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Cavity shielding - always necessary ?

donnyb

Member
Messages
536
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
 

AdmiralB

Member
Messages
3,063
I have a lot of guitars, and comparatively few of them have shielded cavities. I notice no differences in noise between the two varieties.
 
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walterw

Platinum Supporting Member
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37,735
i'll defer to Car Talk's director of chicken soup, Kent Hoyt.

shielding will indeed reduce the extra noise you get when you let go of the strings, and will otherwise cause no problems.

i like the MG chemicals nickel supershield spray for this, one good spray coat dries in like 2 minutes and is nearly as conductive as solid copper foil (so way better than is needed here).
 
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Zexcoil

Vendor
Messages
5,687
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...
 

donnyb

Member
Messages
536
Thanks for the lead on the nickel spray Walter. I have never seen it in Australia. Any Aussies reading this and know of this or a similar product that's readily available here ?

Still seeking comments on if there is any weird stuff lurking if mixing passive and active pickups, especially in a piezo /Classic 57 marriage I cited in my original post. Thank you.
 

ahhlou

Member
Messages
778
Shielding a control cavity is always a good idea from an electronics point of view. You will appreciate it if you gig on stage with neon beer signs nearby...

A few tips. Conductive paint is easy to install (at least two or three coats). Don't forget to ground it with a screw/eyelet/wire to ground and test it with an ohmmeter. Also Don't forget to shield the cover and ground it as well. Finally, the job is not complete unless you shield the pickup cavities, wire routes and pickguard (if present).

Is it worth it? If you play the guitar at home or it is extremely valuable or vintage... probably not. If you use it regularly on stage or in a studio... probably.
 

AdmiralB

Member
Messages
3,063
Still seeking comments on if there is any weird stuff lurking if mixing passive and active pickups, especially in a piezo /Classic 57 marriage I cited in my original post. Thank you.
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.
 

T Dizz

Member
Messages
20,842
Shielding a control cavity is always a good idea from an electronics point of view. You will appreciate it if you gig on stage with neon beer signs nearby...

A few tips. Conductive paint is easy to install (at least two or three coats). Don't forget to ground it with a screw/eyelet/wire to ground and test it with an ohmmeter. Also Don't forget to shield the cover and ground it as well. Finally, the job is not complete unless you shield the pickup cavities, wire routes and pickguard (if present).

Is it worth it? If you play the guitar at home or it is extremely valuable or vintage... probably not. If you use it regularly on stage or in a studio... probably.
how can I test the shielding with my OHM meter? I want to do this next build. what should it read?
 

SamBooka

Member
Messages
2,224
Somethign that wasnt pointed out (or I didnt notice and am not paying attention). Even if your cavity isnt shielded most of your cable runs are .. so you are aprobably good.
 

ahhlou

Member
Messages
778
how can I test the shielding with my OHM meter? I want to do this next build. what should it read?
Once you have the shielding in place and grounded (screw/eyelet connector/wire to known ground like the back of a pot) you can test the connectivity with a DVM (multimeter). Set it to ohms (low range 100 ohms for example). connect the probes between the signal ground (input jack) and various locations within the shielded cavity. It should read near zero on the multimeter. A few ohms fluctuation is fine (even bare wire has resistance) but the closer to zero the better.

You can test the grounding of your bridge using the same method and (if installed) the shielding in your PU cavities, pickguard, etc.
 

T Dizz

Member
Messages
20,842
Once you have the shielding in place and grounded (screw/eyelet connector/wire to known ground like the back of a pot) you can test the connectivity with a DVM (multimeter). Set it to ohms (low range 100 ohms for example). connect the probes between the signal ground (input jack) and various locations within the shielded cavity. It should read near zero on the multimeter. A few ohms fluctuation is fine (even bare wire has resistance) but the closer to zero the better.

