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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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Link Posted: Thu Oct 06, 2011 6:58 pm Post subject: |
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Some days ago I spent some time putting the variable HV supply together and I noticed two annoying things:
1) The transformer doesn't seem to like to be driven with a square wave and it is squealing, a bit too annoyingly for my taste.
2) The H-bridge gets a bit too hot for my liking
After playing around a bit I found that the transformer really has to be driven by a sine wave, or at least something that almost looks like one so over the last few days I designed a new variable voltage supply. It uses the same square wave generator, a two stage lowpass to filter the square down to a sine and an audio driver chip to drive the transformer. The high voltage stack has been unchanged. I even made room for a heatsink on the board in case the large copper area isn't enough to keep the driver chip cool enough.
I have the new design and layout attached.
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HV_VAR2_PCB.pdf |
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HV_VAR2_sch.pdf |
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_________________ ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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mightym
Joined: 04 Jun 2011 Posts: 6 Location: Okrahoma
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Link Posted: Sat Oct 08, 2011 12:44 am Post subject: |
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Thanks for the detail Kim, The fog is slowly starting to lift...
John
As I understand what you are doing, the film is more, or less tightened top and bottom ( in the vertical ), and then the outer edges are stretched to take out any remaining wrinkles, then start again until you are satisfied no wrinkles?
The Mylar you use is aluminum coated, yes?
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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Link Posted: Sun Oct 16, 2011 6:55 pm Post subject: |
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I put the first complete speaker together, the picture shows it in relation to the ESL-0.5. To hide the stretching tape I used a silvery gray tape that nicely bridges the color between the shiny silver of the membrane and the black of the stators. Most of that tape will be covered by the powder coated strip used to hide the screws anyway.
They were actually playing while taking the pictures, it sounded very good. I will try to make some measurements tomorrow night when the house is quiet.
_________________ ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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Link Posted: Tue Oct 18, 2011 2:58 am Post subject: |
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So tonight I measured the frequency response for the first time, it looks like this
I have to say that it looks quite good. When comparing it to the response of the ESL-0.5 as shown on page 4 of this thread it can easily be seen that this one does not have the broad dip between 150Hz and 350hz. It can also be seen that the exponential spacing nicely avoids the resonance peak.
_________________ ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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beun
Joined: 28 Jun 2006 Posts: 676
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Link Posted: Sat Oct 22, 2011 7:02 pm Post subject: |
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This morning I went back to the original variable high-voltage supply and found a few fixable errors in it.
1) The square wave that the oscillator produced didn't have a 50% duty cycle meaning that there was DC going into the transformer. It becomes a whole lot better with a few component changes which reduces an annoying buzz in the transformer and it keeps the H-bridge a lot cooler.
2) The transformer doesn't quite like to be driven by a square wave, but I can resonate out the leakage inductance on the secondary side. I don't have the exact capacitor I need but it works good enough for a test hack.
Speaking about a test hack, I put together the variable HV-supply and the new 1:75 Plitron transformer and am playing music again. I have to do some measurements but the speaker efficiency is a lot better that with the old 1:50 transformer.
Be careful HIGH-VOLTAGES, don't touch the picture in the wrong place
_________________ ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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AnalogRocks Forum Moderator
Joined: 08 Mar 2006 Posts: 26690 Location: Toronto, Ontario, Canada
TV/Projector: Sony 1252Q, AMPRO 4000G
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Link Posted: Sat Oct 22, 2011 7:23 pm Post subject: |
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beun wrote: |
Be careful HIGH-VOLTAGES, don't touch the picture in the wrong place |
Damn I touched it with wet hands...
_________________ Tech support for nothing
CRT.
HD done right!
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beun
Joined: 28 Jun 2006 Posts: 676
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beun
Joined: 28 Jun 2006 Posts: 676
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Link Posted: Thu Oct 27, 2011 3:01 am Post subject: |
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With the help of the customer I have been making more frequency response measurements. In the plot below there are three overlayed plots measured with different resistors in series with the transformer primary, namely 1.1 Ohm, 0.7 Ohm and 0 Ohm.
I am getting the impression that the amplifier doesn't quite like it when there is no series impedance, at least not trying to produce high level high frequency signals. I didn't notice anything weird on music. The response without any series resistance is remarkable flat though.
I will do some experiments but my guess is that the series resistor will end up around 0.4-0.5 Ohm.
_________________ ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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garyfritz
Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO
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Link Posted: Thu Oct 27, 2011 3:41 am Post subject: |
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I wonder how many of those bumps are caused by your room? Too bad you don't have an anechoic chamber handy. Have you ever tried hauling a speaker to some quiet country location and measuring the speaker response *outside*?
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beun
Joined: 28 Jun 2006 Posts: 676
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garyfritz
Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO
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Link Posted: Thu Oct 27, 2011 11:59 am Post subject: |
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It would take a helluva lot of damping material to do anything to the response at 200Hz or below. Garage might help but it will also create a big echo chamber. Out away from everything, set on grass instead of concrete, would be a lot closer to an anechoic chamber.
But that's just to get the best-looking and most accurate measurement, so your chart is comparable to the big boys' charts. For an in-room measurement, that's a beautiful response curve.
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beun
Joined: 28 Jun 2006 Posts: 676
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