[obobskivich]

Hello guys, I'm just about to pull the trigger on a ESP 950 setup, so I'm hoping for a little feedback first.

Which amp would you recommend for this headphone? I think it's coming with a Stax SRM1 MK2 amp, but it may be the E90 energiser. So what would you guys say are the differences between these two, sonically?

Also what is a  power amp and SUT? (I don't know the meaning of those terms). Maybe you can just post a link to more info.

And what is an Amphenol connector (what does it do, what is it for)?


Thanks...

The power amp is what it needs to drive it - all speakers do. The E/90 is Koss' in-house designed and built power amp for the ESP/950. There are third-party amps that can also fulfill the role of the E/90, generally amps designed for STAX Pro Bias, as its similar enough to the ESP/950's bias (STAX Pro is 580V; the ESP/950 are 600V) - STAX makes a variety of amps, and there's also amps from third-party mfgrs (e.g. Woo Audio).

"SUT" is "Step-up Transformer" - usually I've seen this called an "energizer" (both STAX and Koss used this terminology back in the 1970s and 1980s); it's a transformer and bias supply that will adapt the outputs of a conventional hi-fi amplifier to drive electrostatic headphones, so you'd run from an integrated amp into the energizer, and then the energizer into the headphones. Koss does not build any that are compatible with the ESP/950, and as far as I know STAX does not build any currently (but has built models that will do Pro bias) - Woo currently builds one though.

Amphenol is a manufacturer of various connectors and plugs, like Molex or Neutrik - the specific connector being discussed here is the plug that STAX uses for their headphones, which is required to build your own Koss to STAX adapter cable (you'd need the "STAX end" (the "Amphenol connector") to re-terminate either the ESP/950 themselves (bad idea) or the Koss extension cable (good idea; it allows you to build an adapter without modfying the headphones themselves (Koss also generally won't warranty products that've been hacked up - hacking up the cable gives you an adapter that lets the ESP/950 retain compatibility with the E/90 as well as various amps that are designed for STAX).

I have no idea, sonically speaking, about any of the STAX amps - I've got the E/90 and I'm very satisfied. It's perfectly compatible, and the system sounds quite good. I will acknowledge that I'm very skeptical of "differences between amps" though, especially given the hilarious prices that many amps (especially electrostatic amps) can reach these days.

 

[DecentLevi]

Thanks for your reply, that's some really helpful and advanced info.
 
So if I understand correctly, the Koss ESP 950 was made with an accompanying power amp, so no energizer needed. And an energizer is the same as a SUT, that works as transformer/amp to make an electrostatic headphone work with a normal amp - right? So if I'm getting an ESP 950 with the E90 energizer then I can just connect the E90 to my DAC, and my 950 headphones to the E90, right?
 

I highly recommend a power amp + good SUT
 
Big upgrade over E90 energizer

So, what kind of a big improvement does a power amp + good SUT make over the E90 energiser? And which config. were you referring to - only the Yggy/Rangarok or is there something more affordable that sounds comparatively better than just the E90? Thanks again

 

[ardgedee]

Koss makes the terms confusing because they refer to the E/90 as an energizer. The rest of the world calls it an amplifier. It can power the headphones when connected directly to a sound source (DAC, turntable, etc.).
 
Using a Stax-compatible amp or energizer requires an adaptor cable. When people here refer to the Amphenol connector, it's a plug used to build an adaptor cable. If you don't have much experience soldering and don't have the equipment necessary, you're better off buying an adaptor cable from Darren Fong or one of the cable hobbyists here on Head-Fi.
 
The E/90 works fine. You'll receive one with your headphones whether or not you want it. So give it a try before upgrading to a third-party amp or energizer.

 

[youngarthur]

I bought the ESP 950/Amp. combo,expecting to use a Stax amp,BUT, was very surprised how good these sound. The treble is well controlled,the Mids are lush, the Bass,a bit lacking for me, but  with a little EQ,excellent. For me,these are a keeper,along with HD 800/Shure 846. Also use the ESP 9B,wonderful,for the price.

 

[crazychile]

  Thanks for your reply, that's some really helpful and advanced info.
 
So if I understand correctly, the Koss ESP 950 was made with an accompanying power amp, so no energizer needed. And an energizer is the same as a SUT, that works as transformer/amp to make an electrostatic headphone work with a normal amp - right? So if I'm getting an ESP 950 with the E90 energizer then I can just connect the E90 to my DAC, and my 950 to the headphones to the E90, right?
 

I highly recommend a power amp + good SUT
 
Big upgrade over E90 energizer

So, what kind of a big improvement does a power amp + good SUT make over the E90 energiser? And which config. were you referring to - only the Yggy/Rangarok or is there something more affordable that sounds comparatively better than just the E90? Thanks again

You've got the right idea. The Koss' sound darn good with the stock E/90, and it's really all you'll ever need. Buying a Stax or KGxxx type amp will make them sound a little better but the Koss' have limitations and will only give you just so much. I bought another amp knowing that I would some day make the jump into an upper level Stax model. But budget limitations make me take incremental steps to get there.
 
