[ericj]

I bought a pair of conceptually fascinating pair of headphones recently - the top of the line of Pioneer's piezoelectric film headphones. These are fairly unique, if anybody else attempted to use this technology in headphones I haven't heard about it.

This thread is not about the amazing technology (No magnets! No electrostatic fields!) - this thread is about taking a 30+ year old pair of headphones that look like hell and turning them into something presentable.

The thing is, I got them cheaply. I paid about $30 shipped for three pairs of old headphones, including this one pair i really wanted. Other members of head-fi have paid as much as $100 for a pristine pair of SE-700's.

This first post covers my rebuild of the headband. I peeled the wretched vinyl off of the frame and cleaned off some of the dried out contact cement that Pioneer apparently assembled the entire headphone system with.

I prefer double-sided tape for this sort of thing, and i have a few hundred yards of two-inch-wide double-sided adhesive nonwoven fabric tape, with impressive bonding characteristics. This is Tesa(r) tape, manufactured by Bergdorf in Germany. It's the european version of the stuff that half of japan is held together with.

The entire rebuild procedure took about an hour and a half, with me stopping frequently to take pictures. I had previously disassembled the headphones to bare components and cleaned everything - including the piezo film.

Here's what I started with tonight:



That headband fabric won't lay flat, so, i laminated it with painter's tape.



Much better. Here it is overlaying the meat side of the deerskin suede I'm replacing it with.



I've stuck it to the suede with some lousy 3M double-sided cellotape so it doesn't move around while i cut with the x-acto blade.

And here's the cut out piece:



Looks great, no? This is really nice suede. It's very thin and supple. I've considered making earpads out of it.

Here's one of the internal pieces of the headband with mounting tape applied but not yet trimmed:



Here's the same piece, trimmed and peeled, along with one of the internal pieces of vinyl from the headband, with the backing still on it's mounting tape. You'll notice one edge is thinner than the other - that's where the cable runs.

I've cut the backing around the middle of the plastic piece because this will be the last part i stretch the suede over.



I forgot to take a picture of these stuck together. So here's a picture of the suede piece with mounting tape applied to the tabs on the ends.



The tabs get stretched over the ends of the top inner piece of the headband. I didn't separate the vinyl from the plastic here because the bond was good and clean.

The suede is NOT adhered to the top of the headband on the outside. This is very important for the fit and feel.



Here the suede is stretched over one side of the inner headband piece. See the channel for the cable? Holding the cable in place while stretching over the other side was kind of a pain in the butt.



Almost done. So here's the struts. fwiw these are significantly larger than Beyer struts. I'll post a side-by-side with my DT-880 Studio later so you can see what i mean.



And here's the completed headband:



There is another piece of suede that needs to go in the channel in the middle on the inside, to cover the seam. I'll stick that on later.

Stay tuned for the rest of the assembly - I'm gonna take off for a while and do that.

All pics are clickable, the big versions average half a megabyte (at 85% quality, no less) so they are pretty much for broadband users only. Me, I have multi-gigabit fiber run into my basement.

 

[Duggeh]

An excellent and worthy refurbishment project of an (almost) completely unique headphone. Upon completion of your refitting and polishing of these, could you perhaps give us a run down of the piezo operating principle, which is (apparently) so tricky to get to work as a full range driver and a synopsis of the sound?

 

[ericj]

Thanks, Duggeh. It's an honor to be complemented on this rebuild by such an accomplished Jecklin refoamer.

I'd actually realized how late it was and how long it'd been since i'd eaten, so i had dinner instead. Now I have to find the right diameter heatshrink to keep the cloth-jacketed cable from fraying when i shorten it. It's broken on both ends.

 

[wualta]

Duggeh, let me step in whilst Eric refreshes himself and give you a quick rundown of things piezo. By all means, take a look at Wikipedia and look up piezoelectricity and PVDF/Kynar. Learn how to pole and when not to. Consider the bravity of the company Eric calls Pine Ear taking this wonder material which had only recently been characterized and turning it into a consumer product in the "turn it up to eleven" Seventies.

