True "variable inductor" wah...

[gmoon]

Hello, everybody! New member here.

Anyone else interested in the variable-inductor thing? When I was researching it, I ran across a thread or two--but not a whole lot.

I've managed to hack one up. Be glad to add more info if there's any interest....

Here's a youtube vid:
http://www.youtube.com/watch?v=lL9ToDSFz0E

[alanlan]

Veeeeerry cool! - I like the woodwork!

[Nasse]

SOunds like shit, my cheap computer came with crappy soundcard they say it is bad on every audio forum and it has autowah better than this, and so does many more... looks like finnish pine, fast grow weak wood shitty q wooden construction

[gmoon]

SOunds like sh*t, my cheap computer came with crappy soundcard they say it is bad on every audio forum and it has autowah better than this, and so does many more... looks like finnish pine, fast grow weak wood sh*tty q wooden construction

Nice. Is this a typical reply here?

[jefe]

Nice. Is this a typical reply here?

No, it is not. Normally, if someone doesn't have anything nice to say, then they don't say anything.

[jefe]

I'm at work, I can't hear it... but I just took a quick look at your vid, the wood construction seems fine to me.

[gmoon]

I'm at work, I can't hear it... but I just took a quick look at your vid, the wood construction seems fine to me.

Thanks. I could post the usual excuses: it's very much a work-in-progress; kind of experimental; something about my chops being rusty, etc., etc., etc.

Buy why bother? I don't have much of an ego about that stuff. I just thought someone else might be interested, and that maybe folks here also discussed projects that were unusual and not "fully formed."

(the unfinished pedal is a combo of douglas fir (base) and rough cedar (range stop in front.) It will get treated to sanding and routing later. No circuitry's been added inside, yet--still protoboarded.)

@ alanlan: 

[Nasse]

I´m just kiddin, but this is serious fx forum...

[Arn C.]

Watched the Youtube,  Nice job on the pedal!!!!

Keep up the cool work!

Peace!
Arn C.

[jefe]

Thanks. I could post the usual excuses: it's very much a work-in-progress; kind of experimental; something about my chops being rusty, etc., etc., etc.

Buy why bother? I don't have much of an ego about that stuff. I just thought someone else might be interested, and that maybe folks here also discussed projects that were unusual and not "fully formed."

(the unfinished pedal is a combo of douglas fir (base) and rough cedar (range stop in front.) It will get treated to sanding and routing later. No circuitry's been added inside, yet--still protoboarded.)

@ alanlan: 

I like your attitude. I never make any apologies for my crappy playing. And half-baked ideas get discussed around here all the time... A LOT. If people only presented their completely finished projects here, with all the bugs worked out... there would be a lot less projects to discuss.

I'll give this a listen later when I'm home.

[kurtlives]

Wow, that sounded real good. Very full, thick throaty and vocal. Seems like it has a lot of "substance" to the tone.

Care to show/explain what is happening inside?

[alanlan]

I´m just kiddin, but this is serious fx forum...

Yes, serious about helping out beginners and experienced folk alike.  Not serious as in "holier than anyone else".

[gmoon]

Thanks, Arn C.

Wow, that sounded real good. Very full, thick throaty and vocal. Seems like it has a lot of "substance" to the tone.

Care to show/explain what is happening inside?

Sure--I should upload images to the "general" pictures gallery?

The inductor was scavenged from an old Wurlitzer organ, and was used in the tuning circuit. It's a typical rotational-adjustment variable inductor. It has a ferrite core attached to a brass rod. With the end tap removed, the core slides easily in / out of the cardboard tube that the coil's wrapped around. There's an outer ferrite housing, too. The inductor's range is 550mH to 72mH (I have a cheapo LCR meter--thank you Hong Kong); the core moves ~1.35 inches.

The circuit follows the Kay W-1 wah--but I couldn't find a schematic, so I had to enlarge online photos of the schematic that's mounted inside. My version is somewhat different, of course--the Kay wah used a 3H inductor (plus I'm guess many of the component values.)

I worked it up in LTSpice, which at least got me in the ball park.

It's really nothing but a preamp feeding a passive LCR filter. Just a single transistor. Could a more effective active filter (NFB loop) be used? Sure! I just haven't gotten there yet...

The pedal mechanism was also scavenged from an organ. With the core moving in / out of the inductor, a "well" beneath the pedal housing was needed--hence the wooden platform. The inductor was "jumping" on the last part of the youtube vid--I was tilting the pedal for photos, and it came "unstuck." Easy to fix.

[Andi]

So the treadle actually moves the ferrite core in and out of the inductor coils? That's very cunning!

Nice sound too. Early on, at least, it had a sort of vibey rather than trad wah sound to it. I liked it.

[aron]

>but this is serious fx forum...

Yes, we are serious about being nice to one another. Please keep the negativity down.

[anchovie]

I´m just kiddin, but this is serious fx forum...

You missed when I came up with the Riot Zone, then...

[gmoon]

So the treadle actually moves the ferrite core in and out of the inductor coils? That's very cunning!

Nice sound too. Early on, at least, it had a sort of vibey rather than trad wah sound to it. I liked it.

Grazie. It's not a unique idea, but not very common, either.

Since the treadle motion is really an arc, neither the coil or the core move in a truly linear fashion. So both are fixed to flexible anchors.



I had a more sophisticated design, but dropped it. This simple approach seems to work so far.

The inductor, unmodified (except it's been removed from the aluminum housing.)



The modified inductor: the delicate parts re-enforced, length shortened, etc.

[gmoon]

And here's a schematic.

More info:


-- Clearly, a very simple circuit.

-- Substituted the rectifier diode for the emitter bias resistor, and like the change. Even tried an LED, which worked also. Paralleling a resistor with the diode (10K or so) is kinda nice, too.

-- The DC resistance of the inductor is pretty high (185 ohms), which certainly effects the "Q". Might try "rolling my own" inductor...

-- Chose the 2n2222 simply because LTspice had the model. Other BJTs would likely be preferable. Not bad, though.

-- LTspice doesn't like 1M (converts to 1m)--maybe there's another abbrev it will tolerate... Until then, 1000K should be clear enough.

[Nasse]

I am sorry about my stupid post. I was too tired when tuning my bottle blow organ, needed to drop the tuning. And my speakers are crap too, listened with another set and it sounds nice. Nice report, thank you.

[gmoon]

I am sorry about my stupid post. I was too tired when tuning my bottle blow organ, needed to drop the tuning. And my speakers are crap too, listened with another set and it sounds nice. Nice report, thank you.

Thanks...and it's water under the bridge, my friend. We all have those days...