1st post from a Newbie-Shielding tips for wahs Q

[chrisaxeman]

Hi,

Hope everyone is well.

My name is Chris.

This looks like a good place to hang out for solderers.....

I like all sorts of setups,and I have recently completed my first rack system.

One of the mods I did was to do that Craig Anderton CV mod to a GCB-95,and run the CV part via a midi to CV converter.I don't have to run the audio out on the floor this way......

The mod works fine until I put it into the rack,where it hums like a bee.I eliminated ground loop hum as an issue(I build all of my own power supplies with isolated/regulated taps,HiQ toroidals,aluminium boxes which I thought provided shielding etc),and am 100% that the problem is induction from power supply in this section of the rig-I proved this by putting long cables on the wah and taking it out of and away from the rack,where the hum disappears with distance.

I'm assumming the wah inductor is acting like an aerial for the magnetism,and I am interested in anyone's opinion about ways/methods/materials for shielding the wah/inductor,or ways to decrease the magnetism from the power supply(as I said,I thought that aluminum didn't conduct mag),or any de-humming method in general.

I don't have the real estate or conviction to perform a component relocation,and this is the only glitch in my rig,so I'd like to fix it where it lay.

Any opinions please would be greatly appreciated.

Thanks in advance.

Chris......

[Rich G.]

Hi Chris!  I'm very interested in your topic as I'm about to embark on the same project.  I have my parts, it's just a matter of putting things together.

It definitely sounds like induction from a power supply transformer into the inductor.  Is the cover of the inductor shielded?  How about the case of the pedal guts?  What happens if you put a grounding clip from the case to ground?

This could be tough since the inductor is basically a single coil pickup and we all know how those hmmmmmm.

[Peter Snowberg]

Welcome to the forum Chris.

You could try magnetic shielding around the inductor. I would suggest trying a piece of iron pipe around the inductor to try to channel the flux out of your signal. A 3/4 or 1 inch galvanized pipe coupling should be a good size (along with being cheap and available).

I don't know how that will otherwise affect the operation of the inductor but the change should be minimal if you can suspend the inductor in the middle of the pipe with wax or something like that to keep it from touching the walls.

This will be a good thread to watch I think.

[jplaudio]

if you cant move the transformers you have to shield the inductor.
look at these products
http://www.lessemf.com/mag-shld.html#277
the prices are fair for a small amout of the mu metal foil
I have purchased the foil in sheet from car stereo distributors where it is sold to shield electronics. The foil can be cut and shaped into boxes or cylinders to fit the component you want to shield. you can tack solder the pieces together. with a couple of layers you should be able to eliminate the hum.
be sure there is a small space all around the inductor and do not ground the foil any where in the circuit. You may find one shape will work better than another so try a cylinder and then a box construction. be sure to cap any cylinder shapes
Another source might be a old TV or tape deck where the mu metal or similar material was used but this is thicker material that is hard to work with.

[chrisaxeman]

Hi Chris!  I'm very interested in your topic as I'm about to embark on the same project.  I have my parts, it's just a matter of putting things together.

It definitely sounds like induction from a power supply transformer into the inductor.  Is the cover of the inductor shielded?  How about the case of the pedal guts?  What happens if you put a grounding clip from the case to ground?

This could be tough since the inductor is basically a single coil pickup and we all know how those hmmmmmm.

Hi Rich,

How's it goin'?

I guess you're the same Rich G. from HRI,from which you'll be very aware that DIY is a dirty word around that place-I wouldn't dare ask a question on "Gear Talk" like this! The answer would be like "buy a Teese!" :roll: .

It is an interesting thing to do for a wah,so far it is good for me,only this mag problem and the fact that the EBMM pedals I use out of my All Access(that sends midi cc to the CV converter) have a crap taper.I'll be changing them to a linear pot.My setup has no audio on the floor,and phantom powers from the rack

There is no extra shielding in the wah pedal at all,and as I'm not using the mechanical part of the pedal any longer,I'm considering putting it in a dedicated enclosure.This will make the shielding work/experiments easier to do as well.As you are aware,the PCb is pretty small,and will get me some real estate back on this rack shelf.

Single coil-like,yes,but I'll sort it out!

Maybe a dual inductor setup-a humbucking wah?

Chris.......

[chrisaxeman]

Welcome to the forum Chris.

You could try magnetic shielding around the inductor. I would suggest trying a piece of iron pipe around the inductor to try to channel the flux out of your signal. A 3/4 or 1 inch galvanized pipe coupling should be a good size (along with being cheap and available).

I don't know how that will otherwise affect the operation of the inductor but the change should be minimal if you can suspend the inductor in the middle of the pipe with wax or something like that to keep it from touching the walls.

This will be a good thread to watch I think.

