[mikeg]

Although a comprehensive review and extensive discussions of the Koss ESP/950 electrostatic headphone are provided in the following threads, I'd like to describe my most recent experience with it, and my evaluation of its performance.
http://www6.head-fi.org/forums/showt...ight=esp%2F950
http://www6.head-fi.org/forums/showt...hlight=esp-950

Shortly after purchasing a refurbished ESP/950 through Amazon.com, I noticed distortion in the left channel. I then shipped the unit for repair to Koss, under their lifetime warranty, without the need for any proof of purchase, or any other documentation. And, within two weeks, Koss returned a perfectly operating unit to me. They fully resolved the problem by replacing the energizer/amplifier component, which I consider to be outstanding service by Koss. There was a $6 S&H fee.

After an approximately 100 hour burn-in, I tested the ESP/950, when powered by: 1) the 9 volt, 1 amp wall wart that Koss supplied with it; 2) it's battery pack, which requires six C-cell batteries; and 3) an Elenco Precision (model XP-603) 0-30 volt, 3 amp regulated DC power supply, which was recommended by Head-Fi member edstrelow in posting #62 in the second of the above two threads. I performed listening tests, using the following two CDs: "Time Out - The Dave Brubeck Quartet"; and JS Bach's Brandenburg Concerto #4. I compared the performance of the ESP/950 to that of an HD600 headphone, when driven by an RA-1 amp and also by a high quality 300B tube amp., and I also compared the ESP/950's performance to that of a K340 headphone, when powered by the 300B tube amp.

IMO, the sound signature of the Koss headphone most closely resembles the sound signatures of the HD600, and the K340; as opposed to the sound signatures of a K1000, or an RS-1. And, this is why I chose to compare the ESP/950's performance to that of the HD600 and K340.

It quickly became clear that the performance of the Koss headphone dramatically improved when powered by the Elenco regulated power supply. The improvement was almost as dramatic when it was powered by its battery pack (using fresh batteries); i.e., the ESP/950 achieved about 90% of the performance that it achieved when powered by the Elenco unit. But, its performance declined dramatically when powered by the 9 volt 1 amp wall wart that Koss supplied with it.

My observations regarding the ESP/950's performance are as follows:

1) When powered by its 9 volt, 1 amp, wall wart, the performance of the ESP/950 was similar to, though inferior to, the performance of the HD600 (i.e., when the HD600 was driven by an RA-1 amp). Bass reproduction of the Koss headphone was lacking, its sound stage was small, its instrument separation was poor, and its overall sound spectrum reproduction was poorly resolved.

2) When again powered by the Koss wall wart (as above), and compared to the HD600 driven by a high quality 300B tube amp (instead of the RA-1 amp), the HD600's performance was substantially superior to that of the ESP/950.

3) When powered by the Elenco regulated power supply, the ESP/950 produced powerful bass, it's instrument separation and sound spectrum resolution improved dramatically, and its sound stage increased somewhat. When powered by the Elenco unit, the ESP/950's performance was superior to HD600's performance, even when the HD600 was driven by the high quality 300B tube amp.

4) When powered by its battery pack, using fresh batteries, the ESP/950 performed almost as well as it did with the Elenco power supply; i.e., it's performance was still superior to that of the HD600 driven by the 300B tube amp.

Although the ESP/950 produced excellent sound when powered by the Elenco regulated DC power supply, and by its battery pack when using fresh batteries, its performance (as well as that of the HD600) were noticeably inferior to that of the K340 headphone. The differences were mostly in size of sound stage, instrument separation, sound resolution, and breathing space between instruments. What I'm trying to communicate is that the ESP/950 is a fine headphone system when powered by a high quality power supply (as opposed to its wall wart), and that its sound signature resembles that of the HD600, although its performance is superior to that of the HD600. To be more accurate, the sound signature of the ESP/950 resembles that of an HD600, with a little bit of the Grado RS-1 sound thrown in. It's like a mix of these two headphones, although the emphasis on the Sennheiser sound.