The Koss' are the gateway drug of electrostatics. Many will buy them and keep them forever. Some will get a taste of what electrostatics do and then jump into the Stax end of the pool with hand built amplifiers that take the experience up a few notches.

 

[doctorjazz]

I did find an improvement with a Stax amp (?323b, or something like that), but they are fine with the included Koss amp/energizer. Makes sense to just try it out first, see if you want to go up the food chain...

 

[paradoxper]

Test the waters with the Koss energizer and then quickly move up the chain. The 950 is kind of endgame-ish with the right amp.

 

[DecentLevi]

Thanks very much for clearing everything up about this electrostat rig, folks. I'm set to have the standard Koss set on Saturday.
 
Upgrading to another energizer won't be in my budget for quite some time, but here's an idea - if we all pitch in maybe we can share the KOSSt of an upgraded amp and pass it around... better yet if more pitch in we can buy an Orpheus 2 

  to share (LOL or maybe my brain's fried right now). But one day I would love to read (or even hear) about a Koss ESP 950 compared to either Orpheus!

 

[DecentLevi]

PS- The user who's selling me the ESP 950 will bring over the Stax SRM1 MK2 amp so I can compare it to the E90 Energizer with the 950. I suppose you guys would like to hear my comparison?

 

[crazychile]

  PS- The user who's selling me the ESP 950 will bring over the Stax SRM1 MK2 amp so I can compare it to the E90 Energizer with the 950. I suppose you guys would like to hear my comparison?

Yes.

 

[doctorjazz]

Sure, compare away!

 

[doctorjazz]

I believe I will be selling my 950 and Stax 323B with adapter, will bring them to the Stamford meet this Saturday, but anyone interested can PM me before hand.

 

[obobskivich]

Thanks for your reply, that's some really helpful and advanced info.

So if I understand correctly, the Koss ESP 950 was made with an accompanying power amp, so no energizer needed. And an energizer is the same as a SUT, that works as transformer/amp to make an electrostatic headphone work with a normal amp - right? So if I'm getting an ESP 950 with the E90 energizer then I can just connect the E90 to my DAC, and my 950 headphones to the E90, right?

So, what kind of a big improvement does a power amp + good SUT make over the E90 energiser? And which config. were you referring to - only the Yggy/Rangarok or is there something more affordable that sounds comparatively better than just the E90? Thanks again

Yes you've got it - the E/90 connects directly to a source (CD player, tape deck, computer, line-out from a DAC, line-out from a phono preamp, FM tuner, etc). The retail package from Koss includes all the cabling you need to make that happen - it accepts both RCA and TRS inputs. From talking to Koss Support on the phone about this, the front and rear inputs should be in parallel, and they report no quality/signal loss by using the TRS jack over the RCA jacks. I use the RCA jacks on mine because it makes my desk look neater (the TRS jack is on the front, the RCA jacks are on the back).

Koss makes the terms confusing because they refer to the E/90 as an energizer.

D'oh. Forgot they kept that word for the E/90 too - was thinking of the E/9 and E/10 "Electrostatic Energizer" and some of the AT and STAX stuff from ages ago. Yes you're absolutely right, and thanks for catching that.

Yes.

+1.

 

[DecentLevi]

Hello guys, after owning my new ESP 950 setup for 24 hours, I've gotten a better understanding of the sound signature. I would like to share my impressions and would appreciate any comments / suggestions. This may come across as a bit scattered, as I'm still trying to quantify the differences. 
 
This will basically be a comparison between dynamic vs. electrostatic headphones.
 
The System which I have is the Koss ESP 950 headphones (new condition, low hours), Stax SRM-1/MK2 (SUP / driver unit / 'amp'), with Gustard X12 DAC (via Wyrd).
+ Project Ember tube amp (will get to that); OR Senn. HD 650 headphones connected to the Ember instead of electrostat setup.
 

​

 

 
Firstly I had done a mini-comparison between the provided Koss E/90 energizer and the Stax amp with the ESP 950's. My reaction with the provided Koss amp was that they sounded like a thinner, slightly more detailed version of the good old HD 650's (yes, they sounded vaguely like a dynamic to me), and I was underwhelmed. Switching to the Stax SRM-1 amp with the ESP 950's, I was immed. struck with an increased sense of presence, realism, soundstage and energy. It was close to the same sound that impressed me enough for it to have been the star of the show for me at a local Head-Fi meet recently. But keep in mind, this was only a very brief once comparison between these two electrostatic amps, so I will follow up in the coming weeks with a more detailed A/B between the two.
 
Now onto the sound impressions of this unit (ESP 950 with Stax SRM-1).
Overall I find these headphones to be detailed / resolving / intricate / liquid, yet also sounding fairly cold / thin / dry and lacking dynamics 'punch'.
 
