Why don't we use inductors in pedals?

[psychedelicfish]

Why is it that we hardly ever use inductors in pedals? I've seen them in wah circuits, but not anything else...

[artifus]

captains log 2023: 'why is it that i no longer see arduino's everywhere?'

[amptramp]

Inductors can be a pain to design with.  If they are not air core (and thus very large for audio frequencies), they have a magnetic core that can become saturated or permanently magnetized.  They are more expensive and larger than capacitors, which do not have saturation or polarization issues.  Also, they conduct DC, so it is rare to see a coupling inductor.  The series resistance can be a problem in some circuits.  Much of this applies to transformers, the closest relative to inductors, although transformers can be used for coupling.

Some people have built graphic equalizers using inductors, but a gyrator circuit is smaller and more predictable than inductor performance.

[R.G.]

What AT said: for what they do, they're
-big
-heavy
-expensive
-not well controlled (i.e. wide variations)
-not in standardized packages so that each one tends to be special

and another one: you can do the same things smaller, lighter, cheaper, more well controlled, with standardized packages with Rs, Cs, and active devices.

Other than, can't think of any reason at all.

[artifus]

question: why are they often seen in the power supply section of uc circuits?

[rousejeremy]

subbed

[Joe]

One example of an EQ that uses inductors:


You can make a variable inductor also: I don't have an exact circuit but take a small audio isolation transformer for example. One coil has a certain impedance to a certain frequency, but that will drop if enough DC is run through the other coil to make the core saturate.

Not really sure how useful that is though =)

[R.G.]

question: why are they often seen in the power supply section of uc circuits?

Frequency.

Microcontrollers in general operate at MHz, perhaps hundreds of MHz. They are pulling current from their power supplies in pulses at those frequencies. It is a Good Thing not to emit RFI, and in some places a crime to do so. So there needs to be some way to choke off those high frequency pulses.

The limitations of inductors become smaller as frequency goes up. The necessary inductors get dramatically smaller, and so the inductors get smaller, lighter, less expensive, and easier to standardize.

In addition, R-C circuits have one problem - they have to have significant gain far above the frequencies they're filtering in active filters, and up in the high RF range, the active devices run out of the necessary gain. So the economics reverse. Inductors for these frequencies get small, cheap and easy, like resistors. to the economic and design ease motivations for avoiding them get reversed.

Or, as they say, horses for courses. Let the punishment fit the crime. One man's ceiling is another man's floor. One man's fish is another man's poisson.

[artifus]

thanks again 

[Paul Marossy]

I will add that it's not easy to find an inductor that is not a 500mH wah inductor or some small micro-Henry value. Try finding the values in that schematic posted above - good luck! Unless you can have a bunch custom made for you, you're kind of up the creek....

[defaced]

People have ordered samples from Wilco re-create that circuit - not sure if that'll still work, but it's been done.  muRata might have some, not sure.  Others have had custom inductors wound.  Others yet have taken to the active device/R/C (gyrator) approach Amptramp and RG mentioned above. 

Some tools for the gyrator approach:
http://sim.okawa-denshi.jp/en/RLCtool.php
http://www.muzique.com/lab/gyrator.htm

Or skip to the end of the novel and see how a few amp guys did it (sorry, it's an Italian forum, you'll need to translate it): http://www.diyitalia.eu/forum/viewtopic.php?f=22&t=4479
There is definitely some good into in there. 

[Paul Marossy]

Personally I'd rather just go with a gyrator for EQ stuff. Although, IMO, an inductor based EQ does sound pretty good.

[bluebunny]

One man's fish is another man's poisson.

R.G. speaks French!  I've just realised his secret identity!  

[duck_arse]

I've said this before and I'll say it again, I love winding inductors. even toroids.

my collection of wrong value inductors is growing, all the time.

[mistahead]

Just looked over the a few things on knocking up inductors out of sheer curiousity and realised that all of the hours I spent winding crystal radio coild as a kit may pay off!

Actually I've got a couple of old pedal sewing machines in a shed somewhere up north and an pretty reliable supply of electric coil motors that could provide the wire, a little measuring and a little pi and I could probably knock up a rig to pedal wind to length from spool (motor) to bobbin at a few meters per second...

You know it has real mojo because it smells like burned lint and blue-smoke!