Hi Peter,

Thanks for the welcome.

Would you tie the "shield" you descibed to ground?

Cheers

Chris........

[chrisaxeman]

if you cant move the transformers you have to shield the inductor.
look at these products
http://www.lessemf.com/mag-shld.html#277
the prices are fair for a small amout of the mu metal foil
I have purchased the foil in sheet from car stereo distributors where it is sold to shield electronics. The foil can be cut and shaped into boxes or cylinders to fit the component you want to shield. you can tack solder the pieces together. with a couple of layers you should be able to eliminate the hum.
be sure there is a small space all around the inductor and do not ground the foil any where in the circuit. You may find one shape will work better than another so try a cylinder and then a box construction. be sure to cap any cylinder shapes
Another source might be a old TV or tape deck where the mu metal or similar material was used but this is thicker material that is hard to work with.

Hi JPL,

Thanks for the info and link.

So you wouldn't ground the inductor shield?Why so?

I had someone else suggest the same thing as you have done with the mu-metal,but he was very specific in regard to connecting the shield back into the mains ground/earth (not the audio ground).

Any further thoughts?

Chris........

[jplaudio]

Chris,
The mu metal works due to the high permeability of the alloy. If you ground the shield the hum can picked up by the audio circuit. There may also be noise present on the ground plane . Basically the mu metal blocks magnetic fields by virtue of its specific properties and does not need to be grounded to work.

[Rich G.]

Yup-- I'm the same Rich G.  Yeah, best not to ask this on HRI.  You'll get steered into the direction of using a buffer (but not in front of a Wah) and a Teese as you mentioned.

I'm going to do the mod on a 18 Vdc 535-Q.  I bought the Taiwanese "BB"  enclosure from Small Bear hoping the guts would fit.  I haven't tried it yet, but it looks like it will work.  It may be a little tight so I'll probably have to forget about using two 9 V batteries and just go with an adaptor, which is what I was going to use anyway.

I plan on sending the CV out to the pedalboard & back via XLR.  I'm worried about the taper I'll get straight from the LDR.  Eventually I'll go MIDI->CV and program the taper... but that's the next project.

So-- is your's naked right now?  meaning it has no enclosure?  If so then definitely an enclosure would help things.  Do you have some pics to share?

[chrisaxeman]

Chris,
The mu metal works due to the high permeability of the alloy. If you ground the shield the hum can picked up by the audio circuit. There may also be noise present on the ground plane . Basically the mu metal blocks magnetic fields by virtue of its specific properties and does not need to be grounded to work.

Thanks JPL,

I'm away woking my roster at the moment,and on the weekend I'll get busy.

Cheers.

[Rich G.]

woking my roster

I'm afraid to ask what that means. :oops:

[chrisaxeman]

woking my roster

I'm afraid to ask what that means. :oops:

Hi Rich,

Meant to say working :oops: .I'm an electrician in a coal mine.This sort of stuff has to wait until the weekend as a result of the rotating roster I work-basically sleep/work for 4 days on night shift. :evil:

As far as your enclosure question,the wah is still in the original pedal housing........

Chris.........

[chrisaxeman]

Hey Guys,

I think I got a result here.

Forgive the cross post,but I got some good info from these guys as well.

The RS mu-metal can did the trick pretty well,but I definately had to ground it with a wire soldered to it.

Quote:
And lastly I found a very nice little mu metal shielding can that is used on cheap audio transformers that properly would fit inside a wah, these are available from RS components (former Radio Spares) order number "210-6469" price 3.77 British pounds..

If you are up for it you should defiantly try it..

Well now I have put in my 2 cents today..

Claus H


Hey Claus,

I got hold of this can.It came with a base also,so I popped the inductor inside,sealed up the base,and soldered the coil back on the pcb.

Works good.  .

I soldered an earth wire to the can and ran it back into the audio ground for the time being(does nothing without it),but I'll put this wire back into the mains ground and see how much it improves(as Lonnie suggests).

Thanks to Clause,Lonnie,Bruce Egnator and Suhr,among the many others who helped me out.

Cheers.

Chris..........

[Hal]

Peter mentioned something about magnetic shielding - and I think he's right.

However, there may be a way to do it that easier than suspending the inductor in an iron pipe.  CD-ROM drives, and I assume also hard drives, in computers need strong "rare earth" magnets to spin discs.  However, we all know that magnet+computer = bad.  Therefore, they actually employ magnetic sheilding.  I once took appart a CDROM drive, and relized something I'd never seen before...there was a piece of metal in the drive that a magnet would stick to either side, but when a magnet was on one side, the other side was not "magnetic"....that is, it would not "pick up" feromagnetic materials.  

So bang some of that into shap, and put it on your inductor :-D