FrankCooter

Considering the huge difference in signal chains, I'm not sure that a meet comparison between my 507's amd n3rdling's O2's means much. What we should have done at the last NorCal meet was plug my 507's into the B.H. and done a direct comparison. Hopefully we'll get another chance. What is pretty clear is that the 507's are substantially closer to the O2's than any previous Lambda. I'm curious what the rest of the updated Stax line sounds like.

You guys need to get your feet wet and build something. There are plenty of cost effective, easy to implement, and surprisingly effective DIY designs out there if you dig a little. Make a ton of mistakes, go through a learning curve, and get something successful under your belt before attempting anything as complex as the T2. Got to learn how to crawl before you can run. Consider it the start of a journey.

I'm sure you've considered it, but instead of semiconductor outputs, how about a dht to replace the 6ca7/el34? An 801a would be a pretty close fit. I've seen NOS quads for less than xf2's. Filaments would probably require a seperate chassis.

These showed up yesterday. Wow! Definitely NOT "your father's Oldsmobile". Major upgrade across the board over the 303's. No more thin, etchy, cool, flat, and uninviting midrange. Much warmer, but and the same time more resolution and better, more precise imaging. There's some real depth and layering of the sound stage. Much improved bass. Having never heard these, and not being a lambda fan, I had some reservations. I gave up my K-1000 for these. I'm happy with the trade. Headband could use to be a bit bigger. I have it maxed out and it's fine for my 7 3/8 hat size. I can see where someone with a really big head might find it uncomfortable. Over all, a big "thumbs up"!

Congratulations Craig! It's been an education just following your build. It's also been a little bit like watching someone climb Mt. Everest. I admire not only your skills but your unfazed coolness and dedication in the face of repeated problems and frustration. I really appreciate the way you've extensively documented the journey. Nothing like victory in the end. Enjoy!

I ordered a pair of these yesterday from "Elusive Disc" (last day of the 10% off sale). Hoping your sale had nothing to do with the quality of the 507. At any rate, I'll get to do a "head to head " with the SR-303's and the ESP-950's. They'll also get a chance to go up against the LCD-2. Winner stays, looser goes.

This one's going on the shelf until I can afford a second set of proper magnetics. As is, it's not something I would take out in public. There's some promise, but in addition to the restricted bandwidth, there's a bit of flatness and lack of resolution compared to the D3A/7403 zebrawood amp. I'll try again when I'm able. And no matter what, it was definitely a valuable learning experiance. The big lesson is that electrostatic headphones, because of their low sensitivity if nothing else, are quite compatible with DHT's. Even with a gain of over 400, no special measures were required reduce hum and noise to acceptable levels. Building an all DHT dynamic headphone amplifier for something like a Grado is much more challenging in this area. A valuable find was the 2E22 directly heated pentode that was used for the second stage. This tube is the big brother of Pete Millet's favorite 307A. Triode wired, this tube is a very interesting substitute for a KT88 or EL 34. Premium European examples run only about $40.00. I'm going to convert the 7403 in the original amp to a 2E22 and see what happens. If it works out, then I intend to install a switchable CCS load for the D3A. I think it would be interesting for the listener to switch between a classical interstage transformer and a modern CCS plate load. Maybe there could be a blind "taste test" between the two topologies at the next meet. Thanks again for all the kind words! I'll be back with something new in the not too distant future.

The great cap divide is between the paper in oil traditionalists and the film/foil modernists. Since you guys are building two units, why not build one one way and the second the other? When you're finished , pit the two against each other and let us all know the winner. Doug is absolutely right (as usual) about the size of the output caps. A value of around 5 uf is plenty. I'd also follow his advice about the RIAA caps. Electrolytics are all bad. Blackgates, no longer available, were the best of them. In tube circuits, many of us use motor-run oil in paper types. The Cerefine types, also no longer in current production, were considered a less expensive alternative to Blackgates. These occasionally show up on Ebay. Many here now use Panasonics for power supply filters.

One of the major reasons I don't use them in audio circuits. I find it ironic that it's often easier to source a 1920's tube than a 1990's transistor. The tubes don't blow up either. A transistor is a switch, a tube an audio device , let each do it's thing.

I really appreciate all the positive comments and encouragement! It's definitely part of what inspires me to keep building these dinosaurs. This was kind of a two phase project. I was attempting to build the simplest possible all DHT electrostatic amp, but I was also interested in exploring a new chassis concept. The chassis is solid Gabon ebony with a 1/8" copper top plate. Tubing is plain old Home Depot 3/8" copper water tube. The tubing was cut and bent with basic hand tools. Not a fun task, and I have a pile of pieces that didn't quite fit. I polished them in a drill with 400 grit wet/dry, then spray laquered them. Kind of crude, but it worked. The design emerged out of my affinity for all things Art-Deco. In this particular case, the inspiration was a movie theater marquee. I've been looking for something more rounded and organic, more "tubelike", than the rectilinear forms I've previosly used. I wanted something that was "retro", yet at the same time modern and futuristic. I like this sort of style and intend to explore it further. One of my "pet peeves" about the age we live in is the death of industrial design. Where is Raymond Lowey when you really need him? The amp is still a "work in progress". I'll have more about the circuitry and sonics later.

