Hint: the trafo box is unipolar but the drivers are not

 

http://www.head-fi.org/t/157539/sony-electrets/30#post_2062726

 

Ok so the drivers are dipole based, polarity doesn't matter or does?

It certainly does matter.

Electret drivers use different diaphragm from electrostatic.  Coating them with what you use on electrostaic won't help. 

Electret drivers use different diaphragm from electrostatic.  Coating them with what you use on electrostaic won't help. 

 

Suspicion it would be something like this. Which probably explains why the diaphragm was bare inside the driver and not seal from dust and contact with hair and such. 

 

Any idea on what material I can use to re-membrane the electret driver? Or at least something I can do to fix it?

Will update this post, got a surprise for some of you guys on a repair the previous owner tried performing on an SR-3 New I'am in the process of re-repairing.

 

Ok updating this post now with results (about fucking time).

 

Had some SR-3 New's passed to me to have a look at and repair. This pair in pretty poor condition but had perfectly looking drivers (no pushed in dust protector or punctures). The only problem was no sound output, so thanks to Wachara's original suggestion while ago with informing me to re-coating my own channel imbalanced pair of SR-3 and 5's diaphragms using antistatic and professional ESL solution used to re-coat ESL panel based speakers I decided to try repair these as I've done so to the other 7 SR-3/variety based earspeakers.

 

This was the result of opening one driver up and no amount of re-coat could fix it which now distorts heavily and is about 30db's down in volume output to the other now re-coated and working channel.

 

 

 

Very smart engineering by Stax. Unlike later ES headphone models that have the diaphragm mechanically tensioned by a precision machine then secured to the stator and spacers, SR-1-5's used disc ring secured diaphragms and a spring that sandwiches the membrane with the perfect d/s gap between the membrane and stators.

 

 

Perfect dust protector 

 

 

Diaphragm from good driver...

 

 

Bad driver

 

 

 

Comparison. See the crinkle and membrane sticking out a bit. Seem's the previous owner opened it and tried fixing it. Because the diaphragms have a pre-tension groove which must be installed the right side up during manufacturing process, the previous owner flipped it around and with the spring installed, it stretched the mylar out. Installing it back in the driver assembly outputs huge imbalance and distortion. The only solution is to re-diaphragm the whole thing.

 

Spritzer or Wachara, any idea what mylar um thickness these are and recommendations on next suitable replacement?

 

I tried a coated glad wrap and it worked too lol but I'm after a proper fix.

I like 3 microns Mylar, but anything from 1 to 3 microns should sound wonderful.  You'll have to give them a few trials and errors on diaphragm tension before you are happy with the sound though. 

 

By the way, those drivers look nice.  What is the inner diameter of the spacer holding the diaphragm?

 

Any idea on what material I can use to re-membrane the electret driver? Or at least something I can do to fix it?

 

I have no idea.  But, I think you can convert them into electrostatic.  

I like 3 microns Mylar, but anything from 1 to 3 microns should sound wonderful.  You'll have to give them a few trials and errors on diaphragm tension before you are happy with the sound though. 

 

By the way, those drivers look nice.  What is the inner diameter of the spacer holding the diaphragm?

 

Where can I buy mylar?

 

50mm across from inside the spacer, 55mm from outer diameter. It's two spacer's with the diaphragm glued around the edge.

 

How can I convert it to electrostatic? This is what the inside looks like (not my pics)

 

Where can I buy mylar?

 

50mm across from inside the spacer, 55mm from outer diameter. It's two spacer's with the diaphragm glued around the edge.

 

How can I convert it to electrostatic? This is what the inside looks like (not my pics)

 

 

Oh, I'm sorry.  I didn't know that they're hybrid headphones.  I'm not sure how to make them sing together now.

Electrets cannot be be recharged as they won't ever loose the charge in the first place.  Any imbalance has to have an external cause such as broken cable, parasitic charge on the film, damaged driver frame etc.  The charge won't "wear out" in the foreseeable future.  

