spritzer

Speaking of offboards... As some of you might have spotted, I quite like to push the envelope in making smaller and smaller amps. Going with what Kerry did but in an off the shelf chassis and no SMD parts it is a challenge to shrink something this complicated. PSU isn't ready yet but it is version of the BH design so +/-400V max. That does mean more current though... The chassis is about 10mm wider than a SRM-727, similar height but much shorter. Ohh and far more power... Also, one should never do the chassis artwork 1 hour after they should have gone to bed...

Nope, the output transformers will be ditched and I'll use different output transformers which step up the voltage and acts as a phase splitter. Something like this...

A month to the day and the amp kit shows up at my door yesterday. Classic China shipping with everything thrown into one box with little to no padding between the fragile chassis and a 2.5kg transformer... Well it is serviceable but the real WTF moment are the components that are included. Now the power transformer is pretty decent and run way below max so that will be just fine. The output transformers also look to be nice enough and ditto on the psu choke. Similar to what you find in the Woo, ALO and DNA amps at 15 times the price... What is of no use are the caps, resistors, volume pot, connectors and even the bloody tube sockets. Not a chance in hell any of those caps are real despite the Nichicon or Nippon Chemicon markings. Wasn't expecting anything else but it's still funny. Now what to do with this thing, clearly destined for Stax duty so some Lundahl 1660's on the top panel, add a DC supply for the front end tube, perhaps a simple regulator for it as well and a CCS

I third that as even if you find some super cheap transformer to use in that spot, it's not really worth saving.

That's Wiktor so... yeah...

I really is a bad idea to mess with the cable too much as two things can happen. You break the thin wires inside the housing which lead to the drivers and if they short... the amp won't be happy. The other possibility is managing pull on the cable and some how damage the solder tabs on the drivers. That would be really bad...

Just plugged in my first and favorite SR-007 just now after not touching them for at least 6 months. On the KGSSHV they are nothing short of astounding, the detail they can dig out of even low-fi recordings is just staggering plus the sheer presence of the image they project. It's fun to listen for mastering mistakes or where a piece has clearly been added on afterwards but even most electrostatic transducers would never pickup on that. The ability to be bright on one track and then dark on the next simply can't be rivaled. Then there is that midrange, those voices... It's nice to see you again old friend, I've missed you.

Maybe measured but it is a 150V transient suppressor into a voltage doubler so circa 300V.

Well it could just drive a Stax unit harder but I think they might have their own design. The PWB designs had their own drivers even if they were heavily based on the Stax stuff. Edit: Hi Luc!! The imbalance is pretty much gone now with the left side being just a bit louder

They are electrets but Audiotec also made full blown electrostatics as I've seen the schematic for the energizer. Bias is -300VDC...

Happy Birthday Jeff!!

The aim of the thread is to consolidate all the info that is out there of old and frankly strange electrostatic headphones we come across. I really should have started one of these back in 2005 when I started my collecting but hindsight and all that... So I'll start off with one so rare that there is pretty much no info out there for this set. Here is what it looked like when I got it: These were made by Audiotec in France and aside from some brochures back in the say we know nothing about them. There isn't even a model number on them or a left-right identifier. They are quite big, roughtly the same size as the SR-Omega and the back of the fork is pretty much a clone of the SR-1,2 and 3 setup Stax used. Here are the earcups opened and these do have the honor of having a truly unique earcup design. No screws as they use nails which are friction fitted. Very secure assembly but an utter pain in the ass to disassemble... Not sure what is up with that baffle. It made of the same material as really old PCB's but those traces don't go anywhere. Driver lifter out of its cradle and doesn't this look familiar. Turns out that it's the same or very similar driver to the ones used in the Stax electret models. Never seen one with the mineral wool damping pad being a part of the driver housing though. Same pic but showing a bit more of the green wool pad used on the back of the driver. This keeps the driver in place against the baffle similar to the Magnavox sets but it's a far from ideal setup. There is also very little to keep the back wave from colliding with the front and that foam around the driver is decomposing quickly. Showing the connections inside the cups. The joints simply have fiberglass insulation pushed over them but not secured in any way. Yet another thing that needs to be fixed... Here is the original 6 pin DIN connector. Oxidized all to hell so I simply removed it. Now the important bit, how do they sound. Well I don't have the original adapters so I had to make due with what I have at hand... I knew that the stock transformers used with the Audiotec stuff had very high stepup ratio (1:65) so it was no surprise that the highly modified SRM-007tII didn't manage to drive these even at full volume. I do have a few KGSSHV's here and they did a stellar job with a very balance sound signature. The bass is a bit odd given the housing and all the colorations it adds but not bad at all. Finally here is how they look now but I'll do some further mods to them. They really need a new cable and some baffle insulation... Last but certainly not least, great thanks to Luc for giving me this set to play with.

In a sense yes but also not. It's an odd one...

Yup, more strident than hot though.

Yup and 250$ if I'm not mistaken.

Mk1 drivers won't fit in mk2 frames, at least not properly... They look identical but the Mk2 units are just slightly smaller. It is rather odd that the 007Mk2 gets no respect when the 009's voicing is so similar.

One can never have too many transformers... Nope, it's a company that only does bulk orders so anything below 800$ FOB carries a hefty penalty.

Makes a note to design something even more inefficient...

Every KGSS needs a good home. I was just doing some inventory and I have just about enough parts for two more KGSS and then I'm out. Now I have the strange urge to build a Blue Hawaii though...

The Sigma Nova I have suffered the same damage and the driver was half split open. Not recommended unless you are up for some delicate surgery...

Pain to assemble which is why I went with IKEA...

Some further news, the first use of the new power board: Sorry for fucking up the focus... Works like a charm and fits perfectly in the spot it was designed for. No more flying wire connections for voltage selection and primary connection. Part of this: My personal amp... well until somebody pleads with me long enough and I sell it. That transformer is from my bulk order and it is seriously awesome. Can't tell if the amp is on with an ear right next to it...

That's basically it. Electrostatics only appear to be simple in theory but then again, most don't understand the theory. Take something like the Stax Lambda, almost all of them share the same housing, basic driver building blocks (stators and diaphragm assembly), cable and earpads yet they can sound very different from one another. Hell some use the same diaphragm material yet sound nothing like one another. I blame the turtles....

It's next on my list but I've run out of parts. It will be complete Mouser amp too with Fairchild output devices so part sourcing is made far easier. Also a 400V design is cheaper to build as we can go back to single caps in the PSU. Those Edcor transformers are excellent plus it's easy enough to remove the endbells and mount them sideways.

I like to do things in bulk. Another thing of note, a comparison of the old KGSSHV boards and the new HVk boards in the same chassis...