Folks:
I've touched on this a few times in some other threads.
I'm interested in building some (curved) electrostatic speakers for a home theater setup. I'd like to do four but two is definite - I can arc the front two enough so that the listening couch will be in the primary arc of the speaker output. This thread isn't about that
The speakers, according to Wagner, would be 8Kv. Even with a 63v rails, (200watt roughly) with a 75:1 step up transformer, that's only 4725v!
I was planning on six Opti-MOS amplifiers for a home theater and I've gotten the following information from Randy Sloan:
This is interesting though:
I've been thinking of a Class D or T amp, as I may be able to find a switching transistor that's capable of higher voltages. From email generated from the Class-T thread:
Given that it's seemingly difficult to find high voltage output devices (yes, I know, tubes, that's another thread), I'm thinking now of just building the Opti-MOS and go for a high voltage rail, with subsequently lower power.
Rather surprisingly, the amp that this will replace, an SA-500 from Techniques (yes, ancient) was listed as a 55w amp, but I checked the voltage across the filter and it's high (something like 45 volts, 87 or so rail to rail). So the rail voltage is a lot higher than a 55w amp would normally be, so I'm going to size my replacement Opti-MOS amp for at least that.
I'm eventually going to bi-amp a woofer in the same cabinet as the ESL, so I'm going to build six Opti-MOS's now 'regular'. I'm trying to pick the output voltage of the transformer, I may just pick 90VCT to give a high drive voltage. My feeling is that if I custom wind a 16ohm output transformer for the ESL, I wouldn't be in that high of a wattage but would get the drive voltage I need. The 75:1 output transformers with a 90VCT don't get close to 8Kv anyway, which would explain why some people say ESL's require 'powerfull amps'.
It just doesn't look like a solid state amp can do 8Kv and still be 'hifi'.
Thoughts?
I've touched on this a few times in some other threads.
I'm interested in building some (curved) electrostatic speakers for a home theater setup. I'd like to do four but two is definite - I can arc the front two enough so that the listening couch will be in the primary arc of the speaker output. This thread isn't about that
The speakers, according to Wagner, would be 8Kv. Even with a 63v rails, (200watt roughly) with a 75:1 step up transformer, that's only 4725v!
I was planning on six Opti-MOS amplifiers for a home theater and I've gotten the following information from Randy Sloan:
I'm not aware of any types of high-voltage L-MOSFETs available, and going to D-MOS families would probably destroy the fidelity you are trying to achieve with electrostatic speakers. Some of the "double-die" L-MOSFETs available have Vds parameters of 200-volts, and by going with cascoded outputs (commonly called "totem poleing"), you can raise the maximum rail potentials to 400-volts. This technique would raise the maximum peak-to-peak capabilities with L-MOSFETs (not bipolars) to 800-volts. Of course, this is still a far cry from 8-Kv.
(Randy Sloan)
This is interesting though:
I still believe that L-MOSFETs are the best output devices for the application you are considering, since they are much more immune to reactive loading than bipolar devices. (Randy Sloan)
I've been thinking of a Class D or T amp, as I may be able to find a switching transistor that's capable of higher voltages. From email generated from the Class-T thread:
Driving an 8kV panel directly will require some very VERY exotic output devices. So exotic, in fact, that I haven't found any either. There are a few good candidates in the 1kV range from ST, however, which would allow for a fairly modest turns ratio from your output transformer. Take a look at the STU7NB100 as a possibility. It's Rdson is 1.5 Ohms, so efficiency goes out the window, but I'm guessing you're not all that concerned with efficiency when contemplating an 8kV power supply anyway.
I really think an output transformer is the way to go. The money you will spend on the transformers is offset somewhat by being able to use a less expensive power supply and less expensive (and far more robust) output devices.
Given that it's seemingly difficult to find high voltage output devices (yes, I know, tubes, that's another thread), I'm thinking now of just building the Opti-MOS and go for a high voltage rail, with subsequently lower power.
Rather surprisingly, the amp that this will replace, an SA-500 from Techniques (yes, ancient) was listed as a 55w amp, but I checked the voltage across the filter and it's high (something like 45 volts, 87 or so rail to rail). So the rail voltage is a lot higher than a 55w amp would normally be, so I'm going to size my replacement Opti-MOS amp for at least that.
I'm eventually going to bi-amp a woofer in the same cabinet as the ESL, so I'm going to build six Opti-MOS's now 'regular'. I'm trying to pick the output voltage of the transformer, I may just pick 90VCT to give a high drive voltage. My feeling is that if I custom wind a 16ohm output transformer for the ESL, I wouldn't be in that high of a wattage but would get the drive voltage I need. The 75:1 output transformers with a 90VCT don't get close to 8Kv anyway, which would explain why some people say ESL's require 'powerfull amps'.
It just doesn't look like a solid state amp can do 8Kv and still be 'hifi'.
Thoughts?