Bottlehead Forum
General Category => General Discussion => Topic started by: Doc B. on February 17, 2020, 10:06:41 AM
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PB has been working on an ES headphone amp for a few months now. The ES project was something I had in the back of my head for several years, but it just never floated to the top of the development pile. A few months back Sajeev Ranasinghe of Nectar Sound contacted me asking if we had plans to do an ES headphone amp, and after some conversation he sent a demo pair of his very interesting headphones for us to listen too. http://www.nectarsound.net/?i=1 (http://www.nectarsound.net/?i=1)
So once the development backlog was clear PB set about building up a direct drive headphone amp design. The circuit is a single ended input running into a two stage differential amp using the very linear 5965s and it features a bias supply high enough to run the Nectar Sounds, which require a 500-700V bias supply and can be had with the same 5 pin plug used on the Stax "professional" series. The nice thing about the Nectar Sound bias requirement is that the 580V bias requirement of Stax professional headphone models fits in the same range, so he set about cooking up a 580V supply for both brands of cans and we can also derive the 230V bias voltage of the older Stax cans as well. With the two styles of jacks (5 pin "pro", 6 pin original) that Stax uses available on the front and with the appropriate bias voltage assigned to each one, one could have an amp that will run the Nectar Sounds and any Stax ES headphone too.
We have three evolutionary prototypes in house and we have listened to Nectar Sound, Stax and Koss ES headphones. They all work as expected. The chassis has taken a turn away from our usual flat panel in wood base approach. The bias voltage supply, while operating at a teeny current, is high enough voltage-wise that we felt it made sense to completely enclose the circuit in metal. PB designed the layout so that it could be done as a kit. It would be a pretty involved build with a lot of sub assemblies to build and test. We're spitballing the kit price at around $800-900. If we deliver the amp as a finished product we are probably looking at $1200+.
The audience here is of course heavily biased (pardon the pun) towards kit building. We wanted to get some feedback on whether there may interest in our offering this as a finished product rather than a kit, considering the reasonably high skill level required for assembly. We'd like to hear your preference in this thread.
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I’d emailed Sajeev a few months ago about buying one of his kits but I ended up not - mostly because I wasn’t sure about his instructions would be up to the Bottlehead standard I’m used to. I never saw them, by the way, so maybe they are.
Anyway, I’d be in to build one!
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Sajeev's amp kit is of the board and parts variety where you supply your own transformer and cabinet. And of course it's also a solid state circuit. He has put all of the details of building one of his amps up on his site as an open source design. We felt that the our amps are pretty different and thus the two circuits could give people a chance to try some different approaches. I'm impressed with Sajeev's putting his whole headphone/amp project together, seems like a very competent guy.
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Yeah, I definitely got that impression. My comment should be taken as a criticism of my skills and not Sajeev’s.
Regardless, this seems really cool.
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The audience here is of course heavily biased (pardon the pun) towards kit building. We wanted to get some feedback on whether there may interest in our offering this as a finished product rather than a kit, considering the reasonably high skill level required for assembly. We'd like to hear your preference in this thread.
I wonder whether Headfi might be a good place to gauge interest in the pre-built amp? And maybe send out a few prototypes to some of the regular testers/posters there? Although I'm guessing that would require some kind of sponsorship payment since it's a commercial product. But maybe it'd be worth it as a way of testing market temperature?
I don't think I belong to the target market for either electrostatics or a pre-built amp - I like a lot of low end weight and, like most everyone else on this forum, I like building stuff myself. But kit-builders and diy types make up a tiny fraction of the market out there.
Very cool, though. I hope it's really successful for you guys.
cheers, Derek
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Doc, you mentioned a certain high skill level required to build the ES kit. How difficult would it be compared to something like a Kaiju or BeePre?
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This is a rough idea of what the build would look like, but without the C4S boards that will be installed and a few other things. Not the most difficult thing to build, but certainly a lot more involved than a Crack with lots of p-t-p work that gets a bit tight. Derek is on the right track with his observation - how small a niche is DIY kitbuilders who use ES headphones and want a tube amp? Would the sales volume be worth it to make this only as a kit? If it is only sold finished we don't have to go through the huge amount of work that it takes to write an assembly manual. That is hard to justify if we are only going to sell half a dozen kits. But if a lot of bottleheads have ES headphones or plan to try them it's certainly worthwhile.
This stuff is hard to gauge. For example, one of the kits we stopped making for a while was our very obscure tape path modification kit. It sold quite well then tapered off after a while. I guessed that maybe the folks who wanted one all got one. But then we got so many requests for it we brought it back, and it continues to sell quite well. I guess I need to trade a kit for a crystal ball.
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I built a Crack and looking at the picture I don't see anything that scares me. Just more parts. I lean towards buying a finished product. The high voltages may be a deciding factor for me.
The Stax amplifier market has room for a good quality tube amp. You can easily pay more for a poor sounding Stax brand amplifier and may times more for other offerings. I would guess the market for pre built is 100 times that of a kit.
