New project - Koss esp9

[Dr.Gonzo]

I absolutely can't turn down vintage gear.... especially when it's dirt cheap, so I have yet another thing to fix. Koss esp9b phones & e9 energizer, obviously needs new cushions but so far the drivers & power supply look pretty good, just dissecting them now. Can't wait to have 500 volts strapped around my head!

 

[eiraved]

 

[Dr.Gonzo]

Got the drivers cleaned up, ear pad oil leaked out and corroded the stators and a bunch of crap was stuck between the mylar and brass stators, painstakingly cleaned out with a computer duster and a single bristle from a paint brush.

 

[Dr.Gonzo]

New foam to replace the old rotten ones, 2 different densities to try, both the white & pink foam came with ic chip packaging from Newark.

 

[tubeactive]

If your transistors hurt, just wait until you wear the ESP9 for more than 1/2 hour. They are likely among the heaviest headphones, as well as great sounders...

 

[arts]

I have a set of these stored away that also need to be rebuilt. Pads are gone, but overall they are in very good shape cosmetically. Not operational.

I'll be paying close attention

 

[twiiii]

Esp 9's were my fist Electrostatic headphones. They were fantastic but could e problem prone. So I eventually sold them and bought Sennheiser Dynamics for casual listening and Stax lambdas for serious monitoring. But now that I have my line array speaker there isn really no need for head phones. Though I still have two pair of Stax, a pair of Sennheiser, and a pair of Signets which are the most comfortable to wear for long periods.

 

[Dr.Gonzo]

Been swamped at work but managed to get a bit more done.

One last clean with the computer duster and then these 4 small aluminum screws hold the 2 halves together (4mm nut driver)

3 pieces of very thin/porous tissue paper then a piece of black felt go in each cavity on the backside (opposite the aluminum screw heads)

The felts are on the backside of the driver (inside the cups with a foam sheet and circuit board). The 2 black plastic grills go in the the drive/ear facing side, they appear to have been glued in.


Side note - the tissue paper & felt sequence/count is how mine were when I took them apart, no idea if this is correct or if maybe koss used this to tune the drivers and they differ from set to set.

 

[Dr.Gonzo]

Installed bolts & nylon spacers, foam goes on top of the black felts and then the driver assembly goes into the frame, from the backside install the white plastic shim/insulator under the side of the board where the wires connect then the circuit board. I replaced the resistors, the capacitors were still within spec.

 

[Dr.Gonzo]

This vinyl tape has to go over the screws because they act as the conductors that carry the high voltage from the circuit board to the driver, well... It doesn't have to but your ears might feel a little tingly if you don't put it on! Cleaned the old glue & crud off the tape with ipa and gave it a quick shot of spray adhesive.

Cheap pro4aa ear pads from chamazon, won't know how comfy they are long term until I finish the power supply but the fit actually isn't too bad. Gonna add an o-ring to the retention groove, doesn't seem to need it but it will look better aesthetically.

Tech tip - If stereo sound is desired, repeat everything on the other driver.

 

[Dr.Gonzo]

Starting on the power supply today. Doesn't seem to match any of the schematics I can find. Every picture I've seen of these e9 energizers has 4 transformers, 2 mains & 2 HV, this one only has the 2 HV transformers and the diode multiplier has been moved from the main board to its own koss branded board where the mains xfmr's usually sit. Anyone seen this before?