So, what comes next? I plan to send the ESP/950, together with an Orpheus HE90 Chassis connector, to Peter McAlister, of McAlister Audio, for Peter to assemble an EA-1 electrostatic tube amp. to power this Koss headphone. I'm including the Orpheus chassis connector (which I purchased from Head-Fi member eric343) in order for this McAlister amp. to be configured in such a manner as to be able to drive Orpheus HE90, Stax, and ESP/950 headphones. This will be as close as I can get to a universal electrostatic amp.

So, that's it so far, and I'm really happy with my purchase of the Koss ESP/950 headphone, and with its currently fine performance, and especially because of my anticipation of its outstanding performance with the McAlister AE-1 amp.

I apologize for writing such a long review. But, it's because I didn't have sufficient time to write a shorter one.

 

[PATB]

Thanks for the nice review Mike. I am looking forward to your impressions of the ESP/950 with the McAlister.

 

[catscratch]

Excellent review Mike. On that note, I haven't heard anything from Peter regarding my amp yet. He did tell me that he was overloaded and it was going to be a long wait. So if you've ordered recently, then you can expect it probably no earlier than two months or so! I am very much looking forward to hearing the amp, too.

 

[wualta]

Tell us more about your K340. Is it modded in any way? Does it seem to be amp-capricious, changing character as you change amps?

 

[mikeg]

Quote:

Originally Posted by wualta Tell us more about your K340. Is it modded in any way? Does it seem to be amp-capricious, changing character as you change amps?

It's a really old unit that I picked up on eBay, and that hasn't been modded in any way. I've powered it with the RA-1 and with a 300B tube amp. It sounds better with the tube amp., which seems to pump more than sufficient power into it. I also briefly drove it with an SDS amp, but I can't say that this improved the sound beyond that obtained with the 300B tube amp. Since I use an R10 with the SDS amp, and since I don't plan to use the K340 with this amp, I didn't continue driving the K340 with the SDS.

 

[wualta]

Quote:

Originally Posted by mikeg It's a really old unit that I picked up on eBay, and that hasn't been modded in any way.

Can you tell which of the two major flavors of K340 you have (with reference to the earlier threads on modding K340s by Philodox and Aerius)?

 

[mikeg]

I really have no idea.

Quote:

Originally Posted by wualta Can you tell which of the two major flavors of K340 you have (with reference to the earlier threads on modding K340s by Philodox and Aerius)?

 

[edstrelow]

I am glad you had a good experience with the Koss 950's.

I have had a set for more than 10 years and have had similar good experiences about the Koss lifetime warranty.

After reading much discussion about the importance of good power supplies in audio equipment, I tried a number of outboard power supplies to replace the wall wart provided by Koss and finally settled on the Elenco which was ,as I recall, on sale for about $60.00. As you note, this really pumps up the sound of this unit.

I have not used the battery pack for many years because I have been using the Stax SRM-001 MkII which only needs 2 AA's. Still it is useful to know that this unit performs so well on batteries.

This was my main headphone for several years, although I now use the Stax SRM3/404 set-up. However I mostly listen to classical music and many reviewers fault the 404, certainly with the smaller amps such as the SRM3 and 313 as being somewhat lacking in oomph in the bass region. The 950's with an upgraded power supply give significantly better dynamics for this rock/pop. I recall that when I first tried the 950's with a better power supply my immediate reaction was to start boogying around the room.

Still the Stax have a cleaner sound and maybe deeper bass. They would probably be the first choice for classical listeners.

The 950's seem to have some good design features. Their electrostatic diaphragms are big, I guess about the same size as the 404, but the electrodes are more rigidly consutructed with a hard plastic backing unlike the 404's stiff wire mesh. In that respect I think they resemble the construction of the Stax Omegas.

While circumaural, they do not require a seal and thus you do not have to have as good and tight a fit as the 404s to get proper bass.

The diaphragms are somewhat further back off the ears, again I believe like the Omegas, which I think helps to give a more natural projection to the outer ear than the 404's which sit right on the outer ear. On the other hand, the closer fit of the 404 should help efficiency.

