[soundoholic]

OK., thx for your opinion. Nevertheless, me and my friends find a little advantage in bias increasing, especially with older Stax. With the possibility of immediately change-over to higher bias (580-->660V) after seconds the sound becomes a bit more clear, more vivid, with slight advantage in bass.
But in some recordings, yes, the difference is nearly inaudible.

 

[cjfrbw]

Well, after a couple of weeks, I am enamored of these "new"  "normal bias" 507's.
 
I think I am going to leave them the way they are until they pop, I can't think of any reason to change them unless they fail again.
 
They are giving me the best headphone experience I have had so far.  Hugely expansive, utterly smooth, absurdly lucid, deep and subtle bass when used with my dynaco upgraded srd 7 transformer box, 300b amp, and normal bias.
 
The high frequencies are airy and spacious, I haven't heard anything like it.  The "new" 507's make the traditional normal bias Lambda and 5n sound a bit closed in and compressed by comparison, and less detailed.
 
I was not happy when the original 507's failed, but now I am almost happy they did, because I never would have tried this otherwise.
 
I heard some of the other Stax at the headphone show.  HE60 with prototype Liquid Lightening, 007 with Woo 5/srd7.  Those two sounded good, but a bit inefficient and thick. 
 
 Orpheus HE90 was sweet and seductive tonally, and pillowy with its own amp, but not a detail champ. 
 
 009 with Blue Hawaii variant was extremely detailed, but a bit edgy and sharp, which is a risk of an OTL tube amp with solid state power supply.  
 
These were limited listening with show conditions, so I am sure I would not have exactly the same opinion on extended listening, but I wasn't nearly as bowled over by them a I thought. I am sure other listeners would have entirely different tastes and impressions.
 
The "new" 507 seem to have a great balance of characteristics so far, I find them preferable to the original 507's when they were working.
 
I am shocked because I was just hoping to get them working decently again at a  standard Lambda type performance and instead got a new headphone setup that I really like.
 
Of course, they could explode any day, but so far they are holding up.  I actually would not mind re-doing the mylar every couple of months or so if it means maintaining them at this performance level.
 
I guess I will report back if I try to change the membranes out or they fail but so far so good on both the transformer upgrade and the mylar experiment.
 
More than half the time my DIY stuff is a total wipeout, so this was a nice surprise.
  
 

 

[soundoholic]

@cjfrbw
Congrats once again to your "self-made" 507. I enjoy your reports and be sure, the comparisons to Lambda NB or SR-5 are very positive. Though your impressions would be more weighed, if some other stax hps will be compared to your 507 invention - directly, at pro bias.
I think your 507 mod drivers have now completely other properties and a standard NB 230V must not be the optimal for that. The frame and the stators are, say, as porsche 911, that you drive just 60 miles/h...
I can imagine, you could try to experiment with some more voltage as 270, 300, probabely with 330V too. With DIY made BIAS supply, that could be switched to 4-5 different values.

 

[chinsettawong]

If you are happy with using such a low bias voltage, you might want to try thinner diaphragm.  I really like the sound of 0.9 micron diaphragm.  However, I use 580V bias voltage and the the diaphragm isn't very stable at that voltage.
 
With this very thin diaphragm, you can't put too much tension on it.  It's extremely fragile.  But the sound, especially on high frequencies, is just amazing.
 
Now who says making electrostatic headphones is difficult?  

 
Wachara C.

 

[cjfrbw]

Thank you so much for your comments.
 
I really love these strange hybrid headphones right now, the sound is just so HUGE.
 
 The  normal bias 3n/5n is detailed but the imaging still sounds like it stops around the ears. 
 
 The imaging of the modded 507 goes so far out into space that it helps to defeat the "in the head"  limitation, way out to the right and left above and below.
 
I will probably get around to playing with the membranes again, but for now, hey, if they sound this great, I should just enjoy them for a while and worry about the variable parameters later.
 
Pro bias makes them sound much more incisive, but they become noisy and crinkly as well.  The normal bias gives them the right combo of relaxation and detail, but they are still extremely detailed. It's hard to take them off.
 
Anyway, Wachara is correct, playing with the membranes can be rewarding, it's strange that there must be a lot of good sounding recipes.  I wouldn't destroy a working pair just to do it, though, and making a whole new headset looks like a real challenge.

 

[cjfrbw]

As a follow up technical note:
 
When I was wondering if the problem with the 507 was from the bias, I changed the 100v zeners on the Spritzer bias board with 120v zeners.  This probably bumped the voltages of the bias on both normal and pro bias sockets by 20 percent.  Pro bias could have gone as high as 700v.  
 
I do not have a high impedance volt meter to test these, so I have no way to know the exact bias figures.
 
I replaced the 120v back with 100v zeners, which probably put the pro bias back in the 550 to 600 range and reduced the normal bias voltage back to true normal.
 
Anyway, the "new mylar" 507's work fine now with both the pro bias and the normal bias sockets with the 100v zeners in place.  When the 120v zeners were in place, the pro bias was too high and sounded "crinkley."   With the 100v zeners in place, the pro bias has no sound artifacts and is very incisive and clear sounding.
 
Both sockets still sound wonderful.  Pro Bias:  more incisive, maybe 6db more efficient than normal bias.    Normal Bias:  more relaxed and less efficient, but great as well.   I guess I just have two flavors to choose from, both tasty. 

 

[chinsettawong]

Congratulations!
 
Wachara C.

 

[spritzer]

Any of the Lambda drivers do not like a 700+V bias so it was a good idea to go back to 100V.  800V is very much not recommended... 

