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.
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.