[Brian1234]

I have a Vintage pair of KOSS ESR9 electrostatic headphones and am wondering a few things:

1) Anyone know of any basic info on the net about them?
2) Any idea how good they were and if they may have degraded over time?
3) Can I get replacement pads for them? From KOSS?
4) They havent been powered up in quite a while (10 years?)... should I do anything special to test them? eg: Power up the transformer unit with phones disconnected to make sure I dont get any magic smoke and hurt the phones, etc?

Thanks!

 

[ericj]

You mean the ESP9, I presume.

The pads are interchangeable with Pro4AA pads - you can order a set from koss.com for $5 shipped in the US. Beware that the ESP9 flange is a little bit bigger than a Pro4AA so they will not be easy to install - but they WILL fit.

There is foam inside the earcups that has a tendency to decompose and foul up the electronics. This is worse depending on how caustic your environment is. Like say living next to the ocean, or a Dow Chemical plant.

Also depending on how caustic your environment and your own sweat are, it's not unheardof to find corrosion on the stator wires.

But go ahead and hook them up - nothing bad can happen from trying them out. You may need to let them charge up for half an hour or so.

 

[Brian1234]

Ah yes, it says ESP.9 ... I thought that was a stylized R.

Thanks for the info!

 

[edstrelow]

If the foam has deteriorated it can cause short circuits in the circuit boards inside the cups. No problem except the phones will hardly run! However you can clean up the boards and replace the foam with say foam or felt. Several people here have reported this in the Koss ESP950 thread or the Stax Thread. I did this for the earlier Koss ESP 6 and after three separate cleanings of the circuit boards got the phones working just fine.

Sound-wise the 9's have a good frequency response with extended, but not harsh treble and fairly deep bass, but not as extended at the Stax 404. They seem to lack some of the resolving power of the better Stax phones, by which I mean the detail is not too strong and the ambience is fairly weak. However they are not as harsh sounding as many Stax can be.

What I really like about them is that they give good sound isolation. Amost all the Stax line are open-back so they both leak lots of sound and you will hear lots of outside noise.

Since the Koss run off a regular amp, the sound will of course vary with the quality if the amplifier used to drive the E9 transformer box.

 

[DkossZoSo]

ESP-9 and PRO 4AA ear pads are same. They costs 5 dollars.