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Old 3rd December 2007, 01:48 PM   #1
diyAudio Member
Join Date: Feb 2005
Location: atlanta
Default Help with my Beveridges, please....

Hello, All:

I am having a problem with one of my Beveridge ESLs, in that on power-on, one of the transducer diaphragms is drawn to one of the stators. Rick Beveridge says that this is a symptom of old age...reduced tension on the Mylar..., and that the other 5 diaphragms are probably not too far behind. Apparently, the built in OTL amps will (or can) go to full +/- 5kV potential when first turned on, and this will draw a weak diaphragm into one of the stators. When this problem first appeared, the diaphragm would release itself after a second or two, but now it clings to the stator until power is switched off. This is accompanied by a loud "whine" while it occurs...not very musical and perhaps destructive.

In an effort to prolong the life of these expensive to service transducers, I was contemplating converting them to transformer driven electrostats like the Beveridge 3, which uses the same high resistance stator design and the same aluminized Mylar diaphragms. In these speakers, the stators carry the bias charge and the low resistance diaphragms carry the audio signal.

OK, so can you guys help me design a bias supply and recommend a suitably audio transformer? And/or does anyone here have a schematic for the Bev 3's?

BTW, my version is the original full range one and doesn't have the built-in sub crossover.

Thanks in advance,
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Old 16th December 2007, 12:56 PM   #2
Urban is offline Urban  Sweden
diyAudio Member
Join Date: Mar 2003
Location: Täby, Stockholm

You are sitting on a true jem here. I'm curious about what you state about the Model 3 "the stators carry the bias charge and the low resistance diaphragms carry the audio signal."

I will fill in a little bakground here:

My undersanding of how the Model 2 works is that it is actively driven and is biased +DC, GND, -DC (stator, diafragm, stator) and AC wise, one of the signal phases drives both stators, the other the diafragm. This bias arangement doubles the voltage change seen between stator and diafragm, effectively halving the voltage drive needed for a given sound level. This halving of needed voltage is indeed a good thing, and possibly the only effedtive way to drive a ESL-panel actively, at least to high soundlevels.

I have assumed Beveridge kept the Model 2 bias arrangement in subsequent models, and have been pondering about ways to do the same within a transformer arrangment.

Your (early) Model 2 is a fullrange speaker and the Model 3 is not, thereby beining able to operate with smaller stator - diafragm distance, not needing that much drive. Also a tranformer can give much higher voltage output than an active device, so all-in-all it makes sense they choose this path.

There are a lot of designs for bias supplies on the net, here is a nice one:

The problem with your panels is probably that they need new retightend diafragms. You should also check that the bias levels are about the same, possitive and negative, and that the capacitors driving the panels are not leaky. Lowering the bias will possibly make the panels work, but then at a lower soundlevel. If your amps work OK one option would be to lover the bias they deliver so the diafragms can remain statically stable.

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Old 2nd January 2008, 11:38 PM   #3
diyAudio Member
tsmith1315's Avatar
Join Date: Jul 2003
Location: Doerun, GA
Wow, I haven't heard "Beveridge" for nearly 20 years when a friend who owned a store in Atlanta had a pair come in as an insurance replacement with two bad panels.

Huge cylindrical ESL's with multiple panels and a large down-firing woofer in the base. I wanted them so badly, and for a day or two thought I might actually be able to purchase them on my meager salary. In the end, the original owner wanted them back. Apparently, I never recovered...

Thanks for the memory!

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