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KOSS ESP-950 Thread - Page 47

post #691 of 1421

If you send both the amp and headphones back to Koss then they will lower the bias voltage in the amp as a precaution. 

 

My old sets never had any issues. 

post #692 of 1421

Do you know the technical details of what causes the squeal (In the headphones)?  And what they do to repair?

post #693 of 1421

With electrostatic elements this is usually (always?) due to leakage from the charged membrane to a surface at a lower potential.  It could be due to dust, or other contaminant, most often in my experience at the outer edge of the membrane where there is a sandwich of stator/insulator/diaphram/insulator/far side stator.  A breakdown of insulator material, or foreign material along this edge, will cause this sound.  The higher the volage, the more difficult this is to avoid.  Great materials, clean-room assembly, good protection against dust all will help avoid this.  

 

For repair I would hope they replace elements, unless a good cleaning eliminates the foreign material.  I wonder if anyone knows for sure. I would hate to have the sonics compromised by just lowering the voltage until the squeal goes away.

post #694 of 1421

Especially since a lot of us are using other amps...

 

Still wonder if anyone has had a re-occurrence after repair?

post #695 of 1421

If it helps, I can tell you with mine when I get the squeal, it actually continues to squeal for a good 10-20 seconds+ after I unplug the headphones cable from the amp, slowly reducing in pitch and volume until it finally disappears -- but as soon as I put my thumb to the connector of the headphones cable and discharge it, the squeal goes away.  Then as soon as I plug them back in to the amp, it starts up again.  I'm using the bundled Koss amp.  Not nearly technically knowledgeable enough to know what kind of issue that might imply, but hopefully someone here is. 

post #696 of 1421
Quote:
Originally Posted by shipsupt View Post

Do you know the technical details of what causes the squeal (In the headphones)?  And what they do to repair?

 

It's a bit of an oddity given just how well protected the drivers are against dust.  There is only a solid barrier on the front but the back has many layers that the debris needs to get through.  This might be caused by something deteriorating inside the drivers as this is just so common.  Well either that or the area where the drivers are assembled isn't clean. 

 

I doubt very much they try to clean the drivers so they must replace them.  The ESP is in current production but what that actually means is hard to say.  The design was debuted in 1989 so there could be a huge stock of parts that is being reused.  Koss is a very odd company... 


Edited by spritzer - 3/15/13 at 2:12pm
post #697 of 1421
Quote:
Originally Posted by Jand View Post

If it helps, I can tell you with mine when I get the squeal, it actually continues to squeal for a good 10-20 seconds+ after I unplug the headphones cable from the amp, slowly reducing in pitch and volume until it finally disappears -- but as soon as I put my thumb to the connector of the headphones cable and discharge it, the squeal goes away.  Then as soon as I plug them back in to the amp, it starts up again.  I'm using the bundled Koss amp.  Not nearly technically knowledgeable enough to know what kind of issue that might imply, but hopefully someone here is. 

 

Yes, this is the high voltage leaking down to a level where it is no longer causing a noise when it discharges. Most likely it is dielectric breakdown of insulation material or debris/foreign material from assembly.  I doubt the debris is picked up in the field since they are sealed.

 

Working with coated films that have static build up when coming off the rolls, trying to keep them dust and foriegn material free, keeping employees following the rules about cleanroom work, including booties, hair nets, beard nets, and on and

on is all a major headache.  Then there is the material headache, with 500 volts being much more of a difficulty than lower voltages.  But Stax seems to do it......

 

Some electrostatic speaker companies endured the same problems.

post #698 of 1421
Thread Starter 
Quote:
Originally Posted by obobskivich View Post


Mine never have. smily_headphones1.gif

Mine never have either.  Had 'em a year, previous owner 2 years.

 

Instead of sending them back to Amazon, why not call Koss and send them in for warranty - Koss offers lifetime warranty... just a thought.

post #699 of 1421
Thread Starter 

The squeal comes from dust that got sealed inside the driver's plastic envelope.... which is supposed to seal out dust.

 

I suspect some dust can get in during driver manufacturing.  At Koss' final QC check all is well, but then they get shipped and some dust that was adhering to some surface of the driver gets shaken loose and gets into the stator / diaphragm gap where it allows a small flow of charge, causing the squeal.

 

The drivers are sealed inside dust barriers, just like Stax... basically plastic bags under a little bit of tension.  Dust can't get in... but if some dust is in there already....

