Noise and Grounding questions

[Astronaurt]

Hey there, so I'm a bit of a noob, just gonna lay that out there. I've just been building a Wah pedal based off of THIS SCHEMATIC:

http://fuzzcentral.ssguitar.com/mccoy.php

clean, unmodded, and I'm not using the output buffer.

and I'm having trouble with Noise issues. I'm pretty certain it's a grounding problem. I'll try and explain exactly what's going on: Rotating the pot on one end gives me a good clean signal, the other end has what sounds awfully like mains hum, and right in between switching there is an irritating buzz in the middle of the two extremes. I'm using a solderless breadboard, and lots of open wire, so I thought that it might just be picking up unwanted signals because it's all unshielded, but that doesn't really explain the buzz in the middle. And of course, the buzz is quieter when I have my hand on the guitar than not. I've checked it over, dismantled and rebuilt it several times trying to find where I might've messed up, but this problem keeps coming back to haunt me!

I guess I'm wondering if anyone on the forum can see if this circuit is just unavoidably noisy. If so, if there's any suggestion to what I can mod to get rid of some of it. If that's not the problem, then I think I just don't really understand grounding all that well. I know this was designed to be grounded to the Chassis, so would the internal resistance of said chassis perhaps cut down on noise? Anywho, I'll probably have more questions when I fiddle with it more, but any feedback would be super helpful! I'll try and post pics soon so that y'all can take a look.

[brett]

Hi
the circuit isn't intrinsically noisey, so you've managed to do something different.
It could be either that you have a grounding issue or an input impedance issue (too high).  Check the latter - is the resistor on the emitter of Q1 a small value?  Like 330 or 470 ohms?  If it is correct, then check the DC voltage on collectors of Q1 and Q2.  If the bias is correct (and everything is grounded wrt DC voltage), you'll get about 4 or 5 V on q1 and 7 V on q2 ( - google for better guesses than mine).
If the gain and DC bias is good, then you've probably got an AC grounding issue.  My general rule is to use a chassis or a heavy duty wire (e.g. mains wire) to connect back to a single point at the input jack.  This is a typical "star" grounding system, which is about as good as it gets for stompboxes (except for the ugliness factor).

let us know how you go
cheers

[handlefras]

I'm having a similar problem with the same fuzzcentral wah (which is pretty much a generic wah circuit, right?). I'm getting hum throughout the pot rotation, but it is noticeably exaggerated when in the toe down position. I too built this without shielded wire, and some of the wire runs are definitely longer than any of my other builds. I used two extra pots, one for Q and the other replacing the 470R to adjust gain/bass. Both pots have about 10cm cable runs, with the two wires twisted together. Also included is a dpdt to swap the 'Hendrix cap' with the original 0.01uf. The circuit 'wahs' like it should and all the controls work but I just can't track down the noise!

To narrow down variables I have:
- removed the output buffer (I don't have any input buffer either)
- removed the 3pdt and LED, just hard-wired the input and output jacks directly to the circuit so it is "always on". 
- swapped the BC108s for 2n3904s
- swapped the sabbadius soul inductor for the original crybaby one
- pushed all the wires around with a bamboo skewer

All of the above was to no avail and I'm out of ideas.
I have used star grounding, but because of the pedal layout, I connected all the grounds to the sleeve of the OUTPUT jack as opposed to the input jack like I usually do. Could this be the issue?
Other than moving all the grounds, I plan to go ahead and shield all the long cable runs, but I still think this isn't the root cause. Is there something else I should be looking at? 

[amptramp]

I sort of cringe at any design that does not have any bypass capacitor for the power supply (same complaint as I have with the Fuzz Face).  The power supply may become contaminated with noise and the first stage has no power supply rejection since the transistor output has a high impedance - much higher than the 22K resistor.  A solderless breadboard is probably the worst noise environment you can imagine - large loops of wire, no shielding and if you are anywhere near civilization, lots of AC wiring around you.  Build it on a perfboard and throw it into a box (even an Altoids tin will do, just to check for induced noise) and see if you have the same problem.  Then put an electrolytic capacitor and a ceramic capacitor across the power leads from +9V to ground.  Otherwise, you will have a change in sound as the battery impedance increases.  The voltage of the battery will decline with use, but that is not much of an influence in this circuit - but the impedance will increase and that may cause some change in sound.  I would use a 0.1 µF ceramic rated at at least 50 volts and a 47 µF electrolytic rated at 35 volts.  If you want to see the extent of this, use the "dying battery simulator", a variable 9-volt power supply with a 50 ohm pot in series with the output.  Or just use the pot with the battery and see what the difference is.

The buzzing may come at the centre of pot rotation because this is where the input ot the emitter follower stage has the highest impedance.

Good luck and good hunting!

[handlefras]

Thanks for the input.   
Because I have this wired for a 9V power supply, the dying battery isn't an issue. Note, I have tried the circuit with a battery to eliminate the possibility of hum from my power supply.
Are you suggesting I place both a 0.1uf ceramic and 47uf electro in parallel, then place this arrangement across the 9V jack from the +9V pin to the ground pin?

[amptramp]

Exactly what I am suggesting.  Otherwise, even with the adapter, the nearest bypass capacitance is in the wall wart itself.  The power line has some resistance but more importantly, some inductance based on the loop area of the separation of the + and - power leads.  This is capable of acting as a receiving antenna and picking up noise, so it pays to have some decoupling in the stompbox itself.  The resistance of the power leads help ensure that the ripple current is not divided strictly in the proportion of wall wart capacitance to effect decoupling capacitance.