Fostex T30 isodynamics (what, again?) - Page 2

The original T50, probably the best sounding 'phone they ever made, arguably the best-sounding vintage isodynamic 'phone ever made (at least, in stock form), detailed here. Long out of production and, as it turns out, extremely rare, at least on US eBay. I've seen only one set in two years, which is a shame. I'd hoped to share a few pairs with fellow isodynamic-loving HFers. I think with some work the T30 could be almost-first-best, but it's almost as rare as the T50 and it's not the most comfortable headphone you'll ever wear-- why they didn't construct it like the original T20 and T50 with those huge coddling earpads, I don't know.

 

Interestingly, there was no T40 in the original line. It went T10, T20 (both with 45mm spiral voice coil drivers), then the T30 with a big (~60mm) serpentine voice coil diaphragm on Mylar but conventional disc magnets (though slotted to resemble the T50's bar magnets); then finally the T50, with the big serpentine voicecoil and a grid of rare-earth bar magnets and a heat-resistant Kapton diaphragm and a big jump in price.

Edited by wualta - 6/13/11 at 7:10am

T30 Undressed

We've opened the ATH-2 and Technics EAH-830 preparatory to installing some damping materials, but mostly just to gawk at the internals. There were more variations on the isodynamic headphone driver theme than I imagined, but as I've said elsewhere, I'm not the expert; I'm just on a voyage of discovery. What separates me from the dilettante diddler is, I pronounce voyage as voy-YAWGE, Thurston Howell style. Which, I think you'll agree, makes all the difference.

But that's not important now. We want to look inside the 'phone that was the first major step up in the original 1978 Fostex line, the T30. The sound we've been getting from it is nice, in that with some bass boost the thing has a low end that must be heard to be believed, but the treble kinda dribbles away. Don't get me wrong-- it's smooth, so if we EQ'd it with a multiadjustable EQ unit, like a parametric, we could bring the top end up and it would be reasonably flat.

Still, we've gotten good treble out of the more primitive Yamaha Orthodynamics by damping them, and the next Fostex step up, the T50, has a very extended treble, so we should be able to extract a decent top end from the T30, which has a similar serpentine diaphragm. What's so good about a serpentine diaphragm? It's pretty, for one thing...



..and Fostex has always claimed that it's better behaved than a spiral voice coil diaphragm, such as is used in its own T20. It certainly looks harder to make. I hope you can see the very fine aluminum traces on your monitor. A thing of beauty, I think you'll agree. The T30's driver differs in other ways from the one in the T20, starting with size. It's about 60mm across versus 45. The T30's magnets are stronger than the ones in the Technics; you have to hold them with both hands to screw the clamp down. There's no nodal clamp or damping button or whatever that thing in the Technics is, so that big diaphragm is free to move, baby. The magnets are the usual [ferrite?] discs, but instead of holes there are slots aligned with the M-shaped voice coil traces. See that translucent goo around the perimeter of the magnet? That's silicone grease. The diaphragm is held in a greased clamp. I think the idea here is to help absorb surface waves as they travel toward the edge of the diaphragm so they're not reflected, and also to let the diaphragm stretch a little during big excursions. It's an interesting detail, that's for sure.



And it turns out that the only damping was one of those fluffy fiberglass-looking biscuits stuck to the back of the driver. I think some felt will work wonders here, as it has for the Yamas. We'll have to continue this later, but I have restrainedly high hopes. Stay tuned.

The old T30 thread lives!

The damn thing (the T30, not the thread, which is just another damn thing) has turned out to be even more rare than the T50, if such a thing were possible. I think scompton and I are the only avowed owners. And, brave lad, he's actually got a successful mod for his.

A puzzling headphone, the T30. Well worth trying to acquire, but mechanically quirky. And @#%$&! sadistic uncomfortable.

Mostly it's just bad writing or unclear or I-assume-everyone-knows-what-I'm-talking-about-with-the-caveats-understood writing.

And sometimes I'm just plain flat out wrong about something because I remembered it wrong from 35 years ago or the experiment that led to a conclusion was fatally flawed. That happens. And I'm obsessive about keeping all the old posts up to date so no one ends up flying down a blind alley. I don't expect everyone to have to take the entire voyawge of discovery that I'm taking. So if you come across a dead end or a statement that's obviously false in light of current knowledge, PM me.


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The T30 is fun to play with because of the big fat diaphragm and the fact that it's bassy, which means there's room to play (ie, try different damping strategies), but in real-world practical everyday quotidian terms, there are other isodynamics that will do the job of delivering good sound to your ear and are far more available-- and comfortable. And yes, the old Yamaha Orthodynamics may look clumsy but they really are comfy.

Keep the T30 (and T50) in the back of your head and pounce if one heaves into view, but meanwhile there's the dead-cheap SFI driver which is the current darling in the Orthodynamic Roundup thread. And who knows, maybe a YH-1 will appear and not shoot up over $80. It's gotta happen sometime.


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