[Canman]

Quote:

Originally Posted by eric343 Whoa! This is a bit of an issue... was the HE90 whose channel dropped out repairable? Or was this a temporary symptom?

The channel dropout was temporary. At the NY electrostatic mini-meet, there was an imbalance on the HE-90 with every amp but the HEV-90. Once the headphone was plugged into the HEV-90, it worked fine.

 

[eric343]

I adjusted the KGSS down from a calculated[1] bias voltage of 580V to 500V.

There appears to be little change in the sound. The HE90s are a tad less bright perhaps, with a little better mid-bass response. An improvement, though.

I haven't able to tell a difference with the Omega2s, hooked into the same bias supply. That may simply be due to lack of critical listening, though.

[1] My KGSS' power supply is a rather ugly hack, and the bias supply is output through a 5M/?M resistive divider that makes it impossible to directly measure the bias voltage without a VTVM, which I don't have.

 

[agile_one]

Quote:

Originally Posted by ayt999 http://buy.sennheiserusa.com/ASP/Sen...df/orpheus.pdf

Thanks, Alex - 500V, right there in black and white.

Quote:

Originally Posted by spritzer [That would be 5 Mega Ohms

Thanks - so my 5,000,000 Ohms guess was right.

 

[mikeg]

This is really strong evidence that there is a problem when using amps, other than an HEV90, to drive HE90s. It shows that amps, other than an HEV90, require modification in order to properly drive (and possibly not damage) HE90 and HE60 headphones. Does Jan Meier have any suggestions? Does Jan feel that Stax amps can be used to drive HE90s? Where should we go from here?

Quote:

Originally Posted by Canman The channel dropout was temporary. At the NY electrostatic mini-meet, there was an imbalance on the HE-90 with every amp but the HEV-90. Once the headphone was plugged into the HEV-90, it worked fine.

 

[Jan Meier]

Dear Headfellows,

The issue also appeared when I tested the first batch of headphones in combination with a Stax amp. I've had severall conversations with both the Stax and Sennheiser service departments and we're trying to find a proper solution. Right now this seems to be a simple 5 MOhm resistor to be added to the adapter plug.

Actually, both the Sennheiser technician and I don't feel that the effect is caused by arcing. This would have resulted in truly nasty noises. One channel is simply much lower in sound than the other one. Maybe during starting up there's a strong voltage variation accross the stators that make the membrane stick to one of the stators. The 5 MOhm of the Stax amps seems not be enough to enable the membrane to return to its resting position.

Whatever, I've not yet found any audible damage.

Hirsch has tested an adapter with a 5 MOhm resistor integrated and he has reported to me that this seems to help.

More later

Cheers

Jan

 

[PATB]

Is this problem specific to the Stax amps or to the Gilmore designs as well? I have listened critically to the HE90 using a headamp KGSS and did not notice this channel imbalance. I would have easily noticed this as I am easily distracted by channel imbalance or what not.

I am also curious as to why Eric343 seems to be surprised by this development. Eric343 (and bozebuttons (Ayt999 and NeilPeart with the KGBH)), haven't you been critically listening to the KGSS/HE90 combo for quite some time now?

 

[kevin gilmore]

if you will look here at figure 5
http://headwize.com/projects/showfil...ilmore_prj.htm

you will quite clearly see the correct bias for a number of phones.
It was true in 1996, it is still true now. Sennheiser specs a 10 meg
series resistor, not 5 meg. This is evidently more important than
the correct bias voltage in this case.

Up until 24 hours ago i was completely unaware of this problem.
My crystal ball has been broken for many years now. I cannot
fix or make suggestions to problems i have never heard of.

My he60's work just fine off of 5 meg and 580 volts. And they
have been doing so for a very long time.

