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Old 24th April 2013, 03:12 AM   #1
DDF is offline DDF  Canada
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Default Power Resistor Inductance Measurements

I was asked about power resistor inductance and whether it's an issue in spaker crossovers or not. I ran the MLSSA through its paces on some items in my parts box in the past, I think the attached tells the tale.

Thought I'd share it here.

Dave
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File Type: pdf Resistors- Wirewound Inductance Measurements.pdf (82.3 KB, 134 views)

Last edited by DDF; 24th April 2013 at 03:38 AM.
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Old 24th April 2013, 03:30 AM   #2
DUG is online now DUG  Canada
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Interesting...any "non-inductive" wirewound available?
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Old 24th April 2013, 03:43 AM   #3
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Originally Posted by DUG View Post
Interesting...any "non-inductive" wirewound available?
Yes indeed, for example the Dale NH series. Mills resistors claim non inductance as well.

Unfortunately I had neither available to measure.

Dave
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Old 24th April 2013, 04:50 AM   #4
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Noticed a silly typo (gain vs loss) in the previous file, please use the attached. No changes to data or conclusions
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Old 24th April 2013, 06:43 AM   #5
system7 is offline system7  United Kingdom
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Very interesting, Dave. Nothing like actually doing it, eh?

Am I right in thinking the tale it tells is not to fret about inductance in wirewounds or metal film? This was something that bothered me when I used them in amplifiers.

A few uH is nothing compared to the typical 0.05mH Le inductance of a tweeter.

It makes sense. Resistors are designed to be used at much higher frequencies than we ever use in audio. The double winding technique is designed to cancel out most coil inductance. I had a look at some cables too, and again the self and mutual inductance was an order of magnitude lower than tweeter inductance even with 10 metre runs at audio frequencies.
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Old 24th April 2013, 02:05 PM   #6
AllenB is offline AllenB  Australia
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I like studies like this. When I remember that I used to trim my speaker cables to equal lengths

Thanks Dave.
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Old 24th April 2013, 02:06 PM   #7
DDF is offline DDF  Canada
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Originally Posted by system7 View Post
Very interesting, Dave. Nothing like actually doing it, eh?

Am I right in thinking the tale it tells is not to fret about inductance in wirewounds or metal film? This was something that bothered me when I used them in amplifiers.
Hi Steve,

Interesting thing is that none of these even had the non-inductive wind (where the wire is folded back and then wound clock and counterclockwise simultaneously to canel inductance).

The way I like to look at it is that for woofers or mids, the self inductance of these has absolutely no quantifiable impact. For tweeters, at most its equivalent to changing toe in of the speaker maybe at most a degree or two.

I modeled the Vishay RH-25 inductance for the speakers I posted earlier in the week. It affected the response at 10kHz by at most 0.03 dB. I'm sleeping prettty soundly with the choice.

Dave
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Old 24th April 2013, 05:40 PM   #8
fpitas is offline fpitas  United States
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Makes sense, but I'm sure someone can hear the effects of that extra inductance. Even if it's inaudible
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Old 24th April 2013, 05:54 PM   #9
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Quote:
Originally Posted by DDF View Post
Noticed a silly typo (gain vs loss) in the previous file, please use the attached. No changes to data or conclusions
A very nice effort, thank you for posting.

There is no such thing as inductance (external) of a straight piece of wire. A straight piece of wire will have 15 nH per foot internal inductance, but not external. What you measured was the inductance of the complete circuit loop including the wire being measured. A 3 foot length of any wire should have measured 45 nH, not 1270 nH.

More apropos would be the measurement of lengths of zip, as that should be in the 180 to 200 nH per foot range.

jn
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Old 24th April 2013, 07:27 PM   #10
DDF is offline DDF  Canada
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Originally Posted by jneutron View Post
A very nice effort, thank you for posting.

There is no such thing as inductance (external) of a straight piece of wire. A straight piece of wire will have 15 nH per foot internal inductance, but not external. What you measured was the inductance of the complete circuit loop including the wire being measured. A 3 foot length of any wire should have measured 45 nH, not 1270 nH.

More apropos would be the measurement of lengths of zip, as that should be in the 180 to 200 nH per foot range.

jn
18 gauge diameter is 0.1024 cm, from
American wire gauge - Wikipedia, the free encyclopedia

Plugging that into a wire inductance calculator assuming approximately 90cm length:
Inductance of a Straight Wire: A Calculator

Expected result is 1334 nH. MLSSA measured 1270nH, pretty close.
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