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
 

Attachments

  • Resistors- Wirewound Inductance Measurements.pdf
    82.3 KB · Views: 451
Last edited:
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. :cool:

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.
 
  • Like
Reactions: 1 user
Moderator
Joined 2008
Paid Member
I like studies like this. When I remember that I used to trim my speaker cables to equal lengths :eek:

Thanks Dave.
 

Attachments

  • r.jpg
    r.jpg
    63.7 KB · Views: 607
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
 
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
 
Another place in audio that resistor inductance is significant, is loudspeaker crossover networks.
Values used in crossover networks are usually between 1R (tweeter L-pads) and about 22R (shunt RC across woofer)
This range does not require too many turns and hence has small values of inductance (10s of uH), that just will not be significant at 20kHz
 
Values used in crossover networks are usually between 1R (tweeter L-pads) and about 22R (shunt RC across woofer)
This range does not require too many turns and hence has small values of inductance (10s of uH), that just will not be significant at 20kHz
Maybe yes, in comparison to other factors in the system affecting the overall sound but I have been comparing different makes/types of resistors (and paralleled to the same value) for a couple of years and found that each type and make do have an affect on the sound - whether in a shunt, L-Pad or just in series.

I expect a lot of people will jump on this now and say 'where are your measurements?' - I have made some but I don't think the inductance value is the only factor and the real proof is in the listening. There is more at play than just pure inductance. The materials design and contrustion of a resistor type affects the sound - it does in my system at least.

The resistors I have been comparing are all modestly priced - std white ceramics, metal film/oxides, 5W carbon film (tweeter filter only), Ohmite Audio Gold, Jantzen Superes and Mills MRA.

I would say that some resistors will suit a particular design (or position within a crossover), where maybe another resistor (type or make) will suit another. I hear the differences - maybe these differences are not so clear in a different system, but they are there.

My favourites for use in crossovers are the Ohmite Audio Gold for the quality to cost ratio but they don't necessarily suit all situations. Unfortunately I could not afford to compare the Dueland or Path Audio ranges.

For those who disbelieve, I am happy for you to visit me in the Midlands, UK, and I will demonstrate the differences - my crossovers are external on a board (not covered at present) so easy to swap out components. PM me if interested.
 
Last edited:
I expect a lot of people will jump on this now and say 'where are your measurements?'


Yes. Few resistor threads were closed and supporters were bullied by the unbelievers :D. Very unfortunate. A resistor can make or break a great sounding system. But I also cringed when the supporters are supporting $$$ resistors. The true test of listening ability is that you can find cheap resistor that will outperform a lot of $$$ resistors. You know it because you can hear it, not because it is expensive (which will have some perceivable advantages of course).
 
I would like opinions on why a lot of people say carbon film caps are a no no in crossovers though. I have tried the Kiwame 5W carbon films in the L Pad parallel position for the HF and don't hear any adverse issues.

They appear to open the sound a bit (that's just my opinion of their affect in my system before anyone jumps down my throat).
 
I would like opinions on why a lot of people say carbon film caps are a no no in crossovers though. I have tried the Kiwame 5W carbon films in the L Pad parallel position for the HF and don't hear any adverse issues.

They appear to open the sound a bit (that's just my opinion of their affect in my system before anyone jumps down my throat).

I have never heard people say carbon film resistor is a nono. I have used it for crossover too. Allen-Bradley is also my preferred resistor for output emitter resistor. It is not to be used in feedback and almost anywhere else in an amp.