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In Reply to: RE: One ESL manufacturer who did something potentially lethal posted by Brian Walsh on January 05, 2014 at 21:34:08
Sounds like, from what you wrote, that the mylar bias supply AND the audio step-up transformers were both also located outboard. Is that correct? If so, therefore, the DWs were not directly driven. That doesn't detract from your point that they were potentially dangerous. Those cables would have to be very thick, as you suggest. Any resistance would potentially drop the voltages to possibly ineffective levels. Back in the day, I heard the DWs once or twice. I always thought they sounded like what they were: vibrating gas bags. But I never noticed the huge umbilicals or the outboard electronics box.
In a way, I miss those days of outrageous audio innovation and experimentation, where crazy products like that would actually make it to market. The Beveridge speakers are no exception.
Follow Ups:
It is the insulation...at 7KV you only need like 30 mA to put 200 watts on the panel. so even if the cable serial resistance wold be 10 ohms the voltage drop on the cable would be negligible, a bigger problem would be the characteristic impedance of the cable at the higher frequencies. but that is all resolvable and a simple engineering problem. It would drive the cable nuts even more nuts that one could not change speaker cables :), In any case i would make such amps mono blocks with short cables connected to the backplate with a connector that would shut the apm down if the cable is disconnected, and would not allow physical removal till the panel is fully discharged. I know it would need some sort of control in the backplate. all that is solvable and can be made totally safe, the question is how much of an improvement would one get, and how much would it cost to build.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
No disagreement that it's voltage, not current.
The company in Europe that also makes a dd amplifier for ESLs is Inoxx or Innoxx. Something like that. They do think in terms of an externally mounted amplifier, and they do use short thick wire and some very interesting connectors that are probably safe with the very high voltages involved. Still, it's no wonder that ESL-makers shy away from direct-drive in the US. (For that matter, EU safety rules are even stiffer than here, altho the lawyers there are not as interested in liability claims as they are here.)
is only 3000 V pp. so that is way below what is needed...they list a 5000 v pp but no info on the site...
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
I've emailed them on the subject of driving Sound Labs. I did get one or two responses that each stimulated me to ask more questions. Finally, the line went dead. No response to my last question, sent about 3 months ago. I was asking about their higher voltage amplifier.
At the outset, they had a complete misconception of how the Sound Labs work, telling me that they were a 3-way speaker. I then had to describe the circuit, etc.
In a way, I miss those days of outrageous audio innovation and experimentation,..................
yes...yes Lew in some ways those were the days.....thanks to all for the info on the Beveridge ESLs..............the bais could be outboarded?
I think the bias in the SoundLabs gos up to 7KV........
Based on info from the one guy I know of who actually bought an instrument to measure the bias V on his Sound Labs, right at the panels, you are absolutely correct; I think he measured 7 to 8kV!!!
Just to clarify, because I am not sure what you meant, the mylar on the Bev panels is conductive and not subjected to a bias V at all. The mylar is instead driven by the dd amplifier in concert with the stators. Don't ask me how or why this works as well as it does; I am still thinking about it. But I think this has a lot to do with the fact that my speakers are still working, all 3 individual panels in both spkrs, after 30 years. The Bevs panels are quite reliable.
Lew.... the outboard bias in my other post.........was for the Soundlab an a DD amp.....then the DD amp may work at lower V.......
Funny about the QS preamps an amps..........
your point about the ...The Quicksilver preamp sounded more like SS
Over the yesrs i have had guys beg me to help them get the QS preamps to sound like a tube preamp....but like most of the ARC preamps...I dont get it... lay out look vary good ..part Q is high.....dont sound like glass to minny........
So is it the top end an uper mid... that makes the Beveridges sound diff than the soundlabs would you say?
On the Quicksilver preamp: To a large degree its sound can be tuned by the choice of capacitors. There is some unit to unit variation in the RIAA network, so far as I can tell, because the schematic that Mike Sanders sent me shows slightly different capacitor values from what is actually in my unit. My unit has four .022uF capacitors (two per channel) for RIAA. I replaced them all with Russian SSG types. OMG, what a fantastic improvement. Those are wonderful capacitors. Then also the coupling caps between phono and linestage and between linestage and output make a big difference. However, there are two things in the circuit design that may make it lean toward an SS sound. One is the NFB in the linestage. Another are the zeners used in the PS. I toyed with the idea of revising the linestage to get rid of the NFB, but I did not want to destroy the pristine originality of my unit. Plus, it does sound excellent, and it certainly is not "lean" or harsh sounding. Just a little more toward SS vs "tube". Another upgrade that I did perform on mine was to ditch the 12AU7 at the input to the linestage, in favor of another 12FQ7. (Which is to say that my linestage now uses two 12FQ7s and one 12AX7.) The latter is a much better sounding tube, and I can hear a big improvement. (12AU7 is not my cup of tea at all, no matter how fancy the brand or the vintage.)
I have not heard my SLs in a while, but my impression is that the Bevs do have a subjectively more extended top end. A lot of this may have to do with the way you listen to the Bev. Speakers are sideways facing each other, and I sit only about 7 feet away from a straight line that could be drawn between the lenses of the two speakers. There is a brick wall about 6 feet behind, at the rear of my room, from that same straight line. The SLs are in a much bigger room, are operating in true bipolar, and are farther away from my listening position. HF response will appear to deviate much more, depending upon where you sit or stand.
maybe some thing like this...........
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