Had this up and running for about a week. It's a choke loaded DHT 826 cap coupled to a transformer loaded directly heated 2E22. It's a bit shy on gain (about 400), and the bass rolls off due to the 100H choke on the 826 (need about 300). Still, a very interesting project. Surprisingly little noise and hum. Enough promise here to warrant pursuing this with appropriate parts and a little more sophisticated design. [ATTACH=CONFIG]3597[/ATTACH]

OK, how about a simple para-feed "spud " amp based on Electra-Print 5K:32 @30ma transformers? Again, employing the IXYS10M90S and Obligato caps, this time with something like a 12GN7? Very nice little amp, I've built several along these lines. Ctoole has a similar amp based on the 7788.

I was thinking the 600 volts might actually be an advantage in this case because you could use it to increase the value of the "tail" resistor, more or less substituting for the negative supply often associated with this circuit. Of course, it still puts 600 across the 12AT7 before the tube conducts. Not a good thing. Of course, there's a lot of other ways to "skin the cat" and get a suitable working voltage. A simple single tube regulator might be an answer.

How about another small, relatively inexpensive electrostatic amp? Something like a 12AT7 configured as a long tailed pair, cap coupled to a push-pull pair of EL84's using CCS loads based on IXYS10M90 current regulators. Cap output. Use the cheap but exellent 630v Obligato oil caps all around. Base the whole thing on a single 600V supply. Won't set the world on fire, but it might surprise you. Simple, cheap, point to point, and most importantly, unique to you!

I've heard the Titan and totally agree with you. One of the best speakers I've ever heard. If I had that kind of money, I'd seriously consider owning a pair. All my experiance with Dr. Edgar's ( a great guy!) work was with the older DIY designs originally published in "Speaker Builder" magazine, usually using inexpensive Emminence drivers. No surprise that equipment using professional grade Altec drivers sounded superior. No surprise either that Dr. Edgar's commercial designs employing TAD drivers beats vintage Altec. Love the TAD stuff! If only I was rich enough to play at that level!

Just discovered this thread. For what it's worth, I spent most of the '90's experimenting, designing, and building horn, and other high efficiency speakers. I went through Klipsch Heresy's, Cornwalls, and LaScala's, a number of Bruce Edgar designs, and a lot of Altec gear. In the end, I wound up with dual 515 bass horn enclosures with large format compression drivers driving 1005 multicell horns. If you've got the room, nothing beats an Altec system. For the past 3 or 4 years I've been seeking this sound in headphones. Unfortunately, nothing I've heard to date comes close. Big "thumbs up" on the Altec gear. If you do it right, it's not a bad investment either.

I think that DHT's have the potential to make a signifigant improvement in the Stax mids, which, like the K1000, can be a little too cool and thin for some. However, a 2A3 through an SRD-7 is way too small for the job. A 300B isn't big enough either. On the other hand, an 845 might be very interesting. In the end though, you'll never get the full benifit of a DHT out of the SRD-7. I use a lot of transformers in my designs, but there's no way you can run the output of a 16:1 step-down into a 23:1 step-up without degradation. If you're into DIY, Electra-Print makes transformers specifically for this purpose. I'm building a DHT electrostatic amp now. Should be running later this week. You'll see it here.

You have a good point. Only way to find out if it's practical is to build it. Fortunately, it's simple and I have all the parts at hand. No great loss if it doesn't work out. I've built 2 stage all DHT amps for headphones before. Simple design, but a bitch to get quiet enough for headphone use. You need really well filtered power supplies, especially for the filaments ( I had to add additional filtering to the otherwise exellent Tentabs supplies), the gain needs to be as low as possible, the tubes need to be shock mounted, and you need lots of tubes to sort for the quietest and most stable individuals. PIA, never totally without residual problems, but to me at least, totally worth it. Once you hear a 26 or 112A in a 6SN7 circuit, you'll never be satisfied with the 6SN7 again. In this case, I'm hoping that the low sensitivity of electrostatic headphones will work to the advantage of DHT's. Hopefully, any residual noise or ripple will be too small to make any difference at all. I don't expect any problems with the 2E22 outputs. The 826 first stage is a "pig in a poke" until actually built. Never worked with the 826 before. My guess is, that because of it's high mu (31) and heavy filament requirements (7.5V @ 4A) it won't be suitable. Nothing new for me though, by far the majority of the stuff I build I eventually discard. I have to remind myself now and then of the Thomas Edison story where he was asked by a reporter about how the light bulb was coming. At this point Edison had been working on the light bulb for eight years without success. His reply was something like: "I can't tell you exactly what makes a light bulb, but I can tell you 10,000 things that don't." The fun for me in all this stuff is the journey. Uncertainty and failure make success, should it come all, that much sweeter. I like to think there's still a place in the modern world for the occasional empiricist.

