Why shouldn't I use inductors to build passive tone control circuit?

Can you post a schematic of your circuit? What source and load impedances did you design for / test with?

Part numbers?

Are you sure they aren't 40 micro Henry? I have trouble believing that you're getting that much inductance in that small of a package, and if you are I have trouble believing that your DC resistance isn't through the roof.

At 80Hz a 40 mH inductor would have an inductive reactance of 20 ohms, which means that you would have to have a DC resistance significantly below 20 ohms for the thing to be at all useful. Such an inductor would be pretty darn big -- I'd be surprised at anything less than a few cubic inches, and if you showed me something that weighed 20 pounds I wouldn't be surprised.

Thanks for your help. I admit I didn't really concern myself with that aspect at this stage, When I tested it with LTSpice it seemed to do exactly what I wanted so I just went ahead, intending to use a solve impedance problems later. I don't know what load LTSpice assumes for it when I run the simulation. In the event it was placed in the pre-amp out/power-amp in path of a standard Hi-Fi amplifier.

As you will have realised by now I am a complete novice. Please accept my apologies if this stuff is annoyingly basic. Thanks again

Francis Elers.

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I actually had to use a 22 and an 18 in series. I just checked the Futurelec invoice and it says 18000 uH and 22000 uH (but the Greek Mu symbol) so I think they believe they sent me the right ones since 18000 micro is 18 milli, isn't it? But as I say they are suspiciously small - no more than 1/2 inch largest dimension.

Many thanks for your help,

Francis Elers

What's the DC resistance?

Hello Sir,

Francis.

You might add that bit of info to your simulation and see if it then agrees better with reality.

"Francis Elers"

For that job you really must use a " gyrator " - can be just one op-amp, two Rs and one C.

For 80 Hz, I suggest you go for a lot more than 40mH too, more like about

..... Phil

Well, inductors are prone to picking up hum etc.

Also they have poor tolerance and may be quite non-linear. Use active filters.

Graham

Thank you all very much for your help. I investigated gyrators and SPICE modelled a circuit with one and it seems perfect so I'm going to read up on that solution and forget about inductors for this project.

Much appreciated,

Francis Elers.

I saw the (binary) schematic you posted. Note that most servers don't allow binary attachments in s.e.d. Use

You had 30 ohms + 40 ohms in series across the source. Few audio line outputs will drive such a low impedance.

Thank you. I am very unclear generally about source/load impedance and how to modify (buffer?) it if it is not naturally what you need it to be. I will read up on this as I am beginning to realise that it is essential. Thanks also for the tip about posting binaries

Francis Elers.