mypasswordis Posted July 22, 2010 Report Posted July 22, 2010 Er, yes, that's what we've been discussing for the last past couple of pages.http://www.head-case.org/forums/headphones/785-headcase-stax-thread-332.html#post374083
Beefy Posted July 22, 2010 Report Posted July 22, 2010 eXStata V2! Considering the commercial direction that Cavalli Audio seems to be taking, I think we'll be waiting a while. And as much as the Kevin Gilmores of the world kick arse as designers and builders, I can't see who is going to step up to the plate to give us another project that is so accessible to middling DIY'ers like myself.
faust3d Posted July 22, 2010 Report Posted July 22, 2010 i measure with pabbi1 listening levels... http://gilmore.chem.northwestern.edu/srm1mk2.pdf even so we are pretty close. -60db second harmonic is .1% -85db third harmonic is better than .01% i was quoting DC power supply voltages, not AC voltage swing. What I don't understand is why the eXStatA with it's "1% distortion" still drives my O2 Mk1 better than either of my previous SRM-1 Mk2 Pro ever could. The SRM-1 Mk2 Pro with O2 Mk1 or Mk2 was soft and muted with them, and had to be cranked to max yet still had poor dynamics and drive with either O2. The T1 and GES drove the O2 Mk1 much better than the SRM-1 Mk2 Pro, but I still don't think they could match the SRM-717 with them. Those two still sounded soft around the edges with the 02, and needed more power, while the 717 could play loud, fast and dynamic with them (but still sounded detailed, spacious, warm and crisp at the same time). Not having compared them side by side, I still felt that my experience with the O2/eXStatA was similar to my short experience with the O2/717. I really liked the 717, but I also really like my hybrid eXStatA. I suppose I'll need to find a way to listen to someone else's 717 side by side with my eXStatA some day and see what I think then. Aren't there different types of distortion, when one kind is more musical than the other? Is that the case with the eXStatA? Either way, I still find the eXStatA enjoyable to listen to. Got it. Thanks for clarification. I like SRM-1Mk2 a lot and had it now for few years, for my listening levels, not very loud, it performs very well even with O2 Mk1. To my ears T1S/T1W/T1 sound a bit better (warmer, more coherent and nuanced) with Lambda headphones especially LNS, but not with O2. I tried DIY KGSS and BH sometime ago with O2 and some Lambdas, under meet conditions, and they sounded a bit too cold in comparison, I guess that's the sound signature.
mypasswordis Posted July 22, 2010 Report Posted July 22, 2010 I heard the 007t and assuming it's similar to the T1 variants, I can see where you're coming from. The 007t sounds like a bloated mess imo.
faust3d Posted July 22, 2010 Report Posted July 22, 2010 well there are definitely different kinds of distortion, mainly 2nd harmonic, or mainly 3rd harmonic. and sound signatures are different too. push pull sounds a particular way, whether solid state or tubes. same thing with the various kind of single ended things. There is also soft clipping vs hard clipping. all the stax amps are really singled ended with constant current sources for the solid state amps, and resistors for the tube amps. (the t2 is something else entirely) the exstata output stage is a constant current source. you can add a current source to the exstata gain stage and make it bunches better. The vhv amp i posted a bit ago is the only example of a solid state push pull amp that i know of that actually works. It depends on stacking transistors to meet the necessary voltage requirements, and its performance suffers as a result. This might explain why I like Stax amps, as I always tend to like single ended SS amps and they sound better to me (more coherent and sweet) than big powerful amps even when bass and dynamics suffer. Yet single ended tube triode amps I find too sweet, go figure Another case of different perception of things.
kevin gilmore Posted July 22, 2010 Report Posted July 22, 2010 i just got a copy of the srm323 schematics, and the design is very similar to all the rest, but with the addition of higher voltage power supplies, and 2sa1968's as the current sources. defintely tests even better. My guess is that people would like it very much. At about $600 via ebay (brand new) its definitely in the same range as an exstata by the time you add a case and decent volume knob. http://gilmore.chem.northwestern.edu/srm323a.pdf analysis of srm300 and srm727 coming soon
kevin gilmore Posted July 22, 2010 Report Posted July 22, 2010 and just for fun, a srm323 front end and a push pull output section http://gilmore.chem.northwestern.edu/srm323a2.pdf my front end would work in the same way... 2sa1968's a bit expensive, but some people would really like this. +/-450 volt power supplies... pretty close to that magic +/-500...
KrypticMind Posted July 23, 2010 Report Posted July 23, 2010 re: 717, open it up and listen to it, when the sound goes away, look at the led's and see if all of them are lit. If none of them are lit, then you are having a thermal cutout inside the transformer... the srm1mk2 was made between 1985 and 1990. As such its more than 20 years old. More than enough time for the electrolytics to dry up. So people who still have them and don't like the sound should probably change out all the power caps. At this point the 717's are now 10 years old and probably need new caps too. Thanks for the possible explanation! I'll report back with what happens. It has been on all day, and no problems yet.
