decoherent Posted June 15, 2012 Report Posted June 15, 2012 I've to say the out stage does looks to me a lot like a "paralled" srrp...
kevin gilmore Posted June 15, 2012 Report Posted June 15, 2012 paralled, yes. srpp, definitely not. srpp takes the output from the top cathode and is bad when driving electrostatic loads because of the huge change in impedance over frequency. This takes the output from the plate of the bottom tube. So its a tube driven constant current source. Substantial difference. The reason its doubled up is the cathode to filament voltage limits. No other way to do this with a 5687. Unless you are mikhail and can magically have a filament voltage at both ground and -400 volts at the same time...
justin Posted June 15, 2012 Report Posted June 15, 2012 (edited) paralled, yes. srpp, definitely not. srpp takes the output from the top cathode and is bad when driving electrostatic loads because of the huge change in impedance over frequency. This takes the output from the plate of the bottom tube. So its a tube driven constant current source. Substantial difference. The four 5687 tubes are configured in a SRPP topology, each tube drives one phase of the signal. -A10 wasn't it determined that amp isnt actually SRPP? that's a new one. Advertise something that's bad, when it isn't even made that way…lol Edited June 15, 2012 by justin
kevin gilmore Posted June 15, 2012 Report Posted June 15, 2012 (edited) The latest pictures that were acquired prove that the A10 was in fact wired as srpp. Very hard to determine from the low quality layout. Broskie will argue that due to the load, it cannot possibly be srpp. With very little additional work, this is easy to turn into a super B52, with dc coupled outputs. (+/-125 volt power supplies) (needs a servo to be safe) birgir has decided to tackle this piece of shit next. a full channel on one board including power supply. 5.1 x 3.85 inches http://gilmore.chem....du/dorkstar.jpg Edited June 16, 2012 by kevin gilmore
spritzer Posted June 16, 2012 Author Report Posted June 16, 2012 What can I say, I'm a glutton for punishment. Plus it's what, 300$ in parts plus chassis? Not a whole lot... As for the SRPP, Ray has said many times that the amp is indeed SRPP and it is wired for SRPP. As Kevin said, Broskie would not agree though as the circuit will not behave as SRPP with an electrostatic driver as the load. We countered this by placing 1M resistors to ground after the output caps which will diminish the impact of the wild impedance swings. Not a perfect solution though.
kevin gilmore Posted June 16, 2012 Report Posted June 16, 2012 Whats also interesting is on this version you can build an unbalanced only one with just a single board. Figure the board and all the parts on it to be a total of $100 (the opamps are $21 each), add transformer, box and input output connectors.
decoherent Posted June 16, 2012 Report Posted June 16, 2012 The input section is the stax srx circuit. Which is easy to model, but is hard to explain. And it works and works well. The output stage is a tube constant current source. It would be easy to do the same thing to the bae, which would result in a total of 8 output tubes. The feedback is important and reduces what would be 3% THD to less than .2% THD. At some point these things start looking like, and are the size of the VTL WOTAN. The power supplies get to be very large. Kevin, what are the advantages of the srx input stage? How do you calculate gain and input/output impedance? Will two ccs in place of R1 and R6 make possible to avoid the global feedback?
kevin gilmore Posted June 16, 2012 Report Posted June 16, 2012 (edited) The advantages are more gain and one less capacitor. Trust me, you want the feedback, otherwise it sounds like crap. This is the one that will probably make it to production. http://gilmore.chem....rn.edu/beac.jpg Its 10.8 x 9.2 inches 7 x 6.3v filament supplies. I could split out the front end power supply, then you could run +/-500V for the output stage. The nice thing about this one is auto balance output. In fact you could act like that knucklehead in israel, and swap output tubes with the power on. And no nasty silicon to go up in smoke. Edited June 16, 2012 by kevin gilmore
spritzer Posted June 17, 2012 Author Report Posted June 17, 2012 I can just see me ordering a transformer for this one... "You need how many 6.3V windings???"