 

Never seen electret film for sale and I doubt you could buy just a small roll of it.  It's interesting how it is made though, not something you can do at home. 

That's too bad.

 

Anyway I snipped off the end of the stock 4 pin din alike Sony electret plug and soldered on a spare SR-3 old plug I had.

 

Do these things require some thing with a high ratio transformer or something because the volume is not much even on max through my SRD-7sb MK2. My SRM-1 doesn't even produce much volume to be heard.

 

Opened them up and noticed that they have very thick pentagonal spacers, one of which has the electret film glued. Can I re-use the electret mylar film and add a bridge to one of the spacers which will connect to the bias on one of my Stax amp's, turning them into a full blown electrostat? Or is the existing mylar film no good? 

Edited October 16, 201411 yr by DefQon

One thing I don't get about electrets is how the bias is set.  If it's possible to set the bias (really the rate it loses electrons I guess) then I have an idea in my head that might allow an electret to be driven from dynamic amps at pretty decent SPLs.

 

Defqon, you can buy 2 um Mylar from ebay very easily and it'll last you forever.  There's also a place in AUS that sells 2 thicknesses of Mylar, but don't buy their 1 um "Mylar" as it's garbage and not even PET film.

The step up ratio of the Sony units was very high, at least 1:100 or even higher.  Nothing Stax ever made will work with them. 

 

Electret films have a certain charge built in so you design the driver around that instead of the bias voltage.  The bias voltage is the same principle, just different implementation.

 

You can't recoat a electret diaphragm to use with an external bias supply. 

I guess what I'm really asking is what the equivalent bias is for one of the popular electrets.  As in, given the same driver and D/S gap what would you need the bias to be so that it matches the sensitivity of the same driver with electret film?

 

Are there any Stax electrets I can plug straight into one of the Stax amps without fiddling around with the pins?

Edited October 16, 201411 yr by n3rdling

All the Stax electrets are pin compatible with the electrostatic models.  Similar sensitivity too. 

 

Bias is a very relative thing and with transformer boxes you can have low bias but very high drive voltages.  Not so much with amps. 

How do the Stax electrostatic headphones scale with voltage?

For instance, a model's sensitivity is rated at 101dB@100VRMS at 1khz, if the voltage is doubled is there a 6dB increase of SPL?

It isn't quite that linear and varies from driver design to the next. 

Thx.

What truly determines the bias to be set for an ESL? D/S gap, diaphragm tension, spacer thickness?

I've managed to snag an ECR500+adaptor box so I'll maybe try it.

a little of everything but mainly the gap. calculated with maximum displacement of the

diaphram

Yup, the gap factoring in the displacement and over all insulation properties of the air. 

...so I've had my new SR-009 for two days and I've already started to modify them.   

 

First for the good stuff, these aren't as fucking bright as all the early units I've owned/had access too.  They can be a tiny bit too hot at times but this a marked difference to the earlier sets.  This also means the odd reverberation with voices is also mostly gone.  The bad news is though that the bass has a large gap in the FR simply missing and the imaging is far from good.  Coming off a steady diet of SR-Omega and modified SR-007 SZ2 these two factors are all too apparent.  There is a strong center image but it lacks the cohesive soundstage of the two older models.  I suspect the earpads are to blame for most of this as they are virtually flat compared to the steep angle of the SR-Omega.  As for the bass, it's either down to the diaphragm or there is a small port hiding somewhere in there.  I suspect it is the latter as that "made in japan" piece is highly suspect. 

 

Ohh and this is a set that came from Price Japan and guess what, no channel imbalance.... 

FWIW, another data point to add:

Got my new SR.-009 last week. Also purchased from PriceJapan. Also no channel imbalance.

I was more jesting at the HF thread on the imbalance issue where nobody has the slightest clue and it has been suggested that PJ sets are somehow different... 

 

 

I can't help but get this slight feeling of betrayal when I look at this pile of shit and the epic work ahead of me... 

Edited October 22, 201411 yr by spritzer