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12th September 2013, 10:17 PM  #21 
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... my DIY ribbon
does this mean I can just mount it with a 1ohm resistor and have 4ohm ? not sure I understand that I thought Qts would rise
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13th September 2013, 12:09 AM  #22 
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> does this mean I can just mount it with a 1ohm resistor and have 4ohm ?
You lost me on that one . > not sure I understand that ......... I thought Qts would rise Me neither .... I thought it would stay the same Perhaps because the tester is reading the resistance of the xfmr winding rather than Re .......
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13th September 2013, 07:13 AM  #23  
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Quote:
and with a modest 2:1 autoformer trafo it needs 'something' hence the 1ohm btw, is this correct connection ?
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13th September 2013, 04:24 PM  #24 
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Other way around. The impedance from the center tap to ground
is multiplied by 4 accross the full winding ........
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15th September 2013, 08:39 PM  #25 
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15th September 2013, 09:35 PM  #26  
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Quote:
To calculate how much resistance it has, see the post at: Magnepan Ribbon Tweeter Question Or here's the short version: R = pL/A, where R is in Ohms, and the conductivity of aluminum, p, is 2.6 x 10^(8) Ohmmeters (where 2.6 x 10^(8) = 0.000000026), and L is length in meters, and A is crosssectional area in square meters. From the equation above: Ohms per Meter = .026 / (crosssectional area in sq mm) for aluminum. OR, you could just measure the resistance with an ohmmeter. As mentioned in the linked thread, if your ribbon is pleated, you can measure its resistance with an ohmmeter and then calculate the original unpleated length (assuming you know the thickness and width).
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The electrolytic capacitors ARE the signal path: http://www.fullnet.com/~tomg/zoom3a_33kuF.jpg Last edited by gootee; 15th September 2013 at 09:43 PM. 

15th September 2013, 09:47 PM  #27 
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ahh, you think of Apogee clones etc, with long foil lines glued to a film
yeah, I build a few long time ago and I might do it again they can sound very good but this one is just a small and simple experiment with a piece of kitchen foil, 12mm wide and 150mm long resistor alone was not good attenuated too much never got around winding a trafo and actually dumped the whole thing but this one I have to try
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15th September 2013, 10:16 PM  #28 
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Oh!
Well, standard kitchen foil is about 0.016256 mm thick. So maybe you could just add some length (and/or lower the width) to get a higher resistance. At 12 mm wide, the crosssection is presumably 0.1951 sq. mm. That gives 0.026 / 0.1951 = 0.1333 Ohms per meter! So you really do have only 0.15 * 0.1333 = 0.02 Ohms; basically zero. I'm guessing you don't want to make 15 2meter ones in series, to get 4 Ohms. Let's see, if you cut it down to 3 mm wide, you could get 0.5332 Ohms per meter. Then you'd "only" need 7.7 m to get 4 Ohms. Nope. So let's see, to get 4 Ohms while keeping the same length, it would need to be 4/0.15 = 26.67 Ohms per meter. So the cross section would need to be 0.026 / 26.67 = 0.000975 sq mm. Wow. If the foil is 0.016256 mm thick, then the width would need to be 0.06 mm. Or make it 1 Ohm with a width of 0.24 mm. Ummm... No. Never mind!
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15th September 2013, 10:28 PM  #29 
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nice try, thanks
well, I may have at least one small trafo, just to try the experiment hey, since its only a tweeter, I have some 1A 2x 22V Ccore
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15th September 2013, 10:42 PM  #30 
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Needs to be toroidal .....
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