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electrostatic help needed; koss esp9's (updated)

post #1 of 18
Thread Starter 
These phones are in really nice condition and I was just able to snag some nos fluid filled pads and another energizer, an e9. The e9 that came with the phones is the e9b version.
When using the bias supply (the one that takes power directly from the amp) everything sounds good but when using the transformer the phone get a hum in the left channel only. When I move my hand to the headphones and touch the metal stays the hum gets louder.
I already asked a friend at work that has some electronic experience and he said that a bad transformer could do this in what he called a feedback loop. Along with this I also have the wiring diagram and fault finding specifications which were graciously shared by someone; Polarizer on another site. Here’s a link to a zipped pdf; Koss ESP-9 Electrostatic Headphones - Page 3 - AudioKarma.org Home Audio Stereo Discussion Forums
I know some of you have had these phones; some liked, some hated for various reasons. Does the diagnosis above sound correct? Keep in mind it has been an intermittent problem; sometimes happens after twenty minutes. I haven’t opened either the phones or the energizer yet. I’ll assume the foam is intact as I don’t hear any shorting and that the electrostatic plates are in good condition verified by running the phones in the bias supply mode.
If replacing the transformer can I use one from the e9 in the e9b? as far as I can tell they are the same only the circuit board was changed, along with the addition of resets.
tia. Steve

update:
all updates in green. i finally got a chance to disassemble the phones. removing the ear pad was easy, even replacing was easy. once inside four phillips head screws pop the back cover off. next is a small board the has four bolts, once these are removed the foam is exposed. it was 5/8 of an inch thick and was all in one peice. even though it was intact it was horribly dry and brittle. the electrostatic panel is so thin i almost thought what MAGIC makes these work. there are two additional felt pads on the rear of the panel and two baffle sheets (very thin and just in place to keep the foam from pushing into the felt insert) after removing the foam and cleaning the residue away with a artist brush; a retalatively stiff filbert the panels were reassembled and have tested ok for an hour. I did not find flakes of foam and what little was there was blown out with a small bulb used to clean camera lenses. one of the many wires inside the cup was a little loose; pivoted freely. everything else looked fine except for some oil/silicone which had leaked from the earpeice. that was cleaned up with alcohol; the rubbing kind.

before i went in i realised that it was the phones themselves and not the energizer because it faulted in the bias mode as well as the ac mode. ty spritzer! right again!

i've reassembled the phones to test without a foam replacement to and i can't tell the difference between the panels. i am planning to replace the foam in both with something fresh and suitable. i'm curious why the foam is even there since it doesn't seem to affect damping.
post #2 of 18
The transformer could be at fault but I doubt it. It's much more likely that some of the many diodes and cheap ceramic caps are going bad with age and have to be replaced. I would also take a look inside the cups as the foam will be in bad shape and could have done a number on anything made of copper inside the cups.
post #3 of 18
Thread Starter 
Quote:
Originally Posted by spritzer View Post
The transformer could be at fault but I doubt it. It's much more likely that some of the many diodes and cheap ceramic caps are going bad with age and have to be replaced. I would also take a look inside the cups as the foam will be in bad shape and could have done a number on anything made of copper inside the cups.
thanks Spritzer, i was hoping you'd lend your experience here. i know you're framiliar with these.
just to be clear, these come apart easily? like i said these have yet to be opened. i'm guessing pull the pads off and look for machine screws?

i've always wondered how the foam in there is; i gonna take a look. any suggestions on what kind of foam i'd use to replace it, if it's degraded?

nice to have the trouble shooting guide; actually gives values for resistances for each electrical component. me and my multimeter are going to get friendly!
post #4 of 18

I Thought...

I thought these had a "lifetime warranty."

Why not just ship it to Koss for repair?
post #5 of 18
Quote:
Originally Posted by Gradofan2 View Post
I thought these had a "lifetime warranty."

Why not just ship it to Koss for repair?
They'd probably send back a new Koss dynamic, as they send what they deem to be suitable replacements if they no longer have stock of a headphone.

