The Koss ESP10 thread

[AudioCats]

I have just recabled a couple of my ESP10's, and found there are (at least) two variation in the 10's. So I am openning a thread to share such info, in case somebody might be interested (I could have put it into the ESP950 thread, but a new thread is easier to search)



Variation 1, smooth leath head band:
This variation has a slightly longer coiled cable (about 6" longer than the other); copper strands are wrapped around a fiber reinforcement core and form a min wire, about six such "mini wire" inside each wire.
Flat ribbon cable:
Left outter--bias Left--Left inner (dashline) ---- Right inner (solid line) --- bias right --- right outter

Variation 2, notched (the under side) leather head band:
slightly shorter coiled cable, each wire consist of individual loose copper strands with loose reinforcement fiber. The total conductor size is a bit smaller than the variation 1.
Flat ribbon:
bias left -- left outter -- left inner (dash line) --- right inner (solid line) --- right outter --- bias right.



The plug, with pins pointing toward you, either variation:

----------- left inner and right inner (tied to one pin)---------------

----left outter-----------------------------------right outter-------

-----------left bias -----------------------right bias-------------


The variation 1 ribbon arrangement makes more sense to me. Don't know why Koss made two different kind of cables. Anyway, just in case you might be interested.....

 

[Faust2D]

Do they sound different?

 

[spritzer]

Are the + stators tied to the same pin? That beyond strange since that has a much larger effect on the sound then grounding the - stators.

I just bypassed the Koss mechanics as a whole and ran them with an adapter off a Pro bias socket, wired like a Stax headphone with great results. They are no Lambda killer but the more euphonic sound has its merits.

Btw. Did you mess around with the caps and resistors inside the cups at all?

 

[AudioCats]

not sure which one is the + stator, the ones tied together are the inner stator (the one close to your ear).

I took the 82pf caps out, but left the 22M resistor in there. I can see why the 82pf is needed, the sound can get a little more harsh without them. But the ceramic caps don't sound right anyway, I am getting some silver/mica.

Recabling:
for some reason I like the koss transformer box/stock cable combo better than the T1s/stax ribbon cable combo. The T1s/stax cable sounds thin and harsh and lacks bass (this is the standard Stax push/pull wiring). Sure the Koss box (I am using a modified E/9 driven by a Kenwood KA89 amp) misses some details and is a little muddier, but the sound is fuller and more coherent.

There might be some reason for Koss to use the common inner stator design, after all.

 

[AudioCats]

Quote:

Originally Posted by Faust2D /img/forum/go_quote.gif Do they sound different?

the sound is very much the same.

 

[spritzer]

Quote:

Originally Posted by AudioCats /img/forum/go_quote.gif not sure which one is the + stator, the ones tied together are the inner stator (the one close to your ear). I took the 82pf caps out, but left the 22M resistor in there. I can see why the 82pf is needed, the sound can get a little more harsh without them. But the ceramic caps don't sound right anyway, I am getting some silver/mica.

The inner stator is + since it should be in phase and the back out of phase. Now Koss could have placed the + signal on the back stators to create this mushy, opaque sound and grounded the front stators. The E/10 doesn't have push-pull transformers so the - signal is either fed through a phase inverter or simply referenced to ground like in the older ESP's. I discarded the E/10 long time ago for parts so I can't check to see what Koss were up to.

 

[AudioCats]

Smooth head band ( variation 1).

Pay no attention to the pleather pads, they are aftermarket. The original is plastic.

 

[AudioCats]

notched headband and loose conductor/loose fiber (variation 2)

 

[AudioCats]

Quote:

Originally Posted by spritzer /img/forum/go_quote.gif The E/10 doesn't have push-pull transformers so the - signal is either fed through a phase inverter or simply referenced to ground like in the older ESP's.

I was using a modified E/9, the transformers inside have center taps and are push/pull. The inner stator wires are tied together as ground, right at the socket. Individual floating bias. Never had a E10 so have no idea how it is wired inside.


The main purpose of me starting this thread is so people are aware of the cable variations, just in case somebody wants to reterminate or do a partial recable. The rest of the differences between the two variation are trivial.

By the way, the coiled stock cable might look strange on an electrostatic phone, but it offers great flexibility and convenience during actual use. I quite like it.

 

[spritzer]

The E/10 is nothing like the E/9 or it could be like one of a thousand versions that I've never seen.

Did you modify the E/9 so that you relocated all of the circuitry in the cups into the main unit? I always wanted to do that but always had something better to do...

 

[immtbiker]

Where does the ESP10 stand in the Koss lineup compared to the 950's?

 

[spritzer]

It was the replacement for the ESP9, released in 1978 but only got a lukewarm reception so it was discontinued soon afterwards (early 1980's). The ESP/950 arrived in the early 90's and is a rather drastic departure from the earlier designs though some remnants of the past remain (plastic support for the stators, a lot of damping used etc.). The ESP10 used a very complicated transformer box but the ESP/950 is more like the basic Stax design.

 

[spritzer]

Here is a picture of one of my old sets fitted with SR-007 earpads.

 

[AudioCats]

the sound signatures of the 10 and 950 are somewhat similar, with the 950 being more transparent and refined.

 

[immtbiker]

Thanks.

Interesting approach to a coiled cord version of a Stax-style cable. Doesn't look very effective though (although I have found all coiled cords to be an unnecessary pain in the butt, dating back to my Koss Pro 4AA's and my Beyer DT801's).