measuring crossover inductance, removing winds

[pjpoes]

I don't have a meter that can measure the inductance of something, and I have a pair of .82uh inductors that I need to reduce to .7 or so. I can measure teh DCR, but of course, the difference between the two is so slight I think its a pretty inaccurate way of knowing the inductance. Anyone know about how many turns would need to be removed to get it down, and or any other way to measure inductance. Thanks.
-Matt

[zigzagflux]

I would use a cheap audio amplifier and inject an appropriate sine wave into it. The amp is loaded with the L and probably some resistance. Measure voltage and current of the L.

Do you have a frequency generator, amplifier, and decent meter(s) ?

[pjpoes]

eh I think I will just buy an LCR meter, they don't cost that much. I do have a good meter, but I dont have a signal generator other than this computer and my stereo. I have wanted an LCR meter for a bit anyway.

I also need to order some other parts for the crossovers so I probably will just order the parts I need. I'm glad I measured the capacitors before installing them though. I have a bunch from a different crossover project, and I prefer to combine values rather than buy large one. Combining the two that made the most sense had too much capacitance by almost a full farad. I then combined two smaller values and ended up with almost exactly what I wanted. Much better.

[Theli]

you can use the following to calculate how much you need to unwind:


http://www.lalena.com/Audio/Calculator/Inductor/

[Ron E]

Unwinding my inductor to obtain lower inductance

[Conrad Hoffman]

I've used the formulas in Dickason's book, probably the same ones found elsewhere, and found them quite accurate. Still, for peace of mind, I measure everything. Per the links above, resonating with a capacitor is probably the best way, and you can easily get or measure capacitors to 1%. Just use the PC as a generator and SA, or use a meter to find the peak. I agree that the values aren't that critical, but I still like to hit them as close as possible, and especially to have the two channels matched.

[Inductor]

Hi Matt, all,
I have two ways of doing it,
one, buy a cheap meter (I have an inductance capacitance meter),
the other... well, buy an expensive meter...
both are good for inductances and the first is enough for DIY.
The second is with a much better brand name with good detail in measurements, and also you have a connection to the computer and a microphone for dB's and other software.

To measure speakers you need another kind of set-up though. But that's a different story.