Stupid noob question about buzzing

[rehandalal]

I'm pretty new to DIY pedals and electronics in general. As a starter project I created a little kill-switch pedal (mute switch) that works pretty much as intended. I had a spare 3PDT switch lying around so I ended up using that (I know that it's totally overkill).

The issue I am having is probably grounding related but whenever I touch the aluminum enclosure or the metal parts of the 3PDT footswitch I get fairly loud buzzing. Here's a simple diagram of how it's all wired up:


Any ideas how to solve this buzzing?

Thanks!

[tubegeek]

Any ideas how to solve this buzzing?

I'd bet you are using isolated jacks. If so, connect the ground wire to the enclosure near the "in" jack, I assume it's J1.

[rehandalal]

Thanks for the reply tubegeek! I'm using these jacks:
http://www.neutrik.com/en/audio/plugs-and-jacks/m-series/nmj4hc-s

Just wondering:
a] are those isolated?
b] what does isolated mean in this context?

Apologies if these are even more stupid questions that I should know the answer to.

Thanks!

[tubegeek]

b) the mounting hardware DOESN'T automatically connect their sleeve circuit to the box.
a) looks like it is isolated - if you have a multimeter see if there is continuity between the sleeve of a guitar cable plugged into the jack and the metal of the box itself.

[rehandalal]

Ah! Yes it IS isolated.

I'll solder the ground to the box!

Thanks for the help!

[tubegeek]

I'll solder the ground to the box!

Thanks for the help!

No worries. You may find it easier to solder to a washer and then attach the washer to the box with a screww. Takes a lot of heat to solder direct to the box. The most easiestest way to do it may be to trap a wire under the stomp switch mounting hardware.

[Jdansti]

+1

Edit: I noticed that tubegeek recommended attaching the enclosure ground at the "IN" jack. I think it would work on either jack, but he might have a good reason for doing it that way.

I was typing this when you posted tubegeek, but I'll go ahead and post it.

Normally the plastic jacks do not allow the ground to connect to the enclosure. You'll probably need to connect a wire from the sleeve of one of the jacks to the enclosure. The quickest way is to strip the end that connects to the enclusure leaving about an inch of exposed wire.  Take that end of the wire and wrap it around the threads of one of the jacks, place the jack through the enclosure hole, and tighten the nut on the outside.

You can also use a thin washer that has a solder lug on it.

The other thing you need to do is ground the signal when you want it disconnected from the amp.

[tubegeek]

@jdansti:

or just swap "in" and "out," I think that'd do the same thing...

[Jdansti]

 

  Like pulling nails out of a bucket until I find one pointing toward the wall! 

[PRR]

> I noticed that tubegeek recommended attaching the enclosure ground at the "IN" jack. I think it would work on either jack, but he might have a good reason for doing it that way.

On a large complicated box with lots of amplification: the input is smaller than the output, therefore more liable to corruption, so you tend to take the shield to the input.

In this case, it's small, there's no amplification, there's no apparent difference between "in" and "out" jacks.... shouldn't matter.

[tubegeek]

  Like pulling nails out of a bucket until I find one pointing toward the wall! 

My family and a box of hammers: more similar than different.

[rehandalal]

Thanks for the input everyone!

I think this is finally what this should look like?

[tubegeek]

Edit: I noticed that tubegeek recommended attaching the enclosure ground at the "IN" jack. I think it would work on either jack, but he might have a good reason for doing it that way.

My justification (not to say "reason") is this: shields drain their noise currents to the enclosure. The recommendation I have seen is to do this at the input end to prevent noise currents from being allowed to enter the enclosure where a high impedance circuit can possibly pick them up: in other words, get them onto the enclosure as soon as possible.

Like PRR, I'm not entirely sure this would matter in this application one bit, because I think the path to ground here is the output cable shield and then the input circuit of the next piece of equipment, but my understanding is this is the best practice. It'd be more justifiable if the enclosure had its own path to ground.

I think I picked this up from a paper - maybe by Bill Whitlock? - maybe on the Jensen web site? It's kind of a blur, I've been reading a lot of papers lately, several on system grounding & shielding.

If you're very interested I can sift through the mound of hard copies I've been toting around and see which one I'm trying to cite.

[tubegeek]

@rehandalal: yup.