# A DIY electrostatic amp for intermediate DIYers?



## ericj

I have long lamented the lack of any kind of electrostatic amp that a less than utterly advanced DIYer can safely build. 

 There are plenty of designs out there. Some of them even with board artwork available. But there doesn't appear to be anything for which you can buy a professionally made board and follow a bill of materials that includes parts that are easy to acquire. 

 Looking around at the available designs, there seems to be a preponderance of "no compromise" designs that would be extremely difficult for an intermediate DIYer to build on perfboard, and which cost hundreds of dollars to assemble. And then there are designs that are heavily compromised, or seem to be designed to fulfill a whim or to achieve a goal that is tangential to the objective of good sound. 

 I think the electrostatic contingent of the headphone enthusiast community has expanded sufficiently over recent years that there could be sufficient demand for a well designed, good sounding DIY electrostatic amp with a standardized build and professionally printed boards. 

 The problem at hand, though, is who will make this happen? I'm enthusiastic for sure but i don't have the time or skills to bring the project to fruition. 

 I've decided that instead of just continuing to wonder if it will happen, i should actually see who i can get on board and maybe try and make it happen. 

 I think the basic goals should be:

 1: A total build cost (before casework) that is well under $300. 

 2: Strictly using parts that are in current production or which are otherwise in abundant supply. If possible, no or little reliance on NOS tubes. 

 3: No exotic iron in the power supply. Something off the shelf from a major vendor with a good north-american distribution network, please! Even if we have to buy two of them. 

 4: Must accept single-ended input. Even if it can be built with balanced input, it must be able to accept SE input. Whether that means including an SE-to-balanced conversion circuit on the board is dependent on the design chosen. 

 5: Powerful enough to drive an SR-Sigma in standard configuration. Omega-level power optional (power supply upgrade, probably). We're not trying to replace the Blue Hawaii here. 

 6: One (1) bias supply design that provides 4 or 5 different bias voltages in a single build. Certainly anywhere between 200v and 640v. 1kv for jecklins shouldn't be out of the question, perhaps with the builder modifying the circuit. I forget if there were 'stats with bias lower than 200v, and i don't recall what bias voltage the Beyer ET-1000 takes. Whether this is a supply with multiple outputs or a supply with a multi-position switch is up for debate. 

 As for solid state vs. tubes I'm agnostic as long as these basic goals can be met. I hope to see a day when there are a few of each available to build. 

 I envision the physical build as having two channels on a board that can be cut in half if the builder's case demands it, and another board with the power supply and bias supply. 

 I doubt there is any reason to come up with a completely new amp design - there are many designs out there - but the project may involve updating an existing design to accept obtainable parts, or to have a more pragmatic, more appropriate, or more affordable power supply. 

 So, who else is on board? I'm just a guy beating a drum. I'm willing to be some kind or project leader but i don't have the skills to do this on my own. 

 How many of you would be interested in building this sort of amp?


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## spritzer

You know that I'm in. Hammond has a nice lineup of transformers which we can use and the SE/balanced input isn't a problem as with most circuits you just ground the - input for SE use. 

 The bias supply could be very complicated for those different bias settings but a single 700v supply and then using resistor dividers to get the desired output.


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## pabbi1

Admirable goal, tough row to hoe.


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## ericj

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_You know that I'm in. Hammond has a nice lineup of transformers which we can use and the SE/balanced input isn't a problem as with most circuits you just ground the - input for SE use. 

 The bias supply could be very complicated for those different bias settings but a single 700v supply and then using resistor dividers to get the desired output._

 


 There are opamp solutions to the SE-to-balanced question, and purpose-designed ICs as well. Transformer-coupled works for me too. And some amps don't need you to supply a solution. 

 As for the bias supply, I figure it's reasonable to expect that most hobbiests will want stax normal and pro bias and maybe 620v for the ESP-950. I forget what the ET-1000, HE-90, HE-60, and other oddball 'stats want. I know a lot of them can work ok with a stax supply, but it would be nice to get closer to the designed voltages. 

 Like you say, it could be as simple as a rotary switch to select which divider you're using. 

 I just don't want to end up with a design where we've got the two major stax voltages covered but anything else means you're on your own, off the reservation, and have to come up with some other supply.


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## cetoole

It would seem that an updated KGSS would fit all of your requirements pretty well, and probably the main thing would be designing a new pcb for it. Swap the 2SK389 with LSK389, update the power supply a bit, and you are basically there.


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## ericj

I agree - I'd love to be able to buy KGSS boards. 

 It looks simple enough - but not so simple that I'd dare build it on perfboard. 

 At 24v or 36v I'm comfortable with the concept that i could have a short somewhere or something hooked up completely wrong. 

 But not at 350v. Not with that many parts. I still haven't even attempted a simple point-to-point tube amp, though i do believe that a 6n6p-based cavalli-jones would be Pretty Neat.


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## DKJones96

I know this is a headphone forum, but are you talking about an amp for headphones or an amp for loudspeakers? I've been wanting to build a set of ES loudspeakers, last thing I need is another project but still 
	

	
	
		
		

		
			





 I've always wondered about using microwave transformers for the ESL amp, they have the turn ratio required just not sure if they meet any of the other specs, plus, they'd be cheap(or even free).


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## ericj

Just for electrostatic headphones. Direct-drive for ESL speakers is a whole different game.


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## DKJones96

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Just for electrostatic headphones. Direct-drive for ESL speakers is a whole different game._

 

Ohhh, nevermind!


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## Uncle Erik

I would also be interested in such a design. I've picked up the iron, tubes and a few other pieces to build Dr. Gilmore's all triode amp point-to-point, but it will probably be a couple of years before I can get to it. If there was a PCB-based amp I could knock off and case in a weekend and a couple of evenings, I would fit it in and get a pair of Stax.

 Another benefit of such a design would be that the custom builders could start offering electrostat amps to a wider audience at a fair cost. Right now, you either have to do a very serious DIY build or fork over a few thousand to someone who may or may not provide you with an amp. But if there was a PCB and non-exotic parts, electrostatic amps would be as accessible as a Beta22 or M^3.

 I think this is a great idea and would be happy to help support it.


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## FallenAngel

Sounds nice, but the 700V lethal voltages are a bit scary.


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## ericj

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Sounds nice, but the 700V lethal voltages are a bit scary._

 

Yeah, but 700v is still in the neighborhood of "not substantially more deadly than 100v". 

 If you can build a HV tube amp, you can build a 'stat amp. Just remember to keep one hand in your pocket at all times, and respect the voltage. 

 This wouldn't be for every DIYer for sure. But it wouldn't be strictly for advanced experts either.


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## holland

Hell yes! I'll buy a stat if this comes to pass. The parts hunt for the DIY builds has kept me from getting a stat.


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## pabbi1

Parts hunt is 50% of the battle - I have been hunting electrostat amp parts for 3 months, almost full time. Not the easiest task, and minimum buys for only one part make it pricey for single builders to even try it.


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## TimmyMac

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Parts hunt is 50% of the battle - I have been hunting electrostat amp parts for 3 months, almost full time. Not the easiest task, and minimum buys for only one part make it pricey for single builders to even try it._

 

Perhaps PCB + Q pack group buy is in order then...


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## TimmyMac

Quote:


  Originally Posted by *DKJones96* /img/forum/go_quote.gif 
_I've always wondered about using microwave transformers for the ESL amp, they have the turn ratio required just not sure if they meet any of the other specs, plus, they'd be cheap(or even free)._

 

Microwave transformers are horrible horrible iron, bad core, and definitely not built for 100% duty cycle.


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## cetoole

Yes, but Pabbi, you arnt looking at an arrangement that could be considered normal or intermediate level. 
	

	
	
		
		

		
			





 Would probably be best for any group buy to have at least PCBs and LSK389, everything else is pretty straightforward. Maybe a custom transformer too. KGSS could be done with two off the shelf, but I will probably be getting a custom for mine, just so I dont have to use two separates. Allocating $100 for the transformer and $20 for the PCB, I think I figured about $50 for the parts needed to stuff the PCBs once, so all transistors, resistors, and capacitors. Should come in around $300 or so for a normal build done with a group buy, including a decent, but not excessive, case. More if people want fancy things like stepped attenuators.


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## ericj

Well, looking at the KGSS parts, the 2SC380 is nominally available, but newark (really MCM) only has 53 of them. I don't immediately see another reputable dealer. bdent doesn't have any. 

 bdent has the 2SA1156 "in stock" and nobody else does. 

 2SC3675 is in short supply at newark (60ish). bdent seems to have a good supply at $1.66 each. 

 So if we go with the KGSS as it existed in 2000, I think that bundling a full complement of transistors along with the board is a very good idea. I'm certainly not opposed to it, but it means that we would need buy-in from someone like glass jar audio to really pull it off. 

 Don't get me wrong, I'd love to build a KGSS. But if we're talking about a hundred people building a KGSS at the same time, some parts are going to be in short supply


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## cetoole

2sc380 isnt on the KGSS schematic anywhere; I have no idea why KG even mentioned it in the writeup. Seems BDent only has 197 of the 2SA1156, though this part should be fairly easy to sub. The 2SC3675 is the only part that gets kind of tricky. BDent only shows having 226 of them.


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## KT88

woa, that can be some nice project. I've been looking into DIY for an amp for my HE60's (which will arrive in a month or two for sennheiser).

 the only question now is are there any people here who have the skills, time, and will to put this thing together


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## spritzer

A KGSS would be nice to build but parts are a problem so an all tube amp would probably be better all round. Then there wouldn't be a problem with heatsinks and we could use some very cheap tubes which are in ample supply. 

 As for transformers there are those R-cores on ebay and many other places. I got some recently and they are very nice quality and some even have two 0-xxxv windings which would suit us. Most have filament windings but for a two stage amp we would need two separate windings which could be a problem. 

 The PSU could be something simple (R-C network) or something along the lines of the Gilmore designs. I'm going to be testing a cheaper sub to the 2SA1968 soon so that made the PSU a whole lot cheaper to build. That said, the 450v capacitors aren't cheap but what can you do... 

 We could also always just wire it P-P like this: 
	

	
	
		
		

		
		
	


	








 It would have been much neater if I had been able to buy all the parts I wanted to use but I promised my self to use the cheapest stuff I could find locally.


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## Oublie

Interesting Idea. My final goal is to build my own bh or kgss so if this is ends up as a group buy i'm in. Strangely enough i was talking recently about parts on the Stax thread and the idea of a full tube design would be interesting. I'm a long way from an expert but i would help in any way i able to.


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## krmathis

I really like the idea!
 My DIY skills are quite limited though. But may be willing to give it a go...


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## johnmatrix

I have a the materials list I used to build my KGSS although I used the 2sk. I could post it if that would help people.


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## TimmyMac

As a show of interest, I'm probably in too. I've always wanted to try electrostats...


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## rds

If this materializes I'm totally in.
 Great idea!


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## Keithpgdrb

I am in full support of this idea. I really like the idea of being multiple bias. I love my sr-lambdas, but finding the good amps is a pain. and I would love to be able to have some pro cans as well as maybe some koss? my diy skills are non existent, but I'll get practicing so I can be ready.


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## TimmyMac

Does anyone have approx build costs for the KGSS and KGBH?


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## spritzer

Quote:


  Originally Posted by *TimmyMac* /img/forum/go_quote.gif 
_Does anyone have approx build costs for the KGSS and KGBH?_

 

There is no way to put a figure on that as no two amps are alike. The BH I'm working on will probably be less then 1.2k$ all in all and then there is the cheaper version I'm also trying.


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## AudioCats

only $1.2K, including good tubes?


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## 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.


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## 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.


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## 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.


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## 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.


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## 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.


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## 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.


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## 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?


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## 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/


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## 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.


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## 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.


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## lacrossebowe8

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


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## 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


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## 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.


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## 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


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## 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.


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## spritzer

I could fill a few posts with links to amp designs but many of them aren't suitable for a cheap amp like this. Most are laden with coupling caps which will drive up the price quickly (630v caps aren't cheap if you want something that isn't horrible quality) and some use different voltages which makes the PSU design harder on a budget. We could always just use an unregulated HV supply (like Stax does) but I'd rather have a more simple amp section and a more robust PSU. 

 The old SRX amp is simple enough but it has to be modified to allow bias for the tubes but it can be made to work with a lot of different tubes. The Tubecad amp is identical to the Egmont and you can't get a simpler circuit to build. There is the DC-coupled Gilmore amp with 6H30pi, 6S4A and 0A2's but it has proved to be tough to build and the 3 separate filament supplies quickly add up. 

  Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_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.
	

	
	
		
		

		
			



_

 

These amps are built on the cheap so that's not likely to happen. They are more test beds to compare the different PSU and part choices against the BHSE. 

  Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_obviously he overstates the voltage swing requirement a bit vs. our needs_

 

He was talking about an all out assault at the high end there so it doesn't apply. 1000V P-P should be more then enough but voltage output is only part of the issue. The Koss E/90 would be the best amp in the world if we only needed voltage swing.


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## runeight

None of you has commented on the circuit I posted on the previous page. I will take this as a most gracious politeness on your parts. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I could fill a few posts with links to amp designs but many of them aren't suitable for a cheap amp like this. Most are laden with coupling caps which will drive up the price quickly (630v caps aren't cheap if you want something that isn't horrible quality) and some use different voltages which makes the PSU design harder on a budget. We could always just use an unregulated HV supply (like Stax does) but I'd rather have a more simple amp section and a more robust PSU. 

 The old SRX amp is simple enough but it has to be modified to allow bias for the tubes but it can be made to work with a lot of different tubes. The Tubecad amp is identical to the Egmont and you can't get a simpler circuit to build. There is the DC-coupled Gilmore amp with 6H30pi, 6S4A and 0A2's but it has proved to be tough to build and the 3 separate filament supplies quickly add up. 

 These amps are built on the cheap so that's not likely to happen. They are more test beds to compare the different PSU and part choices against the BHSE. 

 He was talking about an all out assault at the high end there so it doesn't apply. 1000V P-P should be more then enough but voltage output is only part of the issue. The Koss E/90 would be the best amp in the world if we only needed voltage swing._

 

What are the issues besides voltage swings?

 Someone posted a few of KG's requirements such as 100uV/s slew rates and 0.01% THD. And 1000Vpp.

 It seems to me that trying to meet these requirements cheaply will not be easy. Possible, but not easy.

 Any O/P device that is sweeping through 1000Vpp of its transfer curves is going to surface signficant non-linearities. The only tubes that I know about that are super linear over a wide voltage range are vertical deflection tubes and they don't typically operate at these voltages.

 But aside from that, to minimize THD from a tube driving the load (even a no-current-required load like an electrostatic headphone) the plate load resistance matters. Which almost always means a CCS which will mean some number of HV sand devices.

 Slew rates will require fairly fast devices operating at rich bias points so that they can provide the currents needed to drive the capacitances at the inputs of the next stage. These are not coupling caps, just the normal input capacitance of an active device. For example, if one uses a triode with gain for the output stage its driver has to pump the miller capacitance of that triode. This takes a low Zo and current delivery capacity and speed. If the O/P device is a mosfet the same issue applies. This is one of the reasons that KG uses the grounded grid configuration driven by a fet follower in the BH.

 So, if I might enquire again, what are the real requirements for this amp? And what are the engineering tradeoffs you all might be willing to make?


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## nikongod

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_It won't have the lowest possible distortion because we haven't tried to use CCSs and other techniques to improve linearity._

 

a guy could cram a couple 10m45's in there p2p style if he really wanted.
  Quote:


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

This is where I think things get weird.
 The outputs of the amp are going to be hanging out at like 300V above ground. This is safe for bias as it goes through a big fat resistor, but not for stators which are DC coupled without resistors to the output of the amp.

 A cap would be required.

 edited/added:
 the amp should be able to swing as much as you mentioned, but it will require that the pot be swung all the way up... I dont care, and like it! but others have shown opposition to swinging past about 1/2 spin. Probably not as much an issue in the DIY community, but worth considering when the amps start to get sold second hand. scummy thing to think of, but life.


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## pabbi1

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_None of you has commented on the circuit I posted on the previous page. I will take this as a most gracious politeness on your parts. 
	

	
	
		
		

		
		
	


	




 So, if I might enquire again, what are the real requirements for this amp? And what are the engineering tradeoffs you all might be willing to make?_

 

I find it very elegent in it's simplicity, and love the tube compliment, mainly as we are using the 6s4a on other designs. But what is the cost of iron, and what options are available for these windings? And, I don't see heaters - is that the 25v?

 Then there are the other aspects to protect phones - we are talking about some using rather pricey phones with this amp. Usually cheap = risk.

 As for tradeoffs, most here (excluding Spritzer) won't know how to answer - they just want cheap that works. 

 While I do know a switchable bias (have the boards on my desk, and will stuff most of the parts tonight), it simply cannot be done for less than $125, so it will NOT fit the design goals here. It is only mentioned as part of the tradeoffs people are willing to make - what solutions, and, at what cost.


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## spritzer

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_So, if I might enquire again, what are the real requirements for this amp? And what are the engineering tradeoffs you all might be willing to make?_

 

That's my question as well. If it is cheap as chips, simple to build yet can out pace the Stax amps that's not easy to accomplish. The transformer will always be the largest chunk of the budget at up to 100$ and the large PSU caps aren't cheap either. I do like the R-core transformers available on ebay (100w units and the R80-04 unit in particular) for 55$ though they could do with more current handling. 

 If we were to put a CCS on the output tubes then it will be a massive improvement over the plate resistors but it will be almost impossible to do at this price point. Most of the third party amps sold don't even have a CCS like Rudistor, SP, Woo GES and the RSA A-10. That just goes to show how much of a rip off some of those amps are but for 300$ we would have to settle for resistors. As you rightly point out, it will make the performance into any impedance load suffer so the amp will not be an ideal choice for something like the SR-007 but should do fine with a Lambda or the ESP/950. 

 My tube of choice for the output would be 6S4A as they are cheap, can handle enough voltage for our needs and easy 6.3v filaments. Now there might be some Russian equivalents or some obscure TV tubes to try out too.

  Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_While I do know a switchable bias (have the boards on my desk, and will stuff most of the parts tonight), it simply cannot be done for less than $125, so it will NOT fit the design goals here. It is only mentioned as part of the tradeoffs people are willing to make - what solutions, and, at what cost._

 

A fixed HV supply like in the Gilmore amps and then switched voltage dividers would do the trick. It's only two resistors so cheap as hell


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## mark_h

I could possibly get the PCB's made at university, given the vector/.eps design and simple instructions of what is required. The actual process of getting them from press and peel to etched is fairly straightforward, I have used the method to make elements of scale models before, to great effect but that is where my knowledge ends.


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## spritzer

It's also not that expensive to have them made at a board house if they aren't too big. The bottom line is though if we can agree on basic design parameters then we can nail down a schematic and have it drawn up.


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## FrankCooter

How about a small push-pull tube amp with the ouput taken off the primary of the output transformer? John Broskie illustrates this approach in the Nov. '99 issue of "Tube CAD". Basically, he uses the first 3 sections of a Williamson amp. The input is a the first section of a 6sl7, the phase-splitter is the second half of the 6sl7, and the outputs are 6sn7 connected to the primary of the output transformer. Output to headphones is via coupling caps off the transformer primary. The weakness he cites in this approach is the impedance mismatch between the 6sn7s and the output transformer. How about sustituting the 6sn7s with 7189a? The 7189a can take 400v in triode mode and has a gain of about 20. Appropriate Hammond transformers run about $45.00 apiece. Coupling capacitors could be the exellent Russian 630v k-40 pio type. These are available on Ebay for a couple of bucks apiece if bought in bulk. Use a tube rectified power supply with a CLC filter. Total investment could be under $400.00, less if you've got a good junk box. Would this be a potential solution?


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## TimmyMac

We could always just admit that it's not realistic to make a high performance stat amp for $300 and open up the budget a little... or at least include some options on the board for those willing to spend a bit more.


----------



## runeight

Gents, I'm figuring that if I keep posting concepts you will tell me what's right and wrong with them. Then perhaps we can find a cheapo design.

 So here is Poor Man 2. Explanation below:






 Simple and cheap is the name of the game. We know that the most expensive item will be the PS so the amp has to be dirt cheap. Some compromises might have to be made.

 In Gilmore's BH he uses a dual jfet for the input diff amp. For two reasons: 1) to get good matching and 2) to maintain as equiavlent thermal drift as possible. But, these are n-channel devices whose outputs are at a positive rail. This requires him to use the current tunnel to translate the signals to the bottom rail. Very nice circuit, but lots of extra components.

 If we use individual discretes, however, we can use PNP devices for the input pair. And if we select HV BJTs we can run these all the way down to the negative rail. In this case the ZTX560s are 500V devices. The only thing we need to be careful of is their power dissipation.

 The are biased at 1mA each. With a 51k load their collectors are at -450V where they can swing the grid voltage needed for the EL34s.

 The ZTX458 NPN BJTs are there as followers to provide a high impedance buffer for the diff amp so that we can get halfway decent frequency response. The 458s are only 400V devices so we actually have to find higher voltage devices for this slot or connect their collectors to a -300V supply which we can probably get from the -500V supply. Only a few mA are needed.

 The BJT followers drive the tubes. Don't gag on the cathode bypass caps. We need them to get enough gain from the O/P tubes. 

 The amp has no NFB and its gain is over 1000. It can push 900Vpp. It has no NFB at the moment but has decent theoretical THD, less than 1% but more than 0.1%. It will be hard to do better than this without more sophisticated circuitry, but we might be able to tweak here and there. Frequency response into 150pf will not be as good as the BH, but it won't be terrible. I have not looked at slew rate. It might suck, but it might not be too bad either.

 In addition, the CCS on the tail of the diff amp can be driven from an opamp servo so that the stator DC offset is 0VDC. Or we can just put an offset adjust pot on the CCS and hope that it won't drift too much. Also the 820R resistors can be split with a trimpot to equalize the output offsets. They will also drift, however, from thermal flucutations.

 If this were actually built it would be good to thermally glue the ZTX560s together. Best we can do with two packages.

 So, are we getting into the ballpark?


----------



## kevin gilmore

The first cavalli amp as shown outputs 300 vdc continuously. The roughly 560
 volt bias has to be on top of the 300 volts. So 860 volts. Many people
 get very nervous putting what is esentially an unlimited current at 300
 volts on top of your head.

 I did an amp almost exactly like this 10 years ago.

 Otherwise you need output caps.

 The second cavalli amp is similar to a BH except that it is grid drive.
 For large voltage swings on the output grounded grid is much more linear.
 But this will definitely work. The KGST which has not been published yet
 is very similar to this.


----------



## runeight

Agreed on the higher linearity of the GG configuration. This mod could probably be added to the amp above.


----------



## pabbi1

Alex, that is quite good stuff... at least for me who has 4 quads of el34 laying around. Would this also work with kt77 (since I also have a quad of them)?

 Except for the jfets, I have all that laying around, so I'm at about $5 additional cost so far... l
	

	
	
		
		

		
		
	


	




 Seriously, the cheapest el34 are the JJ / Mullard / Electro Harmonix, all about $80 per quad shipped. Any way to keep this with the 6s4a, about $20 shipped? If not, it is what it is.

 Would this require close matching of the tubes, or is there a biasing sequance, theoretically speaking?


----------



## nikongod

As shown, the output stage is idling at only 8ma*2 Why not more? an EL34 can easily take it. At least 20ma 
	

	
	
		
		

		
		
	


	




 80ma @ 1000V (bridge rectified) is within the limits of inexpensive transformers. 

 Would using a long-tail pair for the output stage dump too much gain? It would save 2 caps & 1 resistor. 

 Perhaps the loss of gain in the output stage with a long tail pair&lower impedance plate resistors could be compensated for by reconfiguring the "driver" BJTs to provide a little gain.


----------



## runeight

Pabbi1, answers below. But, before that, here's a grounded grid version. It is slower than the original but can be sped up. Also. we should look into mosfets for the active devices.






 In this amp we have relieved the need to replace the ZTX458s because they are no longer there and the 757s see much lower voltage. In fact, probably 150V transistors could be used in their spots which would lower the junction capacitances a little.

 I don't see why KT77s could not be used. But haven't checked to be sure.

 I started with 6S4 but in this configuration they create a higher Zo for the amp thereby reducing its speed. Which is why I moved to the EL34. But I'll look at them again.

 Tube matching won't hurt. Tubes that are really far apart may be hard to balance. But with a balance control on the diff amp we can probably compensate for anything reasonable. Would you like to see the opamp servo?


----------



## runeight

Nikongod our posts crossed.

 We can probably increase the bias in the EL34s. This changes the op point at EL34 cathode but is probably doable.

 As you can see the GG version relieves us of quite a few components, but it is definitely slower. I haven't worked on this yet. And we may not be able to speed this up enough compared to the first idea. Perhaps this new configuration would resolve the other issues that you mentioned?


----------



## TimmyMac

1000V power supply! I've always wanted to use these 866As I've got lying around... and since I probably can't afford iron for a GM70 or 845 amp...


----------



## FrankCooter

runeight, is there an error in the schematic of your grounded grid amp? The right hand El34 doesn't have a grid connection and the cathode is connected both to the collector and emiiter of the Z1X757


----------



## runeight

Thanks Frank. It's fixed now.


----------



## nikongod

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Nikongod our posts crossed._

 

yepp, yepp no problem

 My comments on a long tail pair arrangement did not consider the option of a grounded grid. I guess there is so much "up in the air" in this that anything can change. 

 If that is the direction, I trust KG's advice, and would go for the grounded grid.


----------



## runeight

In general a GG would be expected to have more linear behavior. Now the usual caveat about sims applies here and particularly the sim pentode models are not that good, but I am not seeing better linearity with the GG. And, it's slower.

 However, the following speeds it up to almost the same speed as the grounded cathode version.






 Don't know where you all would like to go from here, but this design is not bad.


----------



## kevin gilmore

starting to look more and more like a BH. 
 (not necessarily a bad thing)

 Open loop gain going to be very hard to control.
 DC output control also going to be very hard.

 If the input transistors ever get zotched, the preamp or
 source feeding them is going to get blown to pluto.

 The iron and capacitors alone for the power supply are going
 to be $300 easy.


----------



## runeight

Quote:


  Originally Posted by *kevin gilmore* /img/forum/go_quote.gif 
_starting to look more and more like a BH. 
 (not necessarily a bad thing)

 Open loop gain going to be very hard to control.
 DC output control also going to be very hard.

 If the input transistors ever get zotched, the preamp or
 source feeding them is going to get blown to pluto.

 The iron and capacitors alone for the power supply are going
 to be $300 easy._

 

???? I guess it is starting to look like a BH. 
	