You're not the only simpleton Nate. A big part of the reason I use a lot of iron is that it greatly simplifies the design process, and enables someone with basically technician level electronic ability (me) to play at a much higher level than would otherwise be possible. I'm not the only one though, the Japanese DIY community has been big into iron from the beginning of the DHT revival. Most of the tubes I like best were originally intended to be used with iron. Iron in the audio path was abandoned in the late '30's more for reasons of cost than performance. Even today, while it may not produce the best test measurements, there are some applications (such as driving a big DHT like an 845) that are better served by transformers than any modern alternative.

[ATTACH=CONFIG]3391[/ATTACH] Spent the last week or so listening to my newly revived ESP950's and the transformer amp. Don't have any reference points except an EXSTATA and an SRD-7, but I like what I'm hearing and feel there's more to be had. Time to get some DHT's in the mix. I've got a full on 3 stage 845 in the works, but I was thinking about something simpler to start with. Here's a quick sketch of a modest 2 stage design I may try. The 826 has a mu of 31, very unusual for a DHT. Not rare or expensive, but not used a lot because it needs a minimum of about 600V. The 2E22 is actually a directly heated pentode, that aside from the filament and socket, is electrically equivalent to a KT-88.

Got my ESP950's back from Koss yesterday. They replaced the drivers and a number of other electrical and cosmetic components. They work flawlessly and look brand new. Total cost was $6.00 shipping! I bought these used, I have no idea how old they are, but I do know that they have had the drivers replaced under warranty at least once before. I told them the truth that they were deliberately abused and being used with a custom amp. No problems and no costs! I am very grateful and very impressed. Stax and most other companies could learn a thing or two about customer service from Koss.

By contemporary standards, I have a fair amount of high voltage experiance. As a teenager in the late '60's I built kilowatt level amateur c.w. transmitters. Components were almost exclusively WWII military surplus. My friend had a 5kw rig that originally came from a marine transmitting station on the California coast. We set up the transmitter in his parents garage and used it on the 80 meter novice band. It took up half the garage and looked like something out of an old Frankenstein movie. It used 813's as driver tubes. The finals were some huge, irregularly shaped cylinders with a sort of central ball shape, perhaps 16" tall by 8" across the central ball. When we'd fire the thing up, strange things woud happen like nearby flourescent bulbs would glow on their own and you'd occasionally see a sort of St. Elmo's fire effect on the backyard closeline. Obviously, our parents (and the FCC) had no idea what we were doing. I look back now and shutter at our crazieness, but it certinly was educational.

Thankyou, Kevin! I'll go with diode protection box. Sounds like what you used to see in the crossovers of Klipsch K-horns and LaScalas. The 100x probe cost $30.. My scope (an old tube Techtronix) costs $150.. No great loss if I blow it up. Very thin operation here. Aside from the Electra-Print transformers, if it doesn't come from the surplus store, university cast offs, Ebay, or some other scrounged souce, it doesn't happen. It's actually part of the fun to try to make something from next to nothing. In this case I'll admit to a liitle jelousy, your scope probe is worth more than all my test equipment combined!

We had some "words". Actually he felt pretty bad. Just glad it wasn't a pair of O2's. I actually thought about your Chicago "experiance". If you don't mind, I'd appreciate a little lesson in lab testing electrostatic amps. The problem is of course the very high voltage swings involved in these amps. I've got a 100x, 2kv rated scope probe on the way, so I should be able to do some basic sweeps. I own an old HP 331a distortion analyzer, but it's only good up to 300v. I guess I could try it with some sort of resistor divider network. Any suggestions would be appreciated. New territory for me.

[ATTACH=CONFIG]3334[/ATTACH] Here's a picture where you can actually see something. I'm still in the stumbling around part of the learning process with my first digital camera. Got about 15 minutes of listening before going to the bathroom and letting my son have a turn. His idea of a test was the "Gladiator" soundtrack at maxed volume. I could hear it all the way across the house (briefly) and then a huge screetching sound. On paper, this amp puts out 2kv p-p. Both sides of my Koss ESP-950's got blown out. Sent them back to Koss. Told them the truth. Going to put that "unconditional" to the test!