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Wah inductor source


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8/25/1999 2:04 PM
R.G.
Wah inductor source
I should mention this here. In the effect article, "The Wild Mouse" in Electronics Now, the author mentions the use of a Radio Shack audio transformer's primary inductance for an inductor. The inductance is 500-600mH, right on for the inductor in the standard two tranistor wah.
 
8/25/1999 2:05 PM
R.G.

'Swhat I get for being in a hurry. The part number is 275-1386.
 
8/27/1999 10:34 PM
AMZ

For anyone who is interested in using this substitute inductor, the part number is actually 273-1380. It is a 1k:8 ohm audio output transformer. Only the 1k primary is used (ignore the center-tap).  
 
 
 
I first saw this part used as an inductor several years ago in a non-audio project, and then decided to try it in a wah. The sound was "okay" but not nearly as smooth and harmonically pleasing as a real wah inductor - but you can't beat it for $2.00. The size isn't that much smaller than the metal can inductor on my Crybaby contrary to what is mentioned in the article.  
 
 
 
I have a few Mouser transformers that I'm testing in hopes that one will perform well in a wah. I'll post my findings at a later date.  
 
 
 
regards, Jack
 
8/28/1999 4:08 AM
R.G.

Thanks for the help Jack.  
 
 
 
The 1386 number is what is printed in the article on the Wild Mouse, which is the source I used for reference. When I picked up one from the Shack today, they told me that they've always been 275-1380's so apparently the article in "Electronics Now" is in error, although the pinout information in my Wah Pedals article is correct as noted.  
 
 
 
In any case, Aron asked for some pictures on how to use these things; that's why I picked one up. I'll be posting pictures of the 1380 showing which leads to use. I'd let you see them now but I left the &*$%#* diskette at the office.  
 
 
 
Yes, since posting the Wild Mouse review and the Wah article I've heard by both email and posting that an assortment of small audio transformers might be in the right range for a wah. The primary inductances should be about right in that range. In fact, now that we know how the wah circuit works in some detail, we can make intelligent tradeoffs between L and C values vesus impedance level and probably get a range of inductors to work.  
 
 
 
By all means, run us a survey and let us know which will work in this application. It'll be a nice addendum to the Wah article.  
 
 
 
I'm not too surprised that the iron cored audio transformers aren't as smooth and harmonically pleasing as a real wah inductor - I would not have thought for an instant that they would. The harmonics of the fabled Fasel wah inductors come from a core material property, as my article states, and I suspect that any smoothness from other wah inductors may as well. Iron is a fundamentally different ferromagnetic material than the various ferrites, and the saturation flux densities and sharpness are different.  
 
 
 
However, the availability of pre-wound transformers with a secondary winding opens the way to some experimentation that might be interesting. Feeding a current source through the secondary winding gives a way to introduce a magentic bias on the cores, and may let us move the iron to a place that has some slope to the BH curve as well as even harmonic generation, as I noted for the Fasels years ago in spectrum tests.  
 
 
 
By the way, Jack, I've been meaning to ask - does signing all your posts "AMZ" increase your web traffic? You think it would help me to sign all mine "GEO"? What do you think?  
 
 
 
R.G.
 
8/28/1999 2:32 PM
AMZ

quote:
"the availability of pre-wound transformers with a secondary winding opens the way to some experimentation that might be interesting. Feeding a current source through the secondary winding gives a way to introduce a magentic bias on the cores, and may let us move the iron to a place that has some slope to the BH curve as well as even harmonic generation"
 
 
 
 
I picked up a couple of the transformers at R-S yesterday as well. I agree that this is a good area for experimentation. I think it might be interesting to shoot a sine wave through the inductor and measure the distortion components, with and without a micro-current flowing through the secondary. I guess you'd have to do that with a Fasel to get a target profile to emulate.  
 
 
 
quote:
"I've been meaning to ask - does signing all your posts "AMZ" increase your web traffic? You think it would help me to sign all mine "GEO"?"
 
 
 
 
I have the function keys programmed with various strings via a keyboard macro program that I have and just got into the habit of using the sig when I was running my message board. I doubt that there's many visitors to this forum who haven't been to both our web pages.  
 
 
 
regards, Jack
 
8/28/1999 6:01 PM
R.G.

quote:
"I think it might be interesting to shoot a sine wave through the inductor and measure the distortion components,"
 
 
Yep, that's the setup I used for the Fasel vs Crybaby test back in 92 or 93.  
 
 
 
quote:
" I guess you'd have to do that with a Fasel to get a target profile to emulate."
 
 
I did. That was the substance of the original test I did. I still have the harmonic profile in my test data, so the test data already exists.  
 
 
 
I've actually done this experiment on a ferrite wound core, but I didn't have access to the proper lab equipment, so the results were equivocal. Sounded pretty good, though.  
 
 
 
The key to the harmonic generation will be the shape of the core material BH curve's knee. Both materials come in a variety of knee curves, so it'll probably depend on who made the inductor under test.  
 
 
 
 
8/28/1999 7:57 PM
Tobias Karlsson

Mr R.G said;  
 
....Feeding a current source through the secondary winding gives a way to introduce a magentic bias on the cores, and may let us move the iron to a place that has some slope to the BH curve as well as even harmonic generation,...  
 
 
 
How do I hook that up?  
 
As I mentioned at Arons place, I have one of those transformers from a modem in my Cry Baby so it would be easy to try this out.  
 
 
 
Tobias Karlsson in Sweden  
 
 

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