Well, if the bias resistor value has so much effect I see three possibilities :
- one/all panels are leaky
- foil coating lost conductivity by aging
I would first try to gently clean the panels e.g. with a vacuum cleaner
- problem with leaky bias supply diodes or caps
I would replace all diodes (a 1N4007 should work) and the caps in the voltage multiplier..
in any case I would reduce bias resistor value untill senditivity is not getting higher..good luck
Yes as with all ESLs.....all of the above.. thay all leak...like to have one 10years old that did not.....
To get the best out of any esl re-work the bias...vary littel cost ...to gain...better than crossover... caps, wire...,an can YOU set the tone an output with the bias feed res....every type of res i have put in sound diff...1% medel film..1/2watts good place to start..thanks..
i have drop as low as 4megohms.....4ea 1meg 1/2w in series...
vary mindbinding sound...sound vary clost to my Apogee sweet topend...
An when you think you know what these ESL can sound like???....gofig
To get the best out of any esl re-work the bias...vary littel cost ...to gain...better than crossover... caps, wire...,an can YOU set the tone an output with the bias feed res....every type of res i have put in sound diff...1% medel film..1/2watts good place to start..thanks..
i have drop as low as 4megohms.....4ea 1meg 1/2w in series...
vary mindbinding sound...sound vary clost to my Apogee sweet topend...
An when you think you know what these ESL can sound like???....gofig
One more reason to avoid large diaphragm motion if operating in constant voltage mode.
The A-1s that I recently worked on did not have any resistance placed between the HV module and the copper charge ring. I had always thought there was a large resistor included in their mixer box between the HV supply and the diaphragm. But measurements showed negligible resistance.
I just posted a schematic here:http://www.diyaudio.com/forums/planars-exotics/254723-acoustat-mk-series-2.html#post3911097
If the coating is high resistance, the bias feed resistor isn't strictly neccesssary.
Personally I think some amount (10M) is still a good idea to avoid damage if a short develops.
SL panels tend to be rather leaky because of all the horizontal foam strips used to split up the panel.
This is especially noticeable when humidity is high.
Thanks Bolserst..........yes 10meg is good....anyone that tryes this well be posting... i know i had ML for 20years also 10pr have came thought my hands...it like i never heard them....thil i drop the bias feeds....snapet in to foscs....way diff sound....
I had a pr of the older A-1s..........sold off fast...dead short...an that was with NO!....bias feed res...............Wow...
one more thing about the ML tranfourmers bias set up...
in the 90-96s....ML drope the earth feed comeing to the setup...it must be put back to get full output of the panels....ML put the neg leg of the amp ....take it out put the earth back...this thakes the spongynes out ...an gives better foaces to the sound... the earth in coming to the speaker it just not there at the boards input............but cut the ac before you do..
As for jims info on the AC site.....with new panels all my have been well with the 500meg...on paper looks good ...today in my case....20+old panels.. over 50%300days a year..10meg bias feed sounds like new panels...as i said...never had this good of topend on the Acoustat...
i would have to go back to my Apogee..full time...
.good luck
I had a pr of the older A-1s..........sold off fast...dead short...an that was with NO!....bias feed res...............Wow...
one more thing about the ML tranfourmers bias set up...
in the 90-96s....ML drope the earth feed comeing to the setup...it must be put back to get full output of the panels....ML put the neg leg of the amp ....take it out put the earth back...this thakes the spongynes out ...an gives better foaces to the sound... the earth in coming to the speaker it just not there at the boards input............but cut the ac before you do..
As for jims info on the AC site.....with new panels all my have been well with the 500meg...on paper looks good ...today in my case....20+old panels.. over 50%300days a year..10meg bias feed sounds like new panels...as i said...never had this good of topend on the Acoustat...
i would have to go back to my Apogee..full time...
.good luck
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Joachim if this circuit is different than those posted, could we see it?
dennis h
I'd think driving a varying capacitance might also result in amplitude dependent frequency response and phase modulation.
