It was mostly adjusting the design to different parts and the weird stuff were the PCB caps that Stax decided to use... plus the enlarged the amp chassis for no particular reason. In terms of being better than the 252S... nope.

As it turns out, Moondrop are finally releasing the MoonZero soon:

https://www.hifihub.com.br/en/product-launches/moondrop-moonzero-445-electrostatic-headphone-takes-on-the-stax-sr-x1

This image courtesy of Fujiya Avic:

Looks cool and if they can bring them in for under 500$... that is mighty tempting.

Edited September 5Sep 5 by spritzer

@spritzer are you excited for the ES Labs HE90 clone? Will likely run on 580V but same materials, stator and membrane thickness etc...is it something you look forward to or is HE90 still just okay next to 007 Mk1 etc :)

I will buy a set but if they sound like the originals... I probably won't like them. The HE90 has always left me cold, despite how many I've tried. The HEV90 doesn't fix them either, it just muddies up the sound... seriously the input cap on those is a very nasty electrolytic cap. How that is high end is beyond me...

That being said, I've been slowly working on my own clone of the HE90 for a couple of years now. They will never be sold to anybody, just a very stupid and crazy expensive DIY project to fix the HE90's. I have some NOS headbands for them but I'm currently designing a new headband which has more range (as the stock ones barely fit me) and looks like the original. New drivers too but I've only sent out for the first prototype parts for those.

@spritzer What earpads would you recommend for the Hongshu EH-1 that gives a good seal?

I haven't found ones I really like, I settled on some pads off Aliexpress that arrived incorrectly so I'm not sure what listing would link to them. They are 105mm and perforated on the inside which isn't ideal but seem to work okey.

HE90 "clone" first prototypes up and running as of yesterday:

The drivers are all PCB based with 2um mylar diaphragms. They are about 3mm lower in height than stock to accommodate the cable entry and move the connections to the bottom of the drivers.

The housing is resin 3D printed but this is the old version which has now been abandoned for a new one that has yet to arrive. Cables are King Sound (as I had some in stock) and allow me to fit it all in the same housing size as the original. The earpads are ones for the T+A Solitaire that are not a great fit but dirt cheap... so work just fine for this role. I've ordered new genuine pads but I'm not sure if Senn have any in stock.

Next up is to refine the headband design and start to work on prototyping the metal back shell. Now I just wait on parts as usual...

As for the sound, far from finished, even in prototype form but a HE90 with actual bass response... perish the thought!! ;)

On 9/12/2026 at 2:53 PM, spritzer said:

HE90 "clone" first prototypes up and running as of yesterday:

The drivers are all PCB based with 2um mylar diaphragms. They are about 3mm lower in height than stock to accommodate the cable entry and move the connections to the bottom of the drivers.

The housing is resin 3D printed but this is the old version which has now been abandoned for a new one that has yet to arrive. Cables are King Sound (as I had some in stock) and allow me to fit it all in the same housing size as the original. The earpads are ones for the T+A Solitaire that are not a great fit but dirt cheap... so work just fine for this role. I've ordered new genuine pads but I'm not sure if Senn have any in stock.

Next up is to refine the headband design and start to work on prototyping the metal back shell. Now I just wait on parts as usual...

As for the sound, far from finished, even in prototype form but a HE90 with actual bass response... perish the thought!! ;)

Interesting choice to double the diaphragm size...only 0.4um left to reach HE-1 thickness :D

Is that one of the reasons you disliked the HE90? Too thin in body due to this thinness? Btw what are your thoughts on the impact of bias on sound? Like the ES-Labs using 580V instead of 500V but increasing stator distance to stop membrane sticking? The Lambda NB gets so much praise regularly and always wondered if 580V might have been wrong direction afterall for e-stats but changing would be too hard due to all amps having the pro bias etc?

Is the HE-1 2.4um? Odd thickness that, as I believe DCA also use it for their sets.

I just hate working with anything less than 2um and I have so much of the stuff, so that is what I use. As for the bias, any change in that will make a difference but higher bias is always better but comes with its own challenges. There is no benefit from using 230V and the SR-Lambda has its own reasons to sound the way it does, nothing to do with the bias.

Blaming the diaphragm thickness for how something sounds is also very misguided, I adore the HE60 (which uses the same diaphragm material) and I also really like the Lambda Signature, again 1um. It's all about the driver tuning and what sound you are after. My issue with the HE90 was always the utter lack of meaningful bass output at certain spots and that's down to how they were tuned.

Btw. the "clones" are now in a fully redesigned version of the housing (well I've sent out for a newer one still to be made) and fitted onto a NOS headband. First prototypes of the metal backs are also ready and look great. Just have to be fitted to the new housings when they arrive. Parts for the DIY headband are also en route and we'll see if that design actually works. Also probably the final prototypes of the "axles" so I should get them properly made soon. Those who know the HE90, know those are bloody expensive tiny pieces of plastic. Also new spacers, dust cover pieces and a redesigned stator too...

Now fitted with real HE90 earpads and they have no reason to sound this good. Far from perfect but I'd take these anyday over the original. Still a tiny bit on the bright side and with a bit of a midbass hump

Now I just need to make of these "clones" and cram a Stax Lambda driver in it. That upset so many people I kinda have to do it again...