	
	
		
		

		
		
	


	




 But except for the GG output stage, they don't look much the same to me. Besides, how many ways are there to make a HV opamp with tube output stages that must have their plates at 0VDC? 
	

	
	
		
		

		
		
	


	




 Yes, agreed on the OL gain. We haven't yet discussed NFB but it should be possible to add some to handle the OL variations with CL gain.

 Really right on melted input BJTs. Some thought can be put into protecting for this. It may be possible, but it may not with a naked HV input pair connected to a series of BE and BC junctions to -500V.

 KG, you mentioned an amp earlier. Any thoughts about sharing it with the interested parties who started this thread?


----------



## nikongod

Why not cap couple the inputs?
 Kills many birds with 1 stone.

 allows the input transistors to be floated to save the expense and complexity of the 25V PS.
 if the transistors blow the Cap protects the source.

 Im personally more concerned with what happens at the output, where my head is strapped between 2 stators that could have a few hundred volts on them all of the sudden.

 Maybe a cap somewhere in the middle too. It dosnt need to be big, so good quality could still be gotten at a price in line with this project.


----------



## runeight

I thought about that but I didn't think you guys would want a 630V cap at the inputs. But, yes, can be done and would solve some other problems too as you noted. I guess it still comes down to what everyone wants or will accept in the design.

 O/P Protection is another matter . . .


----------



## pabbi1

Obbligato and Mundorf MTube caps both spring to mind... and will work in the budget.

 But, at some point, this budget is gonna leak, and shoppers can find other spec'd parts to meet their budget - down, or up.


----------



## spritzer

Since there are basically no DIY ES projects out there, we could always do two. One cheap and the other about 6-800$ in parts so approaching top end. It would open up options such as CCS for the more expensive one and a better PSU. It could even be the same basic design just scaled differently...


----------



## WilCox

I built Joe Curcio's electrostatic headphone amp about 20 years ago! It was featured in Glass Audio, Volume 1, Number 0. Anyone heard of it? It uses four 6DJ8/6922's. I'll see if I can find the schematic if there is any interest. I should have the remains of the amp somewhere as well, although I know I have scavenged some parts.

 Anyway, I'm in for a DIY build.


----------



## pabbi1

Quote:


  Originally Posted by *WilCox* /img/forum/go_quote.gif 
_I built Joe Curcio's electrostatic headphone amp about 20 years ago! It was featured in Glass Audio, Volume 1, Number 0. Anyone heard of it? It uses four 6DJ8/6922's. I'll see if I can find the schematic if there is any interest. I should have the remains of the amp somewhere as well, although I know I have scavenged some parts.

 Anyway, I'm in for a DIY build. 
	

	
	
		
		

		
		
	


	


_

 

http://www.national.com/an/AN/AN-1651.pdf, page 4.

 oops, NOT the original, but this can have a tube output stage.


----------



## FrankCooter

The Volkswagon is morphing into a Porsche. I greatly appreciate all the time, effort, and engineering expertise that has been put into this thread, particularly by runeight. However, I think we are drifting away from the original purpose of the thread, which was to create a simple, cheap, accessable Stax amp that could be built with readily available components by a person of modest abilities. An amp suitable for the 303 rather than the O2. It may be impractical to attempt "Blue Hawaii" specs in such an amp. Do we really need 60db of gain and a 1kv swing in an entry level amp? It would be a lot more feasable to attempt specs along the lines of the Stax factory offerings.
 Nobody commented on my suggestion to use a small push-pull tube amp (a la Broskie) as the basis of a Stax amp. I'll throw it out again if for no other purpose than to have it formally dismissed. How about a long tailed pair of triode strapped 12gn7a (Pete Milletts fovorite cheapo pentode driver)connected to push-pull triode strapped el34s driving a hammond transformer? Use the primary of the transformer as a center tapped plate choke. Pull the output off the el34s via cheap but exellent 630v Russian p.i.o. coupling caps. Build a 560vdc power supply using an Antec toroid and some motor run oil capacitors. The bias takes care of itself. Parts available in about 30 minutes and a total cost of under $400.00. Simple, cheap, and fairly foolproof. Tell me what I've got wrong here.


----------



## runeight

Well . . . I don't think you have anything wrong. It all comes down to the requirements. If your requirements are more suitable for this amp then your design strategy is right. It just depends on what everyone wants. Thinking on this has been fun for me and if you guys choose to ignore all of it I won't get bent out of shape. I really won't.


----------



## pabbi1

Well, it is time for OP to weigh in - because most others actually discussing this can build more sophisticated designs. Input is needed from those wanting these specs.

 Frank, you had me at motor run... do you have a rough circuit drawn up you could share? Does the $400 estimate include the switchable bias?


----------



## spritzer

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_The Volkswagon is morphing into a Porsche. I greatly appreciate all the time, effort, and engineering expertise that has been put into this thread, particularly by runeight. However, I think we are drifting away from the original purpose of the thread, which was to create a simple, cheap, accessable Stax amp that could be built with readily available components by a person of modest abilities. An amp suitable for the 303 rather than the O2. It may be impractical to attempt "Blue Hawaii" specs in such an amp. Do we really need 60db of gain and a 1kv swing in an entry level amp? It would be a lot more feasable to attempt specs along the lines of the Stax factory offerings.
 Nobody commented on my suggestion to use a small push-pull tube amp (a la Broskie) as the basis of a Stax amp. I'll throw it out again if for no other purpose than to have it formally dismissed. How about a long tailed pair of triode strapped 12gn7a (Pete Milletts fovorite cheapo pentode driver)connected to push-pull triode strapped el34s driving a hammond transformer? Use the primary of the transformer as a center tapped plate choke. Pull the output off the el34s via cheap but exellent 630v Russian p.i.o. coupling caps. Build a 560vdc power supply using an Antec toroid and some motor run oil capacitors. The bias takes care of itself. Parts available in about 30 minutes and a total cost of under $400.00. Simple, cheap, and fairly foolproof. Tell me what I've got wrong here._

 

That's certainly a good plan but I do think it is overkill for use with the Lambdas. They aren't demanding but certainly benefit from more power so we really should be shooting for the SRM-T1 level of performance as that has been the standard issue Lambda amp for over 20 years along with the SRM-1. 

  Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Frank, you had me at motor run... do you have a rough circuit drawn up you could share? Does the $400 estimate include the switchable bias?_

 





 Take a look after the 845's on this schematic above. Instead of an output transformer, Morgan Jones used a P-P choke but it's the same deal as Frank talked about.


----------



## ericj

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Well, it is time for OP to weigh in - because most others actually discussing this can build more sophisticated designs. Input is needed from those wanting these specs._

 

Well, At this point I'm not quite sure what to say. 

 I think there are good ideas around, but as Frank said the VW is becoming a porsche. 

 As a VW driver on my 2nd VW, this causes me some concern. 

 AC-coupled input doesn't bother me much. AC-coupled output would be nice to avoid but not necessarily a dealbreaker. 

 I think spritzer may be right that we might be looking at two amps here. Or two versions of an amp.


----------



## spritzer

Well Bugatti is technically a VW car so that's not a bad thing.


----------



## luvdunhill

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Well Bugatti is technically a VW car so that's not a bad thing. 
	

	
	
		
		

		
		
	


	


_

 

yup, so is Lamborghini


----------



## ericj

Yeah, but i think i'm looking for the GTI 1.8T of 'stat amps rather than the Veyron. Or even Boxster.


----------



## Sherwood

BHSE?


----------



## ludoo

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_yup, so is Lamborghini 
	

	
	
		
		

		
		
	


	


_

 

You mean this?


----------



## pabbi1

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I think spritzer may be right that we might be looking at two amps here. Or two versions of an amp._

 

Nope, this is your spec - reign it in as you see fit. Several of us already have a design close to fruition for our design goals, so, other than curiosity, it really does not apply to us in as meaningful a way as it does to you. So, I (for one) will stop morphing in the wrong way, and we should seperate out more complex solutions for another thread.

 What this does show is that it is easy for feature creep to wash out a limited scope spec. Hold your line, and, get what you want.


----------



## runeight

Gents, if you'll permit me another try . . .

 As you can tell I have not paid much attention to stat amps. I don't know for myself what a good set of specs is, but I can guess. Also, I don't have experiences that tell me, if I were building a simple and cheap amp, what would I want it to have. But I can guess.

 To remedy this, Pabbi1 has introduced my to cetoole. We've had a few background conversations. Colin has suggested that 600Vpp would be enough for this amp. He also has a few ideas for the diff amp.

 But, if you all would accept 600Vpp then this amp gets simpler and cheaper. 600Vpp only needs 350V rails. We can get these from a stock hammond transformer with heater supplies as an added bonus. 450V caps can be used. We can even regulate at this voltage.

 So, with this in mind I have reworked the design to look like this:






 Voltage stresses are relieved everywhere, particularly on the input devices. We can use 6S4s in the GG configuration. As you can see biasing them properly needs a static grid voltage divider.

 I've added CRDs to the bottom followers. I've been waiting to do this until we'd made a little progress. This unloads the diff amp and significnantly increases the bandwidth. And the amp still has no NFB.

 It's theoretical THD at 600Vpp driving 50p is about .05%. Reality will not be this good by any means but this is a good theoretical starting point.

 1db point driving 50p is about 190kHz. Still theoretical. Will be slower in practice, but not a bad number for a no NFB amp.

 Colin has some thoughts on cascoding the input stage using jfet inputs. I didn't do this because it generates too much gain, but we can eliminate this OL gain with NFB. So I'm looking forward to his thoughts.

 There is still the issue of frying the source, but that's easy to fix. And there is still O/P protection. How do other people do that?

 Everything in the amp itself is cheap. The PS won't be too bad. A 300-0-300 transformer with a heater winding will make the split HV supply. A few complementary HV mosfets will make the dual regulator. 15V supply (if it stays) is trivial.

 How are we doing?

 Edit: Dropping this onto a PCB would be close to trivial.


----------



## spritzer

The GTI could be something along the lines of the Tubecad, with a good choice of tubes and a single PSU should be doable for less then 300$. Now if we were to mix 6.3 and 12.6v tube then a whole range of cheap transformers would open up as many have dual voltage supplies. That amp only needs 4 caps to couple between the tubes, a single +/- supply and can be wired for either SE or XLR simply by grounding one of the inputs per channel. Use just one plate resistors to keep costs down and it is a very simple amp. It does need some built in adjustment but that would be easy to do. 

 Now what tubes should we go for. 9 pin is the most obvious choice but something like the GU50 is dirt cheap... 

 edit: Or we could use the one above 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *Sherwood* /img/forum/go_quote.gif 
_





 BHSE?_

 

If it is V10 TDi, then yes!!


----------



## ericj

runeight, I think we're really getting somewhere. 

 I agree that 600vpp would likely be enough.


----------



## runeight

Great. Let's see what cetoole cooks up for changing the diff amp, then we can worry about protection schemes.

 In the meantime, do you want a regulated split HV supply? Or just a basic LRC jobbie?


----------



## spritzer

The amp above would be less then 30$ in parts for each channel so a regulated PSU should fit inside the budget.


----------



## nikongod

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Voltage stresses are relieved everywhere, particularly on the input devices. We can use 6S4s in the GG configuration. As you can see biasing them properly needs a static grid voltage divider._

 

That is NOT grounded grid. The 100k ohm resistor has a BIG effect here. 

 You *may* be able to get away with replacing the 100K ohm resistor with a zener diode or voltage reference tube, but they may add noise and will waste HV current.
  Quote:


 There is still the issue of frying the source, but that's easy to fix. And there is still O/P protection. How do other people do that? 
 

The easiest thing is coupling caps at the output. 
 Next up is a coupling cap somewhere in the middle. Between the input stage and the 2sc2705 with an adjustable voltage reference for each 2sc2705 would allow grounded grid, and output voltage offset adjustment.
  Quote:


 How are we doing? 
 

Please remove the +15V reference for the tail CCS in the input stage. The input stage of the amp is the the only thing that uses it, and although it improves performance and saves a cap it adds complexity & cost. Realistically: an amp like this is either going to "mission creep" to the point of looking like a BH with currently available transistors or have caps. 

 since the rail voltage has dropped to 350, 400V caps can be used, bonus round for the frugal-fi'ers


----------



## runeight

Why yes, there is some effect. But is it really that big? The grid current changes are small even during full plate voltage swings. This is really just a grid leak resistor (and fairly small as they go). So, it is effectively a GG. However, I might be wrong about this so would you be kind enough to follow up? We need to get this right.

 Coupling caps at the input. Done.

 I know we want to avoid caps at the output. I don't see how an internal coupling cap helps. The O/P stage will still need an adjustment and can still go to the positive rail if the tube dies.

 If this is true, then we can't protect with an internal cap. Or, perhaps, I am just missing something?

 If we don't use an internal coupling cap then the absolute O/P stage offset can be adjusted by changing the current source on the tail of the diff amp. And the relative offset between the two sides can be adjusted using a trimpot between the emitters of the diff pair.

 However, in anticipation of a fair critique of this concept, these controls will be very sensitive and possibly impractical.

 So, the other reason I added the grid leak resistors is because they offer the perfect place to adjust the O/P offset individually for each side. Putting a 75k resistor there in series with a 50k pot (or something like that) would make each side independently adjustable and reasonably, but not perfectly, stable.

 Thoughts????


----------



## holland

A totally newb question. I have no idea how any of these voltage swings and biases apply to stats. If my target headphone, which I hear is a good choice with an uprated amp, is the Koss ESP-950, would this amp be considered "uprated" and be able to bias the ESP-950 properly. Note, I have no idea what it means to bias a stat nor why it matters, and will have to research that.


----------



## ericj

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_A totally newb question. I have no idea how any of these voltage swings and biases apply to stats. If my target headphone, which I hear is a good choice with an uprated amp, is the Koss ESP-950, would this amp be considered "uprated" and be able to bias the ESP-950 properly. Note, I have no idea what it means to bias a stat nor why it matters, and will have to research that._

 

Most 'stats can be driven reasonably well by the same amps if they are supplied with the correct bias voltage. 

 Old stax normal bias was 230v. Pro bias is 580v. The esp950 is 620v iirc. 

 The esp950 can be driven quite well by pro-bias stax amps even at the 580v bias. It is of course better to provide the designed voltage. 

 If my plans come to fruition, I hope that this amp will have a bias supply flexible enough for any halfway normal electrostatic headphone. Delivering 1kv bias for jecklin float electrostatics is probably outside of the scope of this amp. They also have panels so big that you'd need much more power than even an omega needs. 

 The short answer is: Yes. And it should sound much better than the E90 amp.


----------



## AudioCats

the Koss spec for 950 bias is 600V. I have tried 580/600/620V in my JRM transformer box driving the 950, and didn't hear obvious difference. The 620v might be beneficial in a blue hawaii, but I doubt it will do much in a more moderate amp.

 20V difference is less than 5% (of the 600V), after all.


----------



## pabbi1

Quote:


  Originally Posted by *AudioCats* /img/forum/go_quote.gif 
_the Koss spec for 950 bias is 600V. I have tried 580/600/620V in my JRM transformer box driving the 950, and didn't hear obvious difference. The 620v might be beneficial in a blue hawaii, but I doubt it will do much in a more moderate amp.

 20V difference is less than 5% (of the 600V), after all._

 

In a KGSS, it _is_ really quite noticeable, so, perhaps it would make a difference here as well. If is done cheaply through resistors, certainly worth a try. It will simply have to be tried to know for sure.


----------



## spritzer

I did most of my bias tests with a T1 doing the driving and the effect was very noticeable. 

 As for the bias a +350v supply gives us ample headroom for all of the bias voltage we really need. Like Eric said we shouldn't be looking at this amp to drive floats as they not only need more bias but also a whole lot more voltage swing. So instead of the normal load resistor we could put spots for two or even three resistor pairs on the board so the amp can have 230, 500 and 580v bias or what ever the builder wants.


----------



## bjarnetv

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_ Like Eric said we shouldn't be looking at this amp to drive floats as they not only need more bias but also a whole lot more voltage swing._

 

my dreams are now officially shattered


----------



## spritzer

Quote:


  Originally Posted by *bjarnetv* /img/forum/go_quote.gif 
_my dreams are now officially shattered 
	

	
	
		
		

		
		
	


	


_

 

Just get Justin to build a 1.2kV bias supply into a BHSE.


----------



## bjarnetv

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Just get Justin to build a 1.2kV bias supply into a BHSE. 
	

	
	
		
		

		
		
	


	


_

 

if i sell my car, and speakers... and all my headphones except the floats, then i might just afford it


----------



## runeight

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_That is NOT grounded grid. The 100k ohm resistor has a BIG effect here. 
_

 

Aha, I see what you mean. We'll have to fix this . . .


----------



## luvdunhill

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_ Nobody commented on my suggestion to use a small push-pull tube amp (a la Broskie) as the basis of a Stax amp. I'll throw it out again if for no other purpose than to have it formally dismissed. How about a long tailed pair of triode strapped 12gn7a (Pete Milletts fovorite cheapo pentode driver)connected to push-pull triode strapped el34s driving a hammond transformer? Use the primary of the transformer as a center tapped plate choke. Pull the output off the el34s via cheap but exellent 630v Russian p.i.o. coupling caps. Build a 560vdc power supply using an Antec toroid and some motor run oil capacitors. The bias takes care of itself. Parts available in about 30 minutes and a total cost of under $400.00. Simple, cheap, and fairly foolproof. Tell me what I've got wrong here._

 

Frank:

 Would would be the reason to do the above over either the Egmont or SR-Xh (I think that's what it's called... aka ES-1) circuits? Don't these two circuits offer great bang-for-the-buck in some sense?


----------



## ericj

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_ Nobody commented on my suggestion to use a small push-pull tube amp (a la Broskie) as the basis of a Stax amp. I'll throw it out again if for no other purpose than to have it formally dismissed. How about a long tailed pair of triode strapped 12gn7a (Pete Milletts fovorite cheapo pentode driver)connected to push-pull triode strapped el34s driving a hammond transformer? Use the primary of the transformer as a center tapped plate choke. Pull the output off the el34s via cheap but exellent 630v Russian p.i.o. coupling caps. Build a 560vdc power supply using an Antec toroid and some motor run oil capacitors. The bias takes care of itself. Parts available in about 30 minutes and a total cost of under $400.00. Simple, cheap, and fairly foolproof. Tell me what I've got wrong here._

 

"under $400" fails to meet the spec of "under $300". 

 I don't want to build an amp with a $55 chunk of iron on each channel. 

 It's a good idea to be sure, if you already have the push-pull amp. Every time i see an old console stereo at a flea market i get my hopes up.


----------



## nikongod

Im not sure that the design runeight is drawing up will be buildable for less than $400 either.

 Increasing the number of HV caps required for the amp and added complexities in controlling the bias of the output stage precisely may even come out more expensive.

 Unless I misunderstood, the signal does not PASS through the transformers in franks description: they are just there to act as a plate choke, so quality becomes somewhat secondary to what you can get to fit in the chassis and budget. He mentioned Hammond iron, but considering that signal dosnt really go through the transformer a "wallet friendly" Asian part could probably be used with adequate results.

 Anyways:
 On the front of runeight's design, here is what I think:
 the output stage, with 6s4(a) tube, here is the operating point, just so I don't REALLY screw this up.
 330V from plate to cathode, 20V cathode to grid, and about 5mA idle current.

 So the crux move for DC coupling after the input is getting and keeping 20V on the emitters of the last transistor while allowing adjustments to fine-tune the bias.


----------



## spritzer

Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_Im not sure that the design runeight is drawing up will be buildable for less than $400 either.

 Increasing the number of HV caps required for the amp and added complexities in controlling the bias of the output stage precisely may even come out more expensive._

 

The amp would be around 50$ per channel but that leaves the PSU... 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *nikongod* /img/forum/go_quote.gif 
_Unless I misunderstood, the signal does not PASS through the transformers in franks description: they are just there to act as a plate choke, so quality becomes somewhat secondary to what you can get to fit in the chassis and budget. He mentioned Hammond iron, but considering that signal dosnt really go through the transformer a "wallet friendly" Asian part could probably be used with adequate results._

 

That's true, just about anything could be used between the tubes but then we have output caps to deal with. They have to be chosen carefully as they can "sing" along. The cheap Russian teflon's should work just fine but I'd rather direct couple the transducers...


----------



## runeight

Gents, here's another iteration. It seems that you're not completely averse to caps and since this is supposed to remain simple . . .

 nikongod was exactly right on the gg error. And his suggestion for using caps in the follower section was also a good one.

 I have chosen to put the caps before the last follower. But they could be put before the first one. I might try that another time.

 I have shown 620k resistors to bias the driver transistors, but this would be a fixed resistor in series with a trimpot for adjusting the output.

 And since you guys hate the 15V supply I've just tied the tail to the +350V rail. A large resistor like this is almost like a CCS and we don't need to be perfect.

 One difficulty with the input stage is its low Zi. Hence, we need fairly large caps on the input and if you want to protect from failure they need to be 400V caps.

 Low freq response with these components is, approximately, 1db down at 3Hz. Driving 50p the high frequency response is about 1db down at 100kHz.

 Something else for your consideration . . .







 Edit: I know that caps might break the budget. We might be able to eliminate the bottom pair. If we keep them they don't need to be 400V.


----------



## runeight

OK gents, here's a few more schematics for you to look at.

 If you're willing to drop the gain from ~1000 to ~300 we can lose the bottom caps. Like this:






 If you want a lower value input cap we can do this (with a bit more complexity):






 And, finally, if you really want a tail CCS we can do this:






 All of these are subject to refinement (such as trimpots in the right places to adjust offset, etc.). I can provide their theoretical performances if you like any of them.

 Although the last looks like a lot of stuff, it is not really that bad.


----------



## runeight

And one more before I head out. The 6S4s have a higher plate resistance than EL34s in triode mode. Hence the 6S4 has a higher O/P impedance and will have a faster HF rolloff under load. This can be remedied by paralleling 6S4s by cutting the plate load resistor in half and then replicating both the tube and its driver transistor.


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_This can be remedied by paralleling 6S4s by cutting the plate load resistor in half and then replicating both the tube and its driver transistor._

 

yup, this definitely works


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## spritzer

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_yup, this definitely works 
	

	
	
		
		

		
		
	


	


_


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## FrankCooter

I'm really enjoying the evolution of runeights design. It is a pleasure to watch someone with real engineering skills at work. but I think there's room for a parallel path here. Actually, I wish we had several.
 You older guys may remember the Dynaco kits from the 60s and 70s. They were simple, straightforward, good by any standards, and were a maximum "bang for the buck". The schematics are still all over the web. Check out the MarkIII and the sc35 designs. Something like this, stripped down to its essentials is about as basic as it gets. The only major change you might want would be a purpose built output transformer. Basically, this would be a 1:1 push-pull in to push-pull out interstage transformer. This gets rid of your output coupling caps, increases the safety of the design, and provides the ability for drive current. Such transformers were common in 1930s designs. Cary still uses them in their push-pull 845 amps . I own a pair that I'm willing to donate if somebody is willing to run with this. Edcore does small production runs without design charges and their prices are very reasonable. Of course this busts the $300. budget, but I think any other electrostatic amp will too. Otherwise, you may wind up reducing this to a Cmoy for Stax.


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## runeight

Hey Frank, I like that: A Cmoy for Stax!! 
	

	
	
		
		

		
		
	


	




 I think a couple of parallel conversations are a good idea. And I had some of the Dynaco stuff so I'm all for it.


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## FrankCooter

I forgot, the single most important thing an output transformer does in this application is that it allows the full use of your B+ for the output voltage swing. This is a great advantage here, both in performance and safety.
 I'm not familiar with the Egmont, but it sounds similar to what I'm talking about. Anyplace you can find a schematic?


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## spritzer

The ESP markets needs more then just one amp project so a transformer solution isn't a bad idea by any means. It's too much for the budget here but I'm sure a few would love to build one, me included. 






 Ok, here is the Egmont and you can see why this is a good "beginners" project. Nobody owns this design so that's one problem out of the way as well. The plate resistors are all wrong though and we should add some feedback to stabilize the amp. I have a working amp built which uses two ECC99's as drivers with four 6S4A's as outputs being fed by a single Blue Hawaii +/-350v PSU. The goal was to build the cheapest amp possible and this was my choice. Now if I could make those 25$ transformers work...


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## ericj

We already know what the electrostatic cmoy is - it's the NatSemi app note that uses low-voltage opamps to drive high-voltage mosfets.

 As for the amp runeight has been developing - this is starting to look pretty reasonable, especially the version with the smaller input cap. I'm unclear on whether this design's output is AC or DC coupled at this point.

 Parallel output tubes are something i can see some builders wanting to do. But probably not everybody. 

 It's probably possible to set up the board for a default of two tubes per channel, with the option to go hell bent for leather with parallel tubes if you wire the 2nd tube offboard 

 I wish i were qualified to make specific comments as to the design, but i'm not. In general I like where things are going, though.


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## runeight

Well ... ericj, if you're interested in the hybrid amps we can have the several conversations going at the same time. 
	

	
	
		
		

		
		
	


	




 I guess if I were to pick one of the schematics, I would pick the middle one of the three. The one with the cascode input stage and the 150k tail resistor. A PCB layout would be fairly small and it might even be reasonable to provide an extra pair of sockets for someone who might like to parallel 6S4s.

 I don't think the cost per amp channel would be very high. And I don't think that the PS would be very expensive either. I can post a PS concept drawing if anyone is interested in keeping this line of thought moving.

 There is a mistake on the schematics (a feature of working at 4am). The 10k collector load resistors should be 18k.

 Edit: I'm sorry I answered the wrong question. The O/P as drawn is DC coupled although the O/P offset would set via trimpot to near 0VDC for both sides.


----------



## nikongod

The middle, or third designs could BOTH be built on the same board with the creative use of jumpers or skipping parts.

 I think the coolest thing so far is that the runeight design, stax SRX, and egmont could all use the same basic power supply board with minor tweaking to voltage references. This would of course allow a whole family of designs to spawn from this project.


----------



## ericj

That's true. A regulated 350-0-350 + switchable bias supply board could almost be popular in it's own right, for people straying from the norm. 

 runeight, thanks for clarifying that we are still talking about a DC-coupled output. Glad to hear it. 

 I have to admit that i see the appeal of both designs. 

 Perhaps i should post a poll thread asking how likely people would be to buy boards or a kit if they were available for a good, affordable 'stat amp. I mean at some point, somebody is fronting cash for a run of boards. Could even be me. I think we have a good feel for the likely success, but I'm not sure how it would compare to some of the recent dynamic amps.


----------



## holland

Like nikongod, I think this can be done with some routing (and silkscreen work?) and jumpers/wires in place. A board that can use CCS or resistor and one or two tubes seems reasonable. I think nikongod is onto something with the PS concept being separate and not tied to any amp.

