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Old 31st March 2011, 08:19 AM   #21
Calvin is offline Calvin  Germany
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Hi,

as bolserst said modern toroids are capable of low enough leakage inductance that bandwidth limits >20kHz are possible. With 80VA-cores (pairs of 230/6V) I achieved >20kHz with 1nF load and with 120VA core-pairs I achieved ~19kHz using a 2nF panel. The specialized Amplimo toroid gave ~3-4kHz higher cutoff frequency. Any EI-core I tried sucked, hardly surpassing 10kHz.

jauu
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Old 31st March 2011, 01:45 PM   #22
SM7UYJ is offline SM7UYJ  Sweden
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Quote:
Bmax = E x 10^8 / (4.44 x f x N x A)

Bmax = Peak AC flux density in core (Gauss)
f = frequency
N = number of primary turns
A = core area cm^2
What if ?

I strip the LV from two 400VA cores, stack the cores, connect the HV side in series for 480V and wind a new 12V LV winding?

From the formula above I should get 2xA and f/2 for the same Bmax and N ?

Roger
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Old 31st March 2011, 02:41 PM   #23
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Quote:
Originally Posted by SM7UYJ View Post
What if ?
I strip the LV from two 400VA cores, stack the cores, connect the HV side in series for 480V and wind a new 12V LV winding?

From the formula above I should get 2xA and f/2 for the same Bmax and N ?
Yes. You can stack two cores and wind a new LV winding thru both cores with the same number of turns as the 12V winding. The result will be that you have increased your saturation capability be a factor of 2 because of doubling the core area(as you noted). But, you will have reduced your step ratio by a factor of 2 as well since only half of the flux in the LV winding will flow in each of the HV windings. So, if one transformer has a step up ratio of 20:1. After you stack two transformers, put the 240V windings in series and wind a new 12V winding thru both cores you will have a step-up ratio of 20:1, but twice the saturation capability.

A simpler alternative for bass panel use:
Simply wire the 240V windings in series AND the 12V windings in series. You will get the same step up ratio(20:1) as a single transformer, but with only half the input voltage across each 12V winding you will have doubled your saturation capability. Leakage inductance is increased, but this won't matter for driving your bass panels.
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Old 31st March 2011, 03:33 PM   #24
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Not sure if you read my last post on the other thread where I had explained what was just stated.

But thanks, Steve,as I couldn't remember if the saturation frequency was reduced by 1 octave or 2 octaves.

Carry on. jer



My 2:nd ESL-attempt
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Old 31st March 2011, 03:42 PM   #25
SM7UYJ is offline SM7UYJ  Sweden
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I read that thread, and it was almost like you wound your toroids that I had in mind - but not quite!

I planed to make a small airgap between the cores and make turn one on the lower core followed by the on on top - going back to the lower one - and so on.

Anyway it was a "mind loop" as my N turns per core only handles half the voltage, the ratio stays the same => easier to connect the LV in series as bolserts says!

Roger
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Old 31st March 2011, 03:49 PM   #26
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I did find that the stacking method worked great for bass but not at the highend or full range due to the extra added capacitance from the extra cores and their associated windings.
I was able to drive my little panel very powerfully and cleanly that it vibrated like a foot massager.
And when I got down below 20hz I could actualy see the diagphram moving in and out using the qaud stacked cores. jer
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Old 31st March 2011, 04:15 PM   #27
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I did test a Double stack with that method and it is the same result as just tying the windings in series and being seperated.

I did try seperating them a bit thinking it would help to reduce the extra added capacitance caused by stacking them, and, to reduce the arcing potentiel between the two cores.
Only the latter made a difference (arcing stopped).

However, It is my beliefe that by stacking the cores ,rather than keeping them seperate, keeps the magnetic fields in the cores uniform to one another.
Possibly reducing any distrotions that may be caused from them not being perfectly equal to one another when the magnetic field is reversed. jer
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Old 31st March 2011, 04:54 PM   #28
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I had gotten confused in my data because of the stacking factor and the disturbution of the magnetic circuit. jer

Last edited by geraldfryjr; 31st March 2011 at 04:56 PM.
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Old 8th April 2011, 01:08 PM   #29
SM7UYJ is offline SM7UYJ  Sweden
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I can play bass with the amps volume maxed!

I got four oil burner ignition trafos from the scap yard today!

220V=>2x5kV, two trafos with primary in paralell and secondary in series for abt. 1:90.

Click the image to open in full size.

Click the image to open in full size.

Here is my self wound 1:100 trafo (2500 turns sec and 25 turns prim).

The ingition trafos work alot better, so I will use them for the bass section.

Click the image to open in full size.

Roger
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Old 8th April 2011, 03:34 PM   #30
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That's an excellent info. Thanks for sharing.

Wachara C.
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