Guitar volume knob issue/question

[alphadog808]

Hey guys,
 I noticed that if I turn my guitar volume or tone on full, my pedal squeals.  If I roll back back a notch, it stops.  Is this because the resistance and impedance is increasing when I do that?  If so, is there anything I can do in my pedal to do the equivalent so I don't have to remember to back the volume off my guitar?  

I've tried messing with the pulldown resistor without success but maybe I didn't use a large or small enough one?  

I have a buffer in the pedal and the pulldown is 10M and the pedal pulldown is 1M.  Not sure if that helps.

Sorry if I'm way off, I'm have alot to learn...

[rousejeremy]

What pedal is it? Are you using shielded wire?

[alphadog808]

It's a wampler pinnacle and I have shielded cables for input and output.  I've done a bunch of stuff to try and stop the squealing, I was spawned a new thread as I was wondering about the guitar volume/tone knob and how it is affecting my pedal so maybe I can mod the pedal to stop squealing, ya know?  Thanks so much for the help!

[GibsonGM]

I believe the effect is caused by the fact that you're adding resistance by turning down the volume pot.  This works with the input capacitance of the device (Miller Effect) to create a LPF, which sends enough high freq's to ground to prevent the oscillation you experience without that resistance being there.

IOW, the pedal is on the verge of oscillating all the time, and that little added series resistance is stopping it.   First, you could try adding something like 100 ohms of resistance at the pedal input, to 'simulate' having rolled back the pot a little.   If that doesn't work,  a small-value cap to ground from the pedal input may help correct this...I'd try anywhere from 100pF up to 10nF, see what happens...the game here is to get that squealing stopped but not lose your highs.

[Gus]

you should have a link for the schematic.  I am guessing it is a DIY build.

Do you have the 470 ohm at the input if so is wired correctly?  You could try a 1000 ohm if you have one.

Are you sure it is built correctly?  Did you check every node for the correct connections and then mark up a schematic with what you checked?

[tjdracz]

I've got the very same problem but with Civil War Big Muff. No shielded wires or anything. I built it first veroboarding it myself from scratch and it worked fine but I've rebuild it the other day using IvIark's vero layout and now at the end of volume turn I get squaling/oscillation. This is the schematic Ive followed: http://www.pisotones.com/BigMuffPi/psst/schm-civilwar.jpeg and layout: http://tagboardeffects.blogspot.co.uk/2012/08/ehx-civil-war-big-muff.html I've no idea why it squeals now with shorter wires and all. Parts are all the same as before and the only real change is probably the transistors being swapped between positions.

[R.G.]

If you have a pedal circuit that has (1) high input impedance and (2) gain, it will amplify whatever noise gets into it through stray capacitances. If you want to make this noise worse, turn up the gain. The output now has amplified noise. Some small amount of this inevitably gets back into the input. But it is so attenuated by its passage through the stray capacitances in the air and through the bypassing of the power and ground wiring that not much happens.

Now turn up the gain. The output noise gets bigger, but the attenuation through the stray paths remains the same percentage. So the noise input gets bigger too. At some combination of gain and phase, there will be enough of the output noise fed back to make the input produce enough of itself to feedback, to ... and it oscillates.

If there is not a lot of excess gain, changing **anything** will usually drop the amount fed back enough so it quits.

This is the condition with the input waving around in the air. If we now connect something to the input, like a guitar output, the situation changes radically. The guitar produces signal, but its input also looks like a  variable impedance too. To the noise that can cause squeal, the guitar looks like a load in parallel to the input impedance of the pedal. In particular, the volume pot of the guitar looks like a variable resistor to ground. This resistance is quite small at either max or min volume, and a maximum of 25% of the pot value when it's in the electrical middle. This loading further reduces the impedance the feedback noise sees, and attenuates the noise feedback. If this is enough to drop the amount of noise below the amount needed to sustain oscillation, oscillation quits.

This is the fundamental reason some pedals squeal in some builds and some open-input, or guitar loaded, or volume pot sensitive situations and not others. Humans want a clear, simple diagnosis. Unfortunately, there often is not one single thing to fix. It's a combination of a huge number of wire positions, board layout, jack wiring, bypass wiring, amount of gain, which-device-where, power supply, power decoupling, input signal size, impedance and phase, phase of the moon, everything.

Sometimes it oscillates with some guitars and not others; generally this is at the peak of the guitar pickup's inductive impedance and at certain volume settings. Changing from a guitar on the input to another pedal in front of it often cures this issue.

Do you remember the song "The Gambler"? Remember "you gotta know when to hold 'em, know when to fold 'em...". Sadly it's that way. No one magic amulet, except, perhaps, learning.

[alphadog808]

R.G., thanks for dropping some big time knowledge!

[PRR]

> If I roll back back a notch, it stops

Try putting 22K in *series* with the pedal input.

As R.G. says, it's complicated. But by your description, I would try this 12-cent experiment.

[Plexi]

I've got the very same problem but with Civil War Big Muff. No shielded wires or anything. I built it first veroboarding it myself from scratch and it worked fine but I've rebuild it the other day using IvIark's vero layout and now at the end of volume turn I get squaling/oscillation. This is the schematic Ive followed: http://www.pisotones.com/BigMuffPi/psst/schm-civilwar.jpeg and layout: http://tagboardeffects.blogspot.co.uk/2012/08/ehx-civil-war-big-muff.html I've no idea why it squeals now with shorter wires and all. Parts are all the same as before and the only real change is probably the transistors being swapped between positions.

I'm having a similar problem with my Ram's Head clone: an ugly and loud scratch noise when it turns down the guitar volume.
This problem dissapears when I use a buffered bypass or any pedal turned on before.
It has a 33k resistor at the input, 1M pull down resistor.

Any idea?

The BM It's outside the box now, I hope it will disappear when I'll box it.

[PRR]

Plug to input, measure the DC Voltage at the guitar end of the cord.

If not real-small (mV), something is leaking.

[Plexi]

Solved late at night! 
Was it a very microscopic tin of hair crossing from the entrance to another track.

Now sounds like heaven (or may I say hell?)

[pinkjimiphoton]

glad ya got it sorted out!!

first thing i thought of was cold solder to ground IN the guitar. that can do it, believe me... especially with that crappy lead free shit they use all over now that just plain...well, sucks.

[Plexi]

Yes..!
BM wasn't "muff'n" at all ...  was like a cheap overdrive pedal. That was my huge frustration.
I can live with a scratch input... but a Muff without all that beast gain? No way

[pinkjimiphoton]

just for shits n grins, try adding an 1n34 in parallel with the clipper marked d4 on the eh board.

should wipe out the ocean of noise and leave the roar intact.

if ya do it and it works for ya... i discovered it messing with a nyc bmp a couple years ago... let me know. i build it into all my muffs now,
don't mess with the tone but nukes most of the hiss.