 I'll definitely be in, but it'll be a few months for me to save up enough cash to build the project and buy the ESP-950. Tough economic times.


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## pabbi1

Hmmmm - 350v reminds me of the Bijou psu... all in for a rock solid regulated psu for $125ish.


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## runeight

Hey, Pabbi1, stop giving away the secrets.


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## pabbi1

Stealing your thunder - just wondering when someone was gonna cue you with 'Where is my psu'? Always saving the best for last. Of course, anyone would have figured it out, but, since I use mine daily / nightly, just thought you deserved a shameless plug - the psu is ROCK solid.


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## runeight

Pabbi1, your wish is my command. 
	

	
	
		
		

		
		
	


	




 Here's a PS that should work. Maybe needs a bit of refinement. Those are 400V complementary mosfets. They will need heatsinking depending on O/P voltage and transformer voltage. It will be difficult to make this variable for wide range of voltages without very large heatsinks. But it should be easy to have several versions where some of the resistor values change depending on O/P voltages and a particular HV secondary is chosen.


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## wiatrob

Aww, Pabbi1 - I thought you were gonna clue me about this {whine whine}

 How _do _you keep up with all this! More reading for me in the AM!!_




_


----------



## pabbi1

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_Aww, Pabbi1 - I thought you were gonna clue me about this {whine whine}

 How do you keep up with all this! More reading for me in the AM!!




_

 

Worry not - this isn't what I am keeping you posted about... 
	

	
	
		
		

		
		
	


	




 Runeight, your work never ceases to amaze... to think that the base of a design has come within a week is, well, pretty astonishing.


----------



## TimmyMac

So... a PSU like that... would it scale well to supply say... the serious EL34 circuits you had on the previous pages? With higher voltage silicon I suppose.


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Here's a PS that should_

 

Alex, what's the output impedance?


----------



## runeight

Quote:


  Originally Posted by *TimmyMac* /img/forum/go_quote.gif 
_So... a PSU like that... would it scale well to supply say... the serious EL34 circuits you had on the previous pages? With higher voltage silicon I suppose._

 

In principle it scales, in practice scaling is hard. This for several reasons.

 In order for the cap mulitplier and regulator to work there needs to be some voltage drop in the filter/regulator section. Let's arbitrarily say 50V. Thus, if we are regulating to 350V we need to have 400V at the first filter caps. This means, of course, that the first caps are 450V caps and this is cutting it close. But, I have done this before with no ill effects over time.

 But, any higher output from the reg means higher input at the first cap. 500V at the reg means 550V at the first filter cap and this means, unless you have big 630V caps around, that we have to put caps in series with voltage equalizing resistors. Furthermore, the rest of the electrolytics will also have to be two in series. It's been done. Lots of times. But it's many more components and complexity.

 The higher voltage fets are not a problem, but The higher voltages require much more careful wiring and spacing.

 And, lastly, the energy storage difference between 350V and 500V is not trivial. Dump one of these caps into a piece of wire and it will vaporize. So, the sucker is dangerous. It's dangerous at 350V, but much more dangerous at 500V.

 Having said all that, it can be done.


----------



## runeight

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Alex, what's the output impedance?_

 

You mean the Zo of the PS?


----------



## spritzer

It looks like the Blue Hawaii PSU might be cheaper in parts and since we already have the layout it would be very simple to have some boards made once the errors have been fixed. There is a cheaper alternative for the 2SA1968's so that's not an issue. 

 We should perhaps also have small +/-15v supply on the board as well so the same PSU can be used to drive pretty much any one of the ESP amps, KGSS, BH, Egmont, SRX etc.


----------



## pabbi1

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_It looks like the Blue Hawaii PSU might be cheaper in parts and since we already have the layout it would be very simple to have some boards made once the errors have been fixed. There is a cheaper alternative for the 2SA1968's so that's not an issue. 

 We should perhaps also have small +/-15v supply on the board as well so the same PSU can be used to drive pretty much any one of the ESP amps, KGSS, BH, Egmont, SRX etc._

 

Including the iron to run it? The Bijou psu uses a $50 Hammond (270DAX, from Angela), where I thought the BH needed a pricier ($100+) toroid - and, the Bijou power boards have been in production for almost a year, already in stock at GlassJar. The BH psu advantage is the lack of a tube.

 But, your point is well taken that there are psu alternatives, pretty well known, and with proven track records.


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## wiatrob

Quote:


  Originally Posted by *holland* /img/forum/go_quote.gif 
_Like nikongod, I think this can be done with some routing (and silkscreen work?) and jumpers/wires in place. 

SNIP

 I'll definitely be in, but it'll be a few months for me to save up enough cash to build the project and buy the ESP-950. Tough economic times. 
	

	
	
		
		

		
		
	


	


_

 

There is something undeniably appealing to a single board with multiple configurations (flexibility? economy?).

 I am looking forward to next weekend when I will listen to a bunch of 'statics and decide whether to succumb to the temptation!


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## runeight

It's just a matter of trade offs, as it always is. 
	

	
	
		
		

		
		
	


	




 The BH supply is not regulated. It uses a CCS to provide current for a zener string. The zener string sets the gate voltage for the mosfet which sets the source voltage. If the mosfet is loaded lightly the voltage will stay pretty constant. And in an electrostatic amp the dynamic current draw appears to be in uA ranges. So this supply is perfectly alright.

 If you want to use this supply for more general purposes the BH supply will not provide as good regulation as one with feedback through an error amplifier (as in the one I drew).

 Once again it comes down to what the need is. If we are certain that the PS is only for electrostatic amps with low dynamic current requirements or if we really don't care about super regulation then the BH supply (or variant thereof) is perfectly alright and a known quantity.

 To make the BH a bit simpler I would make it a true complementary supply (easy to do) so that we can use a transformer with a CT secondary if someone wants to do that. OTOH, KG points out that NFets are cheaper then PFets.

 luvdunhill, if you mean the Zo of the PS that I drew, for typical values it should be around 25mOhms at 1KHz.


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## spritzer

It's always a trade off... especially given the price we have to work with. I for one would love to try your PSU on a few amps I have kicking around but they aren't limited by price in any way. This brings up the issue of having more then one design to choose from with clear ways to upgrade as not everybody wants just a cheap amp to get them going. I'm sure that people would love to be able to build the SP ES amps at a fraction of the price... 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Including the iron to run it? The Bijou psu uses a $50 Hammond (270DAX, from Angela), where I thought the BH needed a pricier ($100+) toroid - and, the Bijou power boards have been in production for almost a year, already in stock at GlassJar. The BH psu advantage is the lack of a tube.

 But, your point is well taken that there are psu alternatives, pretty well known, and with proven track records._

 

Well we (aka non 117v users) can't use the 270 Hammond series so that's either a 370 or something else. I'd rather try some of the R-cores from China which are cheap as dirt. The Bijou PSU is also not +/- so it won't work on a stat amp. Since it uses a tube rectifier using full wave there is very little difference to just using a non-CT transformers with two extra diodes.


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## nikongod

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Including the iron to run it? The Bijou psu uses a $50 Hammond (270DAX, from Angela), where I thought the BH needed a pricier ($100+) toroid - and, the Bijou power boards have been in production for almost a year, already in stock at GlassJar. The BH psu advantage is the lack of a tube._

 

The BH transformer is only more expensive because it requires the 36v winding which makes it a custom job. There are a couple companies that make suitable transformers (without the 36v winding) in the $50 ballpark. A bulk order of BH transformers would probably bring the price into the $65 range.

 Anyways, on the thread of modifying/adapting the bijouish PSU to this project:
 Try adding a CRC filter at the input of the PS. It will solve several problems: the R can be adjusted cheaply to dump off a few volts without stressing the regulators. The HF spikes of a big cap input supply can be reduced. Both are good things IMO.

 Maybe Im prejudiced (aren't we all towards our favorite designs?), but im not a fan of making the mosfets do *all* the work of cleaning the HV lines all by themselves. Even a simple & cheap CRC network makes their life so much easier.


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## runeight

Yes, I kind of agree, however . . . CRC filters take more R and C to reduce ripple to the same level as a cap multiplier. The Cs get bigger and the Rs drop more voltage. If we have lots of voltage to drop before input to reg then I would prefer the CRC too. But if we don't have much to drop then the cap multiplier will do a very nice job with only 5V across it.

 Now, I haven't really put numbers to the PS. First thing would be to pick a transformer to get the first filter voltage. Then work from there down to 350V.

 There are other issues. For example, the 6S4 amp will probably draw about 20mA from each rail (10mA per channel). We can set the CRC filter for that. But, if we supply extra sockets for two more 6S4s then that adds another 16mA (8 per channel). So the R is suddenly dropping almost twice as much voltage. If we leave room for this additional drop then when only single pairs of 6S4s are used the regulator pass device sees much more voltage and gets a lot hotter.

 So . . . a cap multiplier tends to maintain a fairly constant voltage drop (or close enough) when the current demands change. Hence we can design the PS a little tighter and still get good ripple rejection.

 Nonetheless, I agree with the appeal of a CRC before the reg. What this might is simply limit the choices of transformer or . . .

 Build the two regulators onto the board but leave the CRC section p2p. Then when you choose a transformer and a load you select the CRC that works for that to provide at least 365V before the reg. Flexible, but requires some wiring.


----------



## nikongod

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Yes, I kind of agree, however . . . CRC filters take more R and C to reduce ripple to the same level as a cap multiplier. The Cs get bigger and the Rs drop more voltage. If we have lots of voltage to drop before input to reg then I would prefer the CRC too. But if we don't have much to drop then the cap multiplier will do a very nice job with only 5V across it._

 

I agree, a CRC filter can only do so much and they are very inefficient at that, but they do have the "cheap muscle" bouncer effect. they keep the really scummy scum out of the club. 
  Quote:


 There are other issues. For example, the 6S4 amp will probably draw about 20mA from each rail (10mA per channel). We can set the CRC filter for that. But, if we supply extra sockets for two more 6S4s then that adds another 16mA (8 per channel). So the R is suddenly dropping almost twice as much voltage. If we leave room for this additional drop then when only single pairs of 6S4s are used the regulator pass device sees much more voltage and gets a lot hotter. 
 

I think most people are going to know from day 1 that they want to build this with 1 or 2 triodes/ch. accordingly, different resistor values could be recommended for them.

 If the design calls for a 700vct transformer, but 720 is on sale CHEAP somewhere, the difference could easily be accommodated without stressing the regulators.

 The other reason the CRC before the regulator comes into play is if people want to use the regulator board for circuits which have unequal B+/B- as in the SRX. The B+ regulator would have to deal with more current AND more voltage across it. Using different resistors could solve some of this. I guess an all tube design could be built with equal B+/B- if good regulation were assured.
  Quote:


 Build the two regulators onto the board but leave the CRC section p2p. Then when you choose a transformer and a load you select the CRC that works for that to provide at least 365V before the reg. Flexible, but requires some wiring. 
	

	
	
		
		

		
		
	


	



 

you could also jumper the resistor and skip the "input" cap. much cleaner. Im not sure how much board spare it will take up though.


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## runeight

Gents, my drawing with the CCS going to the +350V rail forgot to recognize the power dissipation in the transistor. Over 1W. I've modified the drawing using a cascoded bjt configuration that does a better job. However, the MJE350 must be replace with a higher voltage device. I'm looking for one that's readily available and not expensive.

 The alternative is the magic 150k resistor.


----------



## jcx

Arrow has over 1K of IXTP 01N100D in stock for ~$0.81ea

 no curves but a 100mA, 110 Ohm Rdson, 1000 V depletion mode MOSFET in TO-220 with 25pF Cds and 5pF Crss should be a fine ccs or even tube replacement


----------



## pabbi1

Quote:


  Originally Posted by *jcx* /img/forum/go_quote.gif 
_Arrow has over 1K of IXTP 01N100D in stock for ~$0.81ea

 no curves but a 100mA, 110 Ohm Rdson, 1000 V depletion mode MOSFET in TO-220 with 25pF Cds and 5pF Crss should be a fine ccs or even tube replacement_

 

Yes, I happened to buy 100 of them for something else... you are on the right path here.


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## runeight

Gents, here's a first-pass single channel board for the amp with the 150k resistor. Input caps are left off because I don't know what might be used. Power resistors are Xicon small 5W resistors.

 There is lots of wasted space on this board. Much compaction can be done. It is currently 100mm x 70mm.


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## spritzer

Looks good but how about terminals for input, HV, output and filaments to make it easier to wire? 

 The input cap could be standardized as something like a Wima or Vishay MKP which are cheap and easy to find. If somebody wants to use A-N Silver caps then that's their problem. 
	

	
	
		
		

		
		
	


	




 For the power resistors it could be a good idea to make sure Mills units fit for those of us willing to splurge a bit. They should be roughly the same size though so that could be a non-issue.


----------



## runeight

Ah yes. Just waiting for someone to show more interest. 
	

	
	
		
		

		
		
	


	




Poor Mans Stat Amp

 And here's a 3D. I don't have models for some of the parts.


----------



## spritzer

I'm sure that quite a few are watching but have nothing to say. 
	

	
	
		
		

		
		
	


	




 The only thing that comes to mind are some ventilation holes to help airflow and tie the heater together. I'm not not a fan of even having the heaters on the PCB due to possible noise but this very simple thing has been known to cause confusion so it should be a simple as possible.


----------



## Beefy

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I'm sure that quite a few are watching but have nothing to say. 
	

	
	
		
		

		
		
	


	


_

 

Yo! 
	

	
	
		
		

		
		
	


	



 Watching something like this develop is very nerd-cool, even if I don't understand it all just yet......


----------



## runeight

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I'm sure that quite a few are watching but have nothing to say. 
	

	
	
		
		

		
		
	


	




 The only thing that comes to mind are some ventilation holes to help airflow and tie the heater together. I'm not not a fan of even having the heaters on the PCB due to possible noise but this very simple thing has been known to cause confusion so it should be a simple as possible. 
	

	
	
		
		

		
		
	


	


_

 

OK. Then I guess we'll keep moving.

 I have a different thought on the heaters. I think they can be run AC (although you can always use DC). If the heaters are AC then we should keep the runs off the board. In this case I have used very short traces away from everything else from the connector to the heater pins. Then to run the heaters the builder can twist the wire and run it very close to the chassis and away from the board attaching perpendicular to the board. This has worked on many, many designs and should work here. And then if someone wants to take the time to build a DC supply he can.

 Do you mean vent holes on the PCB itself? If so, easy to do. 
	

	
	
		
		

		
		
	


	




 Does anyone also want the transistor CCS on the tail. It's more work, but that can also be done.


----------



## spritzer

I also assumed we would be using AC heaters (DC is more expensive) so a twisted wire is the best way with short traces on the board. My only concern is to make it "noob proof" as many can't fathom how simple this stuff is and over thinks it. 

 Yeah I was thinking about some vent holes in the PCB to eat up some of that free space and also help it run cooler. Perhaps planting some underneath the power resistors to make them run cooler if the builder were to mount them flush with the PCB?

 You could also add the phase markings to the input and output.


----------



## runeight

OK. I'll add the holes and better lettering. I think I'll leave the heater wiring alone for now until there is more input that something needs to be done. 

 Next rev coming soon.

 Now, the question is becoming is there anyone out there game enough to try this?


----------



## scompton

I'm watching but don't have the experience to comment on anything. The only thing I've built so far is a Starving Student. I'll definitely build one of these after one or 2 other projects.


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## Ynis Avalach

I will probably build one too, in some time.
 Till then I first have to get a stat, selfbuilt or Stax.
 But couldn't comment on half your planning on, lack of experience.
 Really nice work yet!!!!!
 Please please keep going and finish this project! I'm sooo interested in building one


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## runeight

Hey, nice to hear from a few of you. Ynis, I've actually been to Darmstadt. 
	

	
	
		
		

		
			





 Next installment. One thing that is still missing are the offset controls. Here's a schematic of how we might do this. The 50k pot controls the DC offset of both channels and the 500R pot controls the channel balance.

 Anyone have any thoughts about better ways to do this?


----------



## wiatrob

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_ My only concern is to make it "noob proof" as many can't fathom how simple this stuff is and over thinks it. _

 

The voltages alone should make it "noob proof!" Waiver with the PCB?


----------



## luvdunhill

Looks interesting Alex! However, no spot on the PCB for compensation (Cdom)? Either you haven't added it because you're not sure it's needed, or you know it's not needed and didn't add it 
	

	
	
		
		

		
		
	


	




 If it's the second, then it would be an interesting explanation, for me at least.

 Also, for the PSU what about a Maida regulator circuit? Pretty simple to build and low part count.


----------



## runeight

You would have to ask that. 
	

	
	
		
		

		
		
	


	




 In this case the triode is the VAS stage and O/P stage in one package. Since the tube has high enough internal capacitances, siince there are two followers beween the diff amp and the tube, and since the gain here is not that high, the HF response falls off nicely without the Cdom cap. In fact, we have the opposite problem - keeping the unloaded HF response up so that when the amp is loaded with 50pf it will have a decent HF response.

 My guess is that if we added another bjt gain stage between the diff amp and the tube we would need this cap.

 I don't know about the Maida regulator. Can it operate at 350V??


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_I don't know about the Maida regulator. Can it operate at 350V??_

 

yes, I have a circuit operating at 350V, I could draw up a schematic. Here's the basic idea:

http://www.national.com/an/LB/LB-47.pdf

 ... and a simpler version:






 Also, what about this gem:

http://www.supertex.com/pdf/datasheets/LR8.pdf






 If you're willing to shop surplus, there's this:

http://www.selectronic.fr/includes_s...is/HIP5600.pdf

 I'll comment later on the other stuff


----------



## Sherwood

The complexity and voltage may well preclude me from attempting this amp at this stage of my DIY career (how in hell does one solder with one hand in their pocket?) but I am delighted by the process I'm witnessing. Alex, Mark, Bill, Pabbi1, Eric et. al. -- thanks gents. I look forward to getting to a point where I can build this AND have it work.
 Thanks!


----------



## pabbi1

The point exactly - anyone will be able to build this, from what has been modeled to date.

 I will build one, as I have most of the parts laying around, except for a pot, where, in keepin with the spirit of the build, will use the ubiquitous ALPS RK27 pot - maybe pads for that can be added, which will take much mystery out for the less (or those of us who should be far less) confident.

 Also, it would certainly make life easier if the IXYS depletion mode mosfets could be used on the board, or some option for them - just never saw this discussed any further.

 Regarding tubes, it would be a nice option to spec something like this, where we can get the tubes up out of the case, short of air wire (not an easy task for less experienced), or some option ot reverse mount the board with everything but the tubes on the bottom (maybe this is already possible). Heat management rears it;s ugly head here shortly.

 Sorry I'm not much help on the circuit itself, except the formfactor is just, well, outstanding.


----------



## wiatrob

Quote:


  Originally Posted by *Sherwood* /img/forum/go_quote.gif 
_The complexity and voltage may well preclude me from attempting this amp at this stage of my DIY career..._

 

Ah, that's the beauty of old(er)-tech - didja see the amp board? Pretty simple compared to say, anything surface mount. Yes, voltages can be lethal - but so can driving my friend.
	

	
	
		
		

		
		
	


	




 Necessary Precautions and risk Mgmt! And a [size=large]BIG [/size]insulated discharge resistor... 

  Quote:


  Originally Posted by *Sherwood* /img/forum/go_quote.gif 
_..I look forward to getting to a point where I can build this AND have it work.
 Thanks!_

 

Looks like that ball is rolling... Alright, that's enuf pontificating, I'm going off to study up so I can ADD something to these discussions someday!


----------



## luvdunhill

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_or some option ot reverse mount the board with everything but the tubes on the bottom_

 

if you want to do this, I'd recommend sticking with the plate resistors. Having to mount devices to a top plate, or having heat sinks "upside down" can cause issues in their own right.


----------



## lordvader

I'm gonna put myself down as an interested part too 
	

	
	
		
		

		
		
	


	




 FWIW, I don't even have a pair of electrostats, and still want to build this thing !!!


----------



## luvdunhill

n/m too late to be posting


----------



## ericj

Quote:


  Originally Posted by *Sherwood* /img/forum/go_quote.gif 
_The complexity and voltage may well preclude me from attempting this amp at this stage of my DIY career (how in hell does one solder with one hand in their pocket?)_

 

You can use both hands when building it initially. 

 The advice is to keep one hand in your pocket because high voltage is most likely to kill you if there is a path across your chest. 

 If one hand is grounded and the other hand touches +350v, on a good day you'll end up in the hospital. 

 If your feet are grounded, your left hand is in your pocket, and your right hand touches +350v, chances are it will just hurt like heck. They say it's like getting whacked with a hammer. 

 I presume that the power supply board will be fitted with a "hey dummy there's still HV on the board" light and facility for safely and quickly draining the power caps. 


  Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_I will build one, as I have most of the parts laying around, except for a pot, where, in keepin with the spirit of the build, will use the ubiquitous ALPS RK27 pot - maybe pads for that can be added, which will take much mystery out for the less (or those of us who should be far less) confident.

 Regarding tubes, it would be a nice option to spec something like this, where we can get the tubes up out of the case, short of air wire (not an easy task for less experienced), or some option ot reverse mount the board with everything but the tubes on the bottom (maybe this is already possible). Heat management rears it;s ugly head here shortly._

 

Keep in mind that the board as shown is one channel. Adding pads for a volume pot is possible, but it would be a mono pot for one audio channel. 

 As for getting the tubes out of the case - this is very easy. Just use pcb-mount tube sockets which also accept the hardware for under-chassis mounting. 

 Put any components taller than the pcb socket on the bottom of the board, carefully drill the chassis, and bolt the sockets to the chassy. The board dangles from the sockets - quite securely.


----------



## Keithpgdrb

I am also lurking this development. I am very interested in building this, but I have little to no diy experience. But, I only have an electrostatic setup right now, so, this is the am I want to build. unless I pick up some dynamics later. I will continue to follow along and see where that puts me.


----------



## spritzer

Building something like this is very easy but testing it can become difficult. You have to think about wire layout and insulate more then with low voltage circuits but this quickly becomes second nature. This isn't really a problem with PCB's though but just make sure to use a 600v rated wire. 

 Sticking the pot and input wiring on board would require us to think about possible chassis choices as well to make sure it will fit. 

 Should we start discussing possible transformers? We need 2.4A/6.3V for the tubes but what would the HV supply require?


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Put any components taller than the pcb socket on the bottom of the board, carefully drill the chassis, and bolt the sockets to the chassy. The board dangles from the sockets - quite securely._

 

this works in all but two cases. When there's lots of heat being generated from under the board and where there are physical problems related to parts needing to be rotated (for example 3-legged transistors).


----------



## luvdunhill

for transformer, what about Allied 6K3VG at a whopping $26:

Allied - 6K3VG - Allied Electronics


----------



## spritzer

Now Marc... do I need to bring out the shovel, a single 110v primary!!??!! 
	

	
	
		
		

		
			





 It also doesn't have enough filament current as we need 2.4A. 

 I was thinking more along these lines...


----------



## pabbi1

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_this works in all but two cases. When there's lots of heat being generated from under the board and where there are physical problems related to parts needing to be rotated (for example 3-legged transistors)._

 

Runeight did this on the SOHAII boards, which prompted the query.

 And, I believe the model is one chanel, but the +/- on R or L - which means a stereo pot on each board works just fine, as I have done this on more than one build.

 And, this from Ti makes a different approach for rk27 mount.


----------



## krmathis

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I'm sure that quite a few are watching but have nothing to say. 
	

	
	
		
		

		
		
	


	


_

 

Indeed!
 Too blown away with the progress of this thread/design to have any real comments. 
	

	
	
		
		

		
		
	


	




 Great progress guys!


----------



## ericj

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Runeight did this on the SOHAII boards, which prompted the query.

 And, I believe the model is one chanel, but the +/- on R or L - which means a stereo pot on each board works just fine, as I have done this on more than one build.

 And, this from Ti makes a different approach for rk27 mount._

 

Actually that brings up the question of what we're doing for single-ended input.


----------



## spritzer

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Actually that brings up the question of what we're doing for single-ended input._

 

Ground the - phase, same as with most of the other amps we've been talking about.


----------



## ericj

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Ground the - phase, same as with most of the other amps we've been talking about._

 

Forgive my incredulity, but is that really going to work as well as having an inverted signal?


----------



## spritzer

Yes, as it is done with most truly balanced amps. Ever see the small links that Pass and Krell amps (plus many others) have to have in the XLR sockets if you want to use the SE input? You can see it here on the back of a Pass amp but the link simply grounds the - part and is used instead of a switch. You do loose some gain due to the lower input voltage but that's it.


----------



## runeight

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Forgive my incredulity, but is that really going to work as well as having an inverted signal?_

 

Suprisingly enough, it does work when the diff amp is loaded with a CCS on its tail. It acts like a phase splitter with the amplitudes of the two phases being equal.

 However, you also lose half the gain. So if the amp makes 600Vpp with both phases each providing 2Vpp at the input (gain of 300) then it will only make 300Vpp with one input grounded and the other driven with 2Vpp.


----------



## runeight

I have a question on the vol pots. Are you guys going to use one stereo pot for each channel or a single 4 gang pot for both channels?

 If you do the former then an RK27 can be mounted on a single channel board. If the latter, then MHO is that the pot (or attenuator) should be off board.


----------



## pabbi1

For the stated budget, I do not really think there is much choice other than 2x rk27, or something like this, though it is $50, plus shipping. I do have a balanced DACT, but it was $186, iirc.

 The reason I almost always ues 2x attenuation is for the event of channel imbalance between channels (assuming no imbalance between + / -).


----------



## spritzer

We could always use this:

ALPS Quad Potentiometer RK27114MC motorized pot 10K 50K - eBay (item 260356848007 end time Feb-13-09 09:59:27 PST)

 I don't think they are available without the motor but it should be detachable. 

  Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Suprisingly enough, it does work when the diff amp is loaded with a CCS on its tail. It acts like a phase splitter with the amplitudes of the two phases being equal.

 However, you also lose half the gain. So if the amp makes 600Vpp with both phases each providing 2Vpp at the input (gain of 300) then it will only make 300Vpp with one input grounded and the other driven with 2Vpp._

 

That's the downside of SE use but the amp should still be competitive with the Stax amps at and above the price range. What remains to be seen is how it will fare against the SRM-717 which is the best "low cost" amp I've tried.


----------



## runeight

Spritzer, what is it about the SRM-717 that you like?


----------



## spritzer

It has enough power to move the SR-007 and has a very pleasant tonality, a bit warm and with a slightly overblown soundstage but easy on the ears.