Bidoux Posted July 23, 2010 Report Posted July 23, 2010 Does the srm323a2 have a current limiting system on the output stage ?
kevin gilmore Posted July 23, 2010 Report Posted July 23, 2010 as soon as you take the cover off, it does not overheat... srm323a2 definitely has current limiting. Q13 (which you can't see the label) and Q14, Q17 (can't see the label) and Q18 set high enough to protect the transistors, but not to kick in otherwise. not the same kind of current limiting as most of the rest of the amps which are current sources.
spritzer Posted July 23, 2010 Report Posted July 23, 2010 re: 717, open it up and listen to it, when the sound goes away, look at the led's and see if all of them are lit. If none of them are lit, then you are having a thermal cutout inside the transformer... Could also be the slightly over reactive protection circuit. Listen for the output relays... the srm1mk2 was made between 1985 and 1990. As such its more than 20 years old. More than enough time for the electrolytics to dry up. So people who still have them and don't like the sound should probably change out all the power caps. At this point the 717's are now 10 years old and probably need new caps too. Yup and I'm guessing Larry didn't bother to check the offset/balance either... Considering the commercial direction that Cavalli Audio seems to be taking, I think we'll be waiting a while. And as much as the Kevin Gilmores of the world kick arse as designers and builders, I can't see who is going to step up to the plate to give us another project that is so accessible to middling DIY'ers like myself. There are number of designs cooking, all of which are better then the Exstata. As for being easy to build, I for one think an amp could be made a lot easier then the Exstata but that maybe just me... i just got a copy of the srm323 schematics, and the design is very similar to all the rest, but with the addition of higher voltage power supplies, and 2sa1968's as the current sources. defintely tests even better. My guess is that people would like it very much. At about $600 via ebay (brand new) its definitely in the same range as an exstata by the time you add a case and decent volume knob. I had the 323 once and it is indeed great.
kevin gilmore Posted July 23, 2010 Report Posted July 23, 2010 Could also be the slightly over reactive protection circuit. Listen for the output relays... I forgot all about the protection circuit relays on the 717. Yep spritzer is right... What could be happening is that with the cover on, the temperature is going up (normal), and the output dc drift goes out of range and the protection circuit kicks in. So you have to rebalance the differential and set the offset to zero, for each channel.
KrypticMind Posted July 24, 2010 Report Posted July 24, 2010 Pardon my lack of DIY experience and the like, but how would I go about rebalancing the differentials and setting the offset to zero? And listening to output relays?
spritzer Posted July 24, 2010 Report Posted July 24, 2010 First off, take the top off the amp. You will notice two PCB's standing upright in the amp, one for each channel. These have pots marked TVR1 and TVR2 which you can adjust via holes in the side of the chassis. Now the TVR1 pot is the balance and the TVR2 pot is the offset. What you have to do is take a voltmeter, set it to about 30VDC range (or if you have an auto-ranging unit, just set it to DC) and measure at the Stax sockets on the front. Use the diaphragm above and put the red and black probes into + and - for one channel and adjust the balance pot (TVR1) for 0VDC. Now remove the probe from the - output and hook the lead to any exposed part of the chassis for a ground connection. Now adjust the offset pot (TVR2) for 0VDC. You will have to go back and forth between the two adjustments a few times and then repeat for the other channel. Normally it is best to do this after the amp has warmed up for a bit (say and hour or two) but you can set it instantly after power on and then readjust later on. Now there is a relay bank on the output of the amp (the soft "tick" sound you hear when powering up the amp) and if they don't engage then you can't measure at the Stax sockets. This makes things just a little bit trickier though...
Currawong Posted July 24, 2010 Report Posted July 24, 2010 Your best bet really would be to sell the boards and wait for the next release as it will be far, far better. This is what I'm thinking. I can't find easy alternatives for some of the stuff that's missing from the PSU and I'm sure it's going to drive me to insanity right now. Right now I've got my dynamic rig besting my 'stat rig, which means I need a serious end-game amp. Should I start by stuffing Justin's boards that I have, using the up-rated component list for the main board and do the PSU using the regular BOM until the HV PSU is ready? Or should I just take the easy option and wait for you guys to finish everything and just get whatever kit/Mouser project etc. results? Soldering stuff I am sure I have the patience for, beyond a case, jacks etc and wire. Searching for bits and hassling people for help I don't think I can be bothered doing. First off, take the top off the amp. You will notice two PCB's standing upright in the amp, one for each channel. These have pots marked TVR1 and TVR2 which you can adjust via holes in the side of the chassis. Now the TVR1 pot is the balance and the TVR2 pot is the offset. What you have to do is take a voltmeter, set it to about 30VDC range (or if you have an auto-ranging unit, just set it to DC) and measure at the Stax sockets on the front. Use the diaphragm above and put the red and black probes into + and - for one channel and adjust the balance pot (TVR1) for 0VDC. Now remove the probe from the - output and hook the lead to any exposed part of the chassis for a ground connection. Now adjust the offset pot (TVR2) for 0VDC. You will have to go back and forth between the two adjustments a few times and then repeat for the other channel. Normally it is best to do this after the amp has warmed up for a bit (say and hour or two) but you can set it instantly after power on and then readjust later on. Now there is a relay bank on the output of the amp (the soft "tick" sound you hear when powering up the amp) and if they don't engage then you can't measure at the Stax sockets. This makes things just a little bit trickier though... Shamelessly quoted because I will want to easily find this later I'm sure.
