spritzer

Happy belated!!!

I'm too tired to make any sense now but I believe the stock configuration runs at 6mA so it's a significant jump in current draw. There isn't another board run planned but the Gerber files have been posted in the thread and it's easy to just drop any fabhouse and email for a quote. Just ask how much a pair of amp boards and a PSU board would run you. Larger yields are cheaper though.

One has to remember that PCB's are nothing more than painted slabs of copper on a FR4 substrate. To rely on that paint for insulation wouldn't be the greatest idea.

It's not likely that the PCB is at fault but ever relying on the slikscreen for insulation is a bad call IMO. I always raise those caps just 1mm to make sure they can never short. Same goes for any and all top mounted traces and parts that pass over them. This is why we go to such great lengths of tracing everything at the bottom of the board.

Ain't that the truth. We rush from project to project as we keep coming up with something we like. We often loose track which is why we draw up PCB's now as we go along.

Separating the ground makes no sense to me and will likely only cause issues. Having a ground loop breaker on the earth makes sense for a commercial product but there are no problems here with it all star wired together.

400VA is indeed utter overkill and could cause issues with the unregulated voltage and thus causing the PSU to overheat. 200VA is plenty big. That should work just fine.

Try 5 minutes max....

Looks like I'll have to design a PCB this weekend. Ohh well...

Plenty of pots to go around so feel free to drop me a line. I plan to make my own PCB for them soon given how much I like my socket PCB but who knows when I'll get to it.

Looks awesome and the little Alpha pot is slowly but surely conquering the world!!! I just got another 100 so more for everybody.

You are talking about max voltage swing here which is far, far from being linear. If you are aiming to design then worst electrostatic headphone amplifier ever then it's the right track but otherwise I'd start from the beginning.

It's a good approach to discard any recommended setup when dealing with electrostatic output stages. The engineers were not thinking about these requirements as we only care about low distortion voltage swing.

66K is the highest I've seen in a Stax amp (T1 and 006t) but that HEV90 implementation made no sense what so ever. The 6P21S looks interesting but I'd really like to try something with my Bendix 7403's. IDHT's but they are some serious tubes....

Those look like the real deal but the 2SA1968 has such a distinctive casing that fakes are easy to spot. That's why I caught the ones I had as they looked very different so I never fire tested any of them...

The 300B is very voltage limited and can't handle anything like the 211/845 or even a triode strapped EL34. What we want here is voltage swing which is for instance why the 6S4A is such a perfect tube for the job, far better than most of the DHT's. No use anywhere else though which is good for us. If you want to use the 300B/2A3 then you have to use an output transformer for some voltage "gain". B+ of 300V will not get you a whole lot so at least double that but that means the 2a3 won't work. Something like the EML20B with a 600V B+ and anode resistors would work but it's not cheap.

I'm also a bit worried about the "maxing out my meter" comment as the cheap crap doesn't work at these voltages. They give the wrong data and the error range is huge.

Well first off, what are you seeing out of the transformer unregulated? The regulator needs a certain headroom to function correctly.

The BOM is for the 450V version so the voltage divider in the PSU has to be altered for 500V. There is detail of this elsewhere in the thread but nobody ever bothers to update the BOM. Most of the time we don't even bother with BOM's so there is that....

Glad you and Kent got them working again. Winding electrostatic transformers is a bit of a black art and there are plenty of things to consider. Now you just need to find somebody to build a direct drive amp for both the both speakers...

It was never impossible to cram 507 drivers in the Sigma just not a very good idea. Just look at how the drivers were glued... It's also nice to see that indeed all the WES amps are fubar. What a waste of nice caps...

True dat which brings up the 4-pin XLR issue once again. Even Sennheiser have adopted it now...

Would it really matter if they were wired like that? No need for ground with balanced and I doubt any manufacturer will have accomodated for shield at pin 1.

It should be noted that we are well aware of the Electra only having one cap in the signal path but this setup yields better distortion numbers. Personally I'll take an extra cap and lower distortion.

Might also be mixing up % and proof. 30% is easy to reach but 60% is harder.