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Cavity shielding - always necessary ?

Husky

Member
Messages
11,816
Hello. I need some technical advice on the electronics. Not my strong side, especially the theory:confused: !

I am building a Les Paul Junior style guitar, and have finished doing the control cavity rout.
I will be installing a Gibson humbucker at the neck position and a Schaller piezo tune-o-matic style bridge, the latter requiring a 9 volt battery powered pre-amp fitted into the body. I bought the matching Schaller "Flagship" pre-amp for this purpose.

http://guitar-parts.biz/hp425601/Flagship.htm

I have asked Schaller in Germany if putting everything (pots, battery, preamp) into the one cavity created any issues by doing so, and their answer was 'no'.

But just to be sure to be sure, with using the passive and active pickups, and the 9volt power supply etc., is there any electronically related reason for me to shield the cavity with shielding tape or paint, or to position components differently ?


Thank you ,

Don
Always shield the cavities and any wires extending outside the shielded cavity should be shielded, 2 coats of carbon paint is fine. Ideally with a well shielded guitar there is no noise difference hand on or off the strings. There is no tone difference as long as you observe my warning about not shielding the pickup directly.

Make sure you ground the bridge tailpiece or tunamatic for a string ground
 

vortexxxx

Silver Supporting Member
Messages
10,230
Yes Aluminum can affect things lowering resonant peak. Aluminum guitars can be a big issue. Even the shield plates in Aluminum have an effect. If you understand that and it is desirable then that is fine. The thicker it is the more the effect and if you say that is impossible Aluminum is not magnetic think again.

Normal cavity shielding does not change the tone. Use copper, nickel print spray or most common, carbon paint well stirred and 2 coats, do not wrap pickups in copper. Also remember that no amount of shielding will reduce low frequency hum unless it is a faraday cage. Shielding takes care if the high end trash and buzz but hum is induced magnetically. Only way to get rid of that is to play in the dessert or to hum cancel.
What affect does the aluminum have on the guitar's sound? Does it affect certain frequencies?
 

Husky

Member
Messages
11,816
If you want to be totally quiet, yes.

If you have noisy pickups, you'll barely notice the difference.

If you have quiet pickups, you probably won't be bothered by the noise that a shield would stop in most cases.

If you're a stickler, you'll want to do both.

I just had a customer that invoked the "taking a blanket off the amp" analogy when he clipped his shield ground the other day, so there's that...
If you clip the shield connection to ground you just created a potential antenna worse than no shield at all.
 

Husky

Member
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11,816
What affect does the aluminum have on the guitar's sound? Does it affect certain frequencies?
It lowers the resonant peak reducing highs when a simple shield plate. Not drastic but a slight smoothing. Pickups in an complete aluminum body the effect is more drastic in inductance and you loose bass as well. I went bonkers at Fender once installing pickups in an Aluminum body that didn't sound as expected
 

Husky

Member
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11,816
If you're going to mix, you really need to be all one or all the other. I have seen passive and active coexist successfully in two ways (there are probably more):
  1. The two sources have different outputs (i.e. TRS jack and a splitter somewhere downstream);
  2. The two sources are never simultaneously active. This is how I've seen it done with folks who have, say, a passive neck pickup and an active bridge (Vinnie Vincent and I think Dave Mustaine used to do this). This works as long as each has its own controls and the selection is 'either/or'.
If you try to mix, the active circuit will load down the passive side. If you choose high-impedance controls for the active side, that fixes the loading problem but your controls will essentially work like on/off switches rather than volume and tone.

The easiest thing to do if you're going to mix is to put a buffer on the passive side, so it's all low-Z going out.
Only problem with buffering in a guitar is you loose the effect of the distributed capacitance of the cable that sweetens overdrive and makes things squeaky clean. I'd prefer to buffer after 20ft of cable if you really want it to sound right
 

Husky

Member
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11,816
Where shielding really helps is the ability to remove the hands from strings with no extra buzz or noise as well as RF and high freq noise and static from pickguards when the hand brushes across them. Properly done it is a good thing.
As far as aluminum
Check this out.
 
Last edited:

walterw

Platinum Supporting Member
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37,735
As far as aluminum
Check this out.
if i have this right, that's the effect of a crazy-strong neo-D magnet on a conductive but non-magnetic metal when it's moving across it. the moving magnetic field creates a current in the metal, said current creates its own magnetic field that always opposes the original magnetic field, bam you have a resistance to movement.

if you think about it, the copper wires in a pickup are not magnetically attractive, so why would pickup magnets even do anything? it's because moving magnetic fields create electricity, that electricity creates its own magnetic field.

so if i'm right here, the aluminum guard (besides being slightly microphonic) is very conductive, so the pickup magnetic fields easily create eddy currents in it, and said eddy currents affect the pickup sound a little.

it's why you don't cover pickups in copper, the stuff is too conductive, too easily creating eddy currents that fight the original signal and dull the tone.

it's why brass tele neck covers sound duller than less conductive "nickel silver" covers like gibson uses.
 

