The Stax thread (New) - Page 68

That's ridiculous. You'd think after a month and 1600 views he'd get a clue that his asking price is about 4x it's vlue and it's not even a SR-84.

At the other end of the price scale, I just picked up a Koss ESP6 for $37.00. This is their original self-biasing unit with transformers in the earcups. I just got it and it almost works properly. The channels are balanced, even the LED level indicaters on the cups are working, but there are volume fluctuations and bass distortion making me think the bias is not working properly.

However I vaguely recall an old posting, probably on Headwize, that said these older Koss stats, usually ended up with shorts on their circuit boards because the foam deteriorated. But if you cleaned the boards up, they would work fine.

I will try disassembling to see if there is something that that I can work on. I know that Spritzer took one apart, but I don't think he got it working in its original configuration, but just kept the drivers and earcups and ran them off another headphone amp.

This was sold as NOS. Normally I doubt that designation, but this one really looked the part. Not a scartch anywhere, The cable seemed pristine and felt on the back of the adapter boz showed no sign of use. The only real problem was the liquid-filled earpads, which were flat. I hope the liquid didn't end up in the drivers.

Thanks!
I have searched and found some NOS RCA 6CG7/6FQ7 clear-tops. Probably have to order four of them and try them out...

That would be awesome!
I would certainly be interested in buying such an amplifier as well...

Why not plug the SR-404 into the normal bias connector. It might not show its full potential, but it will give you some idea how it sound when driven by the Aleph 3/SRD-7 combo.

Insane pricing!
If it actually were an SR80 it might sell for $100+-. But since it is not, probably an SR30, it might sell for $50+-.

You do not have to reach complete zero when you are biasing, +/-5v are fine. I do usually get to about +/-2v and stop there and this is after the amp has been on for more then an hour.

Glad you like the XF2's. You can also try out the GE or Sylvania "Fat Boy" tubes. They really are 6CA7's and not EL34's so they sound a bit different and are very long lasting. I don't like how they sound but they are good tubes.

First off the the 6CG7/6FQ7 is a bad tube for this application. According to Kevin you can put in 6S4's in the 007t and it should sound better but you need an adapter for this.

The best tubes for Stax amps are 6CG7 tubes made in Japan. They have many different brand names (Raytheon, Toshiba) and they are dirt cheap on ebay.

The harsh nature bothers me a lot and makes the He90 painful to listen to. The original SR-Lambda is bright but they are never harsh which makes them the natural choice on a morning like this when I'm so hung over I just barely could get out of bed

First off a word of warning. Be very careful when you take them apart because Koss used the bolts that attach the PCB's to the drivers as the conductors for bias and music signals. The drivers are in turn connected to the bolts with very thin uninsulated wires that break easily. I learned this the hard way so I completely rewired them with copper wire. Steel doesn't sound that good...

The foam was and still is a bad idea. It makes a mess out of every thing and corrodes the bare copper PCB's. My set even had large amounts of melted foam on the transformers because they were driven too hard. The PCB's were a mess but I cleaned them up and they will go into an external box for a make shift ESP7. The comfort is horrible but they are much better with an ESP9 headband and are pretty comfy with a Lambda headband.

DIYing something like a DHT electrostatic tube amp is on my long term plan but I just don't have the time to put into it currently and my electronics knowledge is too rusty/lacking. I think ultimately developing a good design takes not only knowledge of the field and some maths but practise, experience and a certain degree of trial and error inevitably leading to some redesign. For now I'm just trying to take in what I can to guide the process and relearn or learn as necessary. I hope to get something that sounds good out of this one day if I can find the time but I'd like a nice amp or two to hold me over in the meantime.

True but it should be worthwhile. There is also the option of just buying the Woo Stax amp and stop all this insane fiddling.

I understand that there are better tubes out there than the 6CG7/6FQ7. I am all new to tubes, so I wont risk using adapters, etc. and possibly get into trouble.

I have heard about Raytheon, so will check them out. eBay, here I come...

Has anyone heard the Woo Stax amp?

Patrick

I don't believe so at this point, but forum member Mikeg is waiting on one and I for one am really excited to hear his impressions of it when he get's it. I remember him saying that it will be at the (inter)national meet so hopefully we will get some feedback from attendees also. If feedback is good I know I will be getting one maybe with some minor changes(silver wiring for one). I have corresponded with Jack Woo and he seems to be a great guy.

Yeah, I spotted the little wires in time. I spent about 40 minutes getting the phones apart and sure enough the foam closest to the drivers was a total mess and had corroroded the circuit boards in each cup. But I managed to get this crap off and cleaned the boards with a contact cleaner. Then a bit of progold on as many conatcts as I could see and voila the thing was working pretty well.

I don't think the drivers are damaged, although there is a possibility of fluid from the earpads having got into them. But they seem pretty good and you can even get the electrostatic fart from them when they are pressed in to head, indicating to me that there are no holes in them.

Soundwise it's no Omega or even 404 and I think it needs some break-in. I don't know how many years or decades, this has been sitting around unused. The frequency response test strip which came with it is dated 1969!

My inital impression was that it was muted in the treble. Also Spritzer's recent comment about the Stax transformers lacking macro/micro dyamics seemed to apply as well. There were also some volume anomalies, i.e. long quiet classical passages gradually fade out and them come surging back to life as the volume in the source comes back. I had forgotten that little quirk about self-biasing systems. You wouldn't notice it with rock/pop/jazz, where you tend not to get long passages at low levels.

I will probably take it apart again to clean it a second time, remove and re-apply the various crimped-on contacts and located some better foam and then really give it a break-in.

Why bother with this? Well it is one of only 2 or so electrostatics that are fully enclosed and isolating. It would be nice to get it back to the specs shown in the frequency response test and maybe even tweak it into something better.

Great to hear you got them working again. The drivers are very tough but they don't have any dust covers so keep them in a clean space. I would have loved to be at the meeting where they thought that fluid filled earpads and high voltages were a good idea. My only real issue with the ESP6 is the horrible headband. It would be fine if my ears were two inches higher up.

It's great fun to repair these older phones and make them better then they ever were. A good case is the Suprex PEP-74. They ripped off every last bit from Stax and they were meant to be cheap and sound like it to but with a few simple mods they turn into PRAT monsters. These are the rock electrostatics.