kevin gilmore Posted January 14, 2011 Report Share Posted January 14, 2011 I think that justin really wants a T2. Trouble is, he does not have the 2 weeks of time to build it. Hey mikhail... you wanna help justin out?? Quote Link to comment Share on other sites More sharing options...
Craig Sawyers Posted January 14, 2011 Report Share Posted January 14, 2011 I think that justin really wants a T2. Trouble is, he does not have the 2 weeks of time to build it. And that is a solid two weeks. Not counting my semiconductor difficulties the total integrated build time must have been at least 80 hours, and probably a fair chunk more. Quote Link to comment Share on other sites More sharing options...
spritzer Posted January 14, 2011 Author Report Share Posted January 14, 2011 I quite like the fact that some of the T2 parts wound up in other Stax products from the same ere. K216's as output devices is the first "portable amp" for instance. I think that justin really wants a T2. Trouble is, he does not have the 2 weeks of time to build it. I think Justin and I need to get cracking on cloning research... Quote Link to comment Share on other sites More sharing options...
jcx Posted January 14, 2011 Report Share Posted January 14, 2011 I thought that opening the design to using SS output means major differences in parasitic C, gm, gain linearity, operating points vs the output tube and slow, low gain, bjt ccs are inevitable and that you might be open to examining the engineering principles behind the device choices for our benefit if IXYS Vertical Mosfet are ruled out for gm nonlinearity or Rds the choice between Semisouth JFETs can be determined by how you choose to weight several differences - I don't think 3-5 V difference in Vgs bais point is as important as ~4x higher parasitic (and nonlinear) C particularly when the larger parasitic C values becomes similar to or even more than the ES headphone load C with the T2 "Rush Cascode" gain stage and using ~ same parasitic C device for the ccs you have to drive ~ 2xCrss + 1xCds for ~150pF with the higher C parts, estimating from the graphs you don't get the ordinary Cascode's small signal cancellation of Cds when the 2sj79 gm is larger than the JFET's gm - although its hard to make a very good guess at the JFET 10 mA gm from the datasheet curves there is even a fraction, possibly substantial, additional Cds from the ccs JFET depending on gm and current set R values the ccs certainly doesn't look as "elegant" with the needed positive bias with the lower parasitic C sje170r555 part - but the solutions can be cheap/no more complicated than the preexisting T2 circuitry for the same function if you really need to replicate the T2 operating points to better than any differing manufacturer's tube's variations then you can add degeneration R to the cascode JFET source to match the much lower tube gm; for V operating point just change the Zener V as to how substituting any of the JFET, Mosfet options would effect the "sweetness" of the T2's sound I certainly would guess the doubling the load with added parasitic C and doubling operating current to compensate may have at least some effect Quote Link to comment Share on other sites More sharing options...
luvdunhill Posted January 14, 2011 Report Share Posted January 14, 2011 Lots and lots of things can be changed or simplified. And i encourage you to build one and test it. Good advise. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 14, 2011 Report Share Posted January 14, 2011 There are clearly some things that tubes do way better than transistors. The output tube is one of them. 15 pf input capacitance. Although that really does not matter as much as you might think. An equivalent Rds of about 5k. Also really does not matter except it limits maximum voltage swing. Neither the ixys parts or the semisouth parts are perfect for the job, its the lesser of 2 evils. I plan on trying many semiconductors to see which performs the best. But the ixys parts with the 1500 ns rise times are clearly not what you would want. The slew rate and distortion characteristics are what i'm after. It might be a bit easier to replace just the front end and leave the output tubes. And then you have something similar to the BHSE which is a bunch simpler with a lot less parts. I'm looking at other alternatives and trying to find out where apex gets their complementary 1200 volt fets. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 15, 2011 Report Share Posted January 15, 2011 Andy finally got his working. A bad Rv1 in one of the batteries. I would imagine listening impressions soon. Andy's first project was rebuilding a ES1, and with a bit of help did so successfully. Andy's second project was the T2. Anyone with the time and perservance should have no trouble with this Quote Link to comment Share on other sites More sharing options...
Craig Sawyers Posted January 15, 2011 Report Share Posted January 15, 2011 (edited) WHOOO - well done Andy. A dead Bourns pot was not remotely on my hit list of possibilities - hats off for tracking that down. And hats off to Stax's design and KG's reproduction - seriously robust, both to Andy's wiring problem and once working it seems to stay so (knock on wood...) Looking forward to hearing the report on the sonics! Edited January 15, 2011 by Craig Sawyers Quote Link to comment Share on other sites More sharing options...
spritzer Posted January 15, 2011 Author Report Share Posted January 15, 2011 Good show Andy! Quote Link to comment Share on other sites More sharing options...
blubliss Posted January 15, 2011 Report Share Posted January 15, 2011 Holy Shiiiiiiiiiit!!! This thing is truly insane. It was a tough 3-4 weeks of tracking down the problem, but I have the SR-Omega on my head right now and this is truly not fair to any other amp alive (the ones i've heard) I swapped quickly to the BA-R10 which I already had on and I was really quite shocked. It sounded like I was listening through a wet rag. I am sure that I will still enjoy the combo but the difference is unreal. It was only a brief listen (Schubert piano). I may still need to adjust a bit, had some noise, then I stopped the music and it ceased. So, maybe a turn of the pots is needed. KG has said my first project was an ES-1 and then this but the truth is Steve did all the soldering. I helped all along but we could have done nothing without KGs guidance, hats off to him. Quote Link to comment Share on other sites More sharing options...