Husky

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11,816
if i have this right, that's the effect of a crazy-strong neo-D magnet on a conductive but non-magnetic metal when it's moving across it. the moving magnetic field creates a current in the metal, said current creates its own magnetic field that always opposes the original magnetic field, bam you have a resistance to movement.

if you think about it, the copper wires in a pickup are not magnetically attractive, so why would pickup magnets even do anything? it's because moving magnetic fields create electricity, that electricity creates its own magnetic field.

so if i'm right here, the aluminum guard (besides being slightly microphonic) is very conductive, so the pickup magnetic fields easily create eddy currents in it, and said eddy currents affect the pickup sound a little.

it's why you don't cover pickups in copper, the stuff is too conductive, too easily creating eddy currents that fight the original signal and dull the tone.

it's why brass tele neck covers sound duller than less conductive "nickel silver" covers like gibson uses.
It's lenz's law
https://en.m.wikipedia.org/wiki/Lenz's_law
 

AdmiralB

Member
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3,063
Where shielding really helps is the ability to remove the hands from strings with no extra buzz or noise as well as RF and high freq noise and static from pickguards when the hand brushes across them. Properly done it is a good thing.
As far as aluminum
What's unique about aluminum? This is true of any (or at least most) conductor(s), the article you linked on Lenz' law even mentions copper specifically. To whatever degree the lining of the cavity is exposed to moving magnetic fields, any conductor would experience this.

If you mean specifically in the application of a pickguard shield, I could see that perhaps interacting with the pickups...but it's due to the shape and positioning of the shield, not the material. A copper or brass guard wouldn't be any better.
 

AdmiralB

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3,063
Only problem with buffering in a guitar is you loose the effect of the distributed capacitance of the cable that sweetens overdrive and makes things squeaky clean. I'd prefer to buffer after 20ft of cable if you really want it to sound right
Or, you lose the effect of capacitance that dulls tone and requires you to boost treble to get it back. Those who play wireless (and don't use a 'drag' circuit), for example. Two sides to everything!
 

Husky

Member
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11,816
What's unique about aluminum? This is true of any (or at least most) conductor(s), the article you linked on Lenz' law even mentions copper specifically. To whatever degree the lining of the cavity is exposed to moving magnetic fields, any conductor would experience this.

If you mean specifically in the application of a pickguard shield, I could see that perhaps interacting with the pickups...but it's due to the shape and positioning of the shield, not the material. A copper or brass guard wouldn't be any better.
True and Lenz applies to Copper as well.
However the Aluminum is what is common for vintage thick pickguard shields probably due to the lightness and cost. I don't know if the inductance loss when installing pickups in to an aluminum body is a result of Lenz. I'll leave that up to someone with Physics better magnetic knowledge than me. All I know is what I observed and measured with Aluminum as a thick pickguard shield and Aluminum body. I have not observed any issue with a copper shielded cavity or carbon paint shield. Generally I don't care for Aluminum tape because you can't solder it together in a cavity if going that direction.
 

Husky

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11,816
Or, you lose the effect of capacitance that dulls tone and requires you to boost treble to get it back. Those who play wireless (and don't use a 'drag' circuit), for example. Two sides to everything!
Same thing I was saying, it is the low impedance that makes the capacitance have little effect. However, you can not mimic distributed capacitance with a simple capacitor. If that is what you are going for then it is the way to go I just wanted the OP to know there is a major tone and feel difference.
 

walterw

Platinum Supporting Member
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37,735
What's unique about aluminum? This is true of any (or at least most) conductor(s), the article you linked on Lenz' law even mentions copper specifically. To whatever degree the lining of the cavity is exposed to moving magnetic fields, any conductor would experience this.
i think it's at least somewhat about just how conductive the stuff is as well as how close it is to the pickups.

aluminum is right behind copper as one of the three or four most conductive metals around, and an anodized pickguard is a thick slab of the stuff compared to typical shielding or pickup covers.

shielding paint is way down the list.
 

vortexxxx

Silver Supporting Member
Messages
10,230
So copper shielding in the cavities should have some effect too?

The Jazzmaster with the gold anodized pickguard really sounds great as I upgraded all the electronics and bought 'hot for Jazzmaster' Seymour Duncan pickups. Now you got me thinking if it would sound better with another pickguard. It does add some sympathetic vibrations to the sound which I like though.
 

walterw

Platinum Supporting Member
Messages
37,735
So copper shielding in the cavities should have some effect too?
in the control cavities, no. only if the shielding is really conductive and really close to the pickups should you hear any tone change.
The Jazzmaster with the gold anodized pickguard really sounds great as I upgraded all the electronics and bought 'hot for Jazzmaster' Seymour Duncan pickups. Now you got me thinking if it would sound better with another pickguard.
"better"? says who?

"slightly different" maybe
 

Husky

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11,816
So copper shielding in the cavities should have some effect too?.
I tried to measure that and can find no difference in resonant peak or capacitance or inductance. You need to get close to get pickup to start causing issues. The biggest tone killer is when people shield a Strat cover or wrap the pickup with copper which creates what is essentially a shorted turn. Claptons blackie funny enough the covers were shielded. I have to say it's tone didn't impress me but the player can correct a lot of wrongs.
 

walterw

Platinum Supporting Member
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37,735
Claptons blackie funny enough the covers were shielded. I have to say it's tone didn't impress me but the player can correct a lot of wrongs.
i'd read somewhere that in those days clapton actually preferred the slightly duller tone this created. (of course there were lots of drugs involved too...)
 

SamBooka

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2,224
i'd read somewhere that in those days clapton actually preferred the slightly duller tone this created. (of course there were lots of drugs involved too...)
We all have our reasons for liking what we like… For example people who love MXR Dynacomp pedals which are when the least transparent compressor petals. Then there is Steve Ray Vaughn who loved coiley cords because they don't let too much "sound " through.
 

vortexxxx

Silver Supporting Member
Messages
10,230
I completely forgot that I have a Fano with an aluminum front and back and chambered Lucite in the middle. I enjoy playing it but it doesn't have the harmonic richness that some guitars do when they start overdriving a tube amp.

 




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