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Old 13th May 2011, 07:25 PM   #1
Tyimo is offline Tyimo  Hungary
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Default Lundahl 1676

Hi!

What is the Nominal Z ratio of the LL1676 input transformer?

greets:
Tyimo
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Old 13th May 2011, 07:58 PM   #2
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Really depends on how you connect the windings together.

http://www.lundahl.se/pdfs/datash/1676.pdf
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Old 13th May 2011, 08:43 PM   #3
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The winding ratio is 1+1:2+2 according to datasheet.
Impedance ratio therefore is 1+1:4+4, but note that transformers have no impedance(s).
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Old 13th May 2011, 10:04 PM   #4
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...but don't forget that they have inductances, DC resistances, leakage inductances and stray capacitances, plus saturation inductance limit voltage applied on them on low frequencies, so impedances have to be selected according to this parameters. In quite narrow range, for optimal performances. Never trust sellers of transformers who claim that impedances don't matter.
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Old 13th May 2011, 10:11 PM   #5
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Quote:
Originally Posted by Wavebourn View Post
...but don't forget that they have inductances, DC resistances, leakage inductances and stray capacitances, plus saturation inductance limit voltage applied on them on low frequencies, so impedances have to be selected according to this parameters. In quite narrow range, for optimal performances.
Thanks for completing the story
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Old 13th May 2011, 10:14 PM   #6
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Originally Posted by Wavebourn View Post
Never trust sellers of transformers who claim that impedances don't matter.
Agree!
Please re-read my post if you have any doubt
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Old 14th May 2011, 10:17 AM   #7
Tyimo is offline Tyimo  Hungary
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Thanks, but I asked the Nominal Z ratio .
I think the primary's nominal Z is somewhere between 3K and 4K connected in series.
Am I right?

Tyimo
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Old 14th May 2011, 10:48 AM   #8
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Tyimo,

Once more, the LL1676 has a winding ratio of 1+1:2+2.
Impedance ratios are squared, so a 1:2 winding ratio is 1:4 in impedance terms.
Impedances are determined by the source and/or load, that is what I mean by saying that the transformer has no "impedances". My friend Wavebourn knows exactly what I mean...
For instance, a SE output transformer with 5k to 8 ohms "impedance".
All you can say is that the winding ratio is 25:1, and that the primary will see a 5k (reflected) load when the secondary is loaded by 8 ohms.
This 5k requires a certain amount of inductance.
So you can have transformers with equal winding ratios for different applications (a 5k:8R output transformer for a 300B has the same winding ratio as a 10k:16R for a 211, but otherwise these transformers differ in primary inductance, maximum primary voltage before core saturation at a certain frequency would occur, winding capacities and so on and so on.....).
For the LL1676 you must look at your source / load impedances to see if it is good for your application. When I am right Lundahl specifies primary voltage and inductance, and DC resistances of windings. That should suffice.
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Old 14th May 2011, 11:56 AM   #9
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And also, as noted in post 2, it depends on how you connect the windings. I have the following options:

2:4 step up for an impedance ratio of 4.
2:2 for a ratio of 1.
1:4 step up for a ratio of 16.
1:2 step up for a ratio of 4.

Depending on your signal strength, you may choose 2:4 over 1:2, even though the ratios are the same. You can also use the xfmr in reverse for step down operation.

Beyond that, if you want to know actual inductances, you may want to contact Kevin Carter at K&K Audio.
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Old 14th May 2011, 12:33 PM   #10
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Originally Posted by zigzagflux View Post
Depending on your signal strength, you may choose 2:4 over 1:2, even though the ratios are the same.
With 2:4 (primaries and secondaries in series) there will be 4 times more primary inductance than with parallelled windings, so apart from signal strength also the source impedance is important to notice.
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