pedals are whining...but why?

[alphadog808]

Hi there guys,
  So I've built a zendrive and a Timmy clone with vero boards.  They sound great, but when the knobs are maxed out, the pedal whines.  I believe the frequency changes as I turn the tone knob back and forth.

Strangely, I've been able to narrow down that this only happens if there is NOT a cable plugged into the INPUT.  It doesn't matter if the input cable has a guitar connected or not. 

That being said, would anyone have any ideas why the pedal would whine when nothing plugged into the input jack?  I even tried shielded wire on the input and output to dpdt switch but same problem.

Any advice/ideas would be awesome!

[thelonious]

If your chain is only Timmy > amp, or zendrive > amp, with no other pedals in the chain, does each pedal still whine?

What type of jacks are you using? Are they plastic or metal?

Do the pedals whine when they are on battery instead of power supply?

[alphadog808]

Thelonious,
   Thanks for the response!  My chain is pedal(either timmy or zendrive) to amp.  Nothing else.  My jacks are metal, I think these are the ones I got...

http://www.smallbearelec.com/servlet/Detail?no=558

They whine on battery power as well.  Some things I also tried was:
- different amp
- different room(more like different plug outlet)
- different wallwart
- different cables

Still happens.  Weird tho, it seems usually taking the cable out of the input quiets the pedal...but not in these 2 instances...

[thelonious]

Hmm...

If you can post pics of the pedal guts and/or a quick sound clip or video recording of the whine sound you're hearing, that might help.

What vero layouts did you use?

[alphadog808]

I'll see what I can do.  In terms of the whining, I turn everything up full and then if I mess with knobs other than the gain and volume, I get a whine that changes frequency and I turn it the knob. 

Here are the layouts I used.  Note, I did make 2 timmys and I was told to swap the 100pf cap for a 220pf cap and it stopped the whining.  I guess I could do the same to the other timmy, but considering that the zendrive is whining too, I should try to figure out what's causing this.

[R.G.]

Some pedals whine when the inputs are open or connected to too high an impedance. The input is high impedance and if it's not pulled down by an input, you can get signal coupled in from the output wires capacitively. Connecting up a cable amounts to connecting up a capacitor across the input, which may load the feedback enough to stop it. Some pedals oscillate with a guitar connected, or with certain settings of the volume control, generally in the middle of the range.

It's generally a wiring capacitance issue.

[alphadog808]

RG, thanks for that insight.  That being said, I'm not very good at electronics, how would I go about putting a capacitor across my input?  Or is doing that not the solution?

[alphadog808]

Ok, so I'm not very smart, or very good, but I am tenacious  So I tried a cap on the inputs and it didn't work...tried a few configurations and sizes(what I had available), no dice.  I then thought, let's try a resistor.  

So I put a 510K ohm resistor into the circuit.  One side on the input jack, and the other on ground.  It seemed a little better.  So I added another 510k in parallel.  A little better!  I then added a 3rd one and the whine went away completely!  

So...my question is...what did I do?  And is it harmful to tone?

[closetmonster.]

You added a pulldown resistor, I think.

There a couple of good pages on them at AMZ:

http://www.muzique.com/news/pulldown-resistors/

http://www.muzique.com/news/pulldown-resistor-vs-input-impedance/

I am a noob as well, so I may need to be corrected here, but I believe you are lowering the impedence at the input of the pedal. Pulldown resistors are commonly used to stop popping from input capacitors when discharged via a stomp switch. I would give those two articles a thorough reading. As I understand it, adding a buffer before your signal chain would also drop the impedence coming out of your pickups.

[alphadog808]

Thanks for that man.  I was just confused as if I read RG's post right, he suggested putting a cap in there.  I have since put a linear 10k pot in there to try and see exactly what resistance the pedal wants, but for some reason, I can't get it to work.  The whine dies no matter where the pot is turned.  I checked the resistance and connectivity, I have it set up right, just not sure why it doesn't work.

[closetmonster.]

And it shouldn't affect your tone too much. Pulldown resistors are commonly used/

[closetmonster.]

