spritzer

Exactly. This is how it should be done. Just look at the parts used in that thing, 3 transformers!!

Powered it up a few hours ago with zero drama. The offset and balance were all less than 10V off base so a quick adjustment and were are good. I'll probably have to go in again and change the current for the BJT's as they weren't designed to run this hot. As for the sound, well holy shit sticks this is different. Now we have deep bass, full soundstage and high frequencies. The amp isn't 100% though and it still has too much of a "character" for my liking. The bass slams a bit too much and the top end is not as linear as it should be. Also some slight phase related issues. Next up, fix this fucking bias supply. Not only does it make no sense it's also just an accident waiting to happen. In every Stax amp we have a voltage doubler off the filtered V+ which is then cut down with a divider and further filtered. So why on earth wasn't the regulated V+ used here? This cost a bunch more in parts just to do something stupid.

That would be a plan. A lot of high end studio gear is single ended with transformers on each end so this makes sense. Same reason the ECP L-2 should have an XLR output, we now the difference but 95% of HF have no clue. I'd love to take that amp apart and show how 5K$ amps should be built.

Same thing here, lasted until mid season 3 and gave up.

This is it.

We are dealing with a lot of raw DC voltage here so the only option is to use the isolated diodes. Any other route may work but it probably won't.

Those are not isolated diodes so it will explode quite spectacularly. Same bridge is used.

HF has always favored certain MOT's and more often then not they contribute nothing to the site. Did anybody catch that small issue with the LAu? If set to 240V and run at 220V then it can't get out of protection mode. With ample headroom in the transformer and a regulated PSU this should never happen... That's the plan. Same thing we did for the ESX back in the day. These are the new output resistors using part of the old CCS for mounting. Given that the board will be removed a few times this was needed on the input. This show the new CCS setup and the amount of flux needed to get the sinks to move. I'll clean it up once the mods are done. Closeup and look, color coded 1000V teflon output wires...

It was far off from my max bid... I've seen two of these for sale in the last 10 years and it officially doesn't exist so price was no object...

Do not under any circumstance use those rectifier diodes!!! Use the ones printed on the board. The board always overrules any BOM.

The KSA1156 is a direct replacement for the 2SA1156.

I doubt that very much. Fuck, they could use the 10M90 for the CCS and that Fairchild part for something useable. Never going to happen though.

Some progress: The entire CCS removed and replaced by a single 2SA1968. All transistors are now 2SC4686A's due to their super low capacitance and general awesomeness. The FJP2145 would also have been a good choice that is in current production. The circuit is completely identical. Only thing I've done is remove those bloody mosfets which should never have been there and fix the CCS. So now the output capacitance is cut down to less than 10pf and the huge bump in distortion from the old CCS is gone.

That is certainly possible. Sent the pics to two people I know who assemble PCB's and they are appalled. Not just the soldering but also how utterly impossible any rework is. I've stripped all unnecessary parts off the amp board so I can start building it up again. Already installed are terminal blocks for the input , new power LED (hate blue led's) and safety output resistors. Next up are new BJT's for the output and 2SA1968's for the CCS. Then the amp will be ready for testing again. After that I have to turn my focus to the PSU. The bias supply is utterly fucked and not safe to use. Then I'll add loopouts to the back and rewire the input section.

Well there is a story about those holes. When the Exstata was under development and I was still a part of that, I insisted that the board had holes around the heatsinks to suck up air from underneath. Alex dismissed this but finally gave in when he saw it was a good idea. Here this is taken to the extreme though as it's compromised the structural integrity of the board. One funny thing are the ground traces on top of the board. Almost no other traces are there so why on earth isn't there a solid ground plane? It lowers the noise and there are no drawbacks. Doesn't make any sense...

Time to share my joy with the amp board. To start off with, there is no way in hell this could ever be serviced... by anybody. If something fails in the amp it needs a new amp board as the CCS is utterly impossible to get to and the output devices are little better. The CCS has to be the most stupid design I've ever come across, 12 small sinks in a row, all of them with the overly long screws mounted one way so if KSA1156 nr. 11 or 12 needs to be replaced all of them have to be removed. Alternating the screws and using much smaller ones would have made it possible to service this thing. Anyway, time to crack on... This is how all of the mosfets are mounted. That red bit is similar to mica pads but plastic and flexible. Similar to mica these need thermal paste on both sides to conduct heat properly... How the transistors are mounted. Screw, shoulder washer, transistor, isolating film, heatsink, another shoulder washer, locking washer and the nut. So the screw is floating but to accomplish that they needed to do this: ...drill out the center holes in all the heatsinks. The middle one is a stock unit out of a new box from Aavid. What a colossal waste of time and to make matters worse, this just increases the output capacitance of the amp. That's not something it could afford... The main culprit are these. Data sheet can be found here, look for Coss and remember that two of these drive each side of the headphones and the capacitance of the main Stax lineup is 110pf. The SR-003 is 44pf and it sounds utterly horrid. Here is what the amp board looks like now. Need to remove a bunch of parts and start building up the new CCS. I'll also add terminals for the input, redo the whole input section as the soldering is quite bad. Perhaps I should get some JPS cable for its magical properties? Either that or the 50+ year old milspec silver wire cable Kevin gave me.

Yeah... dbel talking about anything Kevin has designed is going to be fair and honest. Been busy stripping the amp PCB and holy fuck this is cheap. I'm sure they had to force Imagineering to make something so thin. The mounting of the transistors is something truly special. Stay tuned for pictures...

Happy Birthday!!!

Don't I know it. Amp PCB sitting on the bench and I'm pulling heatsinks...

I've heard it thanks to a Hennyo PSU. The spark between the rectifiers blinded me for a bit...

I started the tear down of the amp. Here is the back of the front panel: I'm impressed, this is very, very nicely done. Here is the front panel stripped: Here is a closeup of the sockets. The drawback of these sockets is how sensitive they are to the metal pins. Here is a picture of the power switch and the paint flaking off: Here is the knob or rather the back of it. Nice paint spray effect, why this isn't powder coated I don't know. Far more durable... The sockets, front and back. Pretty nice design. Taken apart. Headamp Teflon socket for comparison ...and here is why they are almost impossible to use. When the Headamp sockets were made extreme care was taken to get the clamping force just right. The pins just need to be moved a bit to loosen the clamping force. Almost impossible to get them out of the chassis though... Bottom of the amp PCB. Let's play spot the cold solder joints... The PSU board.

There was just one Hennyo built amp in circulation and it blew up... as soon as it arrived. Stay tuned for some pics...

Ohh yes, the Exstata is better than the M-10. My Exstata has been on loan for the last few years but I tried it recently just as a refresher and it wasn't nearly as bad. It runs at +/-350V and uses a BHSE PSU though...

I'm a bit worried that the PSU may pose some problems but I can make something useful out of this pile of parts. Moar pics later as I start stripping it down.

Yeah and the M-20 is just about as bad as the M-10. That one is 1500$ though...