yabba235

Making such an amplifier isn't a problem. The problem is making it commercially available for sale. The market is too small to be profitable.

This apex chips has no any radiators - very poor design.

This is exactly what I wrote in the first post - the diagram is not the same as the connections on the board.

OK, thanks for explaining - best regards!

Did you run it with lsa389? What did you change in the schematic? Have you considered using the SOIC version instead of the TO-71 transistors?

Kevin, one more questions: under original schematic resistors r45 and r46 is connect between base q19/20 and emitter q23/24. But in real pcb is connected to base q23/24. I checked it a few times, no mistake - I do not know what to think about it...

Thank's !

Hi! I am renewing 25-years 717's and I observe strange things: I noticed a lot of wet places - as if sweaty - I suspect it has something to do with high voltage, have you noticed such symptoms in your old Stax? It's probably old flux - but these are places where it shouldn't be - output sockets, bottom of heat sinks (between PCBs). The second issue - how does the output protection system work - it draws voltages only from two outputs +L and +P? Because that's what I saw on PCB. What are the soldering points marked 81,82, 83 and Test: R,L,V for? I know that Kevi n had a diagram of this system somewhere, but it is no longer available .

To bad I can't buy it - my only contact with Chinese products is through Aliexpress, but there are no such products there. Since you have it on your table, can you give me some details about its power section? What kind of system will be used, probably none of the modern dc/dc controllers. Maybe a similar system to the old SRM-252S?

spritzer, If it's not a problem, I'll be happy to buy this scrap from you - contact me on pm

Hmm, from the translator: "..Portable (Class A) electrostatic headphone amplifier supports DAC decoding Completed the development of the latest portable electrostatic amp, surpassing Stax D10, Sennheiser kse series and domestic products of the same series, push-pull structure, the latest design, the first in China, adaptable to stax or other stax-5pin standard interfaces, and a full range of bias 580 products Speaking of why it surpasses most portable electrostatic amps on the market, the reason is that this structure is a COMS current mirror push-pull design. Class A portable electrostatic amplifiers on the market are all class D. Fans should understand the difference between class A and class D power amplifiers..." Sounds familiar.....and quite avant-garde housing design

It's not that bad, apex's integrated amps are good enough. As for the transformers on the outputs, I say no to them!

Only a few: bias voltage selection, input selection ( bal/unbal) and power on/off. The first two are implemented based on bistable relays - connecting them requires only momentary power consumption - important when powered by batteries. Last is simple monotstabile switch. Because of the relays, the housing is large, but maybe someday I will find smaller relays or think about another solution. (Instead of a discrete stage, I would see a high-voltage OA here :))

Can you have contact with him? I am also happy to buy these modules. I found them myself a few months ago ( find my post on diyaudio forum) but I have no friends in Japan. Without these chips I will not finish this amplifier.

As for your pcb board: You have big cohones, dude !! BTW: Can you share the source of lt8365 chips in japan ? - I can order them there because only this is what I still need to finish the project.