Alternative Wha inductors

[Aharon]

Contrary to what The Technology of Whas at GEO states the RS transformer does not work on a regular wha circuit(granted the article does not say it works in a particular circuit).
I've tried it twice in a Cry Baby config and it does not even hint at working.
Does anybody have experience with a particular circuit in which this inductor works?.
Thanks for any help.
Aharon

[petemoore59]

I think I 'do' remem reading how adding another inductor [to the existing one] used an RS transformer...whatever that's good for since I can't remem what it recommended, where it was, or how itwas supposed to werk

[RickL]

Are you sure you had it hooked up correctly? I've subbed a RS transformer directly into a commercial Crybady and it worked perfectly fine. I also subbed one into an old Ibanez graphic eq that used inductors and it worked as well.

[R.G.]

The RS transformer does work in the standard crybaby wah circuit - at least the ones I tried did back when I wrote that, and the ones that several people have told me about.

I'm guessing that you have an accidental short between two of the leads or a load resistor on some of the leads. That would make the thing not work.

The transformer has an assortment of leads. Only the two ends of the primary must be connected for use as an inductor in this circuit. If you have any portion of the primary or secondary windings shorted, the thing will no longer look like an inductor to the circuit.

[Aharon]

I used as shown in the article the green and blue terminals.There was no short among the other wires.The wha worked with another non descript inductor.So I guess I'm at a loss.
Aharon

[Paul Perry (Frostwave)]

Aharon, try all possible windings out, the wire color may not be consistent. The winding giving the highest resistance reading would be the likeliest. And, RS have lots of different transformers..

[zachary vex]

you might want to check continuity on those leads on the xformer.

[swt]

Hey guys!. i wind them using old radio ferrite. You have enough ferrite for 4 or 5 inductors. I'm using 0.1 mm wire gauge, as suggested by stuart castledine from england. I can't remember the resistance i used to wound them, but i do remember making lots of taps to get the sound i wanted. It will also depend on the ferrite, because someones have a hole at the center to attach them, and usually radio's ferrite doesn't. I can't remember which case it was, but one will need more wire so as not to saturate the core. The one with the hole will saturate less under the same conditions, due to the fact that air has less saturation. Will anybody try this and help me to compile facts and numbers for other people??. Thanks a lot!!

[brett]

They not only work - they work great!  To get about the right inductance, go for transformers with about 3k ohms of impedance.  8ohm and 1 kohm won't work and will be way off frequency, respectively.

Just a guess, but I think they work well because they are small and saturate easily, and contain soft iron cores, which may be left with a little residual magnetism (which RG thinks might give some nice asymetric effects).

cheers!

[Manolo Dudes]

Anyone know the RS reference number for that xfrmr?

[R.G.]

You may want to read "The Technology of Wah Pedals" at GEO - it has the part number and a picture of the transformer.

[Aharon]

Well that's he problem then,the one in the article is the same that everyone used for the Bobtavia and it's a 1K/8ohm transformer.
If it has to be 3K that explains it.But as Paul said I'll measure the other leads and try again.The wha works fine with the other little transformer I used but who knows the specs,I've had it in my spares box forever.
Aharon

[Manolo Dudes]

You may want to read "The Technology of Wah Pedals" at GEO - it has the part number and a picture of the transformer.

Sorry, RG... I've just realized my mistake. I have read thoroughly your  article and have made my own version of it with very good results.

My mistake was to think that the "RS" you were talking about was "R.S. Components" (UK  based components retailer) instead of "Radio Shack".  :roll:  

Sorry!  :oops:

[Ygor]

I used small power xformer about 1W, 2x12V primary, both windings in series, out of phase, it works well..

[R.G.]

There's a common misconception about transformers that's hitting you here. That misconception is that an impedance spec tells you anything significant about the transformer outside the circuit it's specified in.

There aren't any 3K or 1K transformers. There are only impedance ratios, as in 3K:500 ohms, or 1K:8 ohms. In fact, the impedance ratio is only true if one side of the transformer is loaded to the rated impedance.

For instance, take the Radio Shack (I should have spelled that out, by the way - sorry I confused the issue) 1K:8 ohm transformer. What the "1K:8" tells you is that if you put an 8 ohm resistor on the secondary side, an AC generator on the primary side will act like it is loaded with 1k ohms for those frequencies where the transformer's imperfections are not mucking things up.

The impedance ratio is just that - a ratio. If you take the same transformer and load it with a 4 ohm resistor, it acts like a 500 ohm load to anything connected to the primary.

What the impedance ratio really tells you is the turns ratio. The turns ratio is the square root of the impedance ratio, as in the square root of 1K divided by 8 in our example. For this one, the turns ratio is the square root of 1000/8= 125 or about 11. For every volt that appears on the secondary, you had to put 11 volts on the primary.

Audio transformers are rated this way because what matters most often in them is impedances and power.

Power transformers are always concerned with voltages, so they're rated directly in terms of the turns ratio. For instance, a 120:11Vac transformer tells you that if you put 120V on the primary, you get 11Vac on the secondary. You'd get 1 volt on the secondary if you put 120/11 or 11V on the primary.  Hey! wait a minute! That's the same as the 1K to 8 ohm transformer.

Yep. It is. A 1K to 8 ohm transformer has the same voltage ratio and impedance ratio as a 120:11 volt power transformer.

So are they interchangeable? Absolutely not.

The power transfomer has been designed for the ability to handle 60Hz signals with 120Vac on its primary - and probably a large amount of power, too. The little radio shack transformer has been design to handle frequencies as low as 300Hz and only a few volts on its primary.

What's the difference? It's in the primary inductance, wire size and resistance, and the corresponding physical size of the tranformer.

The power line transformer needs a much bigger primary inductance to keep the lower 60Hz power line frequency from burning it up. It needs much larger wire to keep from burning up under the higher currents it handles, too. So you really can't figure out what the transformer primary inductance is from its impedance ratio. They're not related.

(note - you CAN figure out primary inductance from power specifications and frequency handling specs, at least a minimum value)

The primary inductance is what is being used in the misuse of the 1K:8 radio shack transformer. It's going to be specific to the power rating of the transformer (about 400milliwatts in this case) and the frequency handling specification.  It's quite possible for another maker's 3K-to-something transformer to have a similar primary inductance, or a wildly different one. Ditto a power transformer.

You put your finger on it all right - another maker's transformer will be different.

[brett]

Thanks for the explanation re truns ratio, RG.  

But what if the impedance specs quoted by transformer manufacturers are for a specific frequency (eg. 1kHz)?  Then you could work out the inductance from the impedance, couldn't you?  (Z=2.pi.freq.L ?).  

Just from scanning lots of specs, it seems that this MAY BE how the quoted Z is obtained.  Not just from the turns ratio, but from the approximate inductance (L above).  If it was the turns ratio, wouldn't they simply quote that?  When the inductance gets up to several hundred millihenries, the associated impedance must be getting important for circuit design.  So isn't that why an impedance is specified?  Maybe it's approximate, but it seems to me that it is likely to be a true impedance, and is related to a true inductance.

In any case, I'd recommend a 3k transformer, and MAYBE a 1k transformer ofr a wah inductor, but I think that you'd be wasting your time with anything under 1k or over 10k.  

Let's test some and see what the relationship is between the quoted inductance and impedances are.  In the meantime, try that 8 ohm transformer in a wah and see how it sounds.