Koss ESP-9 Electrostatic Headphones

No, red and black are ground!

Fired these bad boys up today. I got some new ear pads from koss, With a little heat got them to go on nice.
Sound ........ Super just as I remember them. Can't believe the still work this good after all theses years . :banana:
 
I have two energizer boxes for the 9's. Can anyone tell me why one box (otherwise it is exactly the same) has an extra brown wire besides the black, red, white and green? Also, does anyone have a schematic for these boxes?
 
Is it part of the same covered harness? If not, dies it have the same terminal? Also, is the box for the 9 or the 9b as they are different. The 9 had a common ground for both channels and this caused severe problems for amps where the common was above ground or the channel grounds were not commmon. It has a common wire for each channel but they were a common ground. Hence, the box had a 4-wire harness.

The 9b had separate grounds that cured the issue the 9 presented. I've had both models and neither had a 5th wire. My 9b was manufactured by Koss as one of two pair several years after manufacturing had ended and the instructions only have the 4 wires.
 
It is not a "b" model. The brown wire comes right out of the harness where the four others come from. My boxes say "/E.9" What issues where being caused? I can't tell without opening mine up I suppose if they share the same ground (tied together) as one another.
 
I've had mine for years and never really listened to them cause I used a tube amp and never hooked them up. When I did listen to phones and that was very rarely, I would grab a pair of dynamics I had laying around. Just in the last week I've really started to listen to them and there is no comparison in the two. The quality of bass is awesome compared to the little bass the dynamics had. The 9's on a quality FM station is a joy and revelation to listen to. Now it's gonna be time to spin some vinyl through them. I've never had to pleasure of listening to any other stats but i can't imagine them getting to much better than these.
 
The only competition is from Stax and it is a question of what type of sound you like. The Stax has more air, sounds thinner than the Koss. I've tried the Stax and liked them alot and could have easily lived with them had the ESP-9s not existed. I've not tried the ESP-950, maybe one day.

Da, the problem is that if the amp has isolated or floating grounds you can get anything from a hum to a burnout due to voltage differences. A number of amps with output transformers had the "Common" above ground and one of the taps was at ground and if connecting the phones as instructed it would short the amps causing major repairs. My ARC D76a was such an amp. The 9b went to isolated grounds for each channel to eliminate the problem.

I'm at a loss as to the 5th wire. My original ESP-9s only had 4. I'd suggest hooking up the 4 color coded wires as instructed and seeing it the unit works. I'm going to GUESS and it is ONLY a GUESS that possibly the 5th wire is a chassis ground meant to connect to the same point as the turntable ground to minimize hum if the amp ground is floating. The instructions did not have included a schematic for the box. I'd suggest calling Koss and see if the repair department has a copy, they should even if they do not repair them any longer. The only other thing I can suggest is to open the box and see if you can trace the wire in the circuit or send it to someone like Terry Dewickt who should be able to read the circuit.
 
My only guess would be some kind of ground too. I can't imagine what else it could be. Do or have you or heard of people doing upgrades to these boxes such as cap upgrades to improve on the older caps? Or have you ever looked inside to see if there are any caps in the signal path? Just curious.
 
My friend did some mods on the AC section on his (I posted a thread about it a while back), and they really reduced the hum that came when running the cans off of AC. Now it is almost completely inaudible, way below the noise floor of the HarmonKardon 230A he is driving them with.
 
I've got a pair of the original stax sr-lambda cans. and they are wonderful. I prefer them to the koss. but then again, the koss is still in production, with warranty.

I love my stax. The midrange is so full and lush. but they are really a mirror to your source. if any part of your system is weak, it gets revealed with the stax. The excel with classical and acoustic type recordings. but I do enjoy a bit of prince every now and then. The bass is full and deep, but does lack a bit of the "slam" you get from a dynamic can. the highest end stax are said to not have this problem.

as far as being expensive, i got my set for 300 bucks, which included the "energizer" that you hook up to a speaker amp. Nothing I've heard can match this package at this price. bang for your buck if I may. stellar.
 
What Koss model are you referring to? The 9s have been out of production except for 2 pair for well over 20 years.
 
I've not heard a set of 950s. They seem a might to find at any of the Koss dealers I've tried. Each has said gee sorry, we don't stock it but if you want a pair you can prepay and we'll get it for you.
 
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