Bottlehead electrostatic headphone amp

[frankg]

Info about an upcoming electrostatic amp from Bottlehead.  https://forum.bottlehead.com/index.php?topic=12157.0

[garageboy]

 photos here

[Jon L]

I'm glad this Bottlehead doesn't have input and power connectors on top of the chassis and everything is enclosed in metal case.  

Awaiting sound impressions from customers...

[JimL]

Just saw this and went to the Bottlehead link in the first post. From what it says, it seems like the output  stage uses plate resistors and 10mA/channal standing current. They do use their C4S CCS in the design, but apparently not in the output stage. I should point out that the SRM-T1 series uses plate resistors with 9.6mA/channel, and without the CCS mod is not very happy driving the SR-007s. I would expect similar problems with the Bottlehead amp.

[HiGHFLYiN9]

I just saw the email today, the Bottlehead Stat. Looks like it comes in bright blue, yellow and red powdercoat with black screws. I personally find it very hard on the eyes with all the contrasting screw heads everywhere, but were it polished with some brass screws it might look okay. 

[spritzer]

I was sent this and it was posted on SBAF so one can expect the level of discourse over there:

There is so much here that I don't even know where to start.    First off, they claim this circuit is "unique"...well it isn't.  Old as the hills this one, same as the old TubeCad stuff, the Rudistor amps, the prototype Schiit built, that Trilogy H1 piece of shit and I've been building similar amps for the last 15 years.  Stax also released something similar in the 60's so no...not unique. 

The amp circuit is simple and works well enough for a cheap amp so nothing wrong with that.  I also like that they used a CCS on the front end (though they claim it is on all stages but that's not true) but my issue is with the PSU and the bias supply.  What an utter clusterfuck....  The circuit requires a bipolar PSU so with a center tap transformer the bias supply can be a bit tricky but simple to solve really.  I just don't understand what the hell they did with that delay circuit.  It's just adding tubes because... tubes?  Makes no sense at all. 

The bias supply seems to be driven off a tap for some reason.  Also, those ballast resistors look like RN55 units and they are nowhere near adequate for the job. 

Smaller issues, twisted output wires are a no no, not sure what's up with those output "sockets" and an unregulated heater supply is never a good idea.  Still I like the colors.  Might have to do something like that... 

[kevin gilmore]

so its a balanced amp with only unbalanced inputs.

only 2 gain stages so its already low on voltage gain, and then if you put in 12bh7 as output tubes it has even less voltage gain.

stax jacks with what looks like heatshrink on the pins? no 5.1k safety resistors, relying instead on the current source to limit output stage current.

electrolytics not secured to anything.

nice chassis.

 

[spritzer]

I also like the plastic stick on bumpers on the electrolytic caps so they don't short to the bottom panel... 

[garageboy]

Twisted output is not good because of capacitance issues, or something else?

[spritzer]

Yup, adding capacitance is always a bad idea. 

[luvdunhill]

Glad someone figured out tube pins could be used for decent Stax sockets