----------



## TimmyMac

Offboard attenuators give a lot more flexibility as far as casing goes, so that would get my vote.


----------



## TimmyMac

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_We could always use this:

ALPS Quad Potentiometer RK27114MC motorized pot 10K 50K - eBay (item 260356848007 end time Feb-13-09 09:59:27 PST)

 I don't think they are available without the motor but it should be detachable. _

 

ALPS Quad Potentiometer RK27114 Pot RK27 10K o 5K Audio - eBay (item 260356448120 end time Mar-04-09 14:35:08 PST)


----------



## pabbi1

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_We could always use this:

ALPS Quad Potentiometer RK27114MC motorized pot 10K 50K - eBay (item 260356848007 end time Feb-13-09 09:59:27 PST)

 I don't think they are available without the motor but it should be detachable._

 

Of course they are... Balanced rk27. Just not in 50k. 
	

	
	
		
		

		
			





 Still, $50ish, so the rk27 (x2) is still the cheapest at $40ish, shipped. At least 13% of the build cost is attenuators any way you look at it. Well, unless cost is the only driver, with inevitable consequences.


----------



## marcus1

Hi

 Another non EE type watching this project with great interest - thanks to all those participating in the design.
 Is the thinking that once the design has been finalised, someone would build it and possibly compare it to say the SRM-717 mentioned previously?


----------



## spritzer

I will certainly build it and compare to what ever amps I will have at the time plus impressions based on memory of all the other amps I've tried over the years.


----------



## runeight

Now just, please remember that we are trying for cheap and easy to build. I have not got a clue as to how this amp will sound or compare. Please don't set unreasonable expectations. 
	

	
	
		
		

		
		
	


	




 Is there anyone who might consider breadboarding a version of this? I think we can use a modified version of the BH PS using an easily obtainable transformer. If someone could breadboard this up we would know very quickly if it's worth having boards made.

 It almost looks like it could be breadboarded for less than $150. The biggest cost will be the transformer, pots, and jacks, and then tubes.

 Any takers out there???


----------



## spritzer

There are no unreasonable expectations on my part... honest!! 
	

	
	
		
		

		
		
	


	




 I just checked the inventories of the two local electronics stores here and they do not have the transistors (they do have the 2SA1145 but thats it) or the diode in stock so I can't throw together a prototype. All I need is the amp boards so I'll see if I can put in an order to Mouser soon.


----------



## ericj

It's simple enough that i could probably breadboard it. 

 If i had that kind of time I'd finish my Stacker II. 

 Still, I'll consider making the 1st prototype for a few days.


----------



## runeight

Well, while you guys are noodling on what to do here's what I mean by a modified BH split HV supply. Seems like there are good 260-0-260 rcore transformers around. And there is a Hammond that fits this spec with a 6.3V/3.5A heater winding.

 I've left of the bias doubler.


----------



## runeight

Now if it were me I would add these two caps. They improve the ripple rejection and they slow down the rise of the HV to give the tube a chance to warm up.


----------



## runeight

And, while we're looking at schematics I think I'm liking this better for the tail CCS.


----------



## n_maher

I've got one spare 100k Quad Alps pot (w/ extraneous motor), if one of the prototypers/early adopters wants a cheap pot, I'll let it go for $25.


----------



## runeight

More eye candy. The board and the 3D.

Poor Man Stat amp


----------



## pabbi1

I can't build without a board, so I would be a poor breadboard prototyper, but do have parts for a Bijou psu to prototype boards.


----------



## runeight

Gents, I have costed out the latest amp and PS schematics.

 The mouser parts come out to about $50. This is everything but the jfets and the 470u caps in the PS. I selected Panasonic EDs for these. They are $9 each from Digikey and there are four of them.

 So the total for two channels and one PS is $86 plus some change for the jfets. Add some shipping and say $100.

 You will need a transformer, tubes, jacks, pots and a case. Eventually, there will be board cost.

 My guess is that a basic amp with no boutique components can be built for about $200. Possibly less.

 So, if this amp has respectable SQ (totally unknown at the moment) it will fall well under the $300 limit set by ericj at the beginning. And for $300 you can add $100 worth of fancy stuff.


----------



## Juaquin

As an EE (still in school), I just have to say this is badass. I'm still looking at the circuit trying to figure out exactly what's going on (we have analog circuits classes, but never with an application to audio), but it's cool to see it develop. Props to all involved.


----------



## HeadphoneAddict

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Gents, I have costed out the latest amp and PS schematics.

 The mouser parts come out to about $50. This is everything but the jfets and the 470u caps in the PS. I selected Panasonic EDs for these. They are $9 each from Digikey and there are four of them.

 So the total for two channels and one PS is $86 plus some change for the jfets. Add some shipping and say $100.

 You will need a transformer, tubes, jacks, pots and a case. Eventually, there will be board cost.

 My guess is that a basic amp with no boutique components can be built for about $200. Possibly less.

 So, if this amp has respectable SQ (totally unknown at the moment) it will fall well under the $300 limit set by ericj at the beginning. And for $300 you can add $100 worth of fancy stuff. 
	

	
	
		
		

		
			



_

 

Wow. I'm very curious to hear how it performs.


----------



## TimmyMac

I'd prototype it... if I had electrostats to test it with!


----------



## spritzer

I have most of the parts needed so I'll put together a BOM today and post here if Alex doesn't beat me to it. Since I don't want two BOM's floating around, what voltage rating is on those Wima caps and is that a 3mm led?


----------



## runeight

spritzer you have a pm.


----------



## MrMajestic2

Quote:


  Originally Posted by *TimmyMac* /img/forum/go_quote.gif 
_I'd prototype it... if I had electrostats to test it with!_

 

Me too, but I will buy Electrostats for testing


----------



## Postal_Blue

Add me to the list of excited onlookers. I have built 2 Cavalli amps both of which I love. I have every intention of building this one. A thousand thanks to those involved in this project, with an accompanying "Darn you I was done buying/building headphone gear" Now to score a deal on some Stats


----------



## spritzer

Quote:


  Originally Posted by *MrMajestic2* /img/forum/go_quote.gif 
_Me too, but I will buy Electrostats for testing 
	

	
	
		
		

		
		
	


	


_

 

The Stax SR-003 is an excellent headphone for testing amps as they are sensitive enough to pickup hum and are cheap if something were to go wrong. As a plus they sound very good if the comfort is a bit off for some people.


----------



## ericj

So, the only potentially difficult to source part is the 2sj74 jfet, it seems. newark says they have 29. bdent seems to have a good supply.

 if someone is unable to source this part, is there a likely replacement?


----------



## runeight

There is no good replacement that I am aware of. Other pfets could perhaps be used in this slow, but they might not have as good audio quality. Let me see if I can find one or two.


----------



## MrMajestic2

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_The Stax SR-003 is an excellent headphone for testing amps as they are sensitive enough to pickup hum and are cheap if something were to go wrong. As a plus they sound very good if the comfort is a bit off for some people._

 

Yeah, I was thinking of that model. This would give me an excuse for trying out electrostats


----------



## ericj

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_There is no good replacement that I am aware of. Other pfets could perhaps be used in this slow, but they might not have as good audio quality. Let me see if I can find one or two._

 

I guess I'm only really concerned if it's a discontinued part. mouser / digikey / allied don't carry it at all. newark carries it through their MCM acquisition but only has that small quantity.


----------



## wiatrob

Might Electret's be a good set of phones to 'smoke' test with??


----------



## scompton

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_Might Electret's be a good set of phones to 'smoke' test with??_

 

It wouldn't test the bias which is what will destroy the headphones if it's high.


----------



## wiatrob

Quote:


  Originally Posted by *scompton* /img/forum/go_quote.gif 
_It wouldn't test the bias which is what will destroy the headphones if it's high._

 

Agreed, i was suggesting this as an extra failsafe


----------



## pabbi1

I'd far rather torch some electrets than my he60 - remember, there are no throw away earbuds in the electrostatic world to test with.

 So, is there a cheap way to include external test points for bias and offset, just in case? Or, at least good test points on the board, safely away from anything 'sparky'?


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I guess I'm only really concerned if it's a discontinued part. mouser / digikey / allied don't carry it at all. newark carries it through their MCM acquisition but only has that small quantity._

 

It is indeed discontinued by Toshiba.


----------



## Ynis Avalach

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_I'd far rather torch some electrets than my he60 - remember, there are no throw away earbuds in the electrostatic world to test with.

 So, is there a cheap way to include external test points for bias and offset, just in case? Or, at least good test points on the board, safely away from anything 'sparky'?_

 

Uh yeah that would be a great thing to have, espacially since this is a quiet cheap amp to built and so probably some with not so much experience would try this. So some test point for probes to test?


----------



## spritzer

You can find them on ebay but who knows if the sellers are reputable...


----------



## ericj

I think i'd start my testing with an SR-30 electret driver that's already showing some damage (getting quiet).

 Probably go from that to a working SR-30, then SR-5 . . .

 As long as we have test points for the bias voltage it's not too scary. Users who build with switchable bias might want to invest in a panel volt meter for their amp. Also worth pointing out here: the bias supply is going to have a big (5meg?) resistor on the output. The test point should be before this resistor, as many volt meters have too low an impedance to give a correct reading. 

 Also, I wonder how likely it would be that we can build with a fixed low-bias for a 6 pin socket and fixed or switchable or variable bias for a 5 pin socket (stolen from an SRD-4 or simply a WPI socket with the center hole filled in with epoxy or something).


----------



## runeight

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_It is indeed discontinued by Toshiba._

 

I thought that Linear was making these parts now. I must have this wrong though.

 In any case, other jfets can be used such as 2N5460. Their performance will not be as good but they will work with a few resistor adjustments. There are probably others in the J series like J177(??) that might also work.


----------



## spritzer

Here is one way to make the WPI sockets 5 pin only:





 I have no idea where one could get those plastic plugs but I found a bag of them. I think they were used to plug holes for the shelves on bathroom interiors or something like that...


----------



## ericj

Yeah, linear systems seems to only be making the N-channel parts. 

 So long as builders have options if they can't find the ideal part, I'm satisfied. 

 Thanks for looking into it.


----------



## runeight

Has Toshiba offered a newer, replacement for this part? It seems to be very popular and I am wondering why they've dropped it.


----------



## runeight

Actually, the 2SJ103 would probably be the best replacement. Will still require a resistor change in the tail resistors. I think the 2SJ103 is in current production.


----------



## spritzer

I can get the 2SJ103's here locally so I'll try them out if there are any issues with the 2SJ74's I bought off ebay. I've also put in the order to Mouser but one of the mosfets for the PSU are on backorder so it may be another two weeks before I get the parts.


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Actually, the 2SJ103 would probably be the best replacement. Will still require a resistor change in the tail resistors. I think the 2SJ103 is in current production._

 

nope, Linear does not make any p-channel JFETs.

 The 2SJ103 is not as quiet and has low Gm. Looks like you need 6 or so to equal one 2SJ74? Also, the junction capacitance differs. The good thing is, they are higher voltage parts. There's a reason people hoard 2SJ74...

 What about the Fairchild/Siliconix J271:

http://www.fairchildsemi.com/ds/J2%2FJ271.pdf


----------



## runeight

Yes, that might be a better part. Is there a spice model for it anywhere?


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Yes, that might be a better part. Is there a spice model for it anywhere?_

 

.MODEL J271_XN PJF(Beta=1.6m Betatce=-500m Rd=1 Rs=1 Lambda=25m Vto=-2.519 Vtotc=-2.5m Is=461.5f
 + Isr=4.402p N=1 Nr=2 Xti=3 Alpha=32.54u Vk=393.2 Cgd=10.83p M=278.9m
 + Pb=1 Fc=500m Cgs=15p Kf=0.6206f Af=1)

 .MODEL J310_XN NJF(Beta=3.384m Betatce=-500m Rd=1 Rs=1 Lambda=17m Vto=-3.409 Vtotc=-2.5m Is=193.9f
 + Isr=1.881p N=1 Nr=2 Xti=3 Alpha=7.533u Vk=74.1 Cgd=6.2p M=464.7m
 + Pb=1 Fc=500m Cgs=6.2p Kf=4.634e-002f Af=1)


----------



## runeight

Thanks. Better, but the 2SJ74 still outperforms it. As we know.


----------



## luvdunhill

I think that's as good as you're going to get... The fact you can get them at Mouser is very convenient, and they are relatively new design. 

 Also, for the PSU caps, I'd consider the CDE 450V snap-in caps, or even the CDE 500V caps sold at Mouser. They are comparable to the Panasonic caps and measured at a higher temperature. Furthermore, I think I'd go with smaller capacitance values, just to make this thing a little safer.


----------



## ericj

Thanks guys. I'm just trying to identify potential roadblocks that might discourage people from attempting a build. 

 I know we're not going to have an amp with all parts sourced from a single vendor (unless someone sells kits) - I just want to keep the acceptance factor high. 

 We should specify the best part, and almost everyone will use it, but i think some people are wary of building amps that require rare parts if there are no clear alternatives to the original specified parts. 

 I have to admit that there are probably people who would be better off discouraged from attempting a high-voltage build, and here i am shouting from the, er, forum, that anyone who'd be comfortable building an HV tube amp - or at least succeded in building something like the SOHA II - probably has the skills needed to build this one without dying, and should absolutely join the fold and heat up their soldering iron.


----------



## runeight

Yes, there is a lot of energy in these caps.

 We can reduce their size with attendant increase in ripple or Zo of the passive regulator.

 The nature of the amp, however, helps us. With perfect parts there would be no dynamic current draw at all from either PS. The tail CCS would keep that input stage constant and the phase of the output stages would make their draws exactly cancel. Even with real parts the dynamic current requirements are not that large. Which means that we probably don't need a super regulator. Which means that the last cap can be reduced substantially. I don't know about the first filter cap though. It still needs to handle the input ripple.

 But, we can try lots of things if the amp is worthy of the effort.


----------



## wiatrob

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Thanks guys. I'm just trying to identify potential roadblocks that might discourage people from attempting a build. 
SNIP
 or at least succeded in building something like the SOHA II - probably has the skills needed to build this one without dying, and should absolutely join the fold and heat up their soldering iron._

 

As someone who bears a resemblance to that description 
	

	
	
		
		

		
			





: my 2 cents.

 Multiple vendor sourcing would not be an issue for me, if the parts combination were more synergistic. Considering the projected cost of the amp and the prices of the headphones they are going to drive, the extra shipping isn't an issue.

 There will always be a class of newly minted intermediate builders willing to step up to more complex (er. dangerous) designs, with a likely to desire increase perceived performance more boutique-y or 'burlier' parts.

 The ideas of flexibility that has been expressed here could lead to two tiers of build on the same board - lower capacitance for a 'safer' (tho not much so) build, and higher cap options sound good.

 Your analogy to the SOHAII is a good one - the build philosophy that seems to be settling out of this discussion seems more in line with that design, rather than a 'bare bones' SSMH - type. Still affordable, but (hopefully) with a level of perfromance fitting to the headphones being driven.


----------



## ericj

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_As someone who bears a resemblance to that description 
	

	
	
		
		

		
		
	


	




: my 2 cents.

 Multiple vendor sourcing would not be an issue for me, if the parts combination were more synergistic. Considering the projected cost of the amp and the prices of the headphones they are going to drive, the extra shipping isn't an issue._

 

It's not so much that - but what of, say, our kiwi friends? 

 What if someone still wants to build one of these in 10 years?


----------



## runeight

These are all really good points. Having release a few amps now I am keenly aware of the need for global accessibility and parts alternatives.

 I just hope that spritzer's prototype leads to good results.


----------



## spritzer

Most of the parts are available from Mouser and those that aren't are easy to source. Here's to hoping that it will sound good...


----------



## Fitz

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_What if someone still wants to build one of these in 10 years?_

 

Or more importantly, if someone needs to _repair_ one down the line.


----------



## luvdunhill

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Most of the parts are available from Mouser and those that aren't are easy to source. Here's to hoping that it will sound good... 
	

	
	
		
		

		
		
	


	


_

 

My goal would be all parts from Mouser except tubes and sockets, hence the JFET and cap recommendation.


----------



## spritzer

Good point, I never even though about the caps so it's good to have somebody paying attention. 
	

	
	
		
		

		
		
	


	




 In other news I did some work on the amp today and fitted the tube sockets (chassis type as I don't have any PCB units) and hooked up the filament wires. I'll also start on the PSU if I have the time as I have the main caps and enough parts to build the bias supply.


----------



## ericj

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Good point, I never even though about the caps so it's good to have somebody paying attention. 
	

	
	
		
		

		
		
	


	




 In other news I did some work on the amp today and fitted the tube sockets (chassis type as I don't have any PCB units) and hooked up the filament wires. I'll also start on the PSU if I have the time as I have the main caps and enough parts to build the bias supply._

 

You mean you don't have a stack of BH power supplies on the shelf above your workbench? 

 my image of you is shattered . . . just shattered . .


----------



## Sherwood

Birgir, do you even have "Mjolnir" engraved into your soldering station? I too am heartily disappointed.


----------



## spritzer

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_You mean you don't have a stack of BH power supplies on the shelf above your workbench? 

 my image of you is shattered . . . just shattered . ._

 

I do have a stack of burned out BH psu's if that makes you feel any better. The plan is to build the amp like others would do so that means the stock PSU. I could whip up a BH PSU in 20 minutes but without the parts needed for the amp it's not needed. 

  Quote:


  Originally Posted by *Sherwood* /img/forum/go_quote.gif 
_Birgir, do you even have "Mjolnir" engraved into your soldering station? I too am heartily disappointed._

 

...and ruin my Metcal!!??!! You sir are mad... mad I say!!


----------



## audionut

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_For the stated budget, I do not really think there is much choice other than 2x rk27, or something like this, though it is $50, plus shipping. I do have a balanced DACT, but it was $186, iirc.

 The reason I almost always ues 2x attenuation is for the event of channel imbalance between channels (assuming no imbalance between + / -)._

 

Pabbi1, Runeight, I'm very interested in building something like this, but have a question. Am I reading these posts right and seeing u would need 2 2 gang stereo pots? I've already built the Bijou, 3 channel Beta 22, CK2III, etc, all of which u use just one 2 gang pot if you're not going balanced. Does a stat amp such as the one being discussed need 2 stereo pots, and if so, how exactly would that be wired. Thanks.


----------



## spritzer

The amp can be used with a two gang pot if you want to use it SE. If you wanted to use in balanced then you need either a 4 gang pot or two 2-gang pots.


----------



## ericj

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_The amp can be used with a two gang pot if you want to use it SE. If you wanted to use in balanced then you need either a 4 gang pot or two 2-gang pots._

 

Wait a minute. I thought we'd just discussed how the amp behaves like a phase splitter and outputs differential even if you're grounding the negative input. You just get half as much gain. 

 But yeah, in that scenario, you could use a single 2-gang pot. 

 I'm debating for myself whether, if i were to build one of these, I'd bother to feed it with one of the various balanced line driver projects that are out there.


----------



## spritzer

You don't need any SE-XLR converter but if you want to run the amp balanced then you need a 4 gang volume control. Whether that is a single unit or two 2-gangs doesn't matter. The amp I'm building will have a single 2-gang pot and RCA inputs only as I don't have any balanced sources.


----------



## ericj

If the input is SE, and we're using a 4-gang pot or two 2-gang, does that mean we just float the input ground by connecting it as though it is the negative signal? 

 You mentioned some transformers early in the thread - what's the price range for an acceptable passive se-to-balanced circuit?


----------



## runeight

If you use an SE input then connect to one of the inputs on each channel and ground the other inputs (i.e., connect to In+ and ground In-). The ground from the source goes to the amp ground too.


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_If the input is SE, and we're using a 4-gang pot or two 2-gang, does that mean we just float the input ground by connecting it as though it is the negative signal? 

 You mentioned some transformers early in the thread - what's the price range for an acceptable passive se-to-balanced circuit?_

 

About $100 US. I'm a fan of the Cinemag CMLI-15/15BPC, which I think sounds as good as the more costly Jensen. 

 The Jensen website has pricing if you're interested:

WELCOME TO JENSEN TRANSFORMERS, INC.

 With the GBP disparity against the USD, I'll probably try the Sowter units sometime soon. Even with shipping to the US, they are comparable to the Jensen pricing.

 I'm not sure if there are other budget options. Our own dsavitsk might know


----------



## ericj

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_If you use an SE input then connect to one of the inputs on each channel and ground the other inputs (i.e., connect to In+ and ground In-). The ground from the source goes to the amp ground too._

 

So in that configuration is the output single-ended or not?


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_So in that configuration is the output single-ended or not?_

 

the output must always be "balanced" for the electrostatic principle to work.


----------



## ericj

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_the output must always be "balanced" for the electrostatic principle to work._

 

That's what i thought.


----------



## runeight

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_So in that configuration is the output single-ended or not?_

 

When driven properly by SE the O/P will be balanced at half the gain.


----------



## ericj

Alright, sorry for the fuss. The way spritzer worded some of his posts was somewhat alarming.


----------



## HeadphoneAddict

So, if I already own the Jensen Transformers XLR to RCA, then that would let the amp run in balanced input mode with a single ended source?


----------



## spritzer

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Alright, sorry for the fuss. The way spritzer worded some of his posts was somewhat alarming._

 

It's not my fault I'm always sleep deprived...


----------



## wiatrob

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_It's not so much that - but what of, say, our kiwi friends? 

 What if someone still wants to build one of these in 10 years?_

 

True, true...

 Sorry, Gotta learn to think globally here... And less extemporaneously as well


----------



## runeight

Gents, while spritzer is waiting for parts, here's more stuff to noodle over.

 If we lose the 2SJ74s then we'll have to use, as luvdunhill points out, jfets with lower transconductance (less gain). We can reduce the size of the source resistors to get more gain with an increase in distortion. Or we can add gain somewhere else. I avoided this with the first design to try to comply with the "keep it simple and cheap" requirement. But adding more gain is not that bad.

 Here's a possibility. The new 2SC2705s (attached at the base to 1k resistors) are the new gain stage. Their presence substantially increases the gain. I've added some NFB to bring the gain back to about 600. The NFB effectively increases the HF bandwidth and the speed of the amp.

 luvdunhill will be happy to see the Cdom caps back right where they need to be to rolloff the HF response.

 I could be wrong, but I think this version will be stable in a real implementation and it's still not that complicated.

 The bandwidth when driving 50pf goes from about 96kHz (1db) to about 136kHz (1db). These are theoretical numbers but the real bandwidth will definitely increase and probably by amount like this.


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Gents, while spritzer is waiting for parts, here's more stuff to noodle over.

 If we lose the 2SJ74s then we'll have to use_

 

Do we keep the pair of 2SJ74's by the inputs?


----------



## runeight

Sorry, what I meant is that if we can't source the 2SJ74s we'll have to use lower performance jfets such as the 2SJ103 or the J271 that luvdunhill suggested. But they go in the same place in the input diff pair.


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Sorry, what I meant is that if we can't source the 2SJ74s we'll have to use lower performance jfets such as the 2SJ103 or the J271 that luvdunhill suggested. But they go in the same place in the input diff pair._

 


 Ah - Understood - I edited my original post as it sounded a little flip.


----------



## runeight

And, here's an alternative, probably faster way to do it.


----------



## runeight

And, more food for thought for you all . . .

 The main component that limits the speed of the amp now are the tubes. Their plate resistance is significant and really slows down the amp when driving capacitors.

 Put HV mosfets in place of the tubes and the amp would probably scream. I bet even the version that spritzer is building would scream.


----------



## pabbi1

What do the mosfets do relative to cost?


----------



## spritzer

I just got massive heatsinks from Marc so I'm up for some mosfets. No word from Mouser on the order yet so I'll just start populating these Blue Hawaii boards then. Mmmm PRP resistors....


----------



## pabbi1

Boy, I hate losing tubes - this might be where there is a fork in the road with alternate designs? Can mosfet and tube routings be accomodated, and controlled with a jumper?


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Put HV mosfets in place of the tubes and the amp would probably scream. I bet even the version that spritzer is building would scream. 
	

	
	
		
		

		
		
	


	


_

 

heh, that's funny I still haven't replied to your e-mail and this was exactly what I was going to say


----------



## runeight

Folks, I hope that spritzer won't get mad at me, but I keep evolving the way the amp could work.

 First, I am so stupid sometimes. There is a much better CCS for the tail. I used this ring-of-two type on the SOHA II and in other designs, but I was trying to preserve the KSA1156. I think it will have no problems here.

 Changing the locations of the compensation caps really helps the bandwidth along with adding more feedback (as always if the amp is stable).

 Notice that this version uses 2SJ103. J271s will behave about the same.

 Schematic:






 And just so you'll see what I mean, here is the theoretical response curve. Will never happen in really life, but indicates a fairly fast amp if it doesn't oscillate. And this is with 6S4s at the output.

 Amp is driving 50pf:






 The right edge of the graph is 500kHz. So the amp is 1db down at 3Hz and 1db down about 450kHz.

 I wonder now what a real one would do. . .


----------



## pabbi1

Better all the time - is this more or less what is being proto'd?


----------



## mypasswordis

runeight, you're awesome. If this is completed before the summer, I will probably decide to build it. Could you post the graph showing driving a 150pF load? The newer Lambdas are spec'd at around 120.


----------



## spritzer

Nope, not mad but if you could draw up a BOM and send it to me then I can order the extra parts. It looks like my Mouser order is finalized so I may just build both amps for the heck of it.


----------



## runeight

Quote:


  Originally Posted by *mypasswordis* /img/forum/go_quote.gif 
_runeight, you're awesome. If this is completed before the summer, I will probably decide to build it. Could you post the graph showing driving a 150pF load? The newer Lambdas are spec'd at around 120._

 

Driving 150pf. Please remember that this is a sim. Real life must be tested.






 1db point is about 350kHz.

 I'll see if I can sim the slew rate. That's usually a good indicator of stability, ringing, etc.


----------



## Keithpgdrb

I'm one of the lurkers. all this tech talk is a bit daunting. will this amp be able to drive the normal bias lambdas? I know that was in the original idea. I'm trying my best to follow along the development. This is a great process. gotta learn somewhere.


----------



## spritzer

The amp idles at 0v and the bias is a completely separate unit so it will be compatible with all normal bias headphones.


----------



## runeight

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Better all the time - is this more or less what is being proto'd?_

 

spritzer is prototyping an earlier version. But, if I get him a BoM maybe he can try this one too.

 The theoretical slew rate into 50pf is about 70V/us with a little overshoot on a 50kHz square wave with a 1ns edge. This is not spectacular, but it isn't bad.

 There is a way to lower the output impedance of the amp. That would be to add some followers on the O/P. Similar to the follower arrangement in the SOHA II (except a high voltage version) and a variation on what KG has done in the current domain amplifier (see headwize). In fact, that current domain amp is very nicely done front to back.