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I guess I need to trade a kit for a crystal ball.
Just ask Magic 8-Ball!
http://magic-8ball.com/ (http://magic-8ball.com/)
http://www.ask8ball.net/ (http://www.ask8ball.net/)
I tried it myself, but I don't think the results are reliable if the question is asked on behalf of another. See attached. ;D
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I would also mention that this circuit is different than the other electrostatic amp offerings that I have seen in that it does not use a solid state front end, nor does it use feedback around the circuit.
The amp with the C4S upgrades installed is also a tube roller's dream, as you can use 12AT7s, 12AU7s, 12BH7s, 5965s, and all those weird 12AT7 variants with lower gain. The current sink in the differential stage at the output ensures that the stator pins are always sitting pretty close to 0V.
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I've build a SEX and have a Crack cooking up - this doesn't look scary and I'd love to build an electrostatic amp, especially with a constant current source.
One question - will this require any specialist equipment to build? My DMM is limited to 600V - I'm guessing this thing will be pushing voltages (all be it low current) around at well over 1000V.
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Although the bias supply is up around 580V, if you tried to measure it with your meter, the meter would draw enough current that the bias voltage would sag way down. That would be one of the challenging sections to write in the manual, as different meters will give wildly different DC voltages at the bias output, and none of them will be correct.
Otherwise the amp runs off a bipolar supply that is about -380V and +430V.
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Although the bias supply is up around 580V, if you tried to measure it with your meter, the meter would draw enough current that the bias voltage would sag way down.
I guess it's time for that VTVM kit.
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How long does it take to develop an amplifier from prototype to ready for sale as a kit?
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Depends entirely upon what the project is, how many other projects are ahead of it, how much of the circuit uses things we know and how much is new research. The MonAmours came together in a couple months, using circuits and parts we are very familiar with. At the other extreme we've been working on developing a high powered amp for several years, with several prototypes having been built.
All that said the average timeline is probably around a year or two long from initial design development to released product. Within that timeline the part from building a first prototype to product release might be six months to a year. We seem to average about three prototypes before finalizing a production configuration, with the third one being the prototype that is photographed for the manual.
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I guess it's time for that VTVM kit.
Also a tube tester kit.
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I'm interested - looks like an interesting build and sounds like it may give me an opportunity to use my old Heathkit VTVM in the bargain.
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A megOhm resistor at the end of the + plug of a DMM should be enough to measure that bias supply, assuming that you re-calibrate.
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A megOhm resistor at the end of the + plug of a DMM should be enough to measure that bias supply, assuming that you re-calibrate.
No, it won't. Most modern DVMs are 10M ohms. There's a 20M resistor between the bias supply and the bias pin on the output jack, so an extra 1M of resistance isn't going to do much. Even measuring the raw bias supply with a 10M meter pulls it down pretty far. I intentionally designed the bias supply to be ample for the task, but not ample enough to be harmful to meatware.
It is possible to measure each chunk of the voltage multiplier that creates the bias voltage, but it's a bit tedious.
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My opinion is a finished product at first and if demand is there (which I feel will taper out, quickly), then it could graduate into a kit. You could also consider a short manual on how and where to mod the amp (e.g., cap swapping, magic resistor swapping, etc).
I've know you guys long enough to know how much work goes into the manual, kit packaging, stocking supplies, online support of a product, etc. I also have owned three finished amps that PB has build over the years and his build quality is second to none and worth the extra cost. There would be minimal support needed on a finished product.
Another thing to consider is who you are competing against. Unfortunately they have earned their nick name of the Stax Mafia for many reasons. The one that bothers me most is how they are able to sway opinion on products. Getting an amp into circulation and the reception of that amp should also be factored IMHO.
Lastly, these are electrostatic headphones..... The market is very small based on the entry price of the headphones and that makes for an even pickier costumer and all that comes with that type of customer......
Just my two cents
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I'll admit up front that I'm biased but I think it's an opportunity to introduce ES headphones to a new customer. Just googling ES tube amp brings up three that are in the multiple of thousands (1700 to 6200). That price ranges keeps out a lot of customers and leads to things like the Stax mafia.
You have to decide the form factor that works for the business but there is an opportunity, maybe a limited run of Pb buiit to seed the market, there are options. Shoot for something between the BHDac and a new DIY kit. Any open backed headfi customer is right there for the taking, these headphones compare and beat most open backed ones on the market but are limited by the availability of a good amp to drive them. You've solved this. The choice is to jump in or not...
I have limited experience with Stax amps and headphones but the ones I had had a hard time beating out my HD800's and Mainline so I think you can compete easily with a new ES amp available for modestly priced but poorly driven headphones (the complaint of most ES users and reason for defaulting for Stax amps).
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If I picked one up I’d try it with those $285 Nectars.
