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Old 25th February 2010, 02:00 AM   #41
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bolserst,thanks for pointing out a few issues with my measurments.i have been doing some more and taking a more careful and scientificly controled aproach .i am making some graphs on the effects of diffirent turns on the new primary starting with 10 turns to 40 turns in increments of 5 .hopefully i'll get my results and graphs posted by tommrow.i will also explain more in detail compared to the original data .so far so good stay tuned. jer
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Old 25th February 2010, 02:12 AM   #42
Few is offline Few  United States
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Quote:
Originally Posted by geraldfryjr. View Post
thanks for the tips jonas.is there an easier way to insert a new line with out having to hit the spacebar 1000's of times.
The return key? Hitting it twice will give you a gap between paragraphs. Inserting a space after the period ending a sentence, and capitalizing the first letter of the next sentence, will make the sentence breaks easier for all of us to read as well.

Some of this is old school (which probably means I'm old), but I find some of the recent trends such as typing "ur" instead of "you're" and ignoring capitalization to be distracting and a bit annoying. The author saves a couple milliseconds when typing and then burdens every reader with the task of decoding the result.

Few
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Old 25th February 2010, 07:08 AM   #43
bentl is offline bentl  Norway
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bolserst, thanks for the clarification!

I believe that both Sowther and Amplimo transformers have a 4-8 ohm resistance on the primary side - but I may have misunderstood the spec's.




Regards,

Bent
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Old 25th February 2010, 07:20 AM   #44
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Quote:
Originally Posted by bentl View Post
I believe that both Sowther and Amplimo transformers have a 4-8 ohm resistance on the primary side - but I may have misunderstood the spec's.
Don't confuse resistance with impedance... 4-8 ohm is not what you would measure at that winding with an ohmmeter.

BTW, Sowter says something quite different:

From http://www.sowter.co.uk/electrostatic-loudspeaker.php :
"Please note the primary impedance is shown below as a reference for the power rating. You can drive from any impedance (the lower the better)."

What Sowter means is that (and I refer to the table in the above web site): in order to get the voltages required to use that transformer and drive your panel to the specced stator voltages, you need an amp that is specced at that wattage @ that impedance...

Kenneth
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Last edited by kavermei; 25th February 2010 at 07:26 AM.
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Old 25th February 2010, 07:35 AM   #45
bentl is offline bentl  Norway
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Hi, OK I am learning! Electronics is not my profession, so I have a lot to learn.

In a earlier post in this thread you wrote:

"Figure out what peak-to-peak drive voltage you want on the ESL and what the maximum peak-to-peak output voltage of your amp is."

How do I measure the peak-to-peak voltage for my amplifier? What value is to expected from a 50W class a amp?

Would be nice to have some reference numbers to play with; I am working through your "recipie" in MathCad at the moment.

Regards,
Bent
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Old 25th February 2010, 08:07 AM   #46
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Quote:
Originally Posted by bentl View Post
In a earlier post in this thread you wrote:

"Figure out what peak-to-peak drive voltage you want on the ESL and what the maximum peak-to-peak output voltage of your amp is."

How do I measure the peak-to-peak voltage for my amplifier? What value is to expected from a 50W class a amp?
I can think of two ways: guessing or measuring.

1. Measure: open your amp, locate the power supply, and carefully measure the + and - power supply rails with a multimeter. You can always ask a more experienced hobbyist friend if you're not comfortable doing that. Say for example you measure +35V and -35V, then the peak-to-peak voltage that the amp can deliver is a bit less than 70V (the output can't go all the way up to the power supply rails)

2. Guess: if your amp is honestly specced at 50W RMS at 8 ohms, then it can deliver sqrt(50 * 8) V RMS to the load (because P = V^2 / R). That's 20V RMS. From RMS voltage to peak-to-peak voltage is times 2*sqrt(2) (at least for sine waves), so 20V RMS is a peak-to-peak voltage of about 56V.

Other example: if the amp is specced at 50W RMS at 4 ohms, then it can deliver only sqrt(50 * 4) = 14V RMS, and that is 40V peak-to-peak.

I say "honestly specced", because some manufacturers will specify peak power or something instead of sine RMS power. 1000W computer speakers come to mind . But that would invalidate our calculations.

Quote:
Would be nice to have some reference numbers to play with; I am working through your "recipie" in MathCad at the moment.
Great, and if you need more help, don't hesitate to ask the crowd here.

Kenneth
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Last edited by kavermei; 25th February 2010 at 08:11 AM.
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Old 25th February 2010, 08:17 AM   #47
bentl is offline bentl  Norway
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Default Sanity check please

Thanks again for all valuable input.

I have tried to calculate a transformer, enclosed is the calculations.

The calculations and constants are based on the following article:
HOW TO WIND YOUR OWN AUDIO TRANSFORMERS

I guess it will be difficult to interleave primary/secondary windings if I am down to 45 primary windings?

Or have I totally misunderstood the math here?

Regards
Bent
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Old 25th February 2010, 11:17 AM   #48
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Based on those formulas, your calculations look correct. Regarding the core size, however, I'd like to say that this is more of an art than a science, even for transformer companies, and those formulas only give an approx. size. Also you can never be sure of the exact parameters of the core material that you buy.

Therefore, I would suggest that you include a large safety margin in the core size, to reduce the uncertainty. For example, use a 50 or 60mm stacking height, or even a EI 105 core. You will also have more space on the bobbin

Kenneth
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Old 25th February 2010, 11:26 AM   #49
AndrewT is offline AndrewT  Scotland
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The return key? Hitting it twice will give you a gap between paragraphs.
the enter key is often called return key.
This is short for carriage return line feed taken from typewriter days from whence the qwerty keyboard comes.

Using it's correct name describes exactly what the return key does.

The enter key in the numerical keypad, sends a different signal and some software starts a different process when return or enter keys are pressed.
Most software reads these two keys as meaning "start the same process".
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Last edited by AndrewT; 25th February 2010 at 11:34 AM.
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Old 25th February 2010, 11:28 AM   #50
bentl is offline bentl  Norway
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Thanks, I will first try to wind this transformer and test with the laminations and bobbins I have available.

If the result is usable I will possibly go for a bigger lamination - if not I will order step-up trafos from Sowther.

Transformer parts is not easy to order in small quantities, and you can't experiment much before the cost exceeds buying off the shelf trafos.


Regards

Bent
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