NEW Electrostatic headphone amp

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).
 
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.
 
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 docb@bottlehead.com if you would like to order one.

 

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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
 
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.
 
At this time we are just taking orders for built amps. PB was working on a really nice looking green one the other day.
 
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
 
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.
 
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. 
 
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.
 
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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