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Author Topic: ESP-9 revisited  (Read 4295 times)

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chetlanin

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ESP-9 revisited
« on: March 10, 2014, 08:39:32 AM »

or  The Holy Grail of headphone sound.

The old ESP-9 cannot be generally recommended, and for many reasons: Extreme discomfort in wearing, unpleasant mid-centered sound, poor availability, the need for refurbishing, hum issues with a lot of  the E-9 energizers, oil leaked from the pads, extremely stiff cable after all these years, liability to discharging noises, inability to produce really loud sound, and probably more.

However,  if a well-kept unit is found and carefully cleaned and  refurbished with new damping material to the cups and tonally corrected  (and at least  for a few minutes until the pain in the outer ear becomes unbearable), it can give you everything you ever asked for in headphone sound!  Electrostatic timbre and transparency in combination with a strong body of tone + a bass quality that will blow you off the chair. The clue to the two last mentioned factors is obviously the use of the closed-can-principle, rare for stats.
 This bass will make you check if you forgot to turn off the subwoofer!

Even if the quality of the bass is the most mind-blowing single property (of a working and properly EQ-ed unit), everything  in it comes together and makes musical instruments sound more real than I ever thought possible. Yes,  that is the best characteristic, I think: The complete lack of artificiality in the sound of the acoustical instrument.  Even if you do not get the loudness of live sound, these cans make you enter some kind of virtual reality where the level does not matter any more (kind of).

You will be shocked,  say, during a heavily orchestrated forte passage in a symphonic piece, and you think the sound is already completely saturated, when suddenly deep down in the mix you hear a mellow tuba enter with some tune of its own, played in its lowest register! 
The sturdy/heavy construction with the thick metal stators must be another clue to the amazing potential of this  thing.  There seems to be no colouration to speak of at all (seen apart from what easily can be corrected tonally).

To my bafflement the EQ settings I used with the more ordinary baby Koss (ESP-950) were not far from what the old lady herself needed  (even if being a very different animal).  Mids around 1.2 kHz dampened some 6 dB in a rather broad area, bass turned a little up.

Of course the increased bass fed into them will reduce the headroom when trying to play loud. Even un-corrected there are limits, also mentioned BTW by J Gordon Holt (it must be him)  in the old Stereophile review.*
More stuff to follow, some foam refurbishing tips perhaps. (light foam should be used IMO).
Olaf.


*(I was initially a little surprised by this: Did the guys in those days -the days of ELS 57 and LS3/5a and such- really play that loud?  Then it occurred to me that LP records were the dominating source of music at the time.  LP records, and in particular tracked with heavy, old style p.u. arms and typical  high compliance mm cartridges, will make subsonic artifacts with large amplitudes.
(the same thing you can see when the bass membrane of a speaker does obscene movement by LP playback. The diaphragm of any ELS transducer would hit the stators long before they needed, so to speak.  JGH was probably practical minded  enough to not test equipment with much better sub-filters than were in common use).





The mylar diaphragm with its hand painted layer of semiconducting paint. From a noisy unit. Notice that the glue holding the layers in place is attacked at the corners (dark area) The strech is still good.



The outer stator seen from inside. An extra layer of mylar is protecting against dust and electrical contact. The light gray rim is the shim which determines the gap.




« Last Edit: March 10, 2014, 12:18:33 PM by chetlanin »
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chetlanin

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Re: ESP-9 revisited
« Reply #1 on: March 10, 2014, 09:02:50 AM »



Before cleaning, interior of cup (most of foam removed).

 A layer of felt is covering the inner stator and several layers of thin paper (TP?) is covering the felt. This is common to all 6 units I have opened, only the number of TP sheets is all over the place in the different units.

What is the purpose of the very thin and light paper tissues? I would say the dampening effect would be small compare to that of the foam. I wondered if it could have some kind of acoustic DC blocking function. Say, you have a very good seal after a few sweating hours in the studio, and then suddenly tear the phones off your head really fast, as will sometimes be the case. The diaphragm will be sucked forcefully towards the outer stator, and might be damaged through sparks. The little -however light- bits of paper, would possibly do quite a decent job blocking the air-stream, me thinks. (possibly far fetched).  In any case, i have kept the arrangement when refurbishing.



Another picture of the same. Some TP sheets removed. The innermost layer of felt is black.
« Last Edit: March 10, 2014, 11:33:45 AM by chetlanin »
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chetlanin

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Re: ESP-9 revisited
« Reply #2 on: March 10, 2014, 10:07:53 AM »



Full schematics (with the original and most problematic energizer with the two extra transformers delivering some 200V AC to each voltage multiplier).



