[sdiy] filters, inductors & Q

[JH.]

> The good reason 'not to', is the expense & the size and the weight
> and the comparative unobtainability.

Toko inductors are quite affordable and available, and Gyraf use them to
build
passive (with tube makeup gain) equalizers.

I plan to build something like this in the near future as well.

Can't say much about pro's and con's yet - I'll try and listen and see if
I'll like it.

Generally, it's easy to get fairly good inductors in the mH range, up to
100mH.
This means you need low impedance circuits (600 Ohm ...) to make good use
of them in midrange filters. If you want to go low frequency, or high
impedance,
you need more Henries, and that normally means specialzed inductors that
have their price. See www.sowter.co.uk for instance.

I have a Neve input channel clone here on breadboard, and themain things
missing
are a multitapped inductor for mid equalizing, and the output transformer.

Back to the Toko's, apart from running low impedance it would be good to run
them
low level, too, in order not to overdrive them. This might (might! -
actually I don't know yet)
problems with hum from mains trafos, so what I plan is putting a handful of
Toko's
into a small  mu metal enclosure, pot it up with epoxy, and use that as an
inexpensive
multi-tapped inductor such as you need them for passive equalizers.

10k : 600R input transformer, passive EQ, and then a tube amp for gain
recovery
looks like a fun project!

JH.