This is effective mainly for low frequencies (the lower the more) : in the equivalent network representing a real transformer the main inductance is is both voltage and frequency dependant (cause is magnetizing core curve). In parallel to this inductance is a capacitor, which in good approximation is constant for constant charge drive - for constant voltage drive it is more complicated : for small foil excursion it will be also constant (one stator foil cap is geting bigger by the same amount, by which the other stator foil cap is lowered, ac wise these two caps are in parallel - so no net change), for greater excursion one of these two caps will become dominant (up to an ultimate value defined by stator insulator thickness and its dielectric constant) with a square law voltage wise (force is defining stator foil distance)..
so when constant voltage driven foil movement is becoming nonlinear, this parallel cap will also become voltage and frequency dependant - with same distortion effect as described for transformer main inductance above - in the higher frequencie range.
I'd love to see it, but I certainly agree with Dennis and respect your character even more! Our World is a better place due to people like yourself.
Best Regards,
TerryO
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regarding bias charge resistor :
http://www.diyaudio.com/forums/plan...ion-electrostatic-speakers-2.html#post1866030
http://www.diyaudio.com/forums/plan...ion-electrostatic-speakers-2.html#post1866030
For equal voltage swing at the stator foil caps (and equal amplifier load) the beveridge (and the final copy) transformer step up ratio can be halved, compared to my suggested circuit from post 6...this is surely a pro for the beveridge..
price to pay are 2 more high voltage caps, one more bias supply, less safety..moreover the necessary charging resistors in the two bias supplies are both in parallel to the stator foil caps for the music signal..
it is a pitty this can not be done for constant charge...if a high value resistor is inserted in series to the foil at the beveridge style, sound would be, well near zero ...constant voltage should be less sensitive to humidity (here circuit from post 6 has lower bias impedance)
price to pay are 2 more high voltage caps, one more bias supply, less safety..moreover the necessary charging resistors in the two bias supplies are both in parallel to the stator foil caps for the music signal..
it is a pitty this can not be done for constant charge...if a high value resistor is inserted in series to the foil at the beveridge style, sound would be, well near zero ...constant voltage should be less sensitive to humidity (here circuit from post 6 has lower bias impedance)
the web page from pio sound (final successor - Website hosting & domeinregistratie - Xel Media) is gone ...
Hi,
sputtered Aluminum still seems to be the longest lasting low-ohmic coating for this application.
But it certainly does not last infinite.
I don't know of any low-ohmic transparent coating that remains longtime functional on a soft flexible vibrating membrane.
Even if they solved the bonding problems -probabely with kind of plasma treating of the membrane- it must be insured that the coating's ageing process doesn't lead to vibration related microcracks within the coating layer.
It is already an interesting manufacturing problem as how to stretch the film without creating microcracks within the coating.
Besides reliablity, the Finals never fulfilled the claims.
Not as efficient as specced, not as low-THD and not as low going in the bass.
I wonder what happens to those guys owning a broken Final?
Will they get any service at all, since nobody but the former Final crew knows if and how to repair the stuff?
So, I share Your doubts.
jauu
Calvin
sputtered Aluminum still seems to be the longest lasting low-ohmic coating for this application.
But it certainly does not last infinite.
I don't know of any low-ohmic transparent coating that remains longtime functional on a soft flexible vibrating membrane.
Even if they solved the bonding problems -probabely with kind of plasma treating of the membrane- it must be insured that the coating's ageing process doesn't lead to vibration related microcracks within the coating layer.
It is already an interesting manufacturing problem as how to stretch the film without creating microcracks within the coating.
Besides reliablity, the Finals never fulfilled the claims.
Not as efficient as specced, not as low-THD and not as low going in the bass.
I wonder what happens to those guys owning a broken Final?
Will they get any service at all, since nobody but the former Final crew knows if and how to repair the stuff?
So, I share Your doubts.
jauu
Calvin
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New member here. Interesting post to follow. I have a set of Beveridge system 2's. No SW.
Joachim, I have not spoken with Rick in about a year, last I spoke with him he was out living in the woods of California away from civilization. Spent some time with him at CES a few years ago when he was trying to relaunch the Bev speakers. Dismal failure there, we just could not rattle the rafters with everybody else, music was not the important issue, volume was.
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