Really odd wah problem

[enigmur]

I have a Vox v487 which I have done a few basic mods to, and put a 3PDT switch in.

Now it all works perfectly, except for when I try add an LED.

When I add the LED I get a rustling sound and sometimes popping, sometimes when I click the wah on there wont be any sound come thru at all. The LED works fine though.

At first I thought it was the LED causing the problems, then the switch itself.

Today I took everything out of the equation. I got rid of the LED from the circuit, I still got the rustling and popping.

I changed batteries, rewired the 3PDT, tried different wires and a 100R Resistor instead of my 370R resistor on the way to the LED -  still get the sound.

So for some reason when I ground the LED, it creates noise in the circuit.

I have the LED wired up properly, and it is grounding to the output.

I can't understand what the problem is, and how grounding the LED is causing problems in the sound circuit.

Any ideas?

[enigmur]

Just got another question about the Wah so might as well post it here.

I have a few small 100K pots from a chorus pedal I ripped apart, and also a SPST switch (i think).

Anywho, would I be able to hook a 100K pot up to where the 33K 'Vocal' Resistor is, and would that allow me to modify that sound with the pot? Is that a use for pots? If it does, it means I could add a pot for controlling volume too.

And with the switch I have, it just just a simple 2 position switch with 3 poles on the back. Could I somehow hook this into the wah so I can switch between it using battery, and it using DC input? Or would I need a different switch?

Cheers

[alderbody]

Today I took everything out of the equation. I got rid of the LED from the circuit, I still got the rustling and popping.

check your 4.7uF electrolytic cap, or any other electro you might have added (DC power filter-cap)

[alderbody]

Anywho, would I be able to hook a 100K pot up to where the 33K 'Vocal' Resistor is, and would that allow me to modify that sound with the pot? Is that a use for pots? If it does, it means I could add a pot for controlling volume too.

And with the switch I have, it just just a simple 2 position switch with 3 poles on the back. Could I somehow hook this into the wah so I can switch between it using battery, and it using DC input? Or would I need a different switch?

Cheers

Yes, you can wire a pot as a variable resistor and use it instead of the 33K Q resistor.

About the volume, you mean the input resistor? People usually put a fixed resistor in there.


You don't need a switch for you power supply.

All you need is the "classic" DC-input jack which disconnects the battery when the jack is in.

[GibsonGM]

snap crackle pop after the LED, eh?  Try checking to make sure your switch connections are clean, that you didn't bone them up when you put the LED circuit in there.  Sounds like the switch contacts could be moving around making that rustle noise. 
 
Switch 'er on, and stick a pencil in there, move things around.  If it's not component (cap?) related, my $ is on either bad connection at switch or internal damage to it. Guess something could be shorting to the case where you did your mods....

Search in the forum for "DC",  "Wall wart" and other assoc. terms to find out how to set up the adapter...

[enigmur]

Thanks guys. I'm not sure if it is a component or my Cap, because it works 100% fine before I add an LED.

I thought it may have been the 3PDT, but I changed the pin layout on it and still have the problem - it's really odd.

I will check for any kind of un-wanted grounding. I'll try a red LED instead of the green which I have in there.

3PDT's cost too much, and are really hard to get, which is a real shame or I would just switch it out and try another one.

Cheers for the info on pot's, I think having a volume knob on my wah would be cool, aswell as a 'sing' knob. I'm going to try that magnet on the inductor thing as well just for a try.

Thanks!

[jonathan perez]

3PDT's cost too much, and are really hard to get, which is a real shame or I would just switch it out and try another one.

you think so? pedalpartsplus.com. ive seen em go for 12 bucks in some places...

Cheers for the info on pot's, I think having a volume knob on my wah would be cool, aswell as a 'sing' knob. I'm going to try that magnet on the inductor thing as well just for a try.

sing knob? what do you mean by sing?

[enigmur]

A pot controling the vocal quality of the wah.

Just wondering how you wire the pot in? Not sure which lugs to put where.

Cheers-

[jonathan perez]

vocal quality is still a little vague.

Q, maybe? 100k pot, 1st and middle lug.

how about a rotary switch to control the sweep capacitor range? .01-.068.

[enigmur]

Yeah I definately want to try that, just have to get one of those to do it. At the moment i'm just going to install a socket and try out some of the new caps I ordered.

[enigmur]

What would happen if i was to put a pot across the Sweep Cap? http://www.diystompboxes.com/smfforum/index.php?topic=54239.msg414617#msg414617 - scroll down for what I mean. Would this do something odd to the sweep?

Yes by vocal I meant the 'Q' mod I believe.

[jonathan perez]

i cant say the pot would do much, doesnt seem entirely useful, really.

[enigmur]

If I add a pot to control volume or the Q, do it place it instead of the resistor (i'd think so), or do I place it aswell as the resistor in the same holes?

Thinking about it, i'd think it would totally replace the resistor.

I will let you know how it goes tonite, and I'll try it out at band practise. Drilling thru the case may prove hard.

[alderbody]

Thinking about it, i'd think it would totally replace the resistor.

Yes, it would.

Drilling thru the case may prove hard.

Not necessarily. It's just that the walls of a typical Wah shell are relatively thicker.
The material is the same, easily drillable aluminium alloy.

EDIT: If that noise remains, try replacing the electro. It's very common for them to go bad.

[enigmur]

Ok I'll have a go at swapping out the electro cap, I think i have a 4.7uf one somewhere. Do different values do anything here?

[jonathan perez]

10uF will SIGHTLY add for more vocal range, almost clearer wah tone.

4uF and below will make the wah less apparent, closer to a volume pedal.

[alderbody]

10uF will SIGHTLY add for more vocal range, almost clearer wah tone.

4uF and below will make the wah less apparent, closer to a volume pedal.

hmmm...  My experience has it a bit different...

I remember when i used a 10uF, the wah sounded kinda stiff and un-musical to me.

on the other hand, with the 4uF i use now (actual value 4.5uF) i got a better vocality.
EDIT: all the nominal 4.7uF caps i tried had way larger values...

i have a "clumsy" theory about that.

In the human voice, vowels are generally louder than consonants, right?

you can't really shout a "w"...

So, if a wah pedal is supposed to mimic the human voice, the heel down position should be a bit quieter than the toe down.

If the value of that electro determines the balance between a volume pedal behaviour and a Wah pedal behaviour,
then a relatively lower value, might do that trick... Slight Volume increment from "w" to "AAAHH"... 

Maybe that's why they used to put 4uF caps in there, besides the fact that such caps were available at that time.   

[enigmur]

I put in my old 4.7uf cap last night.

I think the LED was drawing too much power because when it turned on, the wah cut out slowly.

I guess I need to find the correct resistor for it.

But, when the LED did come on, I didnt hear that odd scratchy popping sound. It seems to make noise when I move my power leads so I was wondering if the plug onto the PCB has problems?

[enigmur]

What is MCD reffering to in LED's?

The red LED is 40MCD and green is 80MCD.

This seems to be the only indication of a difference, does this have anything to do with power consumption? What strength resistor do I need?