I'm wondering if I'd be sent back an ESP950 if I sent in my ESP10, but it's not worth the risk.
post #6 of 18
Quote:
Originally Posted by ri_toast View Post
thanks Spritzer, i was hoping you'd lend your experience here. i know you're framiliar with these.
just to be clear, these come apart easily? like i said these have yet to be opened. i'm guessing pull the pads off and look for machine screws?

i've always wondered how the foam in there is; i gonna take a look. any suggestions on what kind of foam i'd use to replace it, if it's degraded?

nice to have the trouble shooting guide; actually gives values for resistances for each electrical component. me and my multimeter are going to get friendly!
Pull off the pads and there are screws underneath them. The drivers and PCB's are stuck to the baffle (those screws also carry the signal to the drivers) so be careful with those separate screws.

You can use just about any foam and also some other acoustic materials like wool.

Just keep it in the back of your mind that if you are measuring the components in the circuit you can get a false reading due to other parts affecting the one you are testing.

Quote:
Originally Posted by mypasswordis View Post
They'd probably send back a new Koss dynamic, as they send what they deem to be suitable replacements if they no longer have stock of a headphone.

I'm wondering if I'd be sent back an ESP950 if I sent in my ESP10, but it's not worth the risk.
The lifetime warranty only applies after sometime in the early 1990's and not prior to that.
post #7 of 18
Cool. I can go back to enjoying my ESP10 without regret, then.
post #8 of 18
Thread Starter 
bumped to make it rise for an update; first post.
post #9 of 18
Thread Starter 

another follow up

Another follow up, this time with pictures. Someone might find these interesting or useful. I replaced the foam with stacks of black foam that came in a motherboard box. Closed cell and antistatic properties in four layers. No adhesive was used, simply held in place by volume and the baffle board. As you can see the original foam degrades and literally falls apart when touched.
Gas preamp and Gas amp drive the earspeakers. Theta and Son of Ampzilla respectively.

earpads removed

cup removed, baffle board exposed left side

foam removed, felt exposed on left driver, foam removed and cleaned

original foam block, right side.

foam removal

final photo with associated equipment <last photo went missing>


Edited by ri_toast - 11/19/11 at 3:16pm
post #10 of 18
Brings back bad memories of rotten foam and very oxidized components...
post #11 of 18
Good times.

And by good times, I mean horrible times. And dang, that's a lot of wiring in there. How do they sound now, after the refurb?
post #12 of 18
Thread Starter 
Quote:
Originally Posted by mypasswordis View Post
Good times.

And by good times, I mean horrible times. And dang, that's a lot of wiring in there. How do they sound now, after the refurb?

you think that's alot, you should see the enegizer! four transformers and fifty wires at least!
they sound great, for 1972 they were top of the heap. there is something good to say about the 70's after all. they sound nice like stats should, they are closed unlike most stats, i often thought i'd also like to hear the 10's that you have. when these started to hummm i debated tossing them and bought the fostex t50rp's; which i can enjoy on the go. the Koss have a very "present" bass and decent top end especially on ac power.
i've been listening to a band called Magazine, in particular an album named Maybe It's Right to Be Nervous Now. there are some live tracks on this album that get me goin'. bottom line that's what it's all about, not the hokey-pokey like some people might tell you

my apologies to spritzer, sorry for the bad memories. i'll listen to my stax lambdas later and marvel at how nice they sound too.
post #13 of 18
The ESP10 is indeed open, but obviously not as open as the Lambdas. It has a more solid sound than Stax that is probably present in all of the old Koss ESP sound signatures. I was thinking about buying an ESP9 to try but they go for too much, since I expect them to be worse than my open ESP10 and and I paid about 60 bucks for them. They're very nearly Lambda level and this is before I've done any mods on them.

Looks like you're already a fellow planarhead.
post #14 of 18
Quote:
Originally Posted by ri_toast View Post
my apologies to spritzer, sorry for the bad memories. i'll listen to my stax lambdas later and marvel at how nice they sound too.
No worries. You could also try and bypass all of the Koss electronics in the cups and wire the cable directly to the drivers so you can drive them like a Stax headphone.
post #15 of 18
Thread Starter 

quick update, koss pro4aa replacement pads work and fit great, direction front and back is reversed on the pads otherwise perfect fit. the replacment pads are 5 dollars plus shipping.

i've seen 5 of these headphones sell on ebay in the last month, sometimes for shocking amounts of money. still, a nice closed headphone.

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