A piezo driver is simplicity itself: Hook your audio signal up to a chip of it and sit back and enjoy the music. That's basically all there is. It's like having an electrostat module chemically built into a sheet of plastic. Slap on some aluminization for the wires, and your audio signal reacts against charges embedded in the plastic and the stuff jumps. Coddle it between big soft foamy mitts for structure and a bit of damping and voyla!. The stuff has a very low mechanical impedance, unlike the piezo discs used in the Motorola tweeters, so full range isn't a problem.

No magnets, no electrostatic fields, no coils, no precision manufacturing except the making of the film/diaphragm itself, full range response inherent.

You can perhaps see why Pioneer found the prospects irresistible. They used the same PVDF in their HPM line of loudspeakers, and people on certain other forums still coil in ecstasy around their 30-year-old examples, even though most of them only use the PVDF driver above 12kHz.

The only fly in the ointment is bass, because the PVDF available back then was too stretchy to do really good bass-- the material kinda goes all wet-noodly. It's not bad, it just doesn't live up to expectations. These days, a company might try laminating the PVDF to a thin film of Mylar or tensioning the driver to make a dome, or reformulating the polymer, or any number of other strategies to get better bass out of the stuff.

Meanwhile, we have this tantalizing glimpse. I have the SE-500, and it sounds kinda.. well, Seventiesish. Midrangey, but decent. We'll see if Eric can coax something more out of the SE-700.

PS for Duggeh: If you've ever suspected you could make a Heil driver from PVDF film and do away with the cool-looking but heavy and expensive magnet structure, the answer is, as you know, yes.

By the way, just to put these 'phones into the timeline, the AES paper describing the transducer (microphone, headphone, tweeter) dates to 1974. That's a year before Stax introduced the SR-X Mk 3.



EDIT: Here's the main page of the 2-page owner's leaflet:

A couple of interesting things to note on this first page: In the specifications, the line that originally read Impedance......8 ohms has been crossed out completely and the one that now reads Maximum input power.... 30 V originally read more than 30 V. On the back the instructions shed some light on this by saying The SE-700 has a high input impedance. Which is what we'd expect with a small capacitor across the amp's outputs.

Oddly, some old German brochures for the line of HPM headphones give different diaphragm thicknesses for each model, with the middle of the line SE-500 having the thinnest (6.5 µm), the SE-700 having an intermediate 7.0 µm and the cheapie SE-300 having the thickest (8.5 µm). These discrepancies are reminiscent of the German brochures for the Yamaha Orthodynamic line. Which is true? We don't know, of course.

 

[ericj]

Well, some steps took way longer than they were supposed to, but here we are.



Despite three layers of fabric surrounding the three wires and a nylon cord inside each wire, this cable has breaks at both ends. I'd rather cut three inches off than deal with it twice.

This cord actually literally went for a ride in my washing machine with a load of towels last night. The outer jacket is nylon or polyester or something meltable but the inner layers appear to be cotton.

Sorry, no pics of the inner layers of fabric.

I've added heatshrink as insurance against fraying.



Here the ends are prepped for soldering.



It's just *easier to hook up 1/4" plugs, innit?



This ended up taking me like an hour to accomplish. The heatshrink on the cable had to come off to get it through the strain relief.

And the strain relief had to come out of the earcup.

And it turns out that the strain relief has to be inserted into the earcup from the inside.

Which isn't exactly easy.



Here's the back of the earcup disassembled. The nonwoven fabric is exceptionally thick and leathery. This had to be disassembled to clean crud out of the grille properly.

I used a thin bead of flowable silicone around the edge of the outer grille to re-affix it to the inner grille. I love this stuff because it holds on strictly by surface tension. It's never going to fall off but if i peel it off it'll come without argument.



Ah, here's more of the permatex stuff i like so much. You couldn't pay me enough to make me figure out how to replace the foam mounting for the driver, so, more flowable silicone it is!



I can't figure out why, but the bracket for the audio signal (white, on the right) is cut for the key tab to point away from the cable inlet instead of toward it. I can't remember this being that way during disassembly. This arrangement works, though.



