kevin gilmore

Well for example the fqpf3p50 seems to be out of stock at newark,digikey,mouser... So just because every single part is listed as a mouser part, it may do no good. ksc5042 has been discontinued, mouser is getting one more batch in, then that is done too. Exstata will have to change for the future anyway. thermal breakers are a real good idea on exstata's. Not a bad idea on a lot of other stuff too.

So a default exstata (pair of boards) is 30ma on the +300 line, and 36ma on the -300 line. (actual measured) If one of the two amp boards goes down for some reason, the regulators have to take 6 watts on the +300 line, and 7.1 watts on the -300 line. With the 4.7 C/W heatsink and forced air cooling, the temp of the heatsink is 122F on the +300 line, and 132F on the -300 line. Now if both boards are not connected, the heatsink reaches 172F, and on the -300 line about 192F. And of course with natural convection cooling, well the temp is way higher than that... You would need at least 4 times that much heatsink to prevent the thing from burning up...

The srmxh, srm212,srm313,srm-mk2 and srm323 all have exactly the same number of gain stages as the exstata. In fact my designs have the same number of gain stages too. The first stage, with the voltage translator, and the main VAS gain stage. Output stage is nothing but a current amplifier. Alex says the input fets do all the work. Alex is wrong, all the input fets do is buffer the input and subtract the feedback from the output. Voltage gain is no more than 5. Its the second stage that does all the amplification (voltage gain of 200 or more) and this is where non-linearities really end up going to the final sound. There is absolutely no reason the amplifier cannot be designed such that it can take anything in the range of 2 to 30 ma Idss. All you need is to replace a few resistors with a constant current supply. Just like stax does. One extra transistor, 2 extra resistors once you already have the constant current source for the Vas stage.

Here is the biggest problem i have with that power supply. Anything bad happens, and the load disappears and it goes nuclear. The heat sinks on the power supply are way to small. And absolutely no protection whatsoever. No place to put a fuse to blow if something happens to the load. The reason this is an issue is that people are already building and then quickly selling their exstata's and the build quality is awful. A unknowing customer gets the thing, and something happens, and flames shoot out of the power supply. The heatsinks need to be bigger, and thermal cutouts have to be added to the heatsinks to shut the thing down. And half the power going to the shunt devices needs to be taken up by power resistors bolted to the chassis. This is diy done wrong. If you really want a shunt supply, i came up with the schematics a couple of years ago. The current sources have shutdowns built into them, so if the load disappears the current into the shunt supply also disappears. If you use the right devices, it is only one extra opamp per rail. With any of the stax designs, standard cheap parts for the fets work fine as long as they are matched to each other. Plenty of range to zero the amp in after that.

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)

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

this one looks like fun FOXNews.com - World's Strongest Beer Launches at $762 a Bottle

see our problem is this idiot agency called the fancy candy company who mandates that the output of those little toys is -88dbm. Pretty much useless these days. so its not that the devices are crappy, its that they don't put out enough power. Fortunately there is solutions, and the one like the sony actually does fit into the rf input line and switches itself in and out as necessary. I like my solution better. Its completely portable.

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.

That part is not so bad. When they give me 4 hours of machine time, i know what to do... I have each and every tool memorized as to position in the tool bin. The really bad part is dealing with the polisher and finisher. The polisher ended up with a huge job, and pushed my stuff off a week or two. So on the current batch i will be lucky to have the chassis finished by the end of next week. probably one more week. I'm sure justin has to deal with this in a massive way. The amp board (of which you need two) is going to be 8.25 x 6.25 The power supply board is going to be 9.3 x 7.7

i'm not going to make 2 runs of boards. will probably change this one to use the 1000 volt fet as the current source, then you can run it on +/-500. Tired of custom chassis work (except for myself) so i'm making this as easy as possible to build.

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.

if someone can build an exstata they will be able to build this... http://gilmore.chem.northwestern.edu/kgsshvhs.bmp slap it in any case you want. power supply this way will be next. perfect for pabbi1's wood boxes.

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...

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

they don't all suck. this one works great. FM25B - Professional Synthesized FM Stereo Transmitter Kit - Ramsey Electronics and you can add a 1 or 5 watt booster (illegal or course) and transmit a mile or more. Very clean.

its also a jfet. in any case i will try and buy a few and test them. i assume people are using them as current sources, would like to know how they actually perform.

true, but for $10 total more in parts it can be MUCH better.

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.

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.

i'm thinking seriously of doing a version of the board with a simplified current source that performs just as good (1000 volt ixys part, thanks marc) and with standup heatsinks. Will make it lots easier and cheaper for people to build it. Power supply will be the same thing. Hopefully will get started on it friday. Will cut the power supply voltages to +/-450 just to make sure the current source has a bit of headroom. if anyone knows of a depletion mode fet that does more than 1000 volts and will run at 1ma, let me know.

There is more than one frank... I have a MIG2 dynamic amp (similar to BH) with 8 x 6c33's 6 filament transformers alone. Consumes about double the power of the T2. Even though i published schematics, no one but me ever built one. I have an all DHT direct coupled electrostatic amp. Its so expensive i can't even afford it. (plus i never finished doing the high frequency isolated filament transformers) $8k for the tubes alone.

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. Ray samuels is the only moron i know that pushes 317HV's to those kind of voltages. Way in excess of their 150 volt ratings. (i think there is a 225 volt version now) And besides which there is no high voltage version of the negative regulator. Now what you could do is run the transformer on 120 vac, and set the jumpers for 100 vac, then use simple zener/fet regulators... That would work great. And the transformer is going to get a bunch warmer.

the SRM monitor is a different schematic... pretty sure... stock exstata +/-300 volts ... 1.0% THD stock srm1-mk2 +/-350 volts... .1% THD stock srm-313 +/-350 volts... .01% THD I would add an auxilliary power supply that is fully regulated. for the srm1-mk2 it would be +350, -350, -370.

now i remember... the srm-1 mk2 is the one before the srm-717... i think they are close, but i would pick the stax unit, then mod the power supply.