Inductors for audio filters


From: David Taylor (
Date: Mon Nov 14 1994 - 06:46:17 EST

In the belief that Toko inductors were not available here, I have been
experimenting with winding high value inductors (100 and 120mH) on toroids
to make the 1kHz lowpass filter for the R2 that was sent to the list by
John K0JD.

However, a search of a catalog from a Sydney based mail order Co. called
'Farnell Electronics' revealed that they stock the Toko 10RB series chokes
in values from 33 to 120mH. I could have saved myself a lot of winding!!

I now have the required values and am putting together the filter to test,
and am wondering what the higher Q of my hand wound inductors will do to
filter performance. My coils are typically 10ohm while the commercial ones
are ~70ohm. I can always reduce the effective Q with parallel resistors.

The filter is a 7th order elliptical low pass filter with f.cutoff of 850Hz
and minimum stopband attenuation of 70dB intended for CW reception.

Interested in any comments.....

72 David VK3JKP

David Taylor
RMIT (Bundoora Campus)

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