----------



## luvdunhill

Alex:

 slightly unrelated, but is it possible to get a reasonable output stage using a split load phase inverter? Then you could get away with a single triode for each channel, or if some magic tube existed, a dual triode for both channels. I just read up on this and was curious if it could be put to good use in an electrostatic amplifier... 

http://www.aikenamps.com/cathodyne.pdf


----------



## runeight

Well, one problem with the cathodyne (split load, concertina) phase splitter is that it has no gain. A long tail splitter supplies gain. So if you use a split load all the gain must come from somewhere else.

 The other feature is that the split load does not lend itself easily to a diff amp front end (balanced operation). It can be made to work, but it's more complicated.


----------



## runeight

You know, amp design is an evolutionary process . . .

 As I think on each step of this amp I keep asking how to make it faster. The ways to do this are pretty standard - reduce capacitances, increase internal load impedances, increase gain and use NFB while keeping the amp stable.

 So, looking at the latest amp the next logical step is to put followers on the output. This is because the Zo of the tube stage will be very high. Think of this as a high resistor in series with the load capacitor. The higher the Zo the slower the amp can charge and discharge the capacitor through the resistor.

 A follower, however, has a low Zo and it can charge/discharge much more quickly meaning that the slew rate goes up quite a bit.

 Thinking on this I just simply designed a follower output stage. Naturally, to reduce THD in the follower stage it needs a CCS load. And BJTs make good followers.

 Here is the result:







 The added expense is not that high. Any 900V BJT can be used. I chose a Fairchild one because it seems to be easily available in the US.

 Now, as you look at this, if you are familiar with other designs you will see great similarity. That's because there are not that many ways to do these things. For example, if you go look at Kevin Gilmore's Current Domain amp you'll see that it uses a similar O/P follower with a different type of CCS. If you go look at the SOHA II amp (Cavalli Audio) you will see a nearly identical O/P follower buffer.

 So what does this do? It vastly improves the slew rate of the amp into 50pf. Furthermore, not done on the schematic, the tube operating point can be changed so that the tube drives a higher load resistor and, thus, shows less THD.

 I don't know where else to go with this design. I have sim'd KG's current domain amp (a really, really well done amplifier - hard to see why one would do something else) and have compared this amp's performance to it. This amp (theoretically) performs better in terms of speed and slew rate. But I always must remind everyone about not accepting sim results as absolute results. They, however, often very good indicators when you use them correctly.

 Finally, I am thinking that we can dispense with the input caps.

 I think this is about it for me gents. I don't know if we've make a <$300 stat amp. But I think we have.


----------



## spritzer

I like what I see.


----------



## DouglasQuaid

It was neat seeing you take a really simple fet input tube output amplifier and add continual small stages to it until it becomes what might be beast of an amp. I'm currently sourcing parts for Kevin's current domain amp, but it'd be neat if your amp matches it for less cost. I look forward to hearing spitzer's feedback. I'm assuming the tube used won't offer as strong a voice signature as most amps since this is a hybrid design with feedback, which I find to be a good thing. It also helps that this only uses a +/- 350 power supply, instead of requiring custom or multiple transformers.


----------



## pabbi1

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_I think this is about it for me gents. I don't know if we've make a <$300 stat amp. But I think we have. 
	

	
	
		
		

		
		
	


	


_

 

Well, time for proto boards, BOM, and build, eh?


----------



## MrMajestic2

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Well, time for proto boards, BOM, and build, eh?_

 

I'm up for it. Gimme a board and a BOM and I'll build that sucker


----------



## spritzer

Alex just sent me the BOM but I haven't had a chance to look at it yet. I'll go ahead and build the prototype as planned so work on the boards can go on as planned. As Alex pointed out to me we have entered into the need for heatsinks now so that complicates things a bit but it's no Blue Hawaii levels of heat.


----------



## pabbi1

That has always been the rub with the higher end designs - the enormous heat sinks required, making the build more intimidating than expensive... simplicity needs to be considered, minimizing anything more than onboard to-220 heatsinking, if possible. Not everyone has a large, ready source (or collection) of heatsinks.


----------



## runeight

Good point. This will be one of the nice features of this amp. The followers are not required. Leave them off and take the output from the plates of the tubes and you have the previous version of the amp, which performs very well. Put them in if you want the extra performance for the extra effort and heat.

 On a PCB this would be a simple matter of leaving out all of the follower components and wiring a few jumpers.

 How's that?


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Well, one problem with the cathodyne (split load, concertina) phase splitter is that it has no gain. A long tail splitter supplies gain. So if you use a split load all the gain must come from somewhere else.

 The other feature is that the split load does not lend itself easily to a diff amp front end (balanced operation). It can be made to work, but it's more complicated._

 

I guess I was thinking about keeping things simple. A high Gm European pentode running in troide mode for gain and an input transformer for both balanced and single-ended input.


----------



## amphead

Very interesting indeed Runeight!


----------



## runeight

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I guess I was thinking about keeping things simple. A high Gm European pentode running in troide mode for gain and an input transformer for both balanced and single-ended input._

 

Yes, could be done. The splitter could capacitatively couple to a pair of triodes driving the load. The split load splitter, however, doesn't like to see low loads. Something will have to be put between the splitter and the O/P triodes to achieve decent bandwidth. How much gain is needed? It might be better to use the pentode like a pentode.


----------



## runeight

Quote:


  Originally Posted by *MrMajestic2* /img/forum/go_quote.gif 
_I'm up for it. Gimme a board and a BOM and I'll build that sucker 
	

	
	
		
		

		
		
	


	


_

 

OK. 
	

	
	
		
		

		
		
	


	




 A board might look something like this.

Poor Man 3.03

 And a 3D might look like this.


----------



## Beefy

That looks like it needs off-board heatsinks......? Aside from price, that really is a factor that would begin to push this out of reach for many.

 If followers do improve the performance by _that_ much, then it would be really great to be able to have them with on-board heatsinks. How much heat dissipation would we be talking about?


----------



## HeadphoneAddict

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_That looks like it needs off-board heatsinks......? Aside from price, that really is a factor that would begin to push this out of reach for many.

 If followers do improve the performance by that much, then it would be really great to be able to have them with on-board heatsinks. How much heat dissipation would we be talking about?_

 

You just missed it.

 Pabbi1 said, "That has always been the rub with the higher end designs - the enormous heat sinks required, making the build more intimidating than expensive... simplicity needs to be considered, minimizing anything more than onboard to-220 heatsinking, if possible. Not everyone has a large, ready source (or collection) of heatsinks."


 and runeight said, "This will be one of the nice features of this amp. The followers are not required. Leave them off and take the output from the plates of the tubes and you have the previous version of the amp, which performs very well. Put them in if you want the extra performance for the extra effort and heat.

 On a PCB this would be a simple matter of leaving out all of the follower components and wiring a few jumpers."


----------



## runeight

The TO220 packages burn about 3W each. Perhaps there would be board-based heatsinks. I have not looked at the wide variety available and there might be one or two that have the thermal curves needed.

 But, remember, that the no-follower version would be what we set out to make, that is, the basic under $300 good performing amp. Adding the followers puts the amp into another category, but it doesn't ruin the simpler version of the amp. And, if someone built the simple version and liked it, he can always upgrade later.

 Edit: I see that HeadphoneAddict was a few milliseconds ahead of me.


----------



## Beefy

Quote:


  Originally Posted by *HeadphoneAddict* /img/forum/go_quote.gif 
_You just missed it._

 

I saw all that, but why not shoot for the best of both worlds?

  Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_The TO220 packages burn about 3W each. Perhaps there would be board-based heatsinks. I have not looked at the wide variety available and there might be one or two that have the thermal curves needed._

 

Unless my calculations are screwed up, 3W doesn't seem like very much. According to AMB's website, the cascode MOSFETs on a B22 at ±30V see 22V, and at 160mA quiescent current dissipate 3.52W. That is perfectly fine with just a 1.5" heatsink.


----------



## runeight

You know, you might be right.

 Looking at the Wakefield data sheet for their 637 series, the typical TO220 vertial heatsink it says that:

 The 1.5" tall version has a temp rise of 65C for 6W (32.5 for 3W)

 The 2" version has a temp rise of 55C for 6W (27.5 for 3W)

 The 2.5" version has a temp rise of 48C for 6W (24 for 3W)

 So, if the ambient is 25C then we'll have 57.5C, 52.5C, and 49C in best case convective cooling, etc, etc

 I think I would use 2" version minimum because there will be temp rise in the box. 2" is not that bad really.

 Edit: I forgot.

 If we use the 647 series then a 1" tall heatsink will rise 37C for 6W (18.5 for 3W). This is well within board heatsinking territory.

 Glad you brought it up.

 Easy enough to add those heatsinks to the board. Just takes more space.


----------



## Beefy

Score one for persistent ignorance


----------



## wiatrob

Hmmm, where did these 64A's come from? How serendipitous


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_So, if the ambient is 25C then we'll have 57.5C, 52.5C, and 49C in best case convective cooling, etc, etc_

 

well, don't forget you have more heat sources nearby... the tubes 
	

	
	
		
		

		
		
	


	




 I think things will get pretty toasty...


----------



## runeight

Wiatrob, Pabbi1 and luvdunhill MADE me use the 6S4s. 
	

	
	
		
		

		
		
	


	




 Yep, it's going to get toasty inside this box. Here's the big board-mounted heatsinks. I've left them off the 3D so you can see the components, but the outlines are there.

 Are you guys through with me yet?


----------



## DouglasQuaid

Are the tubes meant to be mounted right next to those transistor heatsinks?


----------



## Beefy

Quote:


  Originally Posted by *DouglasQuaid* /img/forum/go_quote.gif 
_Are the tubes meant to be mounted right next to those transistor heatsinks?_

 

We know the transistors sit at 3W...... so we need to know how much heat do the tubes dissipate?


----------



## lordvader

Aren't the tubes going to be mounted on the opposite side of the board, for some sexy top mounted tube pr0n ?


----------



## runeight

Yes, on this board the tubes are very near the heatsinks.

 The tube heaters will burn 3.6W and the plates 1.5W for about 5W per tube. Plus 3W per power transistor. For a total of 22W per channel.

 But gents, swinging 600Vpp with enough juice to drive 150pf burns power. It just does.

 Of course the tube heaters waste 10W that's true, but this is the price of using retro technology. 
	

	
	
		
		

		
		
	


	




 I arbitrarily sized the board. It's 130mm x 100m. Bigger board would give more ventilating space. Or as lordvader suggested, mounting the tubes on the bottom side of the board.

 But, we can make this in any form factor that the folks on this thread want to build.


----------



## pabbi1

I think air wire to get the tubes out of the case is best, as the undermounted components in this case have a lot of heat - here is something I did once, with tubes and Mosfets on top... it was in this case. For this build, given the heat, I think a bigger box will be required.

 Alex, this has really been a treat to watch you work this out... but, what about the psu board?

 Oh, and having a collection of 40+ 6s4a, I might have a few to spare, but, they are $3.95 (plus shipping) from www.Tubedepot.com, which has $3.95 FedEx saver for all tube orders. So, a pair will run about $12.

 Power tubes may be pricier, as there are ez80/ 6bw4 / ez81, which will be more like $20 for a tube. Alex, will one psu drive 2 amp boards?


----------



## holland

I'm impressed. I like the final design very much. Now if only $1K would fall into my lap so I can buy stats too.

 Can the followers on the left end be flipped around to the other side, so the whole thing can be top mounted and the followers put onto a top mounted heatsink as well? Though, I think the earlier layout would allow for external heatsinking (sides) and topmount the tubes without airwiring.


----------



## spritzer

It does look a bit like the Headamp KGSS now. 
	

	
	
		
		

		
		
	


	




 Two suggestions for you Alex though, could you add some ventilation holes underneath the heatsink fins and perhaps remove the ground plane underneath them unless you want to have them grounded.


----------



## runeight

How's this? More room and smaller ground plane.


----------



## spritzer

Brilliant! I may be a bit neurotic about heat but some ventilation holes through the PCB couldn't hurt.


----------



## Beefy

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Brilliant! I may be a bit neurotic about heat but some ventilation holes through the PCB couldn't hurt. 
	

	
	
		
		

		
		
	


	


_

 

There were also originally some holes under the big power resistors. I'm sure it will all come out in the wash


----------



## wiatrob

Ahh, the Cavalli symmetry returns! Are you not sleeping much lately, Alex?


----------



## runeight

No, I am not sleeping that much. Something about an electrostatic amp that keeps me awake. 
	

	
	
		
		

		
		
	


	




 Holes are easy. But, I had to take them out from under the resistors because traces are under there now.

 Here's the pdf:

Poor Man's 3.02

 If anyone seriously wants to make board I'll send you the eagle files. But I think a proto demonstration build would (spritzer's perhaps) is a good idea.

 Edit: the connector labels on the PDF are wrong. Later.


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_No, I am not sleeping that much. Something about an electrostatic amp that keeps me awake. 
	

	
	
		
		

		
		
	


	


_

 

Hmmm... understood - they don't call them the Stax Mafia without reason!

  Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Holes are easy. But, I had to take them out from under the resistors because traces are under there now._

 

I think if the resistors are flown they'll have some circulation - maybe scootch the films outwards a teeny bit, allowing room for boutique cousins


----------



## pabbi1

Are we pretty well there with an iron spec, and might we discuss alternatives?


----------



## MrMajestic2

Did we land on a transformer to use for this project?


----------



## runeight

Transformer should be:

 260-0-260/60mA for tube only

 260-0-260/120mA for follower version

 6.3V/2.5A for four 6S4s

 Seems like there is an rcore that fits this perfectly.


----------



## dBel84

R0080-036

 if only I had stats, I would be all over this 
	

	
	
		
		

		
		
	


	




 ..dB


----------



## MrMajestic2

$34 USD is not too shabby. I can live with that.


----------



## jcx

for 230 Vac out in 115 Vac line locales a pwr xfmr can be made with the "poor man's isolation transformer" approach

 2x identical 115/230 pri transformers with their secondaries connected together (using EI "international" xfmrs and grounding the CT gives good hf shielding too)

 with input wired for 115 line you could connect the output for 230

 for full bridge CT output you could use 3 transformers - each ouput side xfmr 1/2 the VA rating



 I am more than a little concerned by the nonexistent Safety discussion here - the operating currents for higher C cans and high slew rates are lethal

 even lower 6-10mA fault currents could cause involuntary muscle contractions preventing the victim from being able to help themselves (the electrical safety charts show women more susceptible -who knows how much additional safety factor if children could get at the equipment - keylock power switch?)

 wiring, device failures could put way too much stored energy on outputs with the usual over sizing of PS C - better to use less C for safety and make up the difference with better regulation?

 perhaps GFCI on each driver could go a fair ways to improve safety - if sw location and relay DC? blocking V can be worked out


----------



## pabbi1

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_R0080-036

 if only I had stats, I would be all over this 
	

	
	
		
		

		
		
	


	




 ..dB_

 

Yep - ordered one about 3 hours ago... good enough excuse to start looking at stats - Koss 950 are a good new production option.

 Regarding safety, is there anything lacking here moreso than other electrostatic amps, and, if so, can you explain them in detail? Asked mainly because I have never heard anyone zapping themselves with an ES amp. Ever. Not even a Darwin Award recipient (nor candidate).


----------



## runeight

All good points by jcx. Since I am not a stat owner nor do I have much experience, I don't know what others do. Looking at some other DIY amps I don't see very much, if anything, dedicated to this kind of safety.

 It is definitely true that the the voltages, speed, and energy storage in this amp are deadly. I've been here before in physics labs. 

 So, I could use the education too if someone would be kind enough to provide it.


----------



## spritzer

This amp will never be an easy project, no matter how we spin it so it shouldn't be undertaken by anybody that isn't comfortable working with high voltage. That said I've been zapped by a few ESP amps (mostly while working on the phones) and I'm still around. 
	

	
	
		
		

		
		
	


	




 The bias is completely benign as it can't muster up any current but the amp at full output could hurt you. The caps will be quick to discharge once the amp is off and if something were to come loose inside the amp then the chassis ground should take care of it. There is no way to be zapped by the phones, no matter what. 

 Ok.. looks like I'll need to buy a new transformer. 
	

	
	
		
		

		
		
	


	




 I need some silver wire for the BH so it's all good but this may become costly.


----------



## jcx

I would be happy to find out commercial electrostatic headphones qualify as "double/reinforced insulated" for the peak V speced but I haven't seen convincing safety info on manufactures' web sites - anyone have pointers or more info from user manuals?

 Obvioulsy constructors should be experienced/informed, very careful, and GFCI on the workbench power might help too


----------



## pabbi1

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Now if it were me I would add these two caps. They improve the ripple rejection and they slow down the rise of the HV to give the tube a chance to warm up. 
	

	
	
		
		

		
			








_

 

So, is this pretty much the power supply, or do you need some quick proto answers on this? Board files available as well? And, I happen to have some of those leftover 680uF 450v caps from the Bijou - can I mix 2 in with two of the 470uF panasonics, and where might make sense? Otherwise I have 4 Panasonics.


----------



## holland

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Are we pretty well there with an iron spec, and might we discuss alternatives?_

 

I'm curious to know what you have in mind?


----------



## scompton

I assume 6F4 and 6F4A are not interchangeable. With a quick search, I'm finding more 6F4As.


----------



## runeight

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_So, is this pretty much the power supply, or do you need some quick proto answers on this? Board files available as well? And, I happen to have some of those leftover 680uF 450v caps from the Bijou - can I mix 2 in with two of the 470uF panasonics, and where might make sense? Otherwise I have 4 Panasonics._

 


 Yes, that's what I had in mind except that the 2SC2705/2SA1145 should be replaced with ZTX458/ZTX558. These are 400V transistors. Their Vceo is needed because at turn on the 100u caps are discharged and the BJTs see the full supply voltage.

 We can probably relieve the larger caps somewhat. It just depends on the ripple rejection of the amp. We will get a lot of common mode rejection, but imbalances in parts will make this less than perfect. How much less I don't know how to calculate at the moment. And this is where an experiment might be in order.

 A simpler version would just replace the CCSs with resistors. This would eliminate transistor overvoltage problems and might do just as well for this amp. Something like 7k5 at 1/4W replacing the entire CCS gadget from the drain of the mosfet to its gate.

 Another really good protective device would be a zener between the gate and the source. This prevents blowing the GS capacitor if the O/P is ever shorted.

 Shall I draw another schematic? Board will be trivial.

 We need to think on this.


----------



## pabbi1

Yes, please safety first, then additional simplicity where possible, but it does look like time to discuss the psu. And, please, yes to another schematic.

 In general, can I get a range on board size(s)?

 Since the rcore will take two weeks from HK, I was looking at Antek IT250, where this is $39 shipped US (cheaper after shipping than the Chinese rcore). The concern is the secondary ma is sufficient, or not, while the heater amperage looks fine.

 The Hammond alternatives (270ex, et al) are 275v, and ~$60 shipped, which would require some beefy resistors to dissipate down that excess voltage.


----------



## pabbi1

Quote:


  Originally Posted by *scompton* /img/forum/go_quote.gif 
_I assume 6F4 and 6F4A are not interchangeable. With a quick search, I'm finding more 6F4As._

 

6*S*4a... 

 The 6s4a has a 50v higher voltage (plate, i think), 400v vs 450v, but may not at all matter here.


----------



## DouglasQuaid

The PSU you previously suggested resembled Kevin's Fet supply with a compensation cap. I haven't seen too many complaints about its performance.

 As for safety... You're going to be working with 700V voltage swing either way. And without output caps, you will have to make adjustments to potentiometers in the circuit with the amp powered on.

 I have been zapped once at 400V. It was quite enjoyable, honestly.


----------



## runeight

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_R0080-036

 if only I had stats, I would be all over this 
	

	
	
		
		

		
		
	


	




 ..dB_

 

Does anyone have one of the rcores that dBel84 has linked to?? If you do and if it's possible could you please measure the DC resistance of the 260-0 winding (half of the secondary)

 Thanks.


----------



## runeight

Double post. See next.


----------



## runeight

Gents, listening to your various requests, this is one simple way to eliminate the very large capacitors. The only way to do this is active regulation (as in the first PS that I drew) or capacitor multiplication. I chose the latter for this idea.

 There are quite a few zeners. Some of you may gag. However, the common mode rejection of the amp should eliminate some of the zener noise.

 Mosfets are buring less than 1W each. Small heatsinks.

 Notice the very small film cap at the output. No big cap there to discharge directly into the amp. This cap is there just to shape the high frequency response of the PS.






 I'm still not sure about the transformer spec. This needs more work.

 Edit: the ripple from this PS fully loaded at 60mA (both channels running followers) is less than 10uV. Reality won't be this good, but I think it should be good enough.


----------



## holland

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Does anyone have one of the rcores that dBel84 has linked to?? If you do and if it's possible could you please measure the DC resistance of the 260-0 winding (half of the secondary)

 Thanks._

 

171.3-171.6


----------



## runeight

Thanks!!! This means that the 260-0-260 rcore will not work in this PS because the voltage drops in the transformer will be too high.

 More slavery for you guys . . .


----------



## holland

nvm, not VCT.


----------



## pabbi1

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_R0080-036

 if only I had stats, I would be all over this 
	

	
	
		
		

		
		
	


	




 ..dB_

 


 Well, my invoice on this unit, with shipping, comes to $74, so Air Parcel is obviously not the cheapest solution. But, that is also almost twice the cost of the shipped Antek, and more than even a shipped Hammond (~$60 from Mouser, and a little less from Angela, for the US folk). 

 OK, so who all is in for prototyping? I can proto, but can't lead - I have 2 full projects in progress, with some approaching deadlines - and about $4k tied up. I already have a lot of the parts for this, so it is a cheap incremental for me, but, I simply cannot drive boards, etc.


----------



## MrMajestic2

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Well, my invoice on this unit, with shipping, comes to $74, so Air Parcel is obviously not the cheapest solution. But, that is also almost twice the cost of the shipped Antek, and more than even a shipped Hammond (~$60 from Mouser, and a little less from Angela, for the US folk). 

 OK, so who all is in for prototyping? I can proto, but can't lead - I have 2 full projects in progress, with some approaching deadlines - and about $4k tied up. I already have a lot of the parts for this, so it is a cheap incremental for me, but, I simply cannot drive boards, etc._

 

I can proto as well.


----------



## spritzer

I'll probably end up running the amp off a Blue Hawaii PSU since I don't have a transformer that fits and my focus is to get this BH up and running ASAP.


----------



## ericj

I go (somewhat) offline for 3 days with bronchitis and look what happens . . .

 This has turned out better than i expected. Thank you, Alex.


----------



## runeight

You're welcome. I hope that we have an amp that works for everyone. 
	

	
	
		
		

		
			





 In the meantime, because spritzer is relentless - holes: 
	

	
	
		
		

		
		
	


	









 Is this enough holes??


----------



## spritzer

Me likes ventilation. 
	

	
	
		
		

		
		
	


	




 We could perhaps have some proto boards made? While I'm all for P-P it is a pain.


----------



## pabbi1

I am definitely in on a set of boards, just can't manage the buy.


----------



## runeight

I'm checking into the cost of boards. Probably ten of them to make five amps.

 Are there five takers out there. I think we have two at the moment.

 But I do want to say before we go any farther that while I have thought about this amp quite a bit and I have sim'd it every which way that I can think, it is still totally untested. It could fail for some as yet unseen reason. Or it could work like a charm. You guys will please be aware of the risks.


----------



## scompton

Is this a prototype board with a final board later? I want to build this amp, but I need more experience first, but I'm willing to buy boards if they're the only boards that will be made.


----------



## runeight

These would be proto boards. If they work out then I assume there will be enough interest for a larger production run.

 I think the current interested parties are Pabbi1, spritzer, and possible ericj. Have I missed anyone?


----------



## MrMajestic2

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_These would be proto boards. If they work out then I assume there will be enough interest for a larger production run.

 I think the current interested parties are Pabbi1, spritzer, and possible ericj. Have I missed anyone?_

 

Yeah, me.


----------



## runeight

Right. I remember now. I can't keep up with everyone.


----------



## pabbi1

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_I'm checking into the cost of boards. Probably ten of them to make five amps.

 Are there five takers out there. I think we have two at the moment.

 But I do want to say before we go any farther that while I have thought about this amp quite a bit and I have sim'd it every which way that I can think, it is still totally untested. It could fail for some as yet unseen reason. Or it could work like a charm. You guys will please be aware of the risks. 
	

	
	
		
		

		
		
	


	


_

 

Understood - one thing I would like is the ability to use bigger caps in the psu - while the 450v 470/680uf are overkill, I do have them onhand, and would like to see how they work, so can you leave the formfactor for these on the board? Oh, and though I am not zenerphobic (rimshot), can we make sure to lay them down, as tombstoning zeners on other projects was, well, not as visually intuitive as it might could be... finally, after mine is built, would you like to measure it?


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_...If they work out then I assume there will be enough interest for a larger production run._

 

Provided this sounds as good as the sim? 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_I think the current interested parties are Pabbi1, spritzer, and possible ericj. Have I missed anyone?_

 

Hand up! If' n you think I have enough experience. I also have fairly close access to a lot of 'stats ( if I prove to Larry that I won't blow any of them up!)

 I would also be willing to manage BOM updates...


----------



## runeight

If only everything sounded as good as the sims, I'd be a zillionare. 
	

	
	
		
		

		
		
	


	




 I guess this makes you number 5. You'll just need to get some HV chops so you don't kill yourself. This will really be dangerous.

  Quote:


 I would also be willing to manage BOM updates... 
 

Bless you my child.


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_If only everything sounded as good as the sims, I'd be a zillionare. 
	

	
	
		
		

		
		
	


	




 I guess this makes you number 5. You'll just need to get some HV chops so you don't kill yourself. This will really be dangerous._

 

I worked with nixies before I discovered this headphones thing... but I'll brush up on my tech and stay safe...


----------



## spritzer

Try not to lick the circuit boards. That's always a great start...


----------



## Keithpgdrb

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Try not to lick the circuit boards. That's always a great start... 
	

	
	
		
		

		
		
	


	


_

 

CRAP! thats always step 1 for me!!


----------



## Oublie

Any updates guys?

 Spritzer did you get the parts you needed for the proto build.

 Bias wise why not set it up for multiple bias i.e. 200v, 230, 580, and the koss and sennheiser bias setting. ac with a voltage multiplier and swapable zeners for voltage changes. quite a few parts but easy to build even i can build it 
	

	
	
		
		

		
		
	


	




 tube wise what the plan - i probably missed it , i've noticed a few adaptors out the to run different pin configs and different tubes such as 6sn's etc would the design be up to it?


