Yet another wah problem

[danymal_X]

Starting with a Dunlop GCB-95, after adding a yellow Fasel from Aron's store and making a few of the modifications found here: http://www.stinkfoot.se/andreas/diy/mods/dunlop.htm, I ended up with a pedal that is half Wah, half volume... when I rock the peal back I get a really nice sounding wah for not quite half of the travel of the pot... the rest of the way just gives me a complete loss of volume.
When I was working on the project the wires on the pot broke off, and I had to resolder them, but I'm pretty sure I got them in the right place.. (yellow=ccw, blue=cw)
Putting a meter on the pot gets a reading of right around 90Ω at the point where the effect drops off.
The readings at the components I changed are what they should be.
I havent got a new pot to put in, but I guess it could be time to upgrade to a Hot Potz II or something better. (BTW, what is better?)

At any rate, what little wah I do have sounds pretty good, but unfortunately even trying to adjust the pot in the bracket and turn the gear so that I get the most of the effective travel still leaves me with half wah, half volume.

Could this be just a bad pot, (can a pot go half bad?) Or did I maybe miss something in my mod project? Bad inductor? I dont have a meter that reads inductance, (At least i dont think it does)  is there any other way to test it? Measuring resistance across the 68K resistor and also the inductor gives me about 17-18Ω (the Dunlop site says I should have less then 100Ω for this reading.)

Any help/suggestions are greatly appreciated in advance.
Thanks
Dan


The mods I did are (in order):
-3dpt switch
-remove buffer section
-replace 33K resistor in parallel with inductor with 68K (Vocal)
-replace 1.5K with 2.7K (Midrange)
-replace 68K input resistor with 47K (Volume)
-replace .01μF cap with .047μF cap (Sweep Range)
-replace 390Ω Resistor with 330Ω resistor (Gain/Bass)
-replace inductor with yellow Fasel

[jakenold]

Try reverting some of the mods. I think the sweep range-cap is very high! I have installed a 3-way switch on mine, to switch between 0.0068uF, 0.01uF and 0.013uF.

0.047uF is pretty deep in my oppinion.

[danymal_X]

Actually, I have gone back and reverted and re-reverted most of the mods... both before and after this new problem developed. I will actually probably put the 1.5K resistor back in anyways. I like the original sound of that a bit better.

In fact that cap is the first thing I thought of... I replaced it with the original value (same cap, actually,) then a .015, and then put the .047 back in. all of the Mod tips I looked up showed anywhere from .01 to .068
I went with .047 because I also use this same wah for my bass. It seemed to be a good middle ground. (According to the mod pages, the Hendrix wah uses a .022 and the bass wah uses a .068.)

I was plannig on doing the selector switch thing too, but not until I figure this out... I may just end up building a new circuit from scratch eventually with all kinds of fun switches.

Dan

[jonathan perez]

.047 is low, dude. and that may be your problem, indeed.

resolder everything, change the battery, and make sure you put THE RIGHT VALUE RESISTORS in place.

[danymal_X]

Midway, while I do appreciate your input, I'd just like to say that I have in fact checked my solder joints, the values of the resistors I've changed as well as tried several different values of caps, even putting the original back in. I wouldnt have posted until I had at least done some basic troubleshooting on my own...
FYI, this is where i got the cap value from... I'm not trying to be difficult, but according to both of these sources, a cap somewhere between .022uf and .068uf would best meet my needs, as I use this same wah pedal for my guitar and basses:

From Andreas Möller's mod page: http://www.stinkfoot.se/andreas/diy/mods/dunlop.htm

Lower range: The 0.01uF cap controls the frequency range. A lower value shifts the wah higher in frequency, while a higher value lowers it. To shift the wah downwards (using more of the woofy bassy wah sounds), try a 0.015 or 0.022uF cap here. BTW, that cap is the only difference between a GCB-95 and a modern JH-1 Jimi Hendrix wah... the JH-1 has a 0.022uF here, instead of the 0.01uF in the GCB-95. Also, if you come across a bass wah cheap, buy it - you only need to change this cap to turn it into a guitar wah (or the other way around)! The standard bass wah uses a 0.068uF cap in this position. (Thanks to Matt Parlane for providing the bass wah value.)

And:

From - Stuart Castledine's (wah-wah.co.uk) DIY Wah Mod page:  http://homepage.ntlworld.com/s.castledine/greenfuz/wah.html

Sweep Range
Change the sweep by swapping the 0.01µF cap between the emitter of Q2 and the inductor. A smaller value will make the wah sweep more trebly and vice-versa. If you're converting to or from a bass wah, this is the one to change. Try 0.068µF for a bass wah.

So I think I'm safe with the cap value I have chosen.

My question(s) is(are:)
Can a pot go bad so that it behaves in the manner I have described?
Would a  problem with the inductor cause these symptoms?
Has anyone had a similar problem with their wah?
If it is the pot, is there a recommended replacement, other than the Dunlop Hot Potz?


Thanks
Dan

[SHNOZZLE]

Did anyone figure this out, I'm having the same problem.

[R O Tiree]

Did you move the pot when you re-soldered the wires on?  Try moving it by undoing the securing nut, rotate the pot and re-secure. Experiment.

Have a look with a high-power magnifying glass at all the joints you soldered. Have you gone across 2 tracks? Have you broken a track (can happen with repeated soldering and de-soldering)?

Have you fried a transistor? Again, this can happen through over-heating.  De-solder them and check hfe (gain).  Should be in the range 500 to 1500 or so, according to the datasheet at Fairchild.

Have you melted the insulation in the coil in the Fasel?  On its own, it should be about 28 ohms, IIRC.

That's all I can think of right now.

[rockgardenlove]

Sounds like a faulty inductor to me.  Mine was faulty, and I had that exact same issue.

[gabael]

i have the same problem, i have changed the pot of a usa v847 to 100 k logarithmic for more sweep and the pot only sound in half of the travel. Bad conections? , inductor?

[Transmogrifox]

Try removing the pot, and get a 100k trim pot or other pot, put it on the bench and see if the problem still persists when you manually adjust a known-good pot.  Another thing you can do more quickly is to remove the pot and short the wiper to one end, see if it sounds like it should sound stuck on one extreme end of the range.  Then short the wiper to the other side and confirm it sounds like it should sound on the other extreme end of the range.

If it sounds ok without the pot, then you know it's the pot.  If it still misbehaves then you know to start looking somewhere else in the circuit.

[pinkjimiphoton]

the only time i've encountered this kind of phenomenon is in a pot that someone had opened to clean and reassembled wrong. there's a "stop" inside the casing of the pot, and if you put the casing back on wrong, the pot will do exactly as you describe.
IF you opened it, try reclocking the cover to find the proper spot for the pot to sweep right, then crimp down the things to hold the cover on the pot.
this also can happen sometimes if the pot isn't sitting on the gear right and gets forced past the stop.

my advice, if uncomfortable with working inside pots, is to simply replace it.