Four screws hold the earcup together. Pioneer has thoughtfully cut out a slot on the top of the earcup to make room for the wiring that goes through the headband, and included holes where i can tension the contacts on the driver, if, for some reason, i needed to.



More of this light-weight RTV!



The metal rings actually kinda snap into place, but since the permatex stuff isn't an adhesive at all (just a sealant), I figured i should tape them on for the hour or so it'll take the stuff to cure.



I could have worked harder at retaining the earpads, but why? they're recessed anyway. And i might take them off and replace them with a home-made version.

These originally had the same vinyl on the top as you see here on the back, but this got all grody and cracked. So i washed them, and when they came out of the washing machine, all the ear-side vinyl had flaked off and gone down the drain. Huzzah! Soft fabric earpads!



I really need to buy me one of those styrofoam mannequin heads.



See? it's like someone squished a beyer until it was flat.

How do they sound? well, they have bass. But it appears that the right-side driver is damaged -- it lacks highs, and distorts some.

It kinda looked to me like the film had come delaminated from the metal frame along the top on the back of that driver. I'll get my hands on one of those conductive ink pens and try a repair job at some point in the coming weeks.

 

[Inkmo]

man, that's a heckuva refurbishing. hope this turns out well. Do you think replacing the mounting foam with silicon is gonna effect the sound at all?

 

[ericj]

Thanks! Not having to actually sew anything kinda made the headband rebuild dead easy. This is the first time i've used this suede - I've got about a pound of the stuff, four small hides in all.

I need to take some glamour shots of the headphones to show off the work tomorrow.

I don't think that the silicone is gonna change the sound at all. The way this stuff works, it wicks it's way into small gaps and seals them. It's sold as a cure for leaky windshield gaskets - you just literally put a bead of it along the edge of the gasket and it works it's way in via capillary action.

The film is loose in it's frame, and gets tensioned into a shallow dome by the damping foam. The mounting tape just holds the frame in place.

 

[SonicDawg]

Wow, nice work!

Btw, I really love your cable tubing. Where did you get the stuff (cotton)?

 

[krmathis]

Wow! Thats some reconstruction.

Hope you find a right-side driver, or are able to fix the one you have.

 

[spritzer]

Really nice work. It's a lot of fun to restore these old phones.

 

[ericj]

Quote:

Originally Posted by SonicDawg /img/forum/go_quote.gif Wow, nice work! Btw, I really love your cable tubing. Where did you get the stuff (cotton)?

That's bog standard original 30 year old Pioneer headphone cable.

The cable on the beat-to-heck SE-L40 that came with the SE-700 is exactly the same stuff. When my SE-500 shows up later this week i'd be surprised if it doesn't have it too.

An enterprising geek such as myself could get his hands on a length of 5mm nylon cord, though, and separate the jacket from the inner bundle, and use that. The problem is finding it in an attractive color.

Thanks for all the comments, folks. It was a fun process, even though I'm fairly certain i damaged the right driver. I don't know what kind of bizarre glue pioneer used when they built the thing but it's an odd color and very thin - I'm betting it's conductive, so, a circuit pen is probably my best bet.

If that doesn't work, i can just wait around for another beat up pair to turn up on that auction site.

The moments where both drivers seemed to be working when i was listening to them, they were pretty engaging. I didn't listen to them much before tearing into them because i had to fiddle with the cable at both ends to get sound out of either side.

 

[edstrelow]

I hope you get them working. I await a report on their sound!

 

[Uncle Erik]

Beautiful work! You're doing a careful, thoughtful job.

Would you be kind enough to post a full review when you're done?

 

[wualta]

I wonder, would a small ultrasonic cleaner help in getting the crud off the Kynar? Or is it too floppy? Well, just a thought.

 

[ericj]

The de-crudding of my kynar film was performed with a tissue soaked with ethyl alcohol. Worked ok.

I see someone listed a pair of these on that auction site with a purchase price of $25 and somebody jumped on it within hours. One of our own perhaps?

I'll do a review if i get them working. I need to order a fistfull of connectors from markertek tonight so I'll include a circuit pen if they have them.