Can anyone measure the value of an inductor?

Paul, congrats on the rebuild.  I'm in the process of building new crossovers for my Model 19's.  I've got a handheld LCR meter and was astounded by how much my inductors were off by, a couple as much as 25%!  The caps were even worse at up to 50%.  No wonder I've needed a balance control on my preamp...  I went all out and picked up North Creek inductors and all of the caps and resistors are within 1% matching. 

I'm waiting on speaker wire to build the crossovers and plan on burning them in with my Paramounts once the soft start kits come out before putting them into the speaker.  My to do list includes Dynamat for the horns, internal bracing and resealing the cabs.  Hopefully my results are as good as yours!
 
"I've got a handheld LCR meter and was astounded by how much my inductors were off by, a couple as much as 25%!"

I am really surprised by that, one, because all of the parts in my speakers were still within 10% and also I wouldn't have thought that an inductor would drift all that much.  I guess I think of them as little transformers where the winding is what matters and that shouldn't age so much.  But I also don't know that much about inductors!  Just curious what would cause an inductor to drift over time or is it possible that, just like the 846A, they changed the crossover values here and there with the Model 19 while tweaking and didn't publish it.  That was why I was so curious to measure the value of my inductors.  I have read that this specific crossover for the 846A is often found with widely varying values that have nothing to do with drift, so I wanted to know if mine matched up to the schematic or not.
 
Inductors don't drift, but their measured value (if they have a non-air core) will vary with frequency and measuring current. And with exactly what is measured, since the terminal impedance is a combination of several things with different phase angles - some measurements sort these out differently from other measurements. The long-winded answer I wrote, which got lost (see my previous post) went into excruciating detail - probably a good thing it was lost!

Bottom line, never trust an inductance measurement unless you know an awful lot about it and the device being measured! I have a simple-minded choke checker which I use for plate and power supply chokes, and it regularly reads 10% to 30% lower than proper, carefully made measurements done with good instruments. Since I expect that error and have confirmed that it is always with that range of error, it's still useful to me - but it's sure not accurate!
 
As PJ said, I don't have the right tool ;)

I read somewhere that the tolerances with the Altecs was lower than 10%.  For some reason 25% comes to mind but I'm probably wrong on that too....
 
johnsonad said:
As PJ said, I don't have the right tool ;)

I read somewhere that the tolerances with the Altecs was lower than 10%.  For some reason 25% comes to mind but I'm probably wrong on that too....

I got the results from Paul.  They are low by about 25%.  I think you got it right.
 
Grainger,

Yes, they are low, but at least they are quite close to each other.  I ran the test many times on each and got very consistent results.

I had been thinking of selling this little gadget and the software, but no way I'm doing that now -- this thing is just too cool.  I'm going to have to ressurect mycritical headphone cable project.

-- Jim
 
Glad to know I'm not completely crazy ;)

Finished one crossover last weekend and am working on the second now.  Attached is a pic for size reference.  Just a little difference is all :)
 
No joke! I had thought of using the same layout as the original but the heat sinking factor of the large gauge wire made it difficult to solder. I picked up a hydraulic crimper from harbor freight and put 8 tons of force on the crimps instead :)
 
If that's directed at me, I'm using Mogami 12g OFC speaker wire from Redco.com.  They have a great selection of wire for decent prices (no affiliation of course).  I've been using the Mogami wire as speaker wire (and interconnect) for years now and am happy with the sound of it so thought it natural to put it all the way through the system. 
 
Back
Top