spritzer Posted July 24, 2010 Report Posted July 24, 2010 This is what I'm thinking. I can't find easy alternatives for some of the stuff that's missing from the PSU and I'm sure it's going to drive me to insanity right now. Right now I've got my dynamic rig besting my 'stat rig, which means I need a serious end-game amp. Should I start by stuffing Justin's boards that I have, using the up-rated component list for the main board and do the PSU using the regular BOM until the HV PSU is ready? Or should I just take the easy option and wait for you guys to finish everything and just get whatever kit/Mouser project etc. results? Soldering stuff I am sure I have the patience for, beyond a case, jacks etc and wire. Searching for bits and hassling people for help I don't think I can be bothered doing. You would have to do quite a bit of modding to the main board to do the newest upgrades and using the old PSU isn't really an option IMO. Personally I'd just build the KGSS stock and then sell it. It's a great project and going by the exstata thread on HF, a hell of a lot less trouble then building the Exstata. How does the 323 compare to the 717? I didn't have them both at the same time sadly. A used 323 would be a good budget option though and the A model I had was easy to change the voltage on...
Beefy Posted July 24, 2010 Report Posted July 24, 2010 You would have to do quite a bit of modding to the main board to do the newest upgrades and using the old PSU isn't really an option IMO. Personally I'd just build the KGSS stock and then sell it. It's a great project and going by the exstata thread on HF, a hell of a lot less trouble then building the Exstata. What problems are Exstata builders supposedly having? I was one of very few builders with a 'real' problem, the PSU oscillating for a couple of seconds on power up, which is highly likely to be my own fault.
cetoole Posted July 24, 2010 Report Posted July 24, 2010 Use the diaphragm above... Not that it is possible to be too into stax, but I think you must think about them a lot.
kevin gilmore Posted July 24, 2010 Report Posted July 24, 2010 birgir just sent me this... http://gilmore.chem.northwestern.edu/exstata.bmp i guess that not having a car for 2 weeks forces a person to sit in front of a computer for way too long I assume a rational power supply that does not blow up is comming soon. Or just use the kgsshv supply turned down a bit. Should actually work fine at +/-450
spritzer Posted July 24, 2010 Report Posted July 24, 2010 Try two months... Not happy about that but it is mostly fixed now. What problems are Exstata builders supposedly having? I was one of very few builders with a 'real' problem, the PSU oscillating for a couple of seconds on power up, which is highly likely to be my own fault. Oscillations and wild drifts are the nature of the beast when you use 1970's era PCB's and cutting all the wrong corners on the design. As for problems, what about unstable PSU's and the need for 50+ jfets to get a good quad which seems a bit silly given that this is supposed to be a budget design. Now all of this is gone once the new PCB's will land as they are probperly designed and no matching is needed. Plus the whole buisness of distortion being a few orders of magnitude lower and all that... Not that it is possible to be too into stax, but I think you must think about them a lot. Stax bitches!!!!
kevin gilmore Posted July 24, 2010 Report Posted July 24, 2010 (edited) you can always use 2sj74V's... in place of the j271's... then you don't have to match them. Trouble is the price. the srm323 uses 2sj74gr's (although bl's work too) Edited July 24, 2010 by kevin gilmore
Beefy Posted July 24, 2010 Report Posted July 24, 2010 Oscillations and wild drifts are the nature of the beast when you use 1970's era PCB's and cutting all the wrong corners on the design. As for problems, what about unstable PSU's and the need for 50+ jfets to get a good quad which seems a bit silly given that this is supposed to be a budget design. Now all of this is gone once the new PCB's will land as they are probperly designed and no matching is needed. Plus the whole buisness of distortion being a few orders of magnitude lower and all that... How many PSU's have blown up? I haven't seen a single report, other than one from loose wires. Maybe NoNoNoNoNoNo screwed one up, but that is NoNoNoNoNoNo. And considering 50 J271's are still cheaper than it costs to buy a matched quad of 2SJ74, I really don't see a problem. Look, I realise that the Exstata isn't the be all and end all, but don't you think your engaging in just a little bit too much hyperbole?
luvdunhill Posted July 24, 2010 Report Posted July 24, 2010 you can always use 2sj74V's I bought a couple hundred each of 2SJ74V and 2SK170V a while back, but hard to get now. Looking forward to sticking them in the output stage of my little JFET amp. As for needing 50 J271 to get a good quad, that's crazy. Trust me, I'd wager I've matched more than anyone else.
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