----------



## wiatrob

We're getting closer. Design discussion is turning to 'let's build it!'

 The plan is to allow one fixed Stax Normal jack and one jack for any of the variety of the Pro/Koss/other voltages. Parts count is pretty manageable compared to other DIY amps 
	

	
	
		
		

		
		
	


	




 Design tube choice is 6S4 or 6S4A - other's choices will need to be addressed by those more knowledgeable...


----------



## Oublie

Cool,

 i definately want to build one of these when boards are available.


----------



## spritzer

The parts are on their way to me but they are sadly out of date compared to the new design so I'll have to order some more.


----------



## pabbi1

The other salient points are that boards are firming up, and will still be 2 weeks out for fab. Given a few weeks to sort issues, the first impressions of a pseudo final design are still about a month out, so there won't be much to talk about in the mean time.

 One issue the general group might contribute to is the transformer - other than the usual custom wound solutions (too expensive), anyone know of good alternatives in the 300-0-300v to 325-0-325v (120-150mA) range for secondaries, with 6.3v, 3A heater windings? Antek is a player, but Hammond (272dx) looks too pricey and sucks for casing in the given budget range. Other hidden gems would be most appreciated, being mindful of shipping, and delivery time. Vt4c looks great, until the shipping kicks in... 
	

	
	
		
		

		
		
	


	




 Other than that, the overall design is quite elegant, and a really moderate build for a stat amp - now the question is how will it sound? Stay tuned.


----------



## Oublie

Don't know if this is too expensive or not but here's a link to a local company.

Valve PSU Transformers, valve amplifier transformer, Antrim Transformers


----------



## wiatrob

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_...Vt4c looks great, until the shipping kicks in... 
	

	
	
		
		

		
		
	


	


_

 

I'll investigate pricing with Vt4c...


----------



## Vaughn

I've been following this thread with some interest...

 I don't currently own any electrostatics because I thought the amps I had were
 always holding me back sonically(SRM-303, SRM-T1S, T1W).

 I think I will definitely be on board to be a test pig for one of these once the 
 circuit is sorted.

 So, is it a pure tube unit as it stands or is it a hybrid?


----------



## pabbi1

Pure tube, other than some depletion mode Mosfets and passives.

 For perspective on iron, to make a $300 total cost objective, we are looking at Antek and Hammond alternatives, $50-75.


----------



## spritzer

It's a hybrid as the only tubes used are on the output.


----------



## pabbi1

Doh! never mind me... mixing up my builds.


----------



## runeight

Well, to be slightly more correct, it is a hybrid because it uses both tubes and transistors. The primary voltage devices on the O/P are the tubes with BJT followers to increase speed and lower the output impedance.

 Kind of a neat design actually. I like it. We shall see if it is successful in practice.


----------



## audionut

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Pure tube, other than some depletion mode Mosfets and passives.

 For perspective on iron, to make a $300 total cost objective, we are looking at Antek and Hammond alternatives, $50-75._

 

Would the Hammond 270EX listed here at Mouser for $53.27 work? 270ex I'm currently using it in my KGSS build. It uses a 275-0-275 main secondary, which gets me about 390V raw DC to my regulators. The KGSS uses + - 350V supplies. Seems this Hammond would work for this application. Just not sure if the heater windings on this particular Hammond would work for the proposed design.


----------



## HeadphoneAddict

I'll have to beg Wiatrob for help building me one


----------



## pabbi1

Quote:


  Originally Posted by *audionut* /img/forum/go_quote.gif 
_Would the Hammond 270EX listed here at Mouser for $53.27 work? 270ex I'm currently using it in my KGSS build. It uses a 275-0-275 main secondary, which gets me about 390V raw DC to my regulators. The KGSS uses + - 350V supplies. Seems this Hammond would work for this application. Just not sure if the heater windings on this particular Hammond would work for the proposed design._

 

Yes, that is one of our target supplies, as is the Antek AN-3T275, which is toroid, and easier IMHO for mounting in a thinner case without cutting.

 That said, we are still prototyping, and in fact only have simulations at the moment, so until actual builds exist, and properly evaluated, it really is hard to say.


----------



## spritzer

It is way too early for people buying transformers and such except for those of us doing the beta testing. One of the few requirements which aren't likely to change are the heater voltage and current needed, 6.3v@2.4A. The PSU will be +/-350v so something around 280-0-280v will work.


----------



## wiatrob

Quote:


  Originally Posted by *HeadphoneAddict* /img/forum/go_quote.gif 
_I'll have to beg Wiatrob for help building me one 
	

	
	
		
		

		
		
	


	


_

 

No frowney - you get to help test this


----------



## HeadphoneAddict

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_No frowney - you get to help test this 
	

	
	
		
		

		
		
	


	


_

 

OKAY, and I'll repay you with a great tip - remove the mineral wool from behind your SR-Lambda drivers and the SR-lambda will sound closer to the ESP950...


----------



## spritzer

Removing the wool will also unearth some mild colorations in the upper midrange and boost the bass a bit too much for my taste.


----------



## DouglasQuaid

This looks like it could be a really low-profile design. I'm looking forward to updates.


----------



## pabbi1

Can you define 'low profile'? My proto toroid is 4.25" in diameter, and almost 3.5" high - not exactly petite, especially in comparison to Stax amps.

 Proto boards may make it to some builders by the weekend, and most of us have parts waiting, so, given the experimental nature of the design, look for the first flameouts (or initial reports) next week, at the earliest. While not as difficult as other builds, casing remains an issue - well, after the design is proven out in build.


----------



## sachu

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Can you define 'low profile'? My proto toroid is 4.25" in diameter, and almost 3.5" high - not exactly petite, especially in comparison to Stax amps.

 Proto boards may make it to some builders by the weekend, and most of us have parts waiting, so, given the experimental nature of the design, look for the first flameouts (or initial reports) next week, at the earliest. While not as difficult as other builds, casing remains an issue - well, after the design is proven out in build._

 


 I don't think I will have my parts ready for a while due to other ongoing projects.not to mention not having a stax headphone to test it out on..but willl eagerly await results from others


----------



## wiatrob

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Can you define 'low profile'?_

 

Maybe that means: "under the radar..." 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *sachu* /img/forum/go_quote.gif 
_I don't think I will have my parts ready for a while due to other ongoing projects.not to mention not having a stax headphone to test it out on..but willl eagerly await results from others_

 

Better score a pair of 'stats before this amp does for Lambdas what the Orthodynamic thread did for, er Orthos...


----------



## pabbi1

No kidding - I did not even think how this might encourage folks to be even MORE ravenous on the lower end Stax stuff, though I am far more curious how it plays with the he60, Koss 950 and OII. Look for a run on Koss 950 if we are successful, as that could make just under world class electrostat rigs for about $800, with all new gear.


----------



## sachu

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_No kidding - I did not even think how this might encourage folks to be even MORE ravenous on the lower end Stax stuff, though I am far more curious how it plays with the he60, Koss 950 and OII. Look for a run on Koss 950 if we are successful, as that could make just under world class electrostat rigs for about $800, with all new gear._

 

I am planning on getting a pair of the Koss ERP950s...probably used...but till then I have a fellow user here in Portland who has volunteered his 404 for beta testing the amp


----------



## DouglasQuaid

By seeing the board layout pic and noticing the first psu (not sure if he went with the one with the extra set of zeners for the protoboards) it didn't look that large. Perhaps i was thinking on the wrong scale. Looking forward to the next update.


----------



## wiatrob

Quote:


  Originally Posted by *DouglasQuaid* /img/forum/go_quote.gif 
_By seeing the board layout pic and noticing the first psu (not sure if he went with the one with the extra set of zeners for the protoboards) it didn't look that large. Perhaps i was thinking on the wrong scale. Looking forward to the next update._

 

Remember there are two amp boards, PS board, and transformer. We've been doing a lot of tinker toying with layouts...


----------



## pabbi1

Generally speaking, three boards that are ~4x5.75" (or so), and a transformer, so 12"x13" flat was my best layout before getting creative. Since cheap is the goal, large external SCSI cases seem the most ghetto fabulous possibilities.

 She will be dissipating heat, so ventilation will be a premium consideration.

 Finally, for those who don't like tubes, there is SS discussion as well... but, nothing being proto'd until this design clears. But, c'mon - electrostat and tube is like bread and butter - and this with REALLY cheap tubes.


----------



## qusp

intriguing; I shall be watching this with some interest


----------



## Keithpgdrb

I continue to watch. when the specifics are settled, I'm on board. cant wait.


----------



## runeight

Boards are on their way to me from the fab. Hopefully I can get them in the mail over the weekend. Then the fun will begin.


----------



## Keithpgdrb

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Boards are on their way to me from the fab. Hopefully I can get them in the mail over the weekend. Then the fun will begin. 
	

	
	
		
		

		
		
	


	


_

 

I may be a pretty big noob. but I am very excited to see what kind of results come up from testing this design that 100% head-fi made. man this is a great community. I wish you all lived in my town so we could have a beer.


----------



## jcx

this was mentioned over at diyAudio - I wouldn't highly reccomend it but it is a different approach that could be used for ss electrostat amp:

EDN PDF "Class AB inverting amp uses two floating amplifier cells"

 I have played with cascoded optoisolator for active load that should allow all N mosfet pp Class A with previously mentioned Hi V depeltion mode devices

 still not seeing a convincing Electrical Safety story for these amps though


----------



## pabbi1

Status: I have built out the boards (save one inbound resistor for the amp boards), and the psu testing will begin tonight, in a proper flameproof test rig. Resistors for the amp boards should be here today, then (assuming psu stability), amp board testing through the week.

 I have pics, but will keep them internal to the design team for now... unless Runeight allows me to fan the flames.

 Jcx, I simply don't get your point - much less your timing. Can you clarify your intent?


----------



## jcx

Magpie mode - bringing bright shiny objects to the only active electrostatic amp thread

 just pointing to info on different ss alternatives - perhaps another fork could grow if a ss topology caught enough people's attention

 not trying to derail the current well advanced tube version efforts - which clearly has the overwhelming level of interest

 are you saying this is no longer a discussion thread and only open to bulders of the current version?

  Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I have long lamented the lack of any kind of electrostatic amp that a less than utterly advanced DIYer can safely build...

 ...As for solid state vs. tubes I'm agnostic as long as these basic goals can be met. I hope to see a day when there are a few of each available to build... _


----------



## manaox2

Tubes seem so much more likely to yield a good quality cheap design when dealing with native high voltages if I understand correctly. Less parts in the path and no need for converting high to low voltage and back, right?


----------



## runeight

Tubes are natural HV depletion mode devices. And triodes can be reasonably fast when loaded correctly. Hence, tubes are very handy in an HV design like this when you need 1000Vpp swings between the outputs. 6S4 is a sweep tube which means that it is also fairly linear. It's a good candidate in this type of amp except that its plate resistance is higher than we would like making the Zo of the amp higher than we would like. Which is why the final design being built here has bjt followers on the outputs.

 The straightforward replacement for tubes are HV depletion mode mosfets. There are not many of these around, however, so we generally have to find different ways to make a SS only amp in order to have easily available parts.

 It is a bit more work, but it is straightforward to take the amp that we are currently working on and to make it fully SS. But, maybe that's for later. We need to see how well this design performs first.


----------



## Ishcabible

I'm onboard when things are finalized!


----------



## pabbi1

Quote:


  Originally Posted by *jcx* /img/forum/go_quote.gif 
_Magpie mode - bringing bright shiny objects to the only active electrostatic amp thread

 just pointing to info on different ss alternatives - perhaps another fork could grow if a ss topology caught enough people's attention

 not trying to derail the current well advanced tube version efforts - which clearly has the overwhelming level of interest

 are you saying this is no longer a discussion thread and only open to bulders of the current version?_

 

I simply misread your intent - thought this a continuation of another 'electrostats are not safe' tangent. This thread is certainly open for discussion, especially SS, though I personally have zero interest in SS - we'll call it a personal bias, mainly as I have two new hybrid designs currently using tubes, and have never heard any SS sound as good on electrostats than either my BH (a pita with vintage el34) nor the Singlepower ES-1 (warts and all).

 In fact you are just in time on SS discussion as Runeight has just turned his attention that way over the past week, and, may be easier to build. 

 Tubes sound better on electrostats, IMHO.

 I will offer that we are using IXYS MOSFETS in the other design, of which I still have about 90, if they might work their way into a prototype somewhere... maybe Luvdunhill can help cross pollinate this idea, as he is all infatuated with SS also...


----------



## en480c4

After struggling to figure out what my next project was going to be and having a great time with a few different Stax phones at the NY meet this weekend, I'm definitely in for boards once this is ready to go forward.

 This thread was a great read... Thanks for all the time and effort that's gone into the project so far.


----------



## ejmcgee

Please count me in too, if possible.
 Need a dedicated e'stat amp to drive my ΛPro's and O2's.


----------



## Emooze

Just spent the better part of a few hours reading this thread all the way through and decided I haven't learned enough "cool stuff" at school yet.

 I will be all for this build when you guys get it finalized, great job!


----------



## pabbi1

Well, then definitely stay away from the Stax thread - it will take a month to read... 
	

	
	
		
		

		
		
	


	




 Ok, first psu test was successful, so proto is moving along. Not doing a blow by blow, but, this was the first significant milestone. We have powah.

 Pretty amazing to go from idea to reality in under 60 days on an international group design - and community service at that.

 Much work yet to be done - so, good karma will be essential.


----------



## wiatrob

I have my proto boards, and I am really tempted to crank out the PS. The boards are very handsome stuffed. 

 Let's all 'om' for pabbi1 as he takes the next steps!


----------



## DouglasQuaid

Is the protoboard psu the first design or the second design (one zener string or two)?


----------



## runeight

The PS uses four zener strings, two sets for each rail. Each rail has two cap multipliers using the fets to bring the ripple down to something manageable.

 Pabbi1 has now moved to the amp boards. We need some good results here. The rest of us can only watch.


----------



## Beefy

This thread is worthless without pics!


----------



## runeight

Yes, we know!! All of the prototypers are being very kind to me in keeping things a little quiet until we verify that there is a real amp here.

 It's much more risky designing an amp in the open with everyone watching than it is in the privacy of your workbench where you don't reveal anything until it's all perfect. 
	

	
	
		
		

		
		
	


	




 Perhaps there will be good news from Pabbi1 this evening and we will all feel comfortable showing things off.


----------



## pabbi1

Yeah, no pressure, huh?






 Probably pics by the weekend, sooner if things fall right. I'm being 'slow' because I am doing casework along with the board work, much to everyone's chagrin... me included.


----------



## wiatrob

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Yeah, no pressure, huh?
_

 

I know the feeling - Thanks for taking point on this.

 I actually got most of the PS built last night. If I hadn't screwed up the BoM (that I maintain), I'd have had it up.


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Yeah, no pressure, huh?_

 






 Less posting, moar building!


----------



## pabbi1

Wire and fire, baby!

 If only I didn't have to work... 
	

	
	
		
		

		
		
	


	




 Good thing the uber amp has a slight delay, and the hd800 aren't shipping yet.... wild to have $800 in transformers sitting on a plate with absolutely NO wire on them at all. So, I am humping to get this done, stat.

 Thus quoth the Raven, nevermore.


----------



## Emooze

Any updates pabbi1? 

 Reeeaaalllly anxious to see how this turns out.


----------



## runeight

We are making a fix to the PS because mosfets are blowing. This is because the brilliant designer forgot to include protection zeners for the GS junctions. This is not a serious problem, just an oversight, but we have to fix it before proceding any farther.

 It's going to be from days to a week before we get back to firing up the amp boards.

 Fortunately for me the prototypers are patient and good-humored builders.


----------



## smeggy

hehe, this should be really cool if it all works to plan. Another future build...


----------



## mypasswordis

smeggy, you're going to have to get more electrostats, which I've come to realize are superior to orthodynamics. 
	

	
	
		
		

		
		
	


	




 I also eagerly await completion of prototype testing.


----------



## smeggy

Bah, I have 6 stats already, only one left that I may want is the O2 and I can't afford that


----------



## mypasswordis

Er, 6? Oh snap, time to check your profile again.
	

	
	
		
		

		
		
	


	




 I have 5 + Alpha Pro drivers that are just sitting there, and 2 more incoming so I'm catching up. 

 Aye, the only stat I still want is the ESP950, and that's a maybe. It sounds like there's a necessity for Koss's warranty, ie build quality isn't that great. The O2 and 4070 don't really interest me much, mainly because I also can't afford them.


----------



## pabbi1

My interest here is for the 950 as well, as I have other things to drive the he60. In reality, this is for my brother, 'working' in Afghanistan... once he heard the stats, it was all over.

 Yep, a brief delay, but, we'll get it sorted.


----------



## dBel84

good to hear that the 950 is being considered , this is probably the only reason I may consider this amp in the future. ( not for a LONG while yet ) 

 ..dB


----------



## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Fortunately for me the prototypers are patient and good-humored builders. 
	

	
	
		
		

		
			



_

 

Eh, it's just a MOSFET or two! All for the cause!


----------



## smeggy

Their sacrifice will not be forgotten and their MOSFET brethren will continue the fight.


----------



## pabbi1

At least I'm not having to buy 100 of these MOSFETS at a time and match them, oh, and after building a matching rig...


----------



## ericj

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_My interest here is for the 950 as well, as I have other things to drive the he60. In reality, this is for my brother, 'working' in Afghanistan... once he heard the stats, it was all over.

 Yep, a brief delay, but, we'll get it sorted._

 

With the right bias voltage - which is very configurable in the PS design - and the right sockets, which is up to the builder - this amp should drive pretty much all small to medium size 'stats just fine. 

 I mean, I don't know what it would do with a stock esp/9 with it's weirdness in little boards in the earcups, for example, but it should even drive esp/7 and esp/10.

 Pretty much anything that has two stators and a diaphragm in the earcup, aside from jecklins.


----------



## ericj

Addendum - I don't know if it has enough gain to drive the ECR-500 electrets, which have bizzarely wide stator spacing, but i'm sure gonna try . . . .


----------



## smeggy

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Addendum - I don't know if it has enough gain to drive the *ECR-500* electrets, which have bizzarely wide stator spacing, but i'm sure gonna try . . . ._

 

Ooh, I'm liking this more and more 
	

	
	
		
		

		
		
	


	




 I'd love to drive them properly.


----------



## ericj

Spritzer has probably tried to drive an ECR-something with a Stax energizer at some point . . . dunno if he ever owned a 500. 

 iirc the ECR-500 transformers have a higher step-up ratio than you see in stax boxes.


----------



## spritzer

I've used both ESP6 and ESP9's with Stax amps so it can be done but you have to completely bypass the internal circuitry. I've never owned an ESP7 but the ESP10 is easy to use with "Stax amps". 

 I did own the ECR600 and it kind of worked with a Stax amp but there wasn't much volume. The D/S gap is truly huge in the ECR models so that could be the reason or that the phones were busted. 

 To stay on the same line then it is possible to use most Beyer Dynamic ET-1000's with Stax amps (some need a more robust bias supply) and the Suprex phones work as well. The OEM Stax phones (Magnavox, Marantz, Realistic etc.) will work but require some mods to the bias supply (15M ballast resistor or there about). The Micro-Seiki phones could work but need a new cable as they are only 4 pin. 

 Like Eric said before, the Jecklin Floats are a no go. Not only is their bias voltage much higher then anything else out there (1.5kV) but the drive voltages needed are also much higher.


----------



## smeggy

The ECR transfos pack a mighty wallop last time I licked the contacts! 
	

	
	
		
		

		
		
	


	




 Yeah, be interested in driving my ET 1000 too


----------



## mypasswordis

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Like Eric said before, the Jecklin Floats are a no go. Not only is their bias voltage much higher then anything else out there (1.5kV) but the drive voltages needed are also much higher._

 












 They seem very easily driven by any speaker amp through the PS2 transformer box, and I guess I can at least try.


----------



## spritzer

Quote:


  Originally Posted by *mypasswordis* /img/forum/go_quote.gif 
_











 They seem very easily driven by any speaker amp through the PS2 transformer box, and I guess I can at least try._

 

There is a simple reason for that, they use a much higher step-up ratio then Stax and other 'stats and the load is so tiny it will never wear down a normal speaker amp. The norm is around 1:25-1:30 but the Jecklins are at double or even triple that. Even if you would increase the bias voltage (not recommended but will increase the sensitivity) it won't make much of a difference since the amp was never designed to drive a 300pF. I'm pretty sure the only amp that can drive the Jecklins is the Blue Hawaii and it might even need some extra voltage to pull it off.


----------



## mypasswordis

Looks like I'm stuck with using the PS2 box then.
	

	
	
		
		

		
		
	


	




 That's what I get for buying electrostatic speaker panels strapped to my head.


----------



## macm75

I'm about 80% complete (only PS remains) with my Kevin Gilmore design cap coupled "All-Triode" amp, did some searching here to see if anyone else was in the same process, and I found this thread. Extremely looking forward to this new amp you guys are proposing!!! For the apparent price, I'll have to give it a go. Plus I'm sure it will be 8x easier to build relative to what I'm going thru now  Great Work Folks!!


----------



## spritzer

Doing a P-P amp is a lot of fun IMO if it doesn't involve any transistors. 
	

	
	
		
		

		
			





 What caps are you using in the GES )which we normally call the all-triode amp)?


----------



## macm75

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Doing a P-P amp is a lot of fun IMO if it doesn't involve any transistors. 
	

	
	
		
		

		
		
	


	




 What caps are you using in the GES )which we normally call the all-triode amp)?_

 

No complaints - it has been fun - just wish I was listening by now 
	

	
	
		
		

		
		
	


	



 I am using everything in my spare part bins. Caps are a mixture of Obbligato's, Vitamin Q's, Auri-caps's, Rifa's, and Solen's but at least each stage has the same type/value. I wouldn't have built this amp without the collection - so many caps and they obviously get expensive for decent ones.


----------



## spritzer

You can certainly go nuts in the caps department but I doubt it is worth it. There is always a better design that's not _that_ much more expensive to build... 
	

	
	
		
		

		
		
	


	




 I've got way too many amps cooking now but I also have most of the parts for a GES already. Damnit!!!


----------



## Kerry

Quote:


  Originally Posted by *macm75* /img/forum/go_quote.gif 
_I'm about 80% complete (only PS remains) with my Kevin Gilmore design cap coupled "All-Triode" amp, did some searching here to see if anyone else was in the same process, and I found this thread. Extremely looking forward to this new amp you guys are proposing!!! For the apparent price, I'll have to give it a go. Plus I'm sure it will be 8x easier to build relative to what I'm going thru now  Great Work Folks!!_

 

Glad to see you getting along with your build. Let me know how the PS turns out.

 I'm just working on a build of the Blue Hawaii. I had a chance to hear it at the NYC Head-Fi meet a few weeks ago. I was really impressed. 

 I have to say that I was not disappointed going back to my KGTT. Not the same punch as the KGBH, but I'm still very happy with it.

 Sorry for the chatter. I'm also very interested in the results of this thread


----------



## n_maher

Quote:


  Originally Posted by *Kerry* /img/forum/go_quote.gif 
_I have to say that I was not disappointed going back to my KGTT. Not the same punch as the KGBH, but I'm still very happy with it.

 Sorry for the chatter. I'm also very interested in the results of this thread 
	

	
	
		
		

		
		
	


	


_

 

Right, if you were disappointed going back to your amp I'd be headed down to NYC to relieve you of it. 
	

	
	
		
		

		
		
	


	




 As for the chatter, bring it on, we need to hear more from you.


----------



## Kerry

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_Right, if you were disappointed going back to your amp I'd be headed down to NYC to relieve you of it. 
	

	
	
		
		

		
		
	


	




 As for the chatter, bring it on, we need to hear more from you. 
	

	
	
		
		

		
		
	


	


_

 

LOL - I'm just looking to pretty it up. I'm thinking of leather sides and a nice shiny round cover for the transformer. I hope I get around to it before the next meet. So many projects


----------



## spritzer

We do need more DIY 'stat talk so please keep going.


----------



## mypasswordis

How about the German hybrid 6S4A electrostatic design? Any comments on that versus runeight's?

Frame


----------



## runeight

Hey, those guys are pretty clever!!! Have not seen this before.

 Some real similarities and some real differences.


----------



## ericj

Quote:


  Originally Posted by *mypasswordis* /img/forum/go_quote.gif 
_How about the German hybrid 6S4A electrostatic design? Any comments on that versus runeight's?

Frame_

 

If it's the one I'm thinking of, it turned out that the power supply iron alone costs more than cavalli's whole amp.

 Edit: That amp might could be used with alex's power supply, perhaps needing some modifications, but i don't really know.


----------



## Tachikoma

All of his tubed designs use 6S4As, and the project costs vary a fair bit. You're probably thinking of the one that uses 800V in the supply 
	

	
	
		
		

		
		
	


	




 (Just noticed that there's an english version of the website if you scroll down a bit)


----------



## runeight

I have taken some time to look over this website. There is some very smart stuff in his designs. Not that I have any right to pass judgment, only to note that I see what his designs are doing and they seem right on to me.

 I think we can say that his hybrid stat amp could probably fit into the budget that was set out in the first part of this thread, namely, <$300 including casing although he notes that a completed amp could be anywhere from 100EU to 400EU depending on how fancy you made it.

 The amp is reasonably fast (theoretically) and has good slew rate (I'm guessing about 80uV/s into 50pf). I suspect that it performs very well and its design makes it very robust against problems. 

 The amp we are working on here (not yet functioning) will be a bit faster and have a lower output impedance which will help it drive higher capacitance loads. How much this will matter in actual listening tests is unknown to me.

 Thanks for introducing this website into the discussion. It's good stuff.


----------



## mypasswordis

Thanks for taking a look at it and giving some comments.
	

	
	
		
		

		
		
	


	




 Sounds like your amp is the better build and I'm not sure how hard the transistors would have been to source with the German amp anyway. Probably pretty hard.


----------



## ericj

Oh yeah, now that i look at it again, i recall my original objection. 

 Unobtanium parts. Like the jfet pairs. 

 It could be built with a cheap antek toroid, other than that.


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Unobtanium parts. Like the jfet pairs._

 

no more unobtanium than the parts Alex is using...I don't understand this objection... Just because there is a part on a schematic that you cannot get doesn't mean there are plenty of other parts to choose from if you take a few seconds to understand how the circuit works. There are other JFETs that will work (most of which are mentioned in this thread).. just change a single resistor, and voila! There are plenty of substitutes for the other silicon...


----------



## luvdunhill

Alex:

 I have a quick question for you. What does the voltage on the plate with respect to ground look like as the amp comes up? Any predictions? Is it possible that you would have a large DC offset there for 4-5 seconds? If so, I didn't know how much of an issue that could create with the 'phones..


