Jump to content

Inductor tolerance


iso

Recommended Posts

When I measured inductance of my AR2ax crossover choke, it was quite surprise to me to find out that one choke measured 1,6mH and the other one over 2mH. They were supposed to be 1,88mH. However, I measured how much ea choke will weight and unwound enough from heavier one to make weights to be similar. Unwound one measured now 1,72mH. I soldered unwound portion of choke wire to other choke and wound it over to original 1,6mH wiring. Chokes are now at least similar, but 8,5% less than target value. I suppose that this is close enough for 1st order crossover.

This brings me to question how chokes were wound these days? Winding air cored choke to better tolerance should not be too difficult, as core properties should be quite predictable compared to say iron or laminated cores. Similar situation seems to be with DCR of some vintage tweeters, say JBL LE25 and LE26 DCR:s seems to differ quite often 20% from sample to sample, even in pair of similar speakers.

Best Regards

Kimmo

Link to comment
Share on other sites

A browse of the Jantzen and Erse air coils sold at Parts Express shows a range of 1-3% tolerance. I don't suspect this is difficult to obtain with automated winding machinery and the tight tolerances copper wire manufacture can be held to. If you are measuring large differences between two coils in a pair of speakers, it may be due to a short on one of them that effectively shortens the lenght of the wound wire. It happens.

With regard to measuring DCR of vintage tweeters, no surprise there. Stiffining surrounds and/or FF with age could easily alter DCR from original specs - most likely to the high side.

Link to comment
Share on other sites

I don't suspect this is diffults to obtain with automated winding machinery and the tight tolerances copper wire manufacture can be held to. If you are measuring large differences between two coils in a pair of speakers, it may be due to a short on one of them that effectively shortens the lenght of the wound wire. It happens.

I suppose coil winders used rev counters in early 70`s.

Most likely in this case there were no shorted coils as original coil weights mismatched considerably. After rewind chokes tipped the scales at 308g and 312g. Solder joint and heatshrink tubing were most likely reason why overwound coil is somewhat heavier now.

Best Regards

Kimmo

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...