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Old 14th July 2008, 08:34 AM   #11
jzagaja is offline jzagaja  Poland
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Dear Bear,

Quote:
Not enough turns by a factor of maybe 100 or more?
Usually secondary is 6-10 turns and primary is 60 turns. If measured impedance is 4Ohms (bottom graph) than I don't need more turns isn't it?

Top graph is SPL plot.


Quote:
You need coupling between the two windings.
Can you write more?

Usually the biggest problem is to find a good wire. At the moment I'm using some from coils found in TVs.

Should we use Farraday shields between windings? As I understand it is a thin foil with metal layer.

Low efficiency indicates that ribbon contats plus wire has impedance maybe too large compared to the transformer secondary.
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Old 14th July 2008, 08:39 AM   #12
jzagaja is offline jzagaja  Poland
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Quote:
I know folks like Lindahl and others sell amorphous core
transformers, but I am only finding them for tube amp outputs, ribbon microphones and interstage applications. None for ribbon speaker matching.
Sowter makes excellent 9385 ribbon speaker transformer but it cost 114.65 UKP plus tax and shipping.
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Old 14th July 2008, 09:36 AM   #13
Bazukaz is offline Bazukaz  Lithuania
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Quote:
Originally posted by jzagaja
Dear Bear,



Usually secondary is 6-10 turns and primary is 60 turns. If measured impedance is 4Ohms (bottom graph) than I don't need more turns isn't it?

Top graph is SPL plot.

Amount of turns required cannot be calcululated from impedance only. The lower the frequency , the more turns you need to get the same power on the same core. This is because core material is saturated at lower frequencies. The larger core is , the harder it saturates. It is impossible to say if 60 turns is enought without knowing what is the input voltage , lowest operating frequency, and core properties.

Imput vs output volatage is directly proportional to primary/secondary number of turns ratio( N1/N2 = V1/V2).
For example , if you have 60 turns primary and 6 turns secondary the ouput voltage will be 10 times less.
The reason for low effieciency may be to thin wire(much energy is lost in copper) , incorrect turns ratio or something else. Enamel wire should not be wound directly on core since sharp edges can damage insulation.
There is a transformer calculator online at :
http://www.bcae1.com/trnsfrmr.htm

Audio transformers are not so easy to make and I suggest you carefully reading basic operation principles before rushing to make something that works.
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Old 14th July 2008, 01:45 PM   #14
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There is an article that can be found in an old 50's or 60's vintage Wireless World Magazine that decribes the construction of a ribbon tweeter, and the specific construction method for a matching transformer...

Radiotron Designer's Handbook 4th ed. also has a useful chapter on basic transformer winding techniques for audio. There are multiple online resources for transformer theory and practice as well.

I suggest, read, experiment, learn, read, experiment, etc...

The source of the wire is not so important, fwiw, just that you have enough and of about the needed gauge.

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Old 14th July 2008, 08:58 PM   #15
jzagaja is offline jzagaja  Poland
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Now wire is over the gap for both secondary and primary. I've changed primary wire from very thin to standard signal wire, 1mm diameter. Impedance dropped with DC resistance. This part I don't understand. I look for higher impedance like 4 or 8 Ohms. Does it mean I need a lot of copper? Comparison with last wound appended.
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File Type: gif impedance_2.gif (10.7 KB, 162 views)
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Old 14th July 2008, 09:03 PM   #16
jzagaja is offline jzagaja  Poland
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And look.
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Old 15th July 2008, 09:23 PM   #17
jzagaja is offline jzagaja  Poland
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Transformer can be designed with inductance related to one leg of a 4th order xo or to have built-in high frequency shelving for an acoustic lenses. When I replaced magnetic wire with AC mains cable (larger diameter) then I saw a big rising impedance curve. Measured SPL (MLS) and distortion (stepped sine, 1/6oct) appended. Have no idea why such a large inductance, maybe thick cable insulation?
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Old 16th July 2008, 06:59 PM   #18
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Hi,

Not directly related to the subject, but I wonder is that an AP or what software did you use to measure this? Grapsh look nice.
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Old 16th July 2008, 07:25 PM   #19
jzagaja is offline jzagaja  Poland
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It is Arta Software, cheapest, popular application but very powerful. With balanced soundcard like Digigram VX it's perfect for a home constructor.
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Old 16th July 2008, 07:53 PM   #20
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ok thanks, I must admit I feel a bit silly as I use ARTA myself almost every day, but did not recognise it... *blush*

Thanks anyway :-)
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