I believe RG was saying that your guitar cable is acting as a capacitor in the situation, not to wire in a capacitor. Though I may be mistaken.

[Perrow]

I believe RG was saying that your guitar cable is acting as a capacitor in the situation, not to wire in a capacitor. Though I may be mistaken.

You're quite right. Pulldown resistors do form an RC filter with the input capacitor. The lower that resistor is, the more it will affect the tone.

[slacker]

If it only squeals with nothing in the input and works fine in normal use then I wouldn't worry about it.

[alphadog808]

from my trial and error, it looks like I was able to narrow it down to about 100k resistor will do the trick. 

Slacker, I know what you mean, but if I want to sell the pedal in the future, I want to make sure it works 100%.  That and I'd always be scared of having that noise if I'm mic'd up loud.  When the whine happens, it's LOUD.  It would probably kill off a bunch of bats and dogs 

Hmm, if a lower resistor affects tone, I'm thinking 100k is pretty low; I'll have to really give it a once through to see how the tone is modified if any.  Note, I'm just planning on putting the resistor from the input jack to the ground.  I read that I could also try putting it on the input of the board as well, but it seemed that was more for stopping LED pop rather than this type of whine.

Either way, thanks so much for the help, fellas!!

[slacker]

You don't want to put the resistor on the jack because it will affect the tone of the bypassed signal. On those boards there is a 2M or 2M2 resistor from the input to ground, your 100k resistor is now in parallel with those resistors. 2M in parallel with 100k is only slightly lower than just 100k on its own so you can just replace the 2M/2M2 with the 100k.

[thelonious]

+1 on everything slacker said. As others have said, adding the 100k resistor isn't a free ride; it's a tradeoff - you get rid of the whine by lowering the input impedance. If someone has a big pedal chain and no buffer, or they have a long guitar cable, they are going to lose some high frequencies into your pedal. Do a test---try playing your guitar through the pedal as it is, then clip the 100k resistor across the input jack and play your guitar through it. That's the tradeoff you're making in terms of sound. Now use a 25' guitar cable and try the same test.

What you don't want to do is to solve a problem that happens only in circumstances that will seldom be the case (both volume and gain knobs turned all the way up, pedal on, and nothing plugged into the input) but cause a different problem that is more likely to happen (the capacitance of a long guitar cable, combined with the low input impedance of your pedal, rolls off a bunch of highs and makes the pedal sound muddy).

BTW, replacing that 100pF feedback cap with 220pF is just a different kind of tradeoff; in that case you start losing high frequencies the more your gain knob gets turned up. You might want to try both solutions and see which one sounds the best at all gain and volume settings.

Let your ears be the judge...

[alphadog808]

Good points guys.  I'll have to really dig in and figure out what is best.

When this happened on my first pedal, I thought maybe it was my wiring, dpdt or a board issue.  But when the same thing happened on the 2nd build and with a different type of pedal, I thought maybe it's something else?  Could it be my offboard wiring?  This is what I've done for both offboard wirings.

The only thing is I wire up the LED differently, the vero has the resistor onboard, so I go straight to the LED off the board.



Looks ok?  The offboard is common between both builds.  That and the fact that the power jack is located on the top of the pedal so the power and ground have to go past/over the pots to get to the vero.

[thelonious]

The guys at tagboardeffects know what they are talking about, and this layout has been used in hundreds of successful builds. My only comment about it is that sometimes it can be beneficial to use a star ground instead of chaining it from one thing to the next. A lot of people use the input jack ground lug as the point where all their ground wires intersect. That way all the grounds come back to one point and you have less chance of ground loops, LED current probs, etc. But ground loops don't usually sound like "whine", so I think your problem is oscillation like R.G. was talking about.

[alphadog808]

Oh most definitely.  I was just wondering if maybe there was another/better offboad wiring config that might help alleviate the whining problem.

I made my own type of "star ground" via a small rectangular piece of vero board.  I have a ground connected to it and then I octopus out multiple grounds to where they need to go.  It was easier for me to wire up that way.