 

[soren_brix]

  ...
 
The "new" 507 seem to have a great balance of characteristics so far, I find them preferable to the original 507's when they were working.
 
I am shocked because I was just hoping to get them working decently again at a  standard Lambda type performance and instead got a new headphone setup that I really like.
 
.... 
 

I really enjoyed reading your rescue mission getting you 507's back in shape and also impressed that you manged to do quite easily.
 
I am wondering whether your NB 507's are still working? or whether you have done more experiments since?
 
/S

 

[cjfrbw]

  I really enjoyed reading your rescue mission getting you 507's back in shape and also impressed that you manged to do quite easily.
 
I am wondering whether your NB 507's are still working? or whether you have done more experiments since?
 
/S

 
Thanks, it wasn't really "easy" per se just "doable". The 507 is capable of intervention in this manner due to its modular construction.  I have since fractured the headband and will have to repair that as well.  I bought the 507 for durability, so it is a disappointment that they are so disaster prone.  My old original Lamdas have had much better luck, even though they are ancient by comparison.  I am using the 507 earpieces currently with the original Lambda headband.  The strange thing is, I like the original Lambda headband better than the 507 headband, less pressure and more ideal seating.
 
I am enjoying them very much, listening to them right now.
 
I was going to do them over with a different mylar "stretch" and a thinner coat of anti-static material.  However, haven't had the time or inclination, and they sound great the way they are, so why argue with success? The "new" mylar seem pretty durable so far as well: Normal bias outlet with DIY vintage Stancor transformer (modified SRD 5) hooked up to Manley Neo 300b Preamp, sounds great.  I will have to open them up and check out the mylar someday to see what it looks like.
 
I have another rig in another location, but haven't heard anything at shows so far that would make me believe that I could improve my sound in any meaningful way over either rig.  If I did find something I thought was better, I would consider buying it.
 
The only problem with my setups is they are completely unique and non-commercial, so they don't really do consumers any good unless they want to try their own hand at DIY experimentation. For some strange reason, a lot of my audio stuff winds up that way, even though I am a mediocre and dangerous DIY type, I ruin as much as I improve.

 

[soren_brix]

   
Thanks, it wasn't really "easy" per se just "doable". The 507 is capable of intervention in this manner due to its modular construction.  I have since fractured the headband and will have to repair that as well.  I bought the 507 for durability, so it is a disappointment that they are so disaster prone.  My old original Lamdas have had much better luck, even though they are ancient by comparison.  I am using the 507 earpieces currently with the original Lambda headband.  The strange thing is, I like the original Lambda headband better than the 507 headband, less pressure and more ideal seating.
 
I am enjoying them very much, listening to them right now.
 
I was going to do them over with a different mylar "stretch" and a thinner coat of anti-static material.  However, haven't had the time or inclination, and they sound great the way they are, so why argue with success? The "new" mylar seem pretty durable so far as well: Normal bias outlet with DIY vintage Stancor transformer (modified SRD 5) hooked up to Manley Neo 300b Preamp, sounds great.  I will have to open them up and check out the mylar someday to see what it looks like.
 
I have another rig in another location, but haven't heard anything at shows so far that would make me believe that I could improve my sound in any meaningful way over either rig.  If I did find something I thought was better, I would consider buying it.
 
The only problem with my setups is they are completely unique and non-commercial, so they don't really do consumers any good unless they want to try their own hand at DIY experimentation. For some strange reason, a lot of my audio stuff winds up that way, even though I am a mediocre and dangerous DIY type, I ruin as much as I improve.

 
 
I guess your experience in rgrds to ancient/old Stax being better quality is sort of what most people here also states from time to time.
I have a pair of NB Sigma that must be from the first batch at all and it seems to work without any problems, also a pair of NB Lambda that is working fine.
 
Your reworked 507's sort of demonstrates many of the viewpoints Sanders make about electrostats - in rgrds to the stretch of the mylar Sanders seem to be less critical about it; a firm stretch and warm gun treating will do the trick, it might be different when the elements are small?
the fact that you seem to get a pair of 507 that are sound better or at least as good as the original one, at least to your ears, is sort of very intrigueing.
 
I have a pair of 404sig's with a faulty driver and I might try to copy-cat your work
I have tried to figure out where to get the mylar but it seems to be a bit complicated at first.
There are a local distributor  anti-static spray spray so I guess that will be no problem.
 
You did re-do both drivers, right?

 

[cjfrbw]

Yes, I did both drivers.
 
Try this link, they still sell it:
 
http://www.indoorspecialties.com/index1.html
 
Go to:  Click: materials and supplies button, then Click:  Ultrafilm and Super Ultrafilm, where the rolls are available for purchase.
 
They have two thicknesses, I used the higher thickness but it was still pretty darn thin. 

 

[Tachikoma]

I have a question about Stax transformers, and I don't like starting new threads so here goes... I'm looking at a transformer with a 3000:8 ratio to use with a 30W Pioneer M-22, which should give me 300 vrms max. Is 300 vrms typically enough for an O2? I suspect that I hardly ever push my SRM-T1 over ~100 vrms anyway, but given that most "O2 approved" amps seem to do a lot more than that I wonder if its important.

 

[kevin gilmore]

You should probably test the output of the transformer with a 120pf load and look at it with a scope
to see if there are any ringing problems before you hook it to the headphones.

 

[Tachikoma]

Hmm... I haven't actually ordered the transformer so I can't do that, but the guy who makes them doesn't live too far away I suppose... For what its worth, I'm looking at OP44 from http://www.turneraudio.com.au/for-sale-2-output-transformers.html