Inductors in Tone Controls

[Paul Marossy]

Can't respond to this in the old forum, nor did I see it on this new one... 

Hey Paul,

Thanks so much for the info! Those 600mH's would make ideal wah inductors, but I agree with you on the sound of the EQ: the 5-band (same circuit I'm pretty sure) sounds so good to me I thought it worthwhile to upgrade the power supply and all the EQ and coupling caps. I call it the Poor Man's Pultec.  I'll have to keep my eyes peeled for that 7-band version. Thanks again and much obliged!

Mine is actually a 10-band EQ BTW. Yeah, they're really not that bad for a cheap EQ.

did you use a pro LC meter for those values? those things are expensive

No, they're labeled right on the inductors. How easy is that?! 

[JHS]

I like inductors in wahs but not in tonecontrols. I think it's wasted time to search for the "right" inductors for an EQ or tonecontrol, it's way easier to emulate them with gyrators. All you need are 3 Rs, 2 Cs and a NPN-tranny or IC for each inductor. I use a small programm for designing the gyrator. The inductor and filter parameter are the input and the Rs and Cs the output,very easy to use.

In the past it was hard to design a gyrator and it took a hell of time due to the itterating calculation method, but now with the software it takes only about 2 or 3 minutes.

JHS

[Joe Kramer]

Mine is actually a 10-band EQ BTW. Yeah, they're really not that bad for a cheap EQ.

Ah, I got it now.  I believe I've seen that one around too--it's rather large, about the size of a standard stereo receiver.  That's what the 5-band looks like only about half as long.  Thanks again Paul.

Joe

[skumbeg]

What is the program you use?  Sounds interesting.

[wampcat1]

What is the program you use?  Sounds interesting.

I'm interested too, JHS - what program are you using?

bw

[Seljer]

I remember this thread from just a while ago: http://www.diystompboxes.com/smfforum/index.php?topic=47296.0

[RaceDriver205]

What about those Resistor sized RF chokes, would they work in an EQ?

[disantlor]

I think it's wasted time to search for the "right" inductors for an EQ or tonecontrol, it's way easier to emulate them with gyrators.

Don't tell that to the folks over at manleylabs.com,

http://www.manleylabs.com/containerpages/masspass99.html  (yikes!)

[Rob Strand]

> What about those Resistor sized RF chokes, would they work in an EQ?

They work provided you can take into account the relatively high DC resistance.

Take a simple EQ, like the type where the inductors can be replaced with gyrators.   If the original circuit used an inductor with a DC resistance of 10 ohms and the circuit has a  47 ohms resistor in series then the total series resistance is 57 ohms.   So if you use a physically smaller inductor it will have a higher DC reistance say 25ohm and you will have to change the series resistor to 57 (total) - 25 (used inductor) = 32ohm.    If you used a very small inductor which had a DC resistance of 100ohm then you can't get the circuit to work the same as it did before  because you cant decrease the 100ohm to get the target of 57ohm.

In some circuits (particulary filters) you don't have the luxury of adjusting a series resistor.  In these cases you need to simulate the behaviour of the circuit to see whether the inductors resistance is going to modify the circuit's behaviour too much.

The other problem is a lot of schematics don't show the DC resistance of the original circuit.  In this case you can't always know intended behaviour of the the original ckt and so you can't really judge what inductors can be substituted  (with analysis it's possible to make good guesses but that just avoids crap, it doesn't work out what the old ckt did).

[RaceDriver205]

They work provided you can take into account the relatively high DC resistance.

Good point!