Caution: Electrostatic amp compatibility (HE90 owners in particular)

[trbl]

Quote:

Originally Posted by kevin gilmore The ecl86 is a pentode. There are things about pentodes that i still do not like to this day.

Well, half is a pentode anyway.

The obvious advantage that pentodes and beam power tubes have in this application is that they can swing more voltage relative to the plate supply voltage. That can be an issue when the plate supply voltage is limited, or when you want to swing a large voltage and there are few triodes (or triode-connected pentodes or beam power tubes) available. For example an EL-34 in native pentode mode can be used with a much higher plate voltage, for a correspondingly greater voltage swing), than a triode-connected one (since the maximum permissible screen grid voltage is less, and screen grid current/power ratings become of more concern too).

Triodes have nicer clipping/overload characteristics, and are probably better behaved near cut-off. There are tricks that can be done to optimize a pentode or beam power tube for an electrostatic headphone amp to deal with these issues.

Unfortunately these days there are only a limited number of different tube types available, and their quality and long term reliability can be doubtful. So when designing a direct drive electrostatic amplifier, more compromises must be made than in the heyday of tubes when there was a better selection of tubes to choose from.

 

[Hirsch]

Quote:

Originally Posted by kevin gilmore Case 2 sr-007t Add a 14 meg resistor from the junction of the 2 meg and 4.7 meg resistors to ground. Add an extra 5.1 meg resistor in series with the 4.7 meg resistor.

I tried this, but the effect of the resistor to ground was to reduce the impact, spaciousness, and kill off low frequency texture. Bass became a one-note experience, and did not go as deep. Adding the 5.1 meg in series doesn't hurt the sound anywhere near as much, although it may have some effect on the low end. So, bias is back up to 580v, and I need a good VTVM to check for sure (I've got a purported VTVM, more or less, but it's a later model and clearly doesn't have the proper internal resistance). Jan Meier has suggested a bypass capacitor on the resistor in the bias line (0.01 uf), so I may give that a try.

 

[bangraman]

I've had the 007t powered up for a decent portion of the time that I started looking at this thread. The HE90's are proving to be somewhat uncomfortable for long-term listening so they haven't spent that much time on my head... but there have been no channel imbalance problems so far.

 

[bangraman]

Still no imbalance. I can now have a dynamic, the speakers and the Orpheus on at the same time in my homeoffice and I've been checking relative staging.

 

[mikeg]

Since a properly working HE90 should show imbalance, your HE90 is clearly malfuctioning.

Quote:

Originally Posted by bangraman Still no imbalance. I can now have a dynamic, the speakers and the Orpheus on at the same time in my homeoffice and I've been checking relative staging.

 

[dannyandelyse]

so where are we going?

Is the use of a regular KGSS or Stax amp without any mods being used without problems, or is the use of a 5 ohm resistor on the adapter wire suffucient and sonically the way to go, or what? Your thoughts gentleman......

Amazing transducers

Dan

 

[eric343]

5 million ohm!

 

[carlflow]

Ok what is the best fix for the HE 90's and the 007t? Buy the new amp? Add the 5 meg resistor? After reading all the threads I added 5 meg resistors in the cable I made for the HE 60's. Thanks for all the input and the help to everyone out there. Carl

 

[mikeg]

According to postings 34 and 35 at the following thread, addition of the 5 meg resistor may not be needed:

http://www6.head-fi.org/forums/showt...84#post1756584

Quote:

Originally Posted by carlflow Ok what is the best fix for the HE 90's and the 007t? Buy the new amp? Add the 5 meg resistor? After reading all the threads I added 5 meg resistors in the cable I made for the HE 60's. Thanks for all the input and the help to everyone out there. Carl

 

[carlflow]

A big thanks to the people that brought this up. Its given me something to do on these cold days.

 

[gaijin]

Quote:

Originally Posted by carlflow ...with both HE90 HE 60 and Omega II... I'm a retired construction worker:

... thinking of getting into construction.

 

[Hirsch]

Quote:

Originally Posted by carlflow I have found out that you can ajust the bias on the Stax 007t. I have done it on mine. And it is real easy. I used Fluke 73 III and check the bais voltage on my Senn HEV70 it is around 210v I know the story of how it drop when you hook-up the Multimeter. So I also check the bias on the Stax. which is 290v both of these test where done at the frount jack. I have also measured from the restitor in side the 007t. its is around 500v. and 290v behind. For a week now I have tried different voltages and there has been NO channel drop out for me with both HE90 HE 60 and Omega II. When changing the bias on the 007t you have to keep ajusting the Tubes.

The tubes in the 007t have nothing to do with the bias charge to the headphones. The tubes are part of the audio signal, not the static bias charge. Altering the bias voltage of the tubes will simply run them less optimally. You'll lose balance between the triodes, and between the tubes. Tube life may be reduced, and there may be sonic problems.

The bias voltage on the HEV70 should be around 540v, more or less.

I have not heard any channel imbalances with my HE90 since upping the resistor in the bias line to 10 meg (and only had it happen once at the original value of 5 meg). However, I'm looking forward to the more permanent fix.

 

[carlflow]

Quote:

Originally Posted by rickcr42 I for one find it just a bit interesting that an amp formerly considered a POS and way overpriced "flash" is suddenly considered world class with a simple R/C and power supply upgrade. The solens are a good cap for the price but hardly the last word in resolution and metal films not a be all end all either when the well known proclivity towards hardness of some versions is added.It is more selective to position in circuit than it is generic "metal film" that counts. That this amp sounds good overall I have little doubt considering I always thought the original to sound just fine,very free and easy sounding, but I have to wonder how this jibes with the former "it sucks" attitude on this amp here at head-fi. It seems to me only products offered by the original company suck and get bashed openly while our little brand of "in house mods" or "cloning" are considered world class amps.I personally find this very unsettling and it says a lot about certain people who have no trouble "flipping" opinions when it serves to do so. 'Nuff by me on this,proceed

This man has guts! I for one love it,
Its the American way fear and consumption. Scare everyone so they can keep buying. Or make money on somthing they don't need. I get it.

 

[bangraman]

Just curious to see if there have been any updates for this.

 

[Hirsch]

Quote:

Originally Posted by bangraman Just curious to see if there have been any updates for this.

The latest word that I heard from Jan Meier is that the channel imbalance issue was located by Sennheiser, and can be repaired. It's not an amp issue at all. The later batches of the new HE90's already have the fix in place. If you've got one of the earlier new production HE90's and it has a channel imbalance issue with Stax amps, the fix can be applied. I do not know any details of exactly what is done to correct the issue. If your HE90 has no problems out of a Stax amp, you do not need to have anything done.