Hi all..
i always wondered why wah inductors HAVE to be around 500mH, even when is commonly known that it is a LC filter..

why nobody designed or tried (AFAIK) a different inductor value for wah´s and changed the other components of the filter to fit the frecuency band needed?? theoretically..it should work..

what do you think about it?

Impedance scaling and availability of good capacitances.

You are correct in that any* inductance can be resonated at any* frequency by some value of cap. However, the real world limits you in that to get the inductor and capacitor to work in a real circuit, the impedance of the inductor and cap which resonate have to lie within certain bounds. First, you have to be able to find a real capacitor that is stable in value (therefore, not electrolytic) and of an appropriate size to go in a pedal. Next, your inductor has to resonate the available caps AND both inductor and cap have to have an impedance at slightly off-resonance that works with the transistors in the rest of the circuit.

For the components available to the original wah designers, 0.5H inductors and 0.01 caps were a good solution. But there is no perfection embodied there. At some point of making the inductor smaller - which is typically what a modifier wants to do - the caps get out of hand.

* In this context, 'any' ignores certain practicalities, like inductors having resistance which spoils resonance, and inductors having self-capacitance, which means that they can only be lowered in frequency by adding capacitance, things like that.

hmm..
i made some calculations, and you can make the inductor as small as 0.05H..that´s 5000uH wich can be found on any decent electronics store cheaper than a TL072 IC.. even 5 1000uH in series are cheaper than an IC.. 

that inductance with a 1uF cap makes the same resonant freq as the classical combination..and is not hard to find 1uF film or ceramic caps that fits on a pedal..

i think is worth trying, since the inductor is the bigger obstacle to build one (if you get a decent rocker pedal)

This sounds like a good idea. What are you using for your calculations?

the classic LC resonant freq formula:

F= 1/ 2*Pi*sqrt(L*C)

Duh!

Damn i have to learn to simulate circuits with LTspice.....
well..i rather ask you guys!! is nice to interact with RG and aron!

Hi
Using transformer and hand-wound coils (on ferrite and iron), I've messed with differnt L and C values, but nowhere near as low L values as you are talking about.

Quoteand you can make the inductor as small as 0.05H

My main question is whether you can maintain the "saturation" losses and "ringing" distortion that big inductors provide.  Clearly, air-core inductors will be different to ferrite conductors.  On the other hand, you might improve on the standard design!  Certainly, despite them being fairly dissimilarity from the "proper" inductor, the primary coil of those little 1k:8ohm output transformers makes a rather good wah inductor, as long as you adjust the cap a bit. (From memory, the ones I've tried resonate at slightly higher frequencies than a standard inductor when coupled to a 0.01uF cap, but with a 0.015 uF cap they worked well.  At least that's what I think happened. ?)

This is such a good idea.  Go for it and let us know how it all works out.

cheers

Before I got into making devices, I was off into speaker building.  Almost all Hi-Fi speakers have 2 or more inductors in the crossover network.  Might check out Madisound or Zalytron, or crossover networks for info on inductors.   

I built myself a little machine to wind inductors and it works a treat. Does conventional bobbin winding, random winding and low-capacitance honeycomb winding. Playing around with inductors gives far more interesting results than varying the capacitance with a fixed inductor value. There are a lot more variables than just the inductance that have an effect on the sound. You can also make the inductor tunable with different slug materials such as Iron, ferrite, brass and a lot more.

It's Called the Gingery coil winder and will do pickups too.  Takes a bit of effort to make, but is an interesting project in itself.

Quote from: Mick Bailey on April 18, 2008, 04:03:46 PM
I built myself a little machine to wind inductors and it works a treat. Does conventional bobbin winding, random winding and low-capacitance honeycomb winding. Playing around with inductors gives far more interesting results than varying the capacitance with a fixed inductor value. There are a lot more variables than just the inductance that have an effect on the sound. You can also make the inductor tunable with different slug materials such as Iron, ferrite, brass and a lot more.

It's Called the Gingery coil winder and will do pickups too.  Takes a bit of effort to make, but is an interesting project in itself.

sounds interesting..but how do you measure the inductance?

You can get tables for given wire sizes, number of turns etc. The instructions for building the machine came with some guidance but with a little experience you can get fairly close to a particular value. A multimeter that measures inductance would be quite useful to check the exact value as you progress. Measure from the free end at the beginning of the winding to your current position by using a needle to pierce the insulation.

Тоже думал об этом. Даже экспериментировал. И в ЛТ-спайсе, и в железе. Формула резонансной частоты что-то типа 2пи LC^1/2 теоретически верна, но на практике малые L и большие C "жрут" сигнал в ПАРАЛЛЕЛЬНОМ КОНТУРЕ. В последовательном - наоборот. А в параллельном представь - увеличишь ты раз в 100 C и во столько же раз уменьшишь L. Резонансная частота останется та же но сигнал любой частоты будет гораздо охотнее проходить через такую БОЛЕЕ КОРОТЯЩУЮ цепь. Повторюсь - при последовательном контуре было бы совсем наоборот. Но в любом случае надо ловить этот пресловутый "свит спот" - соотношение сопротивления выбранного контура на резонансной частоте с сопротивлением R активных компонентов входящих в состав всей схемы.

Uh... I don't think anyone here knows how to read cyrillic.

Quote from: Mick Bailey on April 18, 2008, 04:03:46 PM
It's Called the Gingery coil winder and will do pickups too.  Takes a bit of effort to make, but is an interesting project in itself.

It's not that hard, Mick!

But seriously, if you are a hard-core DIY-er, be it coils, inductors, pickups or even chokes, this is a must-have device in your little lab of horror.

Quote from: Paul Marossy on April 20, 2008, 07:30:05 AM
Uh... I don't think anyone here knows how to read cyrillic.

Give me enough vodka and I speak it , though... 

Hi
for measuring inductances, try this:
http://www.diystompboxes.com/smfforum/index.php?topic=55093.msg422809#msg422809

cheers