Craig Sawyers Posted January 16, 2011 Report Share Posted January 16, 2011 Holy Shiiiiiiiiiit!!! This thing is truly insane. Yup. That is the reaction I was expecting Quote Link to comment Share on other sites More sharing options...
luvdunhill Posted January 17, 2011 Report Share Posted January 17, 2011 I just got the two more of the 6DJ8 quads off to Andy and Jose. For those that didn't know, I was selling matched Sylvania 6DJ8 quads, with identical construction to the ones that Kevin has successfully used. I had a batch of around 75 of these tubes and have been able to get good matches across all 8 plates. They've been tested by three people, including the irreproachable Mr. Circle Hole Cutter Tech and myself. I have two more quads available if anyone is interested, please PM me. Quote Link to comment Share on other sites More sharing options...
blubliss Posted January 17, 2011 Report Share Posted January 17, 2011 All right, more listening done today and this amp really is amazing. The detail retrieval while remaining smooth is uncanny. Went back to the BA-R10 for a moment and there must have been something wrong yesterday because it's still great too. I think it was having both amps on at the same time plugged into my balanced transformer power thingee. The T2 sucked the life from the BA or some such evil. Quote Link to comment Share on other sites More sharing options...
Voltron Posted January 17, 2011 Report Share Posted January 17, 2011 Major congrat Andy! I am getting more and more excited for my amp even though the BHse built by Nate is already a fantastic option. Many thanks to Nate at first and now Kerry for taking on the project. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 17, 2011 Report Share Posted January 17, 2011 I don't know how much power your transformer is good for, but the T2 is 200 watts for sure, and the BA has to be at least 100 watts. So you are definitely pushing it. T2 can handle -15% line just fine, but i doubt the BA can. Quote Link to comment Share on other sites More sharing options...
Craig Sawyers Posted January 17, 2011 Report Share Posted January 17, 2011 All right, more listening done today and this amp really is amazing. The detail retrieval while remaining smooth is uncanny. Went back to the BA-R10 for a moment and there must have been something wrong yesterday because it's still great too. I think it was having both amps on at the same time plugged into my balanced transformer power thingee. The T2 sucked the life from the BA or some such evil. You have to be careful that your balanced power transformer has enough rating. The T2 amp takes around 120W, plus the power regulator dissipation, plus transformer losses - so at least 200W all up. What is the rating of your balanced transformer? Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 17, 2011 Report Share Posted January 17, 2011 I wanted to be sure i was doing things right, so i brought the test circuit into work where i have more equipment and an easier way to test. The semisouth parts have a significant problem. The massive amount of gate current necessary. Actually measures about 150ma per part, So 300 ma per channel, so to do this an extra 50 volt power supply would be required, spec'd at 1 amp, and referenced to the -500 supply. Plus extra current on the -500 supply. Kind of what you would expect for a jfet. Going to mess with a few of the ixys parts soon. Quote Link to comment Share on other sites More sharing options...
Craig Sawyers Posted January 17, 2011 Report Share Posted January 17, 2011 I wanted to be sure i was doing things right, so i brought the test circuit into work where i have more equipment and an easier way to test. The semisouth parts have a significant problem. The massive amount of gate current necessary. Actually measures about 150ma per part, So 300 ma per channel, so to do this an extra 50 volt power supply would be required, spec'd at 1 amp, and referenced to the -500 supply. Plus extra current on the -500 supply. Kind of what you would expect for a jfet. Going to mess with a few of the ixys parts soon. That is strange, if the spec sheet for the device is taken as being correct. From the transfer characteristics, figure 4, for 20mA drain current, the Vgs is about 2.25V. Reading that voltage off on figure 5 gives an unreadably small gate current at 25C, and only rises to about 50mA at 175C. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 17, 2011 Report Share Posted January 17, 2011 I can't explain it yet either. I am running it at 500 volts with a 1kv supply and 20ma current source. On a decent sized heatsink. The gate current is a factor of 10 more than i expect. Quote Link to comment Share on other sites More sharing options...
blubliss Posted January 17, 2011 Report Share Posted January 17, 2011 (edited) You have to be careful that your balanced power transformer has enough rating. The T2 amp takes around 120W, plus the power regulator dissipation, plus transformer losses - so at least 200W all up. What is the rating of your balanced transformer? I think I have the 1.5RQ, seems like it should handle the load?? My source is plugged in there too but that does not draw much. Equitech 1.5Q Edited January 17, 2011 by blubliss Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 17, 2011 Report Share Posted January 17, 2011 (edited) should have no trouble with that one, 1.5kva. The semisouth parts perform much better at 100ma, but that is clearly silly. I ordered some bimosfets, and igbt's, and some very beefy npn transistors to see if i like any of them. Its very hard to beat out the 6ca7 in that application. Edited January 17, 2011 by kevin gilmore Quote Link to comment Share on other sites More sharing options...
FrankCooter Posted January 18, 2011 Report Share Posted January 18, 2011 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. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 18, 2011 Report Share Posted January 18, 2011 DHT's not really suitable for grounded grid applications. That would require 4 seperate and very well isolated filament supplies that bounce up and down and sit at -450V. I do have an all DHT design for an electrostatic amp. No one in their right mind would build it. Its $6k in tubes alone. If you want to build it frank, i will help... I will supply the 250khz floating filament supplies Quote Link to comment Share on other sites More sharing options...
blubliss Posted January 18, 2011 Report Share Posted January 18, 2011 Listening to the HE90 now and it sounds darn good. I always sensed some brightness in this particular phone as did its previous owner. No sign of that yet. The HE90 does not have the accuracy of the Stax phones, but it is still a presentation I like. Vocals are less in the middle of the head like the SR-007. I have never heard the phone on the HEV90, would love to compare that to what I am hearing now. Quote Link to comment Share on other sites More sharing options...
kevin gilmore Posted January 18, 2011 Report Share Posted January 18, 2011 Well... build yourself a HEV90. You know how But first find a stock of the output tubes. Quote Link to comment Share on other sites More sharing options...
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