Firstly about the dynamics / impact: While these do allow you to hear the 'slam' of every drum, it's just not done with nearly as much volume swing / impact as the likes of a well-driven HD-650. It's very snappy, but not as punchy, which is especially evident in a direct comparison.
 
Mids: while the mids as well as vocals are portrayed in a way that sounds very lifelike and real, I wouldn't quite call it organic and this can seems to have a whole lotta 'planar' sound - in that the mids, while not being recessed, are lacking a great deal of vibrancy / lushness; so are quite sterile / cold and slightly nasal.
 
Detail: While this is one of the most detailed headphones I've tried, this too is like a double-edged sword: On one hand you can hear every nuance including some you may not have heard on other headphones, and it's done in a moderately cohesive way. But on the other hand, nothing really sticks out as much as some may like. It's as if everything is presented in an intricate, slightly holographic way, yet somewhat dull.
 
Soundstage: Yet another conflicting aspect in comparison: The stage seems to have more width on the HD 650's and more height on the 950's, I'm guessing because of their more rectangular shape. This is neither a negative or a positive, just a different experience.
 
Bass weight: The bass on these is very articulate, but not in a way that many would find pleasing, because it's also very clinical and dry-ish with a fast decay, giving an impression that it's somewhat recessed.
 
Energy & tonality: These seem to be on the flatter side of tonally correct, more like a planar sound versus the warm & sweet sound of an HD 650; Intricate polished yet slightly lacking energy / lushness.
 
Now, enter Project Ember 2.0 as a tube buffer 'pre-amp'. This fine little tube amp gives excellent resolution / energy / refinement, and also has an RCA line-out to be used as a tube beffer for another amp. It has vast capabilities to roll many dozens of types of tubes of various shapes, sizes & classes, either inserting directly or with assorted single and / or dual tube adapters.
 
After trying a dozen assorted types of tubes, I noticed the Ember as a tube-buffer into the SRM-1 amp to be excellent at analysing the sound of a tube, and to have a big impact on the sound. Some were either lacking in the bass weight or tonally off, but I found 3 good matches. The #1 being a GE 6SN7 GTA (black base, silver dual triodes and circle of silver paint on one side of the glass). Finally, this tube added a fair amount of much needed weight / authority / definition to the bass. It also kept a good tonal balance, and additionally added some much needed lushness to the mids; it also smoothed out the treble a bit which was incidentally a desirable effect as well. Overall using this tube on the Ember as a tube-buffer to this ESP-950 setup gave a more weighty feel to the bass for improved EDM / pop-ish listening, also made it lusher, smoother and more musical, and without reducing any of the frequency range on either side, and keeping all of the soundstage.
 
I do however still cling to my above descriptions of the sound - because while it is a bit more refined sounding than without the tube-buffer, it still by & large retains those shortcomings. Overall however, if I had to choose between this electrostatic headphone or a dynamic one, I would probably still choose the electrostat. The reason being - although this one is not as punchy / impactful and has a slightly thin character, it is technically superior with it's ability to give more detail and intricate sound, has a different yet equally good soundstage, and perhaps cleaner and more 'effortless'.
 
Closing notes:
 
A lot of the sound characteristics described in this post are due to the DAC (Gustard X12). This is important to note, because on the other hand I remember this same exact pair of ESP 950 and SRM-1 amp sounding somewhat different when testing it at the meet: the Bifrost Uber DAC was used (with AKM 4399 chip). In this case, the dynamics while still not perfect, had a more pleasing 'attack' to the slam, and IIRC, it sounded a bit more sweet/lush. Now there is an even newer multibit Bifrost (multifrost) with with a newer DAC chip, which may make a wonderful pairing with this rig, in theory.
 
Also a large part of my impressions on the sound could be due to brain burn-in. I have spent my whole 36-year life listening to dynamic cans and speakers, so maybe all I need is more time to get used to the sound.
 
However, I would stop far from saying that the ESP 950 would be an end-game by any stretch of the imagination... so onto my comparison between the ESP 950 and Stax SR-009 which I also did at the meet: Stax wins by about 30% in all these regards: punch, detail, lushness, soundstage and bass quality, yet IMO the 950 has slightly more bass quantity.
 
Also, however all testing was done on an 'upgraded' electrostatic amp, I would venture to say that any shortcomings reported in these impressions would be magnified if the E/90 was used - that is to say that things would only sound worse, not better on the stock amp with these electrostats.
 
I truly believe that either of these headphones would be able to outshine the other, depending on the source chain.

 

[recarcar]

   
I truly believe that either of these headphones would be able to outshine the other, depending on the source chain.

 
Thanks for the detailed impressions! I feel about the same way about the 950 compared to the 6x0 series. I've heard them both on a lot of different setups and come away feeling like they are basically on the same level with each having its own strengths and weaknesses. I ended up keeping the 950 because over time I came to really appreciate its very even handed presentation. I think it's one of its biggest strengths when I compare it to other phones. I do remember thinking it was bit dull during the first month or so though. They are both excellent values IMO.