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I have only build a Crack with Speedball still I think I have figured out much of what is going on. On the left are separate channels each with an input and output tube. I found 3 power supplies, 4 if that large tube has something to do with power. What is that tube? Two standoffs for the C4S boards and stepped attenuators. Each section seems very simple with a clean design. As a second kit it looks very doable.
I'm going to change what I wrote previously, I will buy the kit if it is available, if not I'll still buy the finished version.
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What is that tube?
It's a damper diode to soft start the high voltage supply.
The standoffs connect the top and bottom plates together for a little extra rigidity.
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A diode? Awesome!
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We've had some interest expressed by long time customers in having an electrostatic headphone amp built to order. PB and I had a meeting today to discuss pricing and production. What makes sense is to try to get 5 orders going, which makes things like fabrication of the cabinets and custom connectors cost effective. Price will be $1500. So far it looks like we have two interested customers.
I'm attaching a pic of the latest prototype that Peebs put together, for Sajeev Ranasinghe of Nectar Sound. His impression -
"Sounds awesome!!! Lots of bass, smooth, and can handle these headphones."
There are jacks for both styles of Stax headphone connectors, so this will work with any Stax and also Nectar Sound and Koss headphones. We're digging the yellow finish on this one, and I have asked for a red one to sit next to my red Neothoriator amp.
Ping me at [email protected] if you would like to order one.
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Looks like it could Be at home in a Civil Defense office...John
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Hey Doc!
I'll trade you my red one for the Neo, tell you what, I'll throw in some gear that has actually left the planet and we can call it even. ;D
Alonzo
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Did you find the 5 customers for the trial run? Will there be a kit? I definitely would be interested in a kit version to drive my Stax 007.. if this amp can deliver the necessary power.
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At this time we are just taking orders for built amps. PB was working on a really nice looking green one the other day.
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Can it drive the notoriously hard to drive Stax 007 (mk1)?
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The SR-007 says 100dB for 100V RMS. This amp can do close to 600V peak to peak, which is over 200V RMS, so yes, output shouldn't be a problem. The amp would be down a dB or two at 20kHz on the SR-007.
-PB
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As far as I know (and with the risk of making a fool of myself as this is just collected internet knowledge) the issue some amps have with the SR-007 isn't just voltage swing, but how much current they deliver. I am currently running a modified Stax T1 hybrid amp to which I added constant current sources, so there could be more current going to the headphones instead of being burnt by resistors. If there isn't enough current, the headphones cannot produce their low end properly which goes amazingly deep. The author of the mod wrote that the modded amp can deliver up to 9.2 mA to the headphones (instead of max. 3mA in stock config), but from owners of custom energizers values up to 20mA are stated to improve the sound.
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That is an odd sentiment that there's a lot of current required to drive an electrostatic headphone at low frequencies. They are a capacitive load, and the SR-007 will load an amp at 20Hz about as much as an 82 million ohm resistor. I'm having trouble counting all the zeroes, but I think that's 7 micro amps of peak current at 600V peak to peak drive.
I do agree that only having 3mA of operating current is not nearly enough for any electrostatic headphone, and would indeed give a thin, rolled off sound. I run 10mA of current in the output stage per channel, which strikes a balance between keeping the plate load resistors reasonably high, overall dissipation in the output tubes and loading resistors reasonable, but also extracting solid performance.
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Thanks for your replies. So I guess I got confused about the low end. All I can say is that the CCS mod really made the SR-007 sound a lot better on that Stax T1. I'm sure owners of the high-end staxes will be happy to hear about these 10 mA. Stax' own tube amps have a bad reputation for not delivering enough power that might spill to all tube amps.
If you had the kit, I'd buy it now. Unfortunately my wallet says no to a pre-built one. Plus I love the building at least as much as the listening. Should you end up creating a kit, I'd volunteer to buy and build one of the first ones and give detailed feedback about the instructions.
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The kit price would end up being not all that much lower than the finished unit.
-PB
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Ok you got me. And I like green.
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Wow!!
Havent heard VTVM in a long time!!
One of the questions I used to ask prospective electronics tech hires for IBM "back in the day" was "What the difference between a VTVM and a VOM"??
:>)
Alex
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"What the difference between a VTVM and a VOM"??
Vacuum Tube Valley Magazine and Voice of Music? ;)
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Wow....YOU GOT IT RIGHT!!!
;)
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Hi all,
Just registered with Bottlehead.
I'm living in New Zealand and am looking for an electrostatic amplifier for my old Stax SR-5 Gold.
I'd need a complete kit as parts are difficult and expensive to source here in New Zealand.
Any help would be much appreciated.
Thank you!
Regards, Tony.
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I'm happy to make you an amp and send it down there. We decided not to go down the kit road, as these aren't all that easy to debug and really need to be buttoned up in a metal box.
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This is PB's latest completion, in red wrinkle finish.
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Info page is up -
https://bottlehead.com/product/stat-electrostatic-headphone-energizer/ (https://bottlehead.com/product/stat-electrostatic-headphone-energizer/)