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Old 9th November 2004, 01:30 PM   #1
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Default Mic input transformer

Hi guys..

have anyone used the LL1538 mic input transformer from
Lundahl??
The transformer is 1+1:5 and i wonder which
configuration is best for 200-600 ohm mic - the primary in parallel or in series... i guess that each primary has an impedance of 400ohm so parallel will give 200 and series will give 800?
am i correct? and what is better??


thx

here is the link....
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Old 9th November 2004, 01:32 PM   #2
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Sorry... here's the link....
http://www.lundahl.se/pdfs/datash/1538_8xl.pdf
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Old 14th November 2004, 07:40 AM   #3
ulysses is offline ulysses  United States
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Transformers don't have an actual impedance of their own. They only reflect impedances and multiply them by the square of the turns ratio. If you put the two primaries in parallel, the turns ratio is still 1:5, same as if you only used one primary. If you put them in series, then you get 2:5. This means you can have an impedance ratio of either 1:25 or 4:25, which is about 1:6.25. If you assume a microphone source impedance of 150 ohms, then the amplifier will see a source impedance of either 3750 or 937.5 ohms. Likewise, to provide the microphone with an appropriate nominal load, which is typically about 1500 ohms, then you'd have to load the transformer secondary with 37500 or 9375 ohms, respectively.
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Old 14th November 2004, 03:01 PM   #4
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thanks ulysses,

Now I understand thinks better.....
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Old 15th November 2004, 01:02 AM   #5
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Default Re: Mic input transformer

Quote:
Originally posted by udip
Hi guys..

have anyone used the LL1538 mic input transformer from
Lundahl??
The transformer is 1+1:5 and i wonder which
configuration is best for 200-600 ohm mic - the primary in parallel or in series... i guess that each primary has an impedance of 400ohm so parallel will give 200 and series will give 800?
am i correct? and what is better??


thx

here is the link....
LL1538 is OK but fairly colored, you may or may not like that .
Better is the LL7902 or 7903, better still is trannies from Cimag
and the best is probably Jensen. They make a VHQ 1:5 ratio but
you will pay for the quality.

There's also one from Stevens & Billington that Kuei W Y has
had good experience with.

Let me know if you need further info.

Cheers,

Terry
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