----------



## ericj

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_no more unobtanium than the parts Alex is using...I don't understand this objection... Just because there is a part on a schematic that you cannot get doesn't mean there are plenty of other parts to choose from if you take a few seconds to understand how the circuit works. There are other JFETs that will work (most of which are mentioned in this thread).. just change a single resistor, and voila! There are plenty of substitutes for the other silicon..._

 

In the current version of the schematic, the jfet used at the input of this amp can be the discontinued boutique part or any of a few current production parts. 

 All of the other transistors are current production parts, and 6s4 tubes are thick on the ground and quite cheap. 

 Both the 2sc3381 and the 2sj109 are out of production and relatively hard to acquire today. I understand why people like them, and people are welcome to keep designing and building amps that require them, but their use in this amp is precluded by the stated objectives in the 1st post. Replacing a matched, single-package pair with two loose tranaistors is rarely as satisfactory as it might seem - ask dr. gilmore if you don't believe me. 

 If this amp is being built to my spec, and much to my bafflement it seems that it is, i have specifically called for an amp that is good without requiring the worship and quest for an idealized part that cannot be acquired through normal channels or must otherwise be replaced with a less than ideal substitute. I think we've made a good compromise here and made the amp more accessible to a broad audience. 

 Even within those constraints we've come up with something that should be very competitive with the 'no parts barred' designs.


----------



## runeight

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Alex:

 I have a quick question for you. What does the voltage on the plate with respect to ground look like as the amp comes up? Any predictions? Is it possible that you would have a large DC offset there for 4-5 seconds? If so, I didn't know how much of an issue that could create with the 'phones.._

 

Yes. Any amp that uses the plate of a tube to drive the headphones will do this. Unless you have a pre-heat cycle, the tube is not conducting when the rails come up. No matter what you use for the plate load this will pull the plate to the positive rail. As the tube starts to conduct the plate will pull down to the operating point. Depending on the circuit, there may be some overshoot and damping on this pull down.

 Even a plate CCS will work this way because when the tube is not conducting neither is the CCS.

 I don't know how production units handle this, but it would seem to be a common feature of these amps that can only be elminated by additional circuitry.

 If anyone knows a way, I'd like to learn about it.


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Replacing a matched, single-package pair with two loose tranaistors is rarely as satisfactory as it might seem - ask dr. gilmore if you don't believe me_

 

There are substitutes that are dual package as well. Why not use BJT input instead like the Analog MAT02, which is a dual device in a metal can? Again, a few resistors changed and voila!

 With regard to your second point, this is a false assumption. 

 Here's some data (as opposed to a single person's word) to back this up:

diyAudio Forums - JFet matching and measured distortion - Part1 - Page 1
diyAudio Forums - JFet matching and measured distortion - Part 2: LTP - Page 1

 Also, with regard to the 6S4A I'd like to throw a question out there. Anyone notice that the ratings on the datasheet are for the tube being used in a vertical deflection amplifier. I seem to recall other datasheets, where are some that list ratings for class A amplifiers as well as vertical deflection amplifiers, and the ratings differ. Why is this, and is it important to using this tube in electrostatic amplifier applications?


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_I don't know how production units handle this, but it would seem to be a common feature of these amps that can only be elminated by additional circuitry_

 

The amps I've measured, this is ~200V with offsets over 50V-100V between legs. I've measured two production amps, as well as ... well, another amp 
	

	
	
		
		

		
			





 I think this would be a nice thing to address, if possible... kinda like an uber-e12


----------



## ericj

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_There are substitutes that are dual package as well. Why not use BJT input instead like the Analog MAT02, which is a dual device in a metal can? Again, a few resistors changed and voila!_

 

Again, not broadly available. In fact, I can find a few people who say they have a handfull of 2sk109 for sale - I can't find anybody selling the mat02 in small quantities. 

 You're missing the point. This is not the very best 'stat amp ever. This is not the greatest 'stat amp that this schematic could potentially be turned into. It was never intended to be. There are plenty of designs out there for you if you don't like this one. 

 If you're having heartburn over the fact that this design doesn't use the very best input transistors ever, don't build it. 

 What we have instead is an amp that uses parts that are available in any quantity to nearly anybody. You can in fact build almost the entire thing from parts bought from Mouser. 

 This was done intentionally and with a great deal of premeditation. The intention is to provide a design that is no further out of reach for the average DIYer to build than, say, the SOHA II. 

 It's a good goal. Lots of people have responded positively to the idea. If you don't like it, you're in the minority. 

 There's plenty of time to design amps with loftier goals after this one is done.


----------



## Keithpgdrb

Well stated ericj


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Again, not broadly available._

 

Again, you're wrong:

Digi-Key - MAT02FHZ-ND (Analog Devices Inc - MAT02FHZ)

 In fact, there are other grades available as well in quantity 1, ready to ship

 I think _you're_ missing the point. I'm not trying to build the best amp ever, or suggest other designs or modifications to Alex's designs. You immediately dismissed the designs at high-amp.de for non-issues in my opinion and I was floating some ideas on ways to make those work without using unobtanium parts. Also, I was trying to prove some misconceptions wrong about these "silver-bullet" parts like the dual JFETs, which I see you didn't comment on.

 For example, if I published a preamp using a pair of B36 tubes, would you not build it because they are hard to find and expensive, or would you spend some time and realize that there are other substitutions that could do this job, even with a potential loss in performance (for arguments sake).

 I have no idea why when it comes to tubes people are looking for a laundry list of tube types they can roll, but when it comes to solid-state designs they look at a part number and if they cannot find it available at Mouser (case-in-point, the above example of the MAT02, you didn't even look at Digikey) they they throw up their hands and move on to the next design.


----------



## runeight

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Also, with regard to the 6S4A I'd like to throw a question out there. Anyone notice that the ratings on the datasheet are for the tube being used in a vertical deflection amplifier. I seem to recall other datasheets, where are some that list ratings for class A amplifiers as well as vertical deflection amplifiers, and the ratings differ. Why is this, and is it important to using this tube in electrostatic amplifier applications?_

 

This is because of the timing in deflection service. Since the tube is stepping with the sweep it does not see continuous high voltage on the plate. It sees pulses. It's designed to withstand these pulses for very short periods of time without breakdown but it's not designed to sustain continous 2kV HV.

 We are gaming this tube in stat service by expecting that most music has a wide dynamic range and that most of the time, most of the music is low level and the only some of the time it reaches high dynamic peaks. Hence the tube is not seeing continous HV service beyond its class A ratings. However, if you take a 6S4 and put 1500VDC on the plate you are probably asking for trouble.


----------



## runeight

With regard to the running discussion about parts, etc., I think that the stat amp from Germany is a very nice design. It could probably be retrofit with easily available components. IIRC.

 The amp we are building still has the "el cheapo" design goal using easily available parts. I am believing that it will perform better than the other design. That is, I think it will be faster and I understand that slew rate is really important to stat amps.

 But I still have to make one work. Parts are coming in the mail to me to build up some boards.


----------



## luvdunhill

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_This is because of the timing in deflection service. Since the tube is stepping with the sweep it does not see continuous high voltage on the plate. It sees pulses. It's designed to withstand these pulses for very short periods of time without breakdown but it's not designed to sustain continous 2kV HV._

 

right, I understand that, but take this tube as a case-in-point, the 12BH7, which I think (but am not positive) was marketed as an "improved" dual 6S4A:

http://www.r-type.org/pdfs/12bh7.pdf

 Now, in deflection service the maximum plate voltage is 500V, but in class A it is rated to 300V. There are other manufacturers data sheets that corroborate this.

 By this token, even though the 6S4A is rated to 550V in deflection service, what's to say that it's rating in class A/AB1 wouldn't be derated to below or right at 350V? I understand that datasheets are a guideline and all that, but it is something that I was just curious about, not a critique or rant


----------



## ericj

OK, fine, I didn't check digikey. 

 But it's really late in the game to be suggesting changes to this specific project. Boards have been printed and delivered and we're two weeks into prototyping. 

 As for rejecting this other hybrid amp, yeah, transistor rolling seems to be largely not something people are interested in, and something that's often discouraged. 

 I think it has a lot to do with the sheer diversity of transistors vs. the relative simplicity of tubes, and the level of knowledge and experience in DIYers. 

 I mean, if Alex or Kevin or Ti had looked at that design and suggested changes to make it easier for people to source parts, I would have had no problem with that two months ago. But most of the people this amp is targeted to - and it's a broader audience than probably any previous diy 'stat design has really tried to target - simply don't have any idea how to make those changes and have it work properly. 

 If you go back and read about page 4 or 5 of this thread, the german amps were mentioned but i couldn't recall the url and nobody else offered it, and there was an impression given that they'd been looked at already. 

 If there's interest in adapting that design, great.


----------



## luvdunhill

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_transistor rolling seems to be largely not something people are interested in, and something that's often discouraged. 

 I think it has a lot to do with the sheer diversity of transistors vs. the relative simplicity of tubes, and the level of knowledge and experience in DIYers._

 

well, this isn't the place for this discussion, but in summary, your comments above highlight exactly what I don't understand. 

 On the one hand, there are lists of transistor substitutes for things like the original Millet diamond buffer, with various sonic comparisons:

discrete diamond buffer - parts list

 Also, this sort of transistor rolling is very often discussed in the PPAv2, JISBOS, SOHA II and later Millet Hybrid amp discussions, in addition to a number of projects that aren't really discussed on this website. So, I'd argue that people are indeed interested in transistor rolling and do it quite regularly. I can really only think of one place it's discouraged, and that's the beta22.

 Furthermore, I'd argue the _exact_ same parameters that are needed to determine if a tube can be substituted in a circuit, are the ones needed to determine if a transistor can be swapped. There are only a few parameters really, and they have direct analogs on the "glass" side of the house. Actually, there may be less parameters needed on the "sand" side, as you don't have to worry about heaters and various associated ratings, and there are way fewer basing options.

 Again, I don't understand your argument on the diversity of transistors. Different parts, yes, but they function in very much a similar fashion. In fact, I'd argue there is an order of magnitude more "different" types of tubes than transistors. 

 Anyways, thanks for the engaging conversation.


----------



## ericj

I think it's a lot easier to guess if an output power transistor will work in a given circuit than if an input transistor will work. 

 And even then, I've been discouraged from deviating from specified output transistors - even in stable, proven designs - by both Ti and Alex.

 I'm not an EET. My formal training in electronics was a 45 minute glass 3 days a week for one semester in the 7th grade. In 1986. And that's MORE than a lot of DIY amp builders. 

 I'm vaguely aware of the factors that need to be paid attention to when substituting parts, but on the input side, I've got some trepidation. 

 I think that the population of builders who are comfortable substituting parts like an input transistor is much smaller than the population of builders who can successfully order all the parts with no substitutions, put it together, and have it work.


----------



## pabbi1

Hmmmm - I've got 90 2sc3381GR (the real unobtainium, not the pedestrian BL, which are scarce enough). What I am finding, with the current economy, things are available, at reasonable prices, that were not available a year ago, as folks are emptying warehouses - so catch while catch can. 

 That said, Marc (and I along with him on another somewhat similar project) is aiming a bit higher than we are here, and knows exactly what we are doing, here, so I don't see any advocacy for changing PM. Of course, the design can evolve (hope Runeight doesn't tire of the exercise for a while yet), but think the cross pollinization of these designers is EXACTLY what we need more of in DIY, and ought to indulge a bit, especially in the 'infrastructure' type discssions. It really is longer term for here, but rather immediate "over there".

 And, the observation is correct - Marc is NOT a typical DIYer, however much we all may wish that were the case. That the conversation is multi-tenant should not add discomfort to the Poor Man's project, but will actually benefit as other designs using the 6s4a are exploring other operating points. There is yet some circuitry that will be desirable, which may well have already been vetted.

 So, I'd counsel some latitude, and patience - we will all be better for it.


----------



## Emooze

Bump. Any updates?

 And if everything goes smoothly, would there be boards available this summer? I landed myself a good internship and I'm looking for summer projects.


----------



## pabbi1

No real updates, as we are in the troubleshooting phase, so, no eta as yet on boards / kits or whatever form that takes.


----------



## Tachikoma

I have an OT question, but I can't find a better place to ask; why hasn't anyone tried to clone the SRM-717 for a budget stax amp?


----------



## AudioCats

copy right issues


----------



## pabbi1

We have additional design goals, including a configurable bias (high and low), cheap tubes, and, a simple through hole (no SMD) build. We also want to build this with readily available parts from Mouser or Digikey. Other paths are probable (including a SS version of this design), but gotta get this going first.


----------



## spritzer

The 717 would be very hard to DIY for most since it is filled with stuff that is hard to get and needs to be replaced. The KGSS also isn't _that_ different from the 717 in many ways...


----------



## AudioCats

Does it imply that if the 717 is easy to duplicate and fits the criteria, then it will be ok for the head-fi crew to copy it?


----------



## mypasswordis

I don't see how we would be infringing on anything if we just found or made a 717 schematic and built one ourselves... we'd only get into trouble if we started selling them for profit. 

 On the other hand, this Poor Man's should sound pretty damn good, and will be relatively easy to build with easy to source cheap parts. I think the choice would be obvious to me, which one to build. 

 If the tubes are holding back this amp like runeight suggests, I'm interested in an SS version as well.


----------



## FrankCooter

I've just come in to a large quanity of female Stax jacks. I don't know how you guys are fixed for jacks, but I know they' been a problem in the past. If one of you people (Pabbi1 ?) was willing to distribute the jacks I'll be happy to donate a pair of jacks to each person building an amp.


----------



## pabbi1

That is most gracious - though we already snagged at least a couple of the WPI sockets for each builder, and I already had 5 or so... one of our associates has now developed a teflon jack for those interested in a bit better option, with details coming shortly, though not exactly a Poor Man's part... 
	

	
	
		
		

		
			





 Now Frank, what are _you_ doing with Stax plugs?


----------



## FrankCooter

Pabbi1, I stumbled on a box of about 500 while digging around in my favorite LA surplus store. Was going to buy a few, then was offered the whole box for $40.00. Couldn't resist a "bargain"! I'm working on an 813 (a big WW2 era directly heated transmitting tube) based Stax amp. It's very simple, just a standard large set amp. Only difference is the custom Electra-Print output transformer. Not a beginner project though. I'm bringing it to CanJam in LA. You should come.


----------



## spritzer

That will certainly be an interesting amp to say the least and solves some of the cost issues of building a DHT based push-pull amp. Too bad I'm stuck up here in the cold north for CanJam.


----------



## mypasswordis

Is the design similar to Pete Millett's 813 SET amp? The microprocessor-controlled power supply is pretty cool.

813 SE triode amps


----------



## FrankCooter

My 813 amp is very similar to Pete Millett's amp. Pete's work has been an inspiration for me for years. Like Pete's amp, my amp is a simple two stage design using a high gm driver pentode to drive the single ended 813 output. He uses a resistive loaded d3a driver and I use a srrp "mu stage" with a 7788 on the bottom and a 12gn7a on top. Unlike Pete, I use a traditional tube rectified, choke input filter power supply.


----------



## pabbi1

That Tango transformer is $1200 by itself, so I'd say it is pretty safe there are few to no similarities, since we are looking at $300 all in.

 Nope, we are using 350v, max, where it looks like Pete has ~900v.... and no, dynamic != electrostat.

 I have asked Pete in the past to look into electrostatic, but he hasn't to my knowledge.

 Frank, you will have to listen to his 307a at CanJam - it really kicked anything I have ever built.


----------



## FrankCooter

Pabbi1, the 307a is definitely on my "to do" list for CanJam. If I were to build commercial amps, this is the kind of amp I would build. Sorry it kicked your work, but actually it's a positive thing, at least for me. I like it when people raise the bar. We all benefit. You should be inspired to "kick" back. How about a 307a "Special Edition"? You could start with a really beefy power supply with mercury vapor rectifiers. That 6sn7 type driver, (local 7n7?) could be changed to something like a directly heated 112a. Since you don't care about commercial limitations you could go wild!


----------



## mypasswordis

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_That Tango transformer is $1200 by itself, so I'd say it is pretty safe there are few to no similarities, since we are looking at $300 all in.

 Nope, we are using 350v, max, where it looks like Pete has ~900v.... and no, dynamic != electrostat.

 I have asked Pete in the past to look into electrostatic, but he hasn't to my knowledge._

 

Er, yeah, I meant comparing Pete's 813 amp with Frank's, and Frank nicely summed up the differences.
	

	
	
		
		

		
			





 His amp is definitely going to be a bit of a beast.
	

	
	
		
		

		
		
	


	




 It's too bad that Pete Millett hasn't yet looked into designing an electrostatic amp; I'd definitely look forward to his take on one.


----------



## pabbi1

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_Pabbi1, the 307a is definitely on my "to do" list for CanJam. If I were to build commercial amps, this is the kind of amp I would build. Sorry it kicked your work, but actually it's a positive thing, at least for me. I like it when people raise the bar. We all benefit. You should be inspired to "kick" back. How about a 307a "Special Edition"? You could start with a really beefy power supply with mercury vapor rectifiers. That 6sn7 type driver, (local 7n7?) could be changed to something like a directly heated 112a. Since you don't care about commercial limitations you could go wild!_

 

I was only humiliated for a couple of days. Starting to snag the mercury vapors as we speak - assuming 83? In having Pete almost to myself at the last Dallas meet (my 4th such adventure, and to me, beyond cool), I was convinced of two things: Massive psu, and _nice_ iron. Not sure the Lundahl will work, but Tango / James is definitely on the radar. DHT is a requirement. I've been the 6sn7 route with Pete's HA-2, but I hate chasing those tubes, so, it is time for something more exotic, in the 81x family, or even the 307a. That Pete says it is his favorite is good enough for me, after I was disappointed in the 300b, which I believed would be the end all - not so much, or maybe it was the 307a was soo much better - since I had them side by side.

 Maybe I'll just ask him for the 307a - or, if he has done anything else DHT.

  Quote:


  Originally Posted by *mypasswordis* /img/forum/go_quote.gif 
_Er, yeah, I meant comparing Pete's 813 amp with Frank's, and Frank nicely summed up the differences.
	

	
	
		
		

		
		
	


	




 His amp is definitely going to be a bit of a beast.
	

	
	
		
		

		
		
	


	




 It's too bad that Pete Millett hasn't yet looked into designing an electrostatic amp; I'd definitely look forward to his take on one._

 

That Wayne Mcmanus tells me Frank's amp ius the best he has ever heard said it all for me, as I trust Wayne's ears implicitly, and, he has the breadth of experience probably above all at head-fi, given what all he has invested in. And, I'll try Pete again on stats - but, it is not where he has as much interest.

 Then just to get Marc done with Dynafet...


----------



## manaox2

I hope its not causing too much stress on you all, its got to be tough. Best of luck!


----------



## pabbi1

Right now, only Runeight is stressing because something in the sim isn't adding up, whether the variation in the parts, or mismatched assumptions, but PSU is good and the amp circuit is requiring some revision.

 No stress at all - I have 3 amp projects in various stages, and I'm being drawn into a 4th, oh and have a repair / recase to do in there somewhere. 

 That said, I'll build out this amp as first priority, mainly because it has potential for such a wide audience..


----------



## manaox2

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Right now, only Runeight is stressing because something in the sim isn't adding up, whether the variation in the parts, or mismatched assumptions, but PSU is good and the amp circuit is requiring some revision.

 No stress at all - I have 3 amp projects in various stages, and I'm being drawn into a 4th, oh and have a repair / recase to do in there somewhere. 

 That said, I'll build out this amp as first priority, mainly because it has potential for such a wide audience.._

 

I wish I could help, I'm one of those put the peg in the hole guys. No worries anyway guys, no one's life depends on it. Take care of your personal lives first.


----------



## FrankCooter

Pabbi1, in the world of dhts the 300b is a mediocrity. There are much better options for diy. The small, table radio '20s era dhts all sound better than the 300b. These include the 10y,45, 46, 112a, 26, and my personal favorite, the 71a. All these are ideal for a small headphone amp. At the other end of the scale are the big transmitting types such as the 845, 813, gm70, and if you really want to go wild, the Eimac series. Often these can be run at surprisingly low voltages with exellent results. Power supplies are too often an afterthought, they should be a world in themselves. There is no such thing as overkill here. Ideally, the amp should ride the power supply like a flea on the back of an elephant.


----------



## FrankCooter

A few thoughts on mercury vapor rectifiers. First you need to consider the toxicity issue. Nobody in the modern age would ever build a commercial product with them. That said, if handled with care and knowledge, I don't think it's a problem for diy. I use them exclusively after many years of experimenting with lots of different vacuum and solid state rectifiers. The second major issue is implimentation . They require preheating to vaporize the mercury before turning the hv on. When they do come on, they come on all at once like a solid state rectifier. No tube "soft start" here. I use an Amperite octal time delay to hold off the hv. For soft start, I put a damper diode like a 6au4 in series with the rectifier output. The filament of the damper is turned on at the same time hv is applied to the rectifiers. This is a bit of cheating, but it doesn't seem to alter the sonics.
 All in all, adding mercury to your amp seems to be good for a free 15-20% performance boost. Kind of like adding a nitrous oxide system to your hot rod. Probably this is due to their natural regulation ability. Their low constant voltage drop makes for a low impedance, always a good thing in a power supply. Sorry to wander "off thread" here. As you can tell, I'm sort of a fanatic about this stuff.


----------



## smeggy

Wander all you like Frank, this is fascinating stuff to people like me.


----------



## n_maher

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_Power supplies are too often an afterthought, they should be a world in themselves. There is no such thing as overkill here. Ideally, the amp should ride the power supply like a flea on the back of an elephant._

 

This might go down as my favorite DIY quote of all time. Can't wait to meet you in LA Frank.


----------



## smeggy

And all the naysayers talking about my B22 toroid being overkill pfft


----------



## n_maher

Quote:


  Originally Posted by *smeggy* /img/forum/go_quote.gif 
_And all the naysayers talking about my B22 toroid being overkill pfft 
	

	
	
		
		

		
		
	


	


_

 

Apples and oranges my good man, apples and oranges.


----------



## smeggy

Pah!


----------



## sachu

Quote:


  Originally Posted by *smeggy* /img/forum/go_quote.gif 
_And all the naysayers talking about my B22 toroid being overkill pfft 
	

	
	
		
		

		
		
	


	


_

 

The same one is doing perfectly fine on my S22


----------



## TimmyMac

Well that settles it, 866As for my big tube build, whenever that comes around.


----------



## spritzer

Just thinking about a 6SN7 driven 300b makes me throw up a bit and the power supplies are way too often an afterthought. 

  Quote:


  Originally Posted by *smeggy* /img/forum/go_quote.gif 
_And all the naysayers talking about my B22 toroid being overkill pfft 
	

	
	
		
		

		
			



_

 

Now if you were using three S22's then we would be impressed. Some say that I'm crazy for using a S22 to power the +/-15v side of the Blue Hawaii as it draws only a few mA. 
	

	
	
		
		

		
		
	


	




 Now since this is a thread about easy to build DIY electrostatic amps, here is what I'm listening to now:


----------



## mypasswordis

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_All in all, adding mercury to your amp seems to be good for a free 15-20% performance boost. Kind of like adding a nitrous oxide system to your hot rod._

 

Also kind of like enclosing electrostatic speakers with sulfur hexafluoride?

  Quote:


  Originally Posted by *spritzer* 
_Now since this is a thread about easy to build DIY electrostatic amps, here is what I'm listening to now:_

 

Nice, is that the Egmont? And how does it sound?


----------



## spritzer

Quote:


  Originally Posted by *mypasswordis* /img/forum/go_quote.gif 
_Nice, is that the Egmont? And how does it sound?_

 

Indeed it is and it's not too hot driving the SR-Omega/007 hybrid. The bass is flat out awful (way too slow and lacks detail) and the top end is uneven, even harsh at times. The sound is also a bit thin and lacks the depth which the SR-007 can muster up on a good amp. Some of that could be due to the cheap Wima coupling caps but I'm waiting on some parts to add feedback to the circuit and see if makes a change for the better. 

 Btw. How do you like the IKEA transformer cover?


----------



## mypasswordis

Makes your amp look like a flying saucer.
	

	
	
		
		

		
		
	


	




 Way bling.


----------



## HeadphoneAddict

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Just thinking about a 6SN7 driven 300b makes me throw up a bit and the power supplies are way too often an afterthought. 



 Now if you were using three S22's then we would be impressed. Some say that I'm crazy for using a S22 to power the +/-15v side of the Blue Hawaii as it draws only a few mA. 
	

	
	
		
		

		
		
	


	




 Now since this is a thread about easy to build DIY electrostatic amps, here is what I'm listening to now:








_

 

Cool - I like the flying saucer look. You can use it for a bowl-cut haircut too.


----------



## Beefy

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_A few thoughts on mercury vapor rectifiers. First you need to consider the toxicity issue._

 

Pretty overstated toxicity, I would imagine. Modern fluorescent tubes still contain mercury, and nobody seems too concerned about them.

  Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Now if you were using three S22's then we would be impressed. Some say that I'm crazy for using a S22 to power the +/-15v side of the Blue Hawaii as it draws only a few mA. 
	

	
	
		
		

		
		
	


	


_

 

I thought that the S22 had a minimum recommended power draw in the tens of mA?


----------



## luvdunhill

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_I thought that the S22 had a minimum recommended power draw in the tens of mA?_

 

that's easy to satisfy. Just crank up the LED on the sigma22 board.


----------



## spritzer

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_I thought that the S22 had a minimum recommended power draw in the tens of mA?_

 

Driving both boards off the same supply takes care of that. 

  Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_that's easy to satisfy. Just crank up the LED on the beta22 board._

 

B22 aka. the amp that will blind you.


----------



## DouglasQuaid

I'm a bit sad to hear the circuit's acting up after the first run of protoboards were put out. It's times like this I wish I had jumped in on the prototyper list to play around with the design. Unfortunately, I still have my KGSS and Shigaclone to finish before I can consider a new project. Not to mention all the troubleshooting here in the lab has made me a bit tired of staring at schematics and boards.

 I wish you guys good fortune with the rest of the designing. I was hoping to hear a first-level prototype at Canjam, but it looks like I'll have to build my own if I want to hear it. If it's a fun enough alternative to the kgss, I'll give it a shot.


----------



## pabbi1

Quote:


  Originally Posted by *DouglasQuaid* /img/forum/go_quote.gif 
_I'm a bit sad to hear the circuit's acting up after the first run of protoboards were put out. It's times like this I wish I had jumped in on the prototyper list to play around with the design. Unfortunately, I still have my KGSS and Shigaclone to finish before I can consider a new project. Not to mention all the troubleshooting here in the lab has made me a bit tired of staring at schematics and boards.