Horio Posted June 17, 2012 Report Posted June 17, 2012 (edited) The advantages are more gain and one less capacitor. Trust me, you want the feedback, otherwise it sounds like crap. This is the one that will probably make it to production. http://gilmore.chem....rn.edu/beac.jpg Its 10.8 x 9.2 inches 7 x 6.3v filament supplies. Crazy idea but with all that extra space to the sides of the input stage, it would be really sweet to somehow throw in the KG attenuator. That way the amp box could be one of the small compact Hifi2000 1U case like these. Edited June 17, 2012 by Horio
Beefy Posted June 17, 2012 Report Posted June 17, 2012 Crazy idea but with all that extra space to the sides of the input stage, it would be really sweet to somehow throw in the KG attenuator. That way the amp box could be one of the small compact Hifi2000 1U case like these. Now *that* is using your noodle.
kevin gilmore Posted June 17, 2012 Report Posted June 17, 2012 (edited) Except that the attenuator is a 6 layer board which would force the rest of It to also be a 6 layer board and that is a bunch more money. Probably enough room to add the mounting holes for a pair of them. The 1u chassis is impossible due to the height of the caps. Maybe if you lay the caps down. Also the electrolytics are too big, And the attenuator is 1 inch thick Edited June 17, 2012 by kevin gilmore
spritzer Posted June 17, 2012 Author Report Posted June 17, 2012 We could arrange the ecc83's in a line in front of the EL34's but I'm too lazy to do it now....
kevin gilmore Posted June 17, 2012 Report Posted June 17, 2012 (edited) board size with the attenuators on board would be 11.5 x 10.4 rotated input section, board is 9 x 9 inches http://gilmore.chem..../beacssmall.jpg total tube power with filaments 180 watts. going to be perfect for winter. Edited June 17, 2012 by kevin gilmore
kevin gilmore Posted June 19, 2012 Report Posted June 19, 2012 pcb layout tip - if the amp can accept unbalanced inputs, then wire the first 2 sections of the pot for L+ and R+. that way if someone only has a 2-gang pot and only intends to have RCA inputs it will still work i like this idea.
Victor Chew Posted June 19, 2012 Report Posted June 19, 2012 Did some googling and this is what was said - EL34 and 6CA7 are similar. Both, are interchangeable without circuit mods. EL34 are British and the other American. Some have said that the EL34 sounds warmer whilst the 6CA7 harder with more top and bottom. Does this mean that we can use EL34 as an option as well?
kevin gilmore Posted June 19, 2012 Report Posted June 19, 2012 (edited) all of these, roll forever shortest distance socket to socket is 2.3 inches i can make the board bigger if it needs to. 6L6G (and A,B,C versions) 5881 5932 7027 EL34 6CA7 KT77 WE350B Compatible with an adapter 6550 KT88 KT90 Compatible with stupid adapter EL360,3D21 and every other thing mikhail made for the esx Edited June 19, 2012 by kevin gilmore
spritzer Posted June 19, 2012 Author Report Posted June 19, 2012 We need to make one for the KT120 biased at half power... I do think that the EL34 is the best bet and there are no triodes which can handle these voltages and don't cost a bundle. DHT's also bring even more filament hassle and multiplies the cost. The 6CA7 was an attempt to make the EL34 without paying royalty fees to Mullard. They are pretty much the same. I am indeed out of the Alpha pots but I might do another run. Too busy to even think about that now... What's been going on lately is that we are looking at pretty much every possible way to design a Stax tube amp and designing circuit boards so people can actually build them. The board files will be made available so these amps can be built by anyone.
keithpgdrb Posted June 23, 2012 Report Posted June 23, 2012 Great looking project. where did that poor mans amp go? Let us not forget the poor men.
spritzer Posted June 23, 2012 Author Report Posted June 23, 2012 It's just been postponed as there wasn't enough headroom for the feedback. We never release anything unless it is perfect unless "sounding like crap" was part of the plan.
keithpgdrb Posted June 23, 2012 Report Posted June 23, 2012 We shall remain crap free. Shame It didn't work out though. I was itching to build. My stax have even wanting more then the energizer.
deepak Posted June 29, 2012 Report Posted June 29, 2012 Bdent has the 2sa1486 for $3.50 each when 10 are bought
justin Posted June 29, 2012 Report Posted June 29, 2012 Bdent has the 2sa1486 for $3.50 each when 10 are bought im going to have to do something about that. parts.headamp.com, coming soon
luvdunhill Posted June 29, 2012 Report Posted June 29, 2012 Wow, $3.50 is insane. I'd sell 100 in original packaging for that
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