spritzer

If you want to let it go, I'd love to take it off your hands.

I really need to find a McAlister amp for the collection.... 😉

Here is something that has been cooking for a while but I've been just too busy to do anything about it. So JR Audio out of China have been building our amp designs for a while now and I started to hear horror stories almost immediately. They naturally have no right to use our designs and work in their crappy products but since when has that stopped anybody... I have been looking for one of these amps for a while now as I want to rip it apart and well... one owner contacted me. I'm going to ask him to come here and tell his story which is quite the tale. Let's just say Caveat emptor... So here is the amp and it arrived dead which will soon be clear. It is the KGSSHV version and well... it doesn't resemble my amp in any way... 🙄 One funny thing is that the Stax socket is made from nylon so the quality starts there. 😉 Nothing remarkable here but that voltage marking is directly lifted from my amps. Completely identical... Here is where I started laughing, this thing uses clone versions of old PCB's I made back in the day. The amplifier board (as can be seen by the date which they also copied) was in some of the older KGSSHV mini amp but this one is quite a bit bigger. Same goes for the PSU which was in the first KGSSHV minis but this one is 2.5cm wider and 1cm taller. All the components are in the same spots... it's just a bit bigger. Now here is whats wrong with it, see the bridge rectifier in the middle. That larger chunk of plastic shouldn't be sticking out of it. Here is one amplifier section and I just find it hilarious that they do a direct copy of my 7 year old PCB but manage to completely fuck it up while doing it. So all of those resistors are 1/4W units and that is a big no-no. Most are well shy of that power level (though not all) but the voltage ratings for many of those resistors is well below safe levels. It also annoys me (Kevin even more) that they have removed all values off the boards and replaced them with generic labels. We have always pushed for proper markings on all boards so they can be serviced at any time. Another thing clear in that picture are the 10M90's on that small heatsink on the PSU. They have a lot of voltage sitting on the metal tab so they naturally use a silpad and metal screw. Fucking amateur hour here. Another picture of the damage and one more of the underside: One nice attention to detail... or lack thereof is no thermal paste or silpad on the PSU pass transistors. Nothing at all and since the chassis is powerder coated, it has a hard time passing heat through the thin metal below. It's a shame I don't have any of these old PCB's in stock just to show how much of a blatant rip off they are. I'm tempted to order some (as I have the Gerbers for everything) just to show off what they are up to. Now what happens to this amp, well it belongs to me so I'm going throw out the PSU and the transformer plus replace all the necessary resistor on the amplifier boards to make this safe. Then I'll just keep it for shits and giggles. I'll update the thread when I do some more work on this clusterfuck.

I haven't had set for a couple of years now so I haven't played with them at all. I would also check the diodes in the SRD-5 as they can also be toast. As for the coating, just spray into the air and run the diaphragms through the mist. That is a good way to control how much goes on the film.

Those look great and reminded me to post this, a possible cable for DIY electrostatics: https://www.aliexpress.com/item/1005002121174291.html?spm=a2g0s.12269583.0.0.67082dbcJ5CL0I I just got some but have as of yet not done HV tests on it or anything but it's nice and supple, if a bit thin. Well worth a punt and reminds me of the Koss wire but not double insulated.

I do think electrostatics have a long way to go before we see anything resembling complete maturity. The issue is that very few are attempting TOTL units or any real improvements to the tech. Most are just a play on different tech already out there and with some hyperbole attached. The Hifiman units did nothing new, ditto on the Voce and the HE1 uses pretty much identical drivers to the HE90 but with that silly amp design. I also agree that going any thinner on the diaphragms will just cause issues with stability with zero gains. Stax figured that out in the 90's but seem to have forgotten it again... 😉

No tracking info yet so until then I can't say.

It is also fairly low powered too, those transformers are just two 12VA units and with a resistor current source for the output... not a whole lot of potential.

It is very much a rehash of older designs and nothing unique there. The "special bias supply" also doesn't hold a lot of water but good for them to get somebody to give them a patent on something nobody cares about. In terms of performance this is worse than the new SRM-400S for a lot more...and the 400S is a pretty crummy amplifier. A huge step back for Stax in performance.

There has only ever been one MRI designed electrostatic that I know of, the Koss ESP900 which is just a 950 with a closed housing. I've heard that HE60's were used for this but never seen anything in the flesh, plus the HE60 headband is magnetic (plus the screws) so something had to be done about that. The MRI's I've been in all had sound pipes for the audio, simple tubes with the transducers elsewhere and sounded terrible. The Voce and the Hifiman units were indeed unfortunate. The Voce is well built but sounds like crap (electrostatics are all about that vague sound and loose, uncontrolled bass... ) plus that stupid case they insisted on shipping with them. Now the Hifiman Shangr-la jr. sounded good but that build quality and silly price makes it a solid miss.

The PSU's are shared so that shouldn't be the issue but it can be anything, a marginal resistor, marginal transistor etc. etc.

I should be getting one of these to try out soon and can't wait. It wasn't fun sitting out the press embargo... 😉 I would take those measurements with bags of salt given the amps used and the people doing the testing.

I would definitely swap out the rectifiers, they are really a wear item on anything this old.

Voltage divider off the B+ works just fine and hum can be pretty much anything so impossible to tell.

Indeed, that's and excellent way to fix it. If the elastic has stretched too much the same can be done by opening up one side and shortening the elastic.

This is very much the return of Singlehour, same utter incompetence and utter disregard for safety and the customer

I'm not sure what those things are but they are sure as shit not Megatron's. Looks more like a SRX with some version of the Megatron output stage... This is why Kevin and I try to expose these fuckers as they are literally running away with peoples money. On a similar note, I have another amp from JR Audio here now and well... stay put for another horror story. That thing lasted for a few days before the PSU blew up... a sloppy clone of one of my old PSU's BTW.

Stax just tripled the price of the 507 pads and the only other Lambda pads are the 207 pads so slim pickings out there. I've never tried the Vesper units but their other pads have been great.

That is quite normal for these old sets and there can be a number of failure points, bad cable, corrosion inside the driver or the resistive coating on the diaphragm has started to break down.

Normal 51K resistors would work just fine but I'd shoot for a non inductive unit such as the Vishay units Stax use now. They are 7W but that's even better

Thanks for the update Todd! I've received dozens and dozens of emails from some very worried people so I'm glad it is back.

I would place that as top tier stupidity

No, not at all. The 500t is more similar to the 600ltd amp with presumably a bit lower rail voltages but still the same circuit as the T1. I have a 700t here and it is terrible in stock form, just awful. Utterly lifeless but adding a CCS really transforms the thing into something decent.

No, not at all but they are very sensitive to static which is the most likely culprit

I've fixed at least five of these over the years, all with bad mosfets so they just fail. Once swapped out the amps spring to life.