If however you want an absolute part for part he90 clone amp, you
probably know where to go. (with trendy 1% resistors and solen caps)

 

[eric343]

Quote:

Originally Posted by PATB Is this problem specific to the Stax amps or to the Gilmore designs as well? I have listened critically to the HE90 using a headamp KGSS and did not notice this channel imbalance. I would have easily noticed this as I am easily distracted by channel imbalance or what not. I am also curious as to why Eric343 seems to be surprised by this development. Eric343 (and bozebuttons (Ayt999 and NeilPeart with the KGBH)), haven't you been critically listening to the KGSS/HE90 combo for quite some time now?

I am surprised because I have never had issues with my setup. I've noticed a very slight channel imbalance at times, but attributed it to the Alps Blue pot I use in my KGSS.

Anyone who has purchased an HE90 -> Stax adapter from me and does not want to add the 5M resistor themselves, please send them back and I will do so at no charge. (Be warned I'm rather busy with schoolwork, so it may take upwards of a month.)

My address here at MIT:
Eric Schmiedl
70 Amherst St
Cambridge, MA 02142

 

[eric343]

Quote:

Originally Posted by kevin gilmore Sennheiser specs a 10 meg series resistor, not 5 meg. This is evidently more important than the correct bias voltage in this case.

It's possible I used a 10 meg series resistor in my KGSS, and therefore have never had issues with bias voltage.
Quote:

If however you want an absolute part for part he90 clone amp, you probably know where to go. (with trendy 1% resistors and solen caps)

I think you mean HEV90 clone. And I think we're all watching this one quite carefully...

 

[eric343]

Quote:

Originally Posted by mikeg This is really strong evidence that there is a problem when using amps, other than an HEV90, to drive HE90s. It shows that amps, other than an HEV90, require modification in order to properly drive (and possibly not damage) HE90 and HE60 headphones.

Keep in mind that the HE90s appear to work perfectly fine provided a 5M resistor is added to the bias line.

 

[mikeg]

Eric - Although I am totally ignorant regarding the subjects of schematics and electronics, I am concerned about one of Dr. Gilmore's statements in his posting #3, above. He says that "A simple 5 meg resistor in series with the bias line on the adaptors that people have been buying may fix the problem in most cases, but is certainly not ideal." Needless to say, users of HE90s hope to obtain the best sound possible from their $5K purchases, and will probably not be satisfied with non-ideal solutions that are mere compromises. Hopefully, this question of properly powering the newly purchased batches of HE90s can be fully resolved.

Quote:

Originally Posted by eric343 Keep in mind that the HE90s appear to work perfectly fine provided a 5M resistor is added to the bias line.

 

[gurus]

I am under the impression that most electronics have a tolerance for +- 10%, so am I right in assuming that the HE60 when driven with a 580V amp would do no damage. Just make it sound a bit faster!

 

[Edwood]

Quote:

Originally Posted by kevin gilmore All headamp built electrostatic amps have a bias adjust pot on the power supply board. You need a decent digital meter to measure and adjust. You have to do this before the output resistor. If you don't understand this, then contact justin for support. There are other methods!

Nice to know there is room for adjustment.

I know Justin made a crazy KGSS with just about every electrostatic headphone jack on it. Did he have each output at different biases? Or I guess that is now going to have a different fix to allow different biases per output on the same amp?

I guess the ideal solution will be something along the lines of having a switch to change the bias at will. Nice to know everyone caught on to this issue before people had serious problems with their HE90's.

-Ed

 

[mikeg]

Interestingly, in posting #14 (dated 7/11/05) on the following thread, I referred to Peter McAlister's caution that resistors need to be incorporated in adapters that are used for connecting HE90s to Stax amps: http://www6.head-fi.org/forums/showt...eter+mcalister

 

[GoRedwings19]

I have a question for Dr. Jan Meier. When the he90's were being put back in limited production there were also adpators being sold with it to be used in conjuction with either stax amps or Gilmore designed amps.

Does this adaptor have the built in 5 meg resistor or not?

If people bought these adpators from you would it be possible to modify them or would they have to be sent back to you to be modified?