Koss ESP/95x Electrostatic System

https://www.massdrop.com/buy/massdr...leCampaignId=394582&iterableTemplateId=565561

Interesting... I hadn't seen an ESP on Massdrop for sometime until this. Interesting that they tinkered with the package but left the same energizer. Weren't there complaints that the 95x could sound WAY better out of Stax energizers as opposed to the Koss?

 

Yea we had a host of ideas for the Energizer, unfortunately we couldn't make them work within Koss' supply chain (it's cool that this is made in the USA, but it's limiting). Based on the request volume and general excitement around the product, we might be able to justify a separate energizer project in the future, but that'll be pretty far out.

CEETEE's been working on an accessibly priced adapter cable for STAX Pro-Bias energizer, so hopefully we can make that work for folks in the meantime.

 

This came out of the blue, super cool. The stock pads don't do seal very well which is critical for the bass on the esp950.

 

I wonder if they finally fixed the issue with squeal that develops eventually in one or both drivers. I remember muppetface saying that she had like 12 pairs and all of them had the issue sooner or later. My pair had it too. There are other reports of the same issue all over the internet.

 

Yeah, it looks like they swapped out the older pads and added velour memory foam pads?

 

I've been working with someone on an idea for a custom Stax amp. Do we know the max voltage for the Koss? I wouldn't want to burn out the Koss using that Stax amp, if/when it ever gets done.

 

I'm on the list. $500 for an electrostatic solution is guilt free purchase in this era of $2500 iem's.

 

Great price point for getting into electrostats for sure. Will need to take a look at impressions. Thanks Massdrop for weighing in here.

 

I'm not sure, you're better off asking CEETEE, he did all the development work on this one.

 

The Koss has a specified bias voltage of 600 volts, versus 580 volts for the Stax pro bias phones, and the E/90 supposedly puts out up to 2300 volts peak-to-peak, so voltage isn't an issue. Where the E/90 falls down is its wall wart power supply requiring a step-up DC-DC converter in the amp (increased noise/hash), and its very limited current output drive, only 2 mA/channel standing current due to its lack of heat sinking (hard to build heat-sinks out of plastic). Presumably these design decisions were driven in part by the desire to have a portable system that can use a battery power supply.

The desktop size Stax amps (SRM252 aside) have somewhat lower voltage outputs (850-950 volts peak-to-peak for the tube output amps and 1300 volts peak-to-peak for the solid state output amps) but their solid state amp output stages have standing currents of 11-13 mA/channel, and the tube output Stax amps have 9.6 - 15 mA standing current per channel. Note that the tube output amps have lower output voltage limits than the solid state output amps despite comparable power supplies due to their use of resistor plate loads.

Perhaps a more intuitive way of putting it is to look at the output stage standing power. The Koss E/90 has a standing power of 1.2 watts/channel. The Stax amps run 3-5 watts/channel. By comparison the BHSE runs about 14-16 watts/channel. Or, you can also look at the overall power consumption - the Koss uses less than 9 watts, the Stax amps use 30-50 watts, the BHSE 160 watts.

 

I would be in for this but the Feb. ship date is bonkers.

 

I'm a little curious about that part. The product themselves are unchanged, but just the packaged goods changed, right? Is serious retooling needed for the rebranding, or is the production process that slow for these?

 

I'm not so sure about that. Just from visual inspection vs the original product, I'm seeing significant variation of the materials. And it's not completely trivial stuff-- here's a quick side by side:

• I'm guessing that's actually a different plastic, not just different colors (I think I read that this is a difference in the HD6xx vs the HD650 as well). I'm guessing while they can use the mold, they do have to actually produce new parts?
• Sourcing new pads for a production run is probably nontrivial.
• Looks like the grill mesh is different. Not sure if that's a metal or plastic part.
• I think the metal adjustment doohickeys on the 95X are much longer than the mechanism on the 950 would allow? So that looks like it's been re-engineered. This probably also necessitates changes in the plastic molding?
• And then whatever processes produce the branding on the visuals. This is probably the least of the retooling?

 

I've owned this headphone before and heard it from the included energizer and a mid-range stax amp. The included energizer is the achilles heel of this setup.

Should have the option of buying the headphone by itself with an adapter and save people some money to spend on a halfway decent amp.

 

Metal adjuster things - There is nothing about the new photo that would indicate to me that it is anything different than the original. It's just shown at a more extended state. I own a pair of ESP-950s and this looks consistent with what I've seen.

Grille materials - Original is plastic frame with a metal screen. I doubt there would be any cost savings by making the new ones all plastic, or any other good reason to switch. I'm betting this will be the same other than the color.

Pads - definitely different. Maybe the new velour ones changes the distance from 'phones to ears slightly. But I'm thinking the velour isn't going to help bass response any unless they put something else in the foam material to help isolate.

 

Isn't Koss supposed to be really good about warranty stuff? Do they repair/replace headphones with said squeal under the warranty?

 

Holy fajitas, that's an excellent deal then! How much did it cost to get them back in shape, though? I had opportunity to demo the ESP/950 not too long ago and thought it was... alright. Could have been my inability to get a proper seal on that particular pair or the supplied energiser though. Either way, may well be worth investigating if they're that generous with warranties.

 

Koss will generally charge for shipping and that's about it.

 

It is a bit surprising that no sbaf senior measuring/reviewing ears say anything about this collaboration by now. Based on the previous experience, I do not have 100% credibility toward Jude's measurements lol.

Nevertheless, I still think this is an amazing drop, even regarding 500 bucks for headphone only. Long ago, owned esp 950 and liked their tonality very much. Way likable low-mid treble responses than all the Stax (particularly Lambdas) I tried. Of course with the right pad mods, lambdas can do equally good jobs (e.g., attaching senn 6xx velvet pads to lambdas). But I could not like the comfort of such modded ones. On the contrary, esp 950 was super comfy even from today's standards.

The real problem may be to find the right amp to extract full potentials from esp 950. I totally agree that E90 energizer sucks. But as an ex-Stax-fanboy, my journey to look for estat amps was painful. Stax entry to middle offerings were better than Koss but still had compromises. Gilmore and Spritzer's amps (bh, kgss) disappointed me regarding micro-dynamics and resolution (they sounded bright/detail-ish to my ears though)... with a bonus of WTF prices. All these were even more evident after experiencing how Schiit (Jot, Lyr 3) and EC (BW2) amps with good dynamic headphones easily satisfied my tastes with zero DIY knowledge, zero mods, and zero need to dump stupid cash on amps. Note that my estat amp dissatisfaction came from sr009 and lambda sig, not koss esp 950.