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Faraday box

 
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angelodp



Joined: 15 Jan 2008
Posts: 1217
Location: L.A.

PostPosted: Tue Sep 09, 2008 6:45 am    Post subject: Faraday box Reply with quote

Doing some work on a 59 Danelectro. Its been through hell. It was given to me in 66 after it was found in a dumpster with a cracked neck. I fixed that and its been with me all these years. I am building a copper box to shield the pots and jack. The pickup is nicely shielded by the lipstick case. If I understand this concept. All the grounds go to a star ground and the pots & jack & caps go in the box. Pickguard gets a copper layer underneath. Anything else to think about on this??

Best A

PS this guitar kicks ass on both my Dlite & Rocket


Last edited by angelodp on Tue Sep 09, 2008 2:50 pm; edited 1 time in total
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FunkyE9th



Joined: 05 Feb 2008
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PostPosted: Tue Sep 09, 2008 2:07 pm    Post subject: Reply with quote

You can go here..

http://www.guitarnuts.com/wiring/shielding/shield3.php

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Structo



Joined: 17 Oct 2007
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PostPosted: Tue Sep 09, 2008 5:47 pm    Post subject: Reply with quote

Yes when you use copper foil in the cavities and on the pickguard you are essentially creating a Faraday Cage shielding the inside components from RFI, 60 Hz hum not so much.

The Guitar Nuts article on "Quieting the Beast" is interesting but a bit over board if you ask me.
He makes a big deal about using star grounding but if you wire a strat for instance and utilize the back of the volume pot as your common grounding point for all the grounds, it's pretty much the same thing.

His use of a cap in there as a sort of death cap doesn't make much sense since we all know that a cap blocks DC and allows AC current to flow.

Unless you are plugging your guitar into nothing but vintage two prong corded amps where there is a chance the chassis can be hot depending on which way you plug it into the wall, it doesn't make much sense to do this.

I have tried his method without the cap and found it was no more quiet than the typical grounding scheme of using the back of a pot as a connection point for the grounds.

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FunkyE9th



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PostPosted: Tue Sep 09, 2008 6:36 pm    Post subject: Reply with quote

I've used his method, but also do not do the cap. I agree... doing a star ground on volume pot is basically the same as doing a star ground per his article. They acomplish the same thing... to have a single point for ground. However, IMO I think if you are doing a lot of pickup swapping it might be easier to not use the pot. Plus it also avoids having to heat the pot over and over.
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angelodp



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PostPosted: Tue Sep 09, 2008 8:35 pm    Post subject: Danelectro Reply with quote

Since this a Dano... with a cavity that extends through out the interior of the guitar, I am making a copper box to throw it all into. I do get continuity on the pot bodies from the combination of pot shaft and hex nut as I position the components in the box. So I can dispensed with the links from pot to pot for ground. What about the ground lug bent back to make these true variable resistors. My idea is to ground to he outside of the copper box, which is inside the guitar.

a
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FunkyE9th



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PostPosted: Tue Sep 09, 2008 11:40 pm    Post subject: Reply with quote

Have you decided where you are doing your star ground? If you have, why not just route all (including the bent lug, jack gnd, etc) the grounds to that?
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angelodp



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PostPosted: Wed Sep 10, 2008 5:06 am    Post subject: star ground Reply with quote

Ok well i have not made that decision yet... waiting for some stew mac copper tape to arrive for the pickguard. My thought is to run all the ground
runs to the box as you suggest.... not too sure how to deal with the lug ground on the pots?? I am doing graphic and will post. Do i need the lug grounds?? The box is copper and completely encloses the pots, switch and jack, makes contact with the pickguard shield ( copper foil ), as do the pots and jack via their shafts against the copper.

Thumbnail, click to enlarge.


a
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FunkyE9th



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PostPosted: Wed Sep 10, 2008 4:50 pm    Post subject: Reply with quote

If you don't plan on doing a lot of pickup swapping, then a possible option is just solder all the grounds to the back of the volume pot. To really maintain the start ground, you probably should route the bent log from the tone pot to the volume pot (i.e. instead of the back of the tone pot) also.

Another option is something similar to what was in the guitarnuts article. He had a large connector ring and the shaft of the pot goes thru it. So when you tighten the pot against the pickguard it makes all the ground contact.

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jjman



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PostPosted: Wed Sep 10, 2008 5:24 pm    Post subject: Reply with quote

Since there is no ac "power" in a guitar, as there would be in an amp, what it the advantage of a "star ground" strategy? (No I didn't read the article.) Embarassed

There should be no concern about ground loops, right?

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Alexo



Joined: 22 Mar 2007
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PostPosted: Wed Sep 10, 2008 5:44 pm    Post subject: Reply with quote

jjman wrote:
Since there is no ac "power" in a guitar, as there would be in an amp, what it the advantage of a "star ground" strategy? (No I didn't read the article.) Embarassed

There should be no concern about ground loops, right?


+1, I never saw the need for a star ground in a passive circuit, and I never had ground loops in any of my guitars! I suppose you don't want the noise you're shielding to creep up through the ground, but since all your shielding is probably just going to get grounded at the cathode of V1 in whatever amp you plug it into, will it even matter?

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FunkyE9th



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PostPosted: Wed Sep 10, 2008 6:16 pm    Post subject: Reply with quote

A ground loop is a ground loop. It's just a matter of how bad it is. Smile If we go with the reasoning only if you have ac should you worry about ground loops, then one can replace the power supply with a big battery and not worry about ground loops.

Portable devices (no ac) like cellphones, two-way radios still have to follow good grounding schemes. For example they always keep analog and digital grounds separate (maybe sort of analogous having preamp ground and power section ground).

It's been a while, so I hope I explain this correctly or somebody corrects me. It's really hard to explain without diagrams...your ground wires can be modeled as ideal wire with a very small resistor. So if you have a ground loop, you actually have resistance in those wires. So your "ground" is actually not at "ground". So ground potential is actually varying a bit as current flows though it. Those can translate to noise to different parts of the circuit.

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Structo



Joined: 17 Oct 2007
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PostPosted: Wed Sep 10, 2008 8:19 pm    Post subject: Reply with quote

Ange,
Your tone pot won't work the way you have it drawn, I think....

You need to connect the unused lug on the tone pot to the lug on the volume pot.

Thumbnail, click to enlarge.

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angelodp



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PostPosted: Wed Sep 10, 2008 8:56 pm    Post subject: yep Reply with quote

Hi tom, yes I see that now. The original had that linked and also grounded. But since i am relying on the box and contact to do ground i will dispense with the pot ground but have added the wire from vol to tone.

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angelodp



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PostPosted: Thu Sep 11, 2008 3:05 am    Post subject: inside - an more quiet Reply with quote

I adjusted the wiring to include the link for the pots, but it did not work until the link also ran to ground on the pots themselves. As shown here. It all works but the noise reduction is minimal, especially on overdrive. Perhaps all the external wires to the star connection are causing trouble.

So I re-routed all the wires to the star inside the copper box and positioned the star ground inside the box. I have added some foil to the bottom of the cavity.

I'm done for now... its pretty quiet in clean and much better in OD. single coil will never be dead quiet.

Thanks for all the support.

a

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angelodp



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PostPosted: Thu Sep 11, 2008 4:51 pm    Post subject: Final shots Reply with quote

In the end.... this helped with any hum that the pots were picking up, but the pickup still does have an exposure to EMI and some slight noise. Its better for the work done.



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