Inductance of wirewound sand cast resistors

[Amphiprion]

Praxis was giving me problems today while I was taking some T/S measurements, so I set up a simple resistive divider using a 1/4W 100 ohm 1% metal film resistor and a 25 ohm 25W sand cast resistor from Madisound. This eliminated the driver from the equation so I could see what was really happening with my setup. But it also made for a chance to measure the inductance of the wirewound resistor since I had a nice metal film to measure it against.

Here's the measurement from Praxis of the 25 ohm 25W wirewound sand cast. Markers are set at ~20Hz and ~25kHz. Measurement taken with Praxis and an Audiophile 2496 sound card (set to 96kHz sampling rate).

Also, CAIG Deoxit works wonders - I'll shortly be cleaning all the contacts in my system with it. It fixed my Praxis issue real quick.

[---k---]

Mark,
I basically slept through my one electrical engineering course and forgot everything else. So help me out. I'm looking at that graph and thinking it looks perfect - flat and 25 ohms all the way across. Is that the point, or did I miss something?

[Amphiprion]

Yep, that's the point. No inductance of any significance for a cheapie no-brand sand cast from Madisound.

[---k---]

I thought that was the point you were making.

You got a PE one to test? A while ago, someone had smashed one and posted pictures of it, and was complaining it wasn't good. I don't remember.

[JonP]

Heh... here we go again...

I seem to remember some trolling like thread about that some time back.

Something like "the more expensive non-inductives aren't any less inductive than the cheaper ones... Ripoff!!" And we're talking something like $1 and $2 resistors... :roll:

I did measurements on various kinds of power resistors with a $3K Hioki LCR meter we have at work... they all were very low in the inductance department. Like single digits to 10's of microhenries. Not millihenries, MICROhenries... That could matter for RF, but for our way down low, near DC Audio Frequencies... it's nothing.

Seems the inductance of wirewounds that are of small value, (like we use for crossovers) is so small you don't really need the "non-inductive" wound ones. If you had a 10K or 100K power resistor with hundreds or thousands of turns, you'd have inductance enough to warrant the counter wound non-inductive types that reduce it...

[---k---]

Heh... here we go again...

You're probably right. Luckily, we have Thomas's iron fisted moderation.