 

The necessarily narrow precision spacing, requirement for absolute parallel-ness and cleanliness of the driver assembly makes building electrostatic 'phones rather difficult, and REPAIR of drivers is just about impossible.  If there's a problem, generally the driver must be replaced. (Unless you have the factory stator alignment and diaphragm tensioning jigs and a Class 10 cleanroom.....)

post #700 of 1421

mine did and now there is no hint of it , and am sure they returned the same pair i sent to them.

post #701 of 1421
Thread Starter 
Quote:
Originally Posted by singh View Post

mine did and now there is no hint of it , and am sure they returned the same pair i sent to them.

They very likely replaced the drivers.

post #702 of 1421

I keep hearing people mention these headphones going for $600-$650. Can anyone send me a link to a place selling it for that price? The lowest price new I've found is almost $800.

post #703 of 1421
Quote:
Originally Posted by Taowolf51 View Post

I keep hearing people mention these headphones going for $600-$650. Can anyone send me a link to a place selling it for that price? The lowest price new I've found is almost $800.

*sigh*

Amazon, at least historically, was letting the price drop to around $650-$700 (which of course becomes "$500 all the time!" when filtered through forums rolleyes.gif), because Koss doesn't seem to enforce MAPs on their dealers. As interest has renewed in the ESP/950, Amazon has evidently reacted, and the price has started to return closer to MSRP. That doesn't seem to have been noticed by the "groupthink" that is happy to declare them a $500-$600 product, and it creates no end of drama when people feel they're being "ripped off" or "overcharged" because a better deal existed at some point in history.

The simpler answer is that people are mistaken. Amazon will still let the price drop down (it's just how Amazon works with products that don't have enforced MAPs), but Koss has consistently charged MSRP through their storefront for years (excepting their 10-20% holiday sales), and I'm not sure who else actually sells these anymore (I know that at various points in history they've been available from Newegg and J&R). If you want to track the price, you can add them to a "Wish List" on Amazon, and it will show you when the price has reduced, or you can use a price-tracker like CamelCamelCamel.com to keep an eye on them.

Here's the Camel's data for them:
http://camelcamelcamel.com/Koss-160416-ESP-950-Electrostatic-Stereophone/product/B000056ULH

You'll notice that $600 (or less) is a fairly rare and short occurrence, but $650-$700 was pretty bang-on from ~2009 to ~2011. But since 2012 it's become more all-over the place (the highest and lowest recorded prices both exist in 2012, for example). $700-$800 seems to be more in-line these days.
post #704 of 1421

>I keep hearing people mention these headphones going for $600-$650. Can anyone send me a link to a place selling it for that price? The lowest price new I've found is almost $800.

 

I got mine from www.headphones.com, for around that price, but they don't always have them on the site and not right now.  It also took them several weeks for them to get them to me.

post #705 of 1421
Quote:
Originally Posted by Taowolf51 View Post

I keep hearing people mention these headphones going for $600-$650. Can anyone send me a link to a place selling it for that price? The lowest price new I've found is almost $800.

 

 

Quote:
Originally Posted by obobskivich View Post
Warning: Spoiler! (Click to show)



*sigh*

Amazon, at least historically, was letting the price drop to around $650-$700 (which of course becomes "$500 all the time!" when filtered through forums rolleyes.gif), because Koss doesn't seem to enforce MAPs on their dealers. As interest has renewed in the ESP/950, Amazon has evidently reacted, and the price has started to return closer to MSRP. That doesn't seem to have been noticed by the "groupthink" that is happy to declare them a $500-$600 product, and it creates no end of drama when people feel they're being "ripped off" or "overcharged" because a better deal existed at some point in history.

The simpler answer is that people are mistaken. Amazon will still let the price drop down (it's just how Amazon works with products that don't have enforced MAPs), but Koss has consistently charged MSRP through their storefront for years (excepting their 10-20% holiday sales), and I'm not sure who else actually sells these anymore (I know that at various points in history they've been available from Newegg and J&R). If you want to track the price, you can add them to a "Wish List" on Amazon, and it will show you when the price has reduced, or you can use a price-tracker like CamelCamelCamel.com to keep an eye on them.

Here's the Camel's data for them:
http://camelcamelcamel.com/Koss-160416-ESP-950-Electrostatic-Stereophone/product/B000056ULH

You'll notice that $600 (or less) is a fairly rare and short occurrence, but $650-$700 was pretty bang-on from ~2009 to ~2011. But since 2012 it's become more all-over the place (the highest and lowest recorded prices both exist in 2012, for example). $700-$800 seems to be more in-line these days.

 

 

On Black Friday, they were creeping down every hour or so and eventually fell to $582.88.  A couple hours later, they were back up to their $999.99 retail.  They had also dropped to $540 in September.  For Black Friday, Koss also had them on special for $650 direct from their website.  Otherwise, they tend to fluctuate between $7-800 as the great obobskivich indicated.  

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