The diaphragm thickness of the 950 is unknown to me but I would guess it to be thicker than the 404, probably more like the older Lamba designs. So they would not be as fast as the 404.

And of course Stax makes large class A amps unlike the Koss which I assume is the standard AB design. I recall one review some years back, probably on Headwize which rated the 950 quite highly on a better amp.

 

[mikeg]

In my first posting in this thread I mentioned my finding that the ESP/950's performance is superior to that of the HD600, when this Koss headphone is powered by an Elenco 3 amp regulated DC power supply. But, the ESP/950's performance is very substantially improved further when driven by a McAlister electrostat headphone amplifier which costs a bit over $700. I received mine (i.e., a McAlister Model EA-4) a couple of days ago, and used it to drive an Orpheus HE90, as well as the ESP/950. I compared the performance of this Koss headphone, when driven by the EA-4, to that of an HD-600, and an SR225, both driven by a Cordia Aria amp. I also compared the sound of the ESP/950 to that of the HE90, and to that of an R10, using the Cordia Aria and a SinglePower SDS to drive the R10. The most dramatic improvement in the ESP/950's performance, when driven by the McAlister amp, was in the size and depth of the sound stage. Suddenly this Koss headphone provided a very large and truly three dimensional presentation. Instruments were well separated, with lots of space between them, and the sound was clear, full, and with lots of punch, throughout the sound spectrum. The effect was much more concert-hall like, more open, and more textured, as compared to the presentation of the HD600 and the SR225. Thus, the combo of ESP/950 & McAlister EA-4 & Elenco Power Supply provides a performance that is considerably superior to either the HD600, and SR225, when powered by the Cordia Aria amp. But, the limitations of the ESP/950 became very clear when its performance was compared to that of the HE90, and the R10. Both of these far more expensive headphones provided a more refined, clear, specious, and detailed presentation than the Koss headphone. The presentation of the R10 was also considerably more refined when driven by the SDS amp, as compared to its performance when driven by the Cordia Aria. The presentation of the HE90, driven by the McAlister amp., was truly magical. Highly refind, extremely spacious and three dimentional, and providing unbelievable detail. I look forward to comparing the performance of the HE90/McAlister combo, to that provided when connecting the HE90 to several other amps, such as a Stax 007, the forthcoming SinglePower amp., and Jason's forthcoming amp. Needless to say, while the McAlister amp. costs a bit over $700, the latter two amps cost several thousand dollars. But, cosmetically (e.g., chasis appearance, paint/finish, and lettering) the McAlister amp. is not comparable to the appearance (i.e., finish) of a SinglePower amp. However, for me, it's the sound and cost that matter most. And the sound of the HE90, and the ESP/950, when driven by the McAlister EA-4 amp., is excellent. In my view, the combo of ESP/950 & McAlister amp & Elenco Power Supply, provide a headphone system that matches or exceeds all of the Grado and HD600 systems that I've heard to-date.

 

[dannyandelyse]

g Quote:

Originally Posted by mikeg In my first posting in this thread I mentioned my finding that the ESP/950's performance is superior to that of the HD600, when this Koss headphone is powered by an Elenco 3 amp regulated DC power supply. But, the ESP/950's performance is very substantially improved further when driven by a McAlister electrostat headphone amplifier which costs a bit over $700. I received mine (i.e., a McAlister Model EA-4) a couple of days ago, and used it to drive an Orpheus HE90, as well as the ESP/950. I compared the performance of this Koss headphone, when driven by the EA-4, to that of an HD-600, and an SR225, both driven by a Cordia Aria amp. I also compared the sound of the ESP/950 to that of the HE90, and to that of an R10, using the Cordia Aria and a SinglePower SDS to drive the R10. The most dramatic improvement in the ESP/950's performance, when driven by the McAlister amp, was in the size and depth of the sound stage. Suddenly this Koss headphone provided a very large and truly three dimensional presentation. Instruments were well separated, with lots of space between them, and the sound was clear, full, and with lots of punch, throughout the sound spectrum. The effect was much more concert-hall like, more open, and more textured, as compared to the presentation of the HD600 and the SR225. Thus, the combo of ESP/950 & McAlister EA-4 & Elenco Power Supply provides a performance that is considerably superior to either the HD600, and SR225, when powered by the Cordia Aria amp. But, the limitations of the ESP/950 became very clear when its performance was compared to that of the HE90, and the R10. Both of these far more expensive headphones provided a more refined, clear, specious, and detailed presentation than the Koss headphone. The presentation of the R10 was also considerably more refined when driven by the SDS amp, as compared to its performance when driven by the Cordia Aria. The presentation of the HE90, driven by the McAlister amp., was truly magical. Highly refind, extremely spacious and three dimentional, and providing unbelievable detail. I look forward to comparing the performance of the HE90/McAlister combo, to that provided when connecting the HE90 to several other amps, such as a Stax 007, the forthcoming SinglePower amp., and Jason's forthcoming amp. Needless to say, while the McAlister amp. costs a bit over $700, the latter two amps cost several thousand dollars. But, cosmetically (e.g., chasis appearance, paint/finish, and lettering) the McAlister amp. is not comparable to the appearance (i.e., finish) of a SinglePower amp. However, for me, it's the sound and cost that matter most. And the sound of the HE90, and the ESP/950, when driven by the McAlister EA-4 amp., is excellent. In my view, the combo of ESP/950 & McAlister amp & Elenco Power Supply, provide a headphone system that matches or exceeds all of the Grado and HD600 systems that I've heard to-date.

Mike,

Nice to see your new amp is everything you were hoping for, Excellent value and yes, I had those Koss phones and they are very, very sweet.

 

[Carl]

Good to see you've finally got everything all set up, Mike, and thanks for the review.


Could you go into more detail about how well the EA-4 performs? I'm trying to decide what electrostatic amp to buy, and the comparitively cheap McAlister unit intrigues me.

 

[kartik]

Mike,
I'm interested in your comparison of the SDS-R10 and the EA-1-HE90. However, the fact that I can substantially improve the performance of my ESP/950 with the ES-1 is indeed very heartening news. Maybe the ESP/950 EA-1 combination is the new affordable king of the mid-range headphone rigs!

 

[mikeg]

Although it sounds wonderful with the HE90, I have no other electrostat headphone amp to compare it with. I'll be attending a meet in Miami on 2/18, at which other such amps may be available. Comparative comments may then be provided.


Quote:

Originally Posted by Carl Good to see you've finally got everything all set up, Mike, and thanks for the review. Could you go into more detail about how well the EA-4 performs? I'm trying to decide what electrostatic amp to buy, and the comparitively cheap McAlister unit intrigues me.

 

[mikeg]

I'll be doing some comparisons of the SDS/R10 to the McAlister/HE90 over the next few days. Since we are now occupied with visiting friends, I haven't been able to listen to these rigs this weekend.

Quote:

Originally Posted by kartik Mike, I'm interested in your comparison of the SDS-R10 and the EA-1-HE90. However, the fact that I can substantially improve the performance of my ESP/950 with the ES-1 is indeed very heartening news. Maybe the ESP/950 EA-1 combination is the new affordable king of the mid-range headphone rigs!

 

[mikeg]

I have come to doubt the correctness of the following conclusion that I posted at the begining of this thread. I stated that "When powered by the Elenco unit, the ESP/950's performance was superior to HD600's performance, even when the HD600 was driven by the high quality 300B tube amp." On further listening, I've grown a bit tired of the sound signature of this Koss headphone. While it does yield a "bigger sound" than that of the HD600, the ESP/950 doesn't resolve fine details of background string instruments as well as the HD600. Although the sound signature of the ESP/950, when powered by the Elenco unit, may on first hearing appear to be more impressive than that of the HD600, more critical listening shows that the HD600 provides finer detail resolution, and a more accurate presentation of the color and tonal differences among background string instruments. I determind this by listening to several selections of classical orchestral music. Before buying an ESP/950, carefully listen to its unique sound signature, and compare it with that of a good dynamic headphone.