A DIY electrostatic amp for intermediate DIYers?

[spritzer]

Quote:

Originally Posted by AudioCats /img/forum/go_quote.gif only $1.2K, including good tubes?

No, of course not. I have boxes of EL34's and some parts will be reused from other projects (part of the chassis from my old KGSS etc.). Also not included is the cost of having the PCB's fabricated.

 

[AudioCats]

dude, by the time all is said and done, it is probably close to $3k, don't you think?

especially if you want to go all-out and do point-to-point with silver/teflon wires.

 

[ericj]

Yup. That's why we're NOT trying to build a no-compromises amp. They cost thousands.

I think what we need, as a DIY community, is an amp that beats all but the top end of the Stax SRM series for just a few hundred bucks in parts and a couple weekends of labor.

 

[pabbi1]

I mentioned this to Pete Millett at the DFW meet today, as in, what about a 'Starving Student Electrostatic amp'. His off the cuff opinion was this could be done with tube far easier than SS. Would not look for any miracles on that front in the near term, but he is working through an obscure range of cheap tubes that might meet the goals of this project.

I'd also throw in the obligatory plug for the venerable NABU case, to help keep overall costs down, Just not imagineable to get that quality case for less, on a consistent basis.

 

[runeight]

Yes, it would be easier with tubes than transistors because they are naturallly HV devices. OTOH tubes may not be quite as fast as really good HF sand. Then again, maybe most of us wouldn't notice.

So, for the sake of someone who has designed quite a few dynamic amps and paid no attention to electrostatic amps or headphones, what are the key issues here? I read the first post about the design goals, but they don't always convey the critical engineering problems. What are they? Other than death or heart failure.

 

[ericj]

yeah, there are several simple tube designs, like this one from 1968:

Electrostatic Headphones Amps
http://www.head-fi.org/forums/5241587-post5.html

recently resurrected as the singlepower es-1 and es-2.

some of the projects on headwize look pretty simple as well.

And then there's the november 1999 tubecad journal article. And the website of some guy in germany that I've seen several times but can never find with a google search. and i don't mean the auridux - i can always find that one. I mean the guy who has solid state, hybrid, and all-tube designs on his website.

As for the key issues, i could try, but someone else would probably state them better than i do.

 

[runeight]

Edit:Ericj, our posts crossed in the mail. I'll look at those links.

In the meantim here's a Poor Man's stat amp. I mean, this is no frills at all.

Setting the tail current will adjust the bias on the stators. The amp will swing at least 500Vpp between the outputs. It will take an SE input.

It won't have the lowest possible distortion because we haven't tried to use CCSs and other techniques to improve linearity.

It needs four voltage supplies plus a heater supply. The 600V can be increased if proper resistors are used.

Stoppers and other details are left out.

Would this amp work?

 

[JadeEast]

There is an amp design in the National Semiconductor application note 1651 that I noticed when I was looking at a RIAA preamp in the same document. Not sure if it's ever been built.

http://www.national.com/nationaledge/jul07/

 

[ericj]

Quote:

Originally Posted by JadeEast /img/forum/go_quote.gif There is an amp design in the National Semiconductor application note 1651 that I noticed when I was looking at a RIAA preamp in the same document. Not sure if it's ever been built. National's Analog Edge - July 2007

At least one guy on headwize built one - he reported that it clips at 400v, even after increasing the power supply voltage, which is really unacceptable.

Also, Kevin Gilmore said it's a terrible design. Which, even if you consider that he's got obvious bias, probably indicates that it's less than what we're looking for.

 

[Sherwood]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif probably indicates that it's less than what we're looking for.

A for effort, though, JadeEast. That is definitely the spirit.

 

[lacrossebowe8]

I would also love an entry level stat amp. i was looking at the kgss but it has several hurdles.

 

[ericj]

Stax DC Tube Driver
AURIDUX, a directly coupled Stax Electrostatic Headphone Tube Amplifier
Frame

Third one is the german site i keep losing track of.

As for critical engineering problems, here's what dr. gilmore had to say:

Quote:

Originally Posted by kevin gilmore /img/forum/go_quote.gif voltage gain 1000 (60db) This is usually the killer for opamp based designs as they give up long before 20khz voltage swing a minimum of 1200 volts peak to peak stator to stator. (spritzer will say that 1800 is better and it is) Very few tubes do this in anything but huge packages, and the number of semiconductors that can do this is small and decreasing every day. full differential output absolutely required. slew rate as fast as possible, >100 v/us and thd as low as possible, <.01 % or it sounds like crap. Able to drive 50pf pure capacitive load. Not so easy, especially for things with opamps in them.

obviously he overstates the voltage swing requirement a bit vs. our needs

 

[AudioCats]

Quote:

Originally Posted by ericj /img/forum/go_quote.gif I think what we need, as a DIY community, is an amp that beats all but the top end of the Stax SRM series for just a few hundred bucks in parts and a couple weekends of labor.

what exactly do you want to beat? SRM-1/MK2 pro? T1?

I don't think you can get an all out victory against the T1 with that kind of budget. SRM1/MK2 on the other hand is a much easier target.

The Auridux on the other hand is actually a very expensive design, I don't think it can be done with just a couple hunderd bucks.

 

[kg21]

yea it would be great if you guys come up with something. Something to compete with the low-mid range stax amps and beat them in bang for the buck.

Oh yea I saw this while I was googling something else stax related:
http://www.audiodesignguide.com/my/stax_amp2.html

 

[ericj]

Quote:

Originally Posted by kg21 /img/forum/go_quote.gif yea it would be great if you guys come up with something. Something to compete with the low-mid range stax amps and beat them in bang for the buck. Oh yea I saw this while I was googling something else stax related: the STAX Amplifier

yeah unfortunately the output iron alone exceeds the target budget.