 I wish you guys good fortune with the rest of the designing. I was hoping to hear a first-level prototype at Canjam, but it looks like I'll have to build my own if I want to hear it. If it's a fun enough alternative to the kgss, I'll give it a shot._

 

Not at all giving up on CanJam... and, I do have an extra set of boards...


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Not at all giving up on CanJam..._


----------



## pabbi1

Yeah... no pressure, huh?


----------



## spritzer

Well, we could just throw a simple amp circuit together and drive it off the PM PSU just to show that it is up and running. A simple ES-1 circuit with a quad of ECC99's and a quad of 6S4A's would be very cheap and easy to make.


----------



## pabbi1

Janus / Vulcan is just waiting for me to change some resistors tonight to stomp out the final 20v of offset (mismatched tubes), and the other side is 0-1v on offset and between channels... bias is at 540v. Just a matter of hours.

 Casing can be welded and powdercoated in two days... pending the stinking welder. So, almost there.

 PM is already cased and laid out, just needs assemply once proto is fixed.

 Now, Nate, about getting four matching quads out of eighty 6s4a....


----------



## spritzer

I should get the Vulcan boards soon as Marc forgot about me...


----------



## DouglasQuaid

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_I do have an extra set of boards... 
	

	
	
		
		

		
			



_

 

Peer pressure is a dirty thing. I'd be happy to take a set to play around with, assuming it's not your personal spare. It should be fun having two DIY Stax amps side by side. Solid-state for the summer to try to cut down on heat sources and the Hybrid for wintertime to keep my room nice and toasty. When the temps break 100, I might have to resort to switching to my dynalo.


----------



## pabbi1

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I should get the Vulcan boards soon as Marc forgot about me... 
	

	
	
		
		

		
		
	


	


_

 

Marc has Dynafet Fever - can't blame him, as I started kitting up a 307a amp yesterday - it is a sickness.


  Quote:


  Originally Posted by *DouglasQuaid* /img/forum/go_quote.gif 
_Peer pressure is a dirty thing. I'd be happy to take a set to play around with, assuming it's not your personal spare. It should be fun having two DIY Stax amps side by side. Solid-state for the summer to try to cut down on heat sources and the Hybrid for wintertime to keep my room nice and toasty. When the temps break 100, I might have to resort to switching to my dynalo._

 

I have them in case we need to try a clean build with work arounds, but if the existing boards will work, no need for me to build a second, as I'm just doing proto duty.


----------



## spritzer

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Marc has Dynafet Fever - can't blame him, as I started kitting up a 307a amp yesterday - it is a sickness._

 

Believe me... I know. Most of today I've been thinking about a mini ES-1 and next job is to check if I have all the parts needed to build one quickly on a perfboard.


----------



## digger945

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Marc has Dynafet Fever ..._

 

I think that's goin' around these parts.
	

	
	
		
		

		
		
	


	



 Probly wont see a cure for at least 6 months.


----------



## n_maher

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_
 Now, Nate, about getting four matching quads out of eighty 6s4a.... 
	

	
	
		
		

		
		
	


	


_

 

We'll figure something out, I'm sure.


----------



## DouglasQuaid

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Believe me... I know. Most of today I've been thinking about a mini ES-1 and next job is to check if I have all the parts needed to build one quickly on a perfboard. 
	

	
	
		
		

		
		
	


	


_

 

is there an es1 schematic out with resistor values and all? The only one I saw was the one Kevin drew and there were no values written. And in that case, does the es2 run same tubes and topology?

 As for dynafet, I wish the new dual-jfet design would get released already.


----------



## spritzer

Here is the original Stax schematic for the amp. 





 I would perhaps tweak the plate resistors but Mikhail didn't. Well unless running parallel resistors takes some sort of thought besides being cheap and not be willing to pay for more expensive resistors. That schematic is lacking any adjustment for the output tubes so that would have to be added though. The ES-1 and ES-2 are identical.


----------



## Wenglish

The progress of this thread/evolution of ideas was very interesting to read through. Color me very interested in this amp. I just wish I had something more substantial than that to add.


----------



## luvdunhill

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_I should get the Vulcan boards soon as Marc forgot about me... 
	

	
	
		
		

		
		
	


	


_

 

I predict you'll have them a week from Friday


----------



## pabbi1

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I predict you'll have them a week from Friday 
	

	
	
		
		

		
		
	


	


_

 

Well, here is something for Birgir to look forward to... oh, and the final coat of Tung oil just went on, so case will be dry in the morning, so money shot tomorrow EXCEPT for the jack...


----------



## krmathis

Looking really nice!


----------



## spritzer

Yay Marc and Al. 
	

	
	
		
		

		
		
	


	




 Here's my contribution, a mini ES-1. 





 Those are just the filaments fired up so now I have to find a working HV supply (I tend to blow them up 
	

	
	
		
		

		
		
	


	




) and see if it catches fire or just makes music.


----------



## Emooze

Wow, both of those look amazing for a first attempt.

 Super impressed


----------



## AudioCats

Quote:


  Originally Posted by *spritzer* /img/forum/go_quote.gif 
_Yay Marc and Al. 
	

	
	
		
		

		
		
	


	




 Here's my contribution, a mini ES-1. 





 Those are just the filaments fired up so now I have to find a working HV supply (I tend to blow them up 
	

	
	
		
		

		
		
	


	




) and see if it catches fire or just makes music._

 

the two pieces of paper under the board has some interesting writing on it, care to share?


----------



## spritzer

Here ya go. This is what Mikhail used to build the ES amps but it lacks one of the most important things, how to set up the filaments. The author of the text does touch on it but far from enough IMO. It's quite clear in the original Stax schematic how they are supposed to be wired.


----------



## AudioCats

in the stax schematic (in the SR-3 manual), all filaments share a single supply tied to the GND, though it does seem a little scary since the cathod is closer to the - rail voltage. 

 Thanks for the link.


----------



## spritzer

Nope, only the first two stages have the heater connected to ground. There is a second winding just for the last stage and it is left floating.


----------



## AudioCats

oops, how did I miss that 6.3v winding on the left side?


----------



## spritzer

You weren't the only one that missed it...


----------



## Vaughn

I've searched and can't seem to find reference to a panel mount jack that is
 compatible with Stax gear. I would also like to find the plug to terminate the cable end.

 Any suggestions?


----------



## manaox2

Quote:


  Originally Posted by *Vaughn* /img/forum/go_quote.gif 
_I've searched and can't seem to find reference to a panel mount jack that is
 compatible with Stax gear. I would also like to find the plug to terminate the cable end.

 Any suggestions?_

 

Allied Electronics I believe has one, though I don't know the part number.


----------



## Vaughn

Thanks, I actually had the page with the correct part bookmarked but now
 the link doesn't work for some reason. The idea of scrolling through 10,000 slightly different connectors has little appeal for me. I'm sure someone here knows the exact part number...please?


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## cetoole

WPI 78-S6S and WPI 86-71-6S are what you need.


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## Vaughn

Muchas gracias!


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## spritzer

Quote:


  Originally Posted by *Vaughn* /img/forum/go_quote.gif 
_Thanks, I actually had the page with the correct part bookmarked but now
 the link doesn't work for some reason._

 

The socket disappeared from Allied for a while so that must be the reason.


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## macm75

Keep in mind the connectors sold thru Allied are crap. It's not the connectors so much but how it fastens to a chassis. It's not a threaded piece - there is a cheap aluminum ring with sharp edges on the inside that apply a force to the perimeter of the connector. Once applied, it's guarenteed to move radially (not in and out, as least, but clockwise/counterclockwise). Use some epoxy to prevent this.
 There is also the Woo Audio connector - call them for details. It's way more expensive but it's very good quality.


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## spritzer

You really need epoxy to fit the WPI connectors but do that and I have lttle to complain about them. I like the genuine Stax sockets more but the WPI is fine for my cheaper projects. There is also a new teflon socket being made but I suspect it will be made in small quantities for the die-hards.


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## pabbi1

I'll post pics of Woo and the new socket in the next few days, assuming USPS plays along.


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## macm75

I hope those teflons are made with 6 pin. What bugs me about my woo connector is that it's 5 pin (although at the time I bought it i did not have the SR-Lambda's). If the connector is going to be custom, I just don't see the point in limiting the use of them to 580V units only.


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## luvdunhill

Quote:


  Originally Posted by *macm75* /img/forum/go_quote.gif 
_It's way more expensive but it's very good quality._

 

very good quality? heh... 6-pin is an option and the center socket is removable as well.


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## jgazal

This design seems to be AC coupled, so my question might be off topic, but I have no other thread to ask that. 

 I've been reading that DC coupled amplifiers are very dangerous when they fail because they pass dc current to the headphones and may burn them. 

 Is it true that electrostatic headphones are less prone to being damaged because their diaphragm is highly polarized? 

 Is it more secure to build a dc coupled amplifier with higher headphone bias (ie, pro-bias instead of normal bias)?

 Best regards!

 Jose Luis


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## Keithpgdrb

Havent heard much on the status of the build for a while. any worthwhile updates?


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## pabbi1

No updates - it rather seems on indefinite hold, with some significant engineering yet to be done.

 Regarding jacks, here are some pics of the new teflon jack first, followed by the Woo.


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## MrMajestic2

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_No updates - it rather seems on indefinite hold, with some significant engineering yet to be done.

 Regarding jacks, here are some pics of the new teflon jack first, followed by the Woo.

http://home.swbell.net/pabbi/jax.jpg

http://home.swbell.net/pabbi/woo1.jpg_

 

Those should be X-Rated 
	

	
	
		
		

		
		
	


	




 Sweet.


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## spritzer

Quote:


  Originally Posted by *jgazal* /img/forum/go_quote.gif 
_This design seems to be AC coupled, so my question might be off topic, but I have no other thread to ask that. 

 I've been reading that DC coupled amplifiers are very dangerous when they fail because they pass dc current to the headphones and may burn them. 

 Is it true that electrostatic headphones are less prone to being damaged because their diaphragm is highly polarized? 

 Is it more secure to build a dc coupled amplifier with higher headphone bias (ie, pro-bias instead of normal bias)?

 Best regards!

 Jose Luis_

 

A moving coil transducer will burn up if fed too much DC but electrostatics don't mind it as much. The SinglePower ES-1/2 amps are all sitting with roughly -100VDC offset so while it compromises the voltage swing it doesn't damage the phones. If you match the actual bias voltage to the offset then it doesn't matter which type of phones you use.


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## jgazal

Thanks, Spritzer, now I see how electrostatic transducers behave with dc. 

 Did you measure the impedance vs. frequency curve of the different models of Stax Omega 2? 

 Do they have peaks and dips across the spectrum or they are flat? 

 I presume that they tend to be flat because they are full range drivers, but does its capacitance nature interfere in impedance vs. frequency curve? 

 Best regards, 

 José Luis


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## cetoole

Quote:


  Originally Posted by *jgazal* /img/forum/go_quote.gif 
_Did you measure the impedance vs. frequency curve of the different models of Stax Omega 2?_

 

You can calculate it, since it is simply a capacitor. Formula for calculating capacitive reactance is 1/(2piFC), where F=frequency and C=capacitance. Stax doesnt state the capacitance of the SR-007 anywhere I have seen, but they do state that the impedance is 170kohm at 10khz, so 1/(170,000*2*pi*10,000)=0.00000000009362F, or 93.62pF


  Quote:


 Do they have peaks and dips across the spectrum or they are flat?

 I presume that they tend to be flat because they are full range drivers, but does its capacitance nature interfere in impedance vs. frequency curve? 
 

Since they provide a purely capacitive load, the impedance is, by nature, not flat with regards to frequency, but fairly high at low frequencies (about 85Mohm at 20Hz) and fairly low at high frequencies (85kohm at 20Khz).


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## jgazal

Thank you! Trying to figure out how these things work, but I think I would need an electronic engineering degree... I will just observe from now on...


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## th12dk

Regarding the AC coupled vs DC issue. Wheather an elektro..amplifier is dc or ac coupled, i dont think you should worry to much about the hardware. Your EARS is what's going to suffer the most. IF!! the amplifier ( be it an AC or DC) melt down it will probably produce a MASSIVE spike going from rail to rail but then again all electronic devices can break. Your speaker-amplifier is dc-coupled.
 In any case im building me an amplifier myself ,DC-coupled, for my old stax lambda signature. Its very much inspired of Audio Research sp-11.


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## runeight

Hello everyone. As you all know this project has gone dark for a while. For two reasons: 1) the first concept only partially worked and 2) i've been swamped with the necessities of work until about two weeks ago.

 However, over the last several weeks a new poor man design has been born. It is simpler than the original and, I think, truly falls into the category of an inexpensive, but well performing stat amp.

 More to come as we make further progress and do some builds ...


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## HeadphoneAddict

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Hello everyone. As you all know this project has gone dark for a while. For two reasons: 1) the first concept only partially worked and 2) i've been swamped with the necessities of work until about two weeks ago.

 However, over the last several weeks a new poor man design has been born. It is simpler than the original and, I think, truly falls into the category of an inexpensive, but well performing stat amp.

 More to come as we make further progress and do some builds ..._

 

Great, thanks! 

 I forget, what will the peak-peak voltage and current capabilities be?


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## runeight

This depends on the PS.

 At the moment, in keeping with inexpensive but good, the target is a split 300V supply. This means about 900Vpp (maybe a bit more) before the amp starts to see its rails.

 The +/-300V supply is targeted at easy-to-get transformers.

 With higher supply voltage the amp can do more. To give some cushion and be very conservative, figure that each side can get to 75V of the rail. For 300V supplies this would be 225V which gives 450V peak and 900Vpp.

 The limit is the O/P devices which are 900V transistors. Each transistor must be able to sustain the difference between the rails. 

 The amp has a simplified follower output stage and so should be able to handle 150pf loads.

 But, nothing has been prototyped yet, so I don't want to get ahead of the process. Just wanted everyone to know that things are still moving, although slowly.

 If we have success things will get posted.


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## nattonrice

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_Regarding jacks, here are some pics of the new teflon jack_

 

That looks amazing!
 Will be awesome if they become available ^^


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## spritzer

They are certainly the best Stax socket you could ever find.


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## nattonrice

Yeah~ 
 The WPI one looks very flimsy by comparison.


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## jcx

Quote:


  Originally Posted by *pabbi1* /img/forum/go_quote.gif 
_No updates - it rather seems on indefinite hold, with some significant engineering yet to be done.

 Regarding jacks, here are some pics of the new teflon jack first, followed by the Woo.










_

 

unfilled teflon is lousy mechanically - creeps forever so any press fits will eventually loosen

 I might consider polystyrene, polyproplylene or UHMW PE


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## spritzer

They aren't press fit, the contact is a machined unit which is inserted into the teflon and then fixed with a nut on the back.


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## Emooze

Glad to know you're all still working on this! Inspires me to work harder to understand more of how all this functions.


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## luvdunhill

Quote:


  Originally Posted by *jcx* /img/forum/go_quote.gif 
_unfilled teflon is lousy mechanically - creeps forever so any press fits will eventually loosen

 I might consider polystyrene, polyproplylene or UHMW PE_

 

Nothing on that jack is press fit.


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## pabbi1

To be fair, the Woo socket is press fit - though it has never shown any inkling of failure over years of use.


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## FrankCooter

So when and how can we buy some of these great looking new jacks? Put me down for half a dozen!


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## wiatrob

Yah like he said! Although to un-thread jack - would probably be overkill for a 'Poor Mans Stat Amp!'


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## luvdunhill

Honestly I'm just looking for a good place to take orders for the next batch, as this site isn't really conducive to such a thing. If anyone is interested, just PM me and whenever I get my act together, I'll forward you to the proper place to reserve them.


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## nattonrice

ygpm ^^


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## Keithpgdrb

excited to see this is still moving along.


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## wiatrob

Yes, a frenzy of activity is happening behind the scenes - hopefully we will have news to share soon.


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## Currawong

I'm keen to see the result of this too.


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## sachu

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_Yes, a frenzy of activity is happening behind the scenes - hopefully we will have news to share soon._

 

Aren't you supposed to be working on some kinda document..stop wasting time on the intarwebs and get to work 
	

	
	
		
		

		
		
	


	




 Btw, awesome job on the K1000 adapter...many thanks.

  Quote:


  Originally Posted by *Currawong* /img/forum/go_quote.gif 
_I'm keen to see the result of this too._

 

Heh..that makes two of us. Getting the case ready for this as well.


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## nattonrice

Quote:


  Originally Posted by *sachu* /img/forum/go_quote.gif 
_Aren't you supposed to be working on some kinda document..stop wasting time on the intarwebs and get to work 
	

	
	
		
		

		
		
	


	


_

 

LOL nothing like a good whipping


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## wiatrob

If, by document, you mean something spelled out on FR-4, that's in the works my friend. There's an excel spreadsheet filled with little numbers to match.


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## mypasswordis

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_If we have success things will get posted. 
	

	
	
		
		

		
			



_

 

Finally got around to subscribing to this thread. I don't mind simpler, it means less things can go wrong.


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## smeggy

not If I'm building it...


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## green0153

hope the project get's finished soon....


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## runeight

We are sneaking up on it. We have one successful build of a new design. Want to have at least two more with listening tests before posting.


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## bidoux

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_We are sneaking up on it. We have one successful build of a new design. Want to have at least two more with listening tests before posting._

 

Can I ask which schematic you eventually decided to keep ? Really nice project !


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## runeight

None. Whole new design. Much better and simpler. I'll explain all when we restart the thread.


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## dBel84

exciting times - i am expecting the prices of esp950 to rocket on the second hand market ..dB


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## Keithpgdrb

Quote:


  Originally Posted by *green0153* /img/forum/go_quote.gif 
_hope the project get's finished soon...._

 

Dude, not cool. Were Lucky to have a community where this can happen at all.


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## smeggy

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_exciting times - i am expecting the prices of esp950 to rocket on the second hand market ..dB_

 

In with the cheap buy early


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## sachu

Honestly..the ESP950 is the best bargain out there right now..I am listening to it with my Stax amp and I can't think of anything that is lacking in this system. 

 Am curious to see how much better this new DIY amp is going to be..


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## FrankCooter

I like the "simpler and better" concept. The original was getting a little out of hand for an intermediate diy project. I haven't built a solid state amp for over 20 years, (lots of tube ones though) but I'm looking forward to building this one. Appreciate all the work!


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## runeight

Yes, the earlier design was done on-the-fly. A little more reflection found a better way.

 One of the downsides to designing in public is that everyone can see things that are marginal. If you just do it on your workbench you can chuck a bad design and no one knows. 
	

	
	
		
		

		
		
	


	




 But I've always liked the forums for the very reason that people can see the design process. I think that's just as useful as talking about the amps and builds. 
	

	
	
		
		

		
		
	


	




 We just need two more builds to come up cleanly. One already has with no problems.


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## smeggy

It's an exciting project for certain. I have a bunch of 'stats here and only the Stax transfo box to run them all, so I'm eager to get a decent stat amp to do them a bit more justice. I'm very happy you took this on based on prior works.


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## wiatrob

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_
 We just need two more builds to come up cleanly. One already has with no problems._

 

Two power supplies and one amp are up, actually.


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## wiatrob

Quote:


  Originally Posted by *dBel84* /img/forum/go_quote.gif 
_exciting times - i am expecting the prices of esp950 to rocket on the second hand market ..dB_

 

Then we can buy new ones without feeling ripped-off!


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## dBel84

is it too early to be demanding pics - all these words are just a tease  ..dB


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## runeight

Yes, just a bit too early. Hang on please.


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## srserl

Quote:


  Originally Posted by *runeight* /img/forum/go_quote.gif 
_Yes, just a bit too early. Hang on please._

 

Hanging on, but losing my grip (on sanity)...actually contemplating the purchase of some stats. This can't be a good path for my wallet.


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## DoYouRight

I didnt know you did any DIY HPA thats cool! This is exciting for me, If there becomes a b22eque stat diy I will finally jump into some stax magix


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## pabbi1

Quote:


  Originally Posted by *DoYouRight* /img/forum/go_quote.gif 
_I didnt know you did any DIY HPA thats cool! This is exciting for me, If there becomes a b22eque stat diy I will finally jump into some stax magix 
	

	
	
		
		

		
		
	


	


_

 


 Ummm, don't know if you were alluding to this being runeight's first stat headphone amp, but, he has a pretty complete track record in dynamic hpa.


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## DoYouRight

HPA = headphoneaddict


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## HeadphoneAddict

Quote:


  Originally Posted by *DoYouRight* /img/forum/go_quote.gif 
_I didnt know you did any DIY HPA thats cool! This is exciting for me, If there becomes a b22eque stat diy I will finally jump into some stax magix 
	

	
	
		
		

		
		
	


	


_

 

 Quote:


  Originally Posted by *DoYouRight* /img/forum/go_quote.gif 
_HPA = headphoneaddict_

 

I don't DIY, so I will need to find someone to help me build this one if wiatrob's prototype performs well. We'll be able to test my SR-003, SR-007, HE60 and Jade with it (sold the Lambda Sig and ESP950). 

 I just want something with a little more voltage swing and current for the O2 than the GES, and so I wait to see what the specs will be on the re-designed Stat amp. I'm basically giving up on getting my KGBH boards built into an amp as a spare to go along with my GES. If I can't get all the parts then I'm stuck with a partial build, and I can't commit to that if it wont be complete. I just don't have the knowledge to source all the parts. 

 I have one other person who "might" build a KGBH for me along side of his, but he wont need my PCB to do it with perf-board. He is still researching the build. So, I have to wait and see.


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## DoYouRight

oh ok cool beans. why not have Justin build you a BH SE? Of all the stats you have which would you pick as best all arounder? 007? and is it mk1 or mk2?


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## wiatrob

To clarify - the design goal of this amp (per EricJ) is not to be a world beater - but to provide an affordable DIY alternative to the commercial Stax products while providing good performance.

 I wouldn't be surprised if the redesign meets or exceeds these goals.


----------



## sachu

Quote:


  Originally Posted by *wiatrob* /img/forum/go_quote.gif 
_I wouldn't be surprised if the redesign meets or exceeds these goals. 
	

	
	
		
		

		
		
	


	


_

 

Indeed!!


----------



## smeggy

*fingers crossed*


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## atothex

Is this the official thread for the poor man's? Sorry, I usually don't check in the DIY forum.


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## pabbi1

I have suggested the Poor Mans Stat Amp get it's own thread, but, it will have to be in DIY, as it is a DIY build. Once folks hear one at some form of meet, then maybe it would get posted in the amps section.

 Mine (two flavors) will debut at a meet in Houston on Oct 18th. Maybe I can get the BH patched by then, and have Vulcan operational, where we can also throw a maxxed KGSS into the mix as well. Then all will really know how it stacks up in the stat world.


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## krmathis

Still really curious what comes out of this... 
	

	
	
		
		

		
		
	


	



 I would need a nice inexpensive amplifier, to make a bedroom rig out of the SR-404.


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## HeadphoneAddict

Quote:


  Originally Posted by *DoYouRight* /img/forum/go_quote.gif 
_oh ok cool beans. why not have Justin build you a BH SE? Of all the stats you have which would you pick as best all arounder? 007? and is it mk1 or mk2?_

 

I can't spend $5000 on an amp when I have two teenagers needing $10,000 total in braces at the orthodontist right now, two cracked teeth of my own with bone loss that will cost $7000 to fix, and a 16 yr old who needs a car if I want to stop driving three kids to school and back myself while my disability takes away all my energy.

 My Jade have been getting the most ear time for stats since they are easier to drive with my Woo GES. The O2 Mk1 are a nice low volume headphone with more depth (but not width) but I get more of a dynamic headphone punch with the Jade.


----------



## DoYouRight

are there any pics of this design pabbi1? please please please


----------



## sachu

Quote:


  Originally Posted by *DoYouRight* /img/forum/go_quote.gif 
_are there any pics of this design pabbi1? please please please 
	

	
	
		
		

		
		
	


	


_

 

its very close to being revealed..patience.

 It is well worth a few more days of waiting


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## atothex

Aww jeez... should I just get an ESP950 unheard?


----------



## sachu

Quote:


  Originally Posted by *atothex* /img/forum/go_quote.gif 
_Aww jeez... should I just get an ESP950 unheard?_

 

The ESP950 is the best friggin deal out there...would be wise to get it before used prices go up.


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## runeight

Folks, new thread with new results. Please go here:

eXStatA Stat Amp


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## DoYouRight

schweet!


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## Satchmoeddie

Maybe some people are more immune to electrical shock than others. It is not the voltage but the current that kills. I worked as an electrician on systems from millivolt WWII ear signaling to MV which is 15KV to 45KV. I never took any direct shocks on any system over 600VAC nominal, but got nailed by 120, 240, and  277 a few times. I still think finding the B+ of an old Valco Supro which was located in the most dangerous place inside the amp anyone could ever find was one of the worst shocks I ever got. I did get nailed by a 7500 volt hi pot one damp rainy day. That was pretty painful too. Maybe I am lucky. Working with electricity 40-84 hours a week you will get zapped. I have seen some people with holes blown in them from 120 volts, and worse from 277. I have no clue why it just scares me and makes me jump, and other people have died. AS one person said, "Keep one hand in your pocket" as it is great advice so as not to pass current across your heart. Also make some jumpers with a 1K-10K  resistor to put across filter caps. They can actually recharge themselves and nail you after you think you have shorted them and have them discharged. Some say they draw energy from other caps in the amp. I have been nailed by them after reforming the things and discharging them upon removal from the power supply and load. They can be fine right after taking them off my reforming rig then you pick one up an hour later and get a surprise. I have been using some old Koss ESP10s, and Staxx electrostatic headphones. My only complaint is the 1970s Marantz amps won't work with the Koss due to a negative feedback loop, so I have to use another power amp, and I do not want to drag one of the tube amps into the shop area.


----------



## Satchmoeddie

Has anyone started making any plans for the electrostatic headphones? I have some transformers that are too high a voltage but too low current to do much else with. I have a beefy one that with a doubler comes out to 700VDC plus, but I have been using those in pairs and making the current high enough to drive some nice tubes along at 77 watts. I used something like KT88s only with a plate cap. They take 800 VDC easily. I ran them through a pair of Partridge designed transformers I had wound with 1,2,4,8,16 ohm taps and 100 volt out for a PA distribution line. Sorry to be cryptic about the tubes I use. For now these are affordable in the Mullard or GEC UK made brand. (affordable on my monthly pittance anyway) My doctor bought the AR RT600s and $10K in 6550 tubes. I would love to know where they went. The govt seized all his stuff for fraud, and some other DEA violations. 600+ wattsx2 in a house? Oh well to each his own.


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