Simplified, signal path only. C is the mid point of the secondary coil of the step-up transformer and also a reference point of the bias voltage. Because of the arrangement with frequency modifying link between this coil and ground, the voltage potential of C will vary with the signal, hence the need for two separate high voltage sections, to keep up stereo separation etc. One could clean out this RC stuff and use a simpler Stax type arrangement, since all FR correction could be done through EQ anyway. But changes would have to be applied to every section, including cables and cups. Time-consuming stuff, if in principle simple enough.
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chetlanin

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Re: ESP-9 revisited
« Reply #3 on: March 10, 2014, 11:21:12 AM »



The old foam has the consistency of a dying mushroom in the woods.



the underside. Shows why a non-refurbished unit will sound over-dampened, as the heavy and  sticky foam rests against the inner stator  (through the covering tissues)



A possible solution if you want to keep the tissues covering the inner stator, but with little pressure on them.




First attempt at a practical implementation. Foam is a very light type. No over-dampening, good sound,



Another picture. I have covered the underside of the connection board with crunched chamonix artificial leather for absorbarion of hf energy, one or two layers. Seen in the background.



crunched chamonix



pleasant stuff to deal with..

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chetlanin

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Re: ESP-9 revisited
« Reply #4 on: March 10, 2014, 12:11:33 PM »



Koss must have got some units in for refurbishing from time to time. How did they solve the issue with the disintegrating foam? They would need a safe and and simple in use solution. An interesting picture on ebay from some time ago may give a clue. The seller had once upon the time visited the Koss factory and had brought back some new pads + the other stuff seen in the photo. It rather suggests that they left some space over the inner stator open. My guess is that they at the same time removed the tissues mentioned earlier. There would be nothing to keep them in place, so to speak, if this was the whole solution. ( Probably no big deal).
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chetlanin

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Re: ESP-9 revisited
« Reply #5 on: March 10, 2014, 01:20:14 PM »



May I mention that while it would be time-consuming to rebuild the cans to work in the way of Stax, it is rather simple to rebuild the belonging energizer to work with Stax phones. Just put in a SRD7 II voltage multiplier board ( the simple schematics for this can be found through google image search, may be in the last instance thanks to Spitzer).
 Of course you have to know which way to turn a diode etc. The unit in the picture works very well. Only the transformers and the top board are active. This a cheap way to get a good sounding driver to ones Stax phones. (I had several E-9 boxes standing around unused). The pins on the connector need to be re-arranged, of course.
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MuppetFace

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Re: ESP-9 revisited
« Reply #6 on: March 10, 2014, 01:21:06 PM »

Let me be the first to congratulate you on a truly awesome thread. Note to pirates: give this chap some karma points!

I have both the ESP950 and its immediate predecessor, the ESP10. IIRC the ESP9 was the model before the ESP10? Anyway, I was really impressed by the sound of the ESP10 considering I scored a barely used set for around $200 USD along with the hefty wood veneered transformer. I gave it a slight tweaking to improve the dreadful stock earpads. Then using a few scraps of speaker wire I had lying around and a $30 T-amp, I had a full electrostatic setup for under $250 that could still hold its own against a lot of modern gear.
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My blog on head-fi: http://www.head-fi.org/f/7879/muppetface
I mostly talk about music there. Weird.

chetlanin

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Re: ESP-9 revisited
« Reply #7 on: March 10, 2014, 01:42:08 PM »

Thanks for the kind word MuppetFace. The ESP 10 probably shared some parts with ESP 9 but seems to be a rather different animal. It must have been their last ESP, before the 950. I have not heard it, just seen it once or twice on eBay (and bid on it). There was an ESP 6 (bulky, with built in energizer), an ESP 7, 8, 9, and 9b not very different from each other. The last two must be the most common. I have one ESP 7 with elegant, if slightly discoloured white cups, like the interior of some American luxury car from the seventies, or something. Otherwise only several ESP 9's. There were several versions of the energizer to all these and I think they had solved the hum problem when they came to the last ones.

Best wishes, and BTW I always thought that your posts in your Taket2 thread ( on a competing forum) contain some the best and funniest ever written stuff about hifi equipment. Olaf
« Last Edit: March 10, 2014, 01:50:40 PM by chetlanin »
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ultrabike

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Re: ESP-9 revisited
« Reply #8 on: March 10, 2014, 05:13:16 PM »

Awesome Olaf! :)p5
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chetlanin

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Re: ESP-9 revisited
« Reply #9 on: March 11, 2014, 12:47:28 AM »

nice of you to say ultrabike!



E-9 energizer, the version of the original schematics



Simplified somewhat. Replacing the supply voltage to the voltage multipliers, it turned out that the multipliers themselves worked flawlessly. The components may look old, but diodes and ceramic capacitors have a long life span. The carbon composite resistors may change a little but they are 10% tolerance anyway.(Also many units will have been i little actual use, probably).



Solder side. The big carbon composite resistors are evening out input impedance of the unit. The value is not critical, and it also differs from the one in the schematic. Silver ring: 10 % tolerance. Circuits were made to take big tolerances. Nowadays 1% resistors is found even in cheap stuff, of course.





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