off!) in wet ripped jeans you will find that voltage applied to your manhood is somewhat disconcerting.
For some reason we never worked out we had two units attached to one fence, and I switched off just one of them. I have never crossed an electric fence without touch testing it again!
 
I have a pair pf the stax earbuds somewhere - 580v bias and 300v p-p drive... in an earbud.

The larger stax models take a bit more than 500uA to drive though: iirc the sensitivity is rated at 100v rms swing, and with say 300pF of capacitance inherent thats about 3mA of drive current at 10khz. The Gilmore designs deliberately target delivering about 10x that per channel on the outputs...
 
davidsrsb said:
Designing a high voltage but low power amplifier that is safe for headphone use without spoiling the sound is hard to get right, so some of these haphazard projects concern me.
How that Stax headphone socket passes any regulation I don't know.
Click to expand...

Not sure haphazard is a apt term for Kevin Gilmore's designs, he has been designing electrostatic amps for many years and the designs have been replicated thousands of times without any use problems that have been reported. Martin is correct that the current Gilmore designs typically output around 18mA.
 
18mA will cause severe pain, cannot let go but unlikely to immediately kill a healthy person, which is why I am surprised to see visible contacts in the socket.
 
Amp all done, no electrocution. A few issues due to some errors on my part but now working wonderfully. Far better than the Stax SRM727 it is replacing, more dynamic and detailed.

Signal wiring Teflon/Silver
Teflon wiring for all the HV stuff
Stepped ladder attenuator
Switching between balanced and single ended inputs and bypass
3D printed brackets for the attenuator and the switching
Custom PCB for the attenuator connections - $2 for 5 from China
Custom transformer with screen and shielding

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516719285_KGSSSmall.JPG.1eae730d804455735e30d3a3b42eeeae.JPG
 
What a fantastic job you did! I recently bought a set of Koss ESP/95X electrostatics from Massdrop, and I'd like to replace the energizer they came with. DIY would be fun -- I'm no EE, but I can solder. As you mentioned, the information for building the KGSSHV is scattered in forum posts. How did you get started with your Carbon?
 
Thanks for the comments. The front panel actually came from Front Panel Express. I used them because they have software that is rather easy to use and they offer a ton of options such as studs on the rear side so you can easily mount items, as well as plenty of graphic and infill options. The unfortunate part is you end up with a spare large plain faceplate that came with the ModuShop case.

As to building the Carbon, the best resource is the KGSSHV Carbon Build Thread on head-case.org You will have to wade through hundreds of pages but the info is all there. There are some very helpful members without whom I would have struggled, especially sourcing a few components. I have a lot of info that I downloaded as well, if you PM me your email I can ZIP them up and forward them. We aware though that the voltage inside the amp can be lethal... I used electrical linesmans gloves for some of the steps when first powering up the amps and adjusting. I got the boards from a board member, but the Gerber files for them are available if you have to get them made. I also have a bunch of parts if you want them when you get started, although you can get most from Mouser, Digikey, or my favorite Arrow.

Cheers
 
MartinC said:
Thanks for the comments. The front panel actually came from Front Panel Express. I used them because they have software that is rather easy to use and they offer a ton of options such as studs on the rear side so you can easily mount items, as well as plenty of graphic and infill options. The unfortunate part is you end up with a spare large plain faceplate that came with the ModuShop case.

As to building the Carbon, the best resource is the KGSSHV Carbon Build Thread on head-case.org You will have to wade through hundreds of pages but the info is all there. There are some very helpful members without whom I would have struggled, especially sourcing a few components. I have a lot of info that I downloaded as well, if you PM me your email I can ZIP them up and forward them. We aware though that the voltage inside the amp can be lethal... I used electrical linesmans gloves for some of the steps when first powering up the amps and adjusting. I got the boards from a board member, but the Gerber files for them are available if you have to get them made. I also have a bunch of parts if you want them when you get started, although you can get most from Mouser, Digikey, or my favorite Arrow.

Cheers
Click to expand...

Ah right... I ruled them out after being quoted "around £200" to make up a single front panel such as yours...
 
MartinC said:
Thanks for the comments. The front panel actually came from Front Panel Express. I used them because they have software that is rather easy to use and they offer a ton of options such as studs on the rear side so you can easily mount items, as well as plenty of graphic and infill options. The unfortunate part is you end up with a spare large plain faceplate that came with the ModuShop case.

As to building the Carbon, the best resource is the KGSSHV Carbon Build Thread on head-case.org You will have to wade through hundreds of pages but the info is all there. There are some very helpful members without whom I would have struggled, especially sourcing a few components. I have a lot of info that I downloaded as well, if you PM me your email I can ZIP them up and forward them. We aware though that the voltage inside the amp can be lethal... I used electrical linesmans gloves for some of the steps when first powering up the amps and adjusting. I got the boards from a board member, but the Gerber files for them are available if you have to get them made. I also have a bunch of parts if you want them when you get started, although you can get most from Mouser, Digikey, or my favorite Arrow.

Cheers
Click to expand...
Hi Martin, I have interest to build the same amp myself, will be glad to get info. Didn't find how to PM you...
 
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