You can test the grounding of your bridge using the same method and (if installed) the shielding in your PU cavities, pickguard, etc.
Thanks! great info!
 

walterw

Platinum Supporting Member
Messages
37,735
Still seeking comments on if there is any weird stuff lurking if mixing passive and active pickups, especially in a piezo /Classic 57 marriage I cited in my original post.
like @AdmiralB says, passive and active don't mix. i assume the schaller preamp has a provision to take a passive electric pickup and blend it internally? if so you're golden, if not you're gonna want to run the piezo and the humbucker to separate outputs and separate amps.

(edit: yes it does, you can run the humbucker right into the preamp, where it gets buffered and mixed with the active piezo signal.)
 
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The_Whale

Member
Messages
6,133
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.
The hardest part about shielding a guitar is taking it apart.

Since it's not put together yet, you might as well take the effort to shield it.

just my opinion
 

donnyb

Member
Messages
536
Hey, thank you all for the replies ! We can learn so much from each other, bit by bit.

Hopefully, I will be able to give more answers here than post questions as time goes by !

The hardest part about shielding a guitar is taking it apart.
Since it's not put together yet, you might as well take the effort to shield it
Sound like good advice. I have been looking for Walter's MG product (shown in this thread) but not available in Australia. Are there any more brand names in the USA like 3M that make a similar product ? I can look for those over here too.

Thank you All again
 
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Mark Robinson

Platinum Supporting Member
Messages
8,420
I'm not a devotee of cavity shielding generally. It may rid you of a tiny bit of almost inaudible hum, but only if you have done a few, much more significant things first. #1 if you have stock Fender type single coils, forget cavity shielding, the hum from coil proximity to ambient fields will be 30 db louder than any benefit. #2 if you run uncovered humbuckers, put covers on them before you bother with cavity shielding. #3 if you have humbuckers with the now popular unbalanced coils, there's a really good chance that the cavity shielding will not get you where you want to be, for clean playing. This includes the Illitch system, which I have and love, but it's unbalanced and though it can make a guitar WAY more usable, it won't get you to perfect quiet in all cases, especially if you need to stand next to or over an amp, and cavity shielding won't make a significant contribution in my experience. I inclued Illitch with buckers, cause that's essentially what it does, makes a buck for a single coil.

If you need studio quiet for super clean Fender sounds, with vintage design electronics, you need some cable length, the right angle and no ballasts or fields in your area. Kinman, DiMarzio and Fender noiseless pickups and of course, EMG pickups, will deliver stone quiet, but a lot of players just don't care for them. I like some gain and I play in very unregulated live venues, so noiseless pickups are always present in one of my guitars at any gig. I have shielding paint, grounded in some of my guitars, but it's not a game changer to me.
 

vortexxxx

Silver Supporting Member
Messages
10,230
I'm going to throw a curveball in this debate. The guitar I had posted about having issues setting up was a Fender Jazzmaster with an anodized pickguard. I've been seeing posts from others with anodized pickguards that their tone increased greatly when the switched to a plastic pickguard. The anodized pickguard is providing shielding, but can it be affecting the magnetic field of the pickups. This is a purple sparkle guitar which looks great with the gold anodized pickguard, so I'd rather not change it. It was a metric pickguard and it was alot of work getting good non-metric components to fit the guard, so I'm not planning on testing the theory unless it makes a really big difference.
 

Mark Robinson

Platinum Supporting Member
Messages
8,420
I remember John Suhr having some opinions about aluminum guards, backed with some data about inductance change, cautionary enough for me to stuff some plans I had.
 

Husky

Member
Messages
11,816
I'm going to throw a curveball in this debate. The guitar I had posted about having issues setting up was a Fender Jazzmaster with an anodized pickguard. I've been seeing posts from others with anodized pickguards that their tone increased greatly when the switched to a plastic pickguard. The anodized pickguard is providing shielding, but can it be affecting the magnetic field of the pickups. This is a purple sparkle guitar which looks great with the gold anodized pickguard, so I'd rather not change it. It was a metric pickguard and it was alot of work getting good non-metric components to fit the guard, so I'm not planning on testing the theory unless it makes a really big difference.
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 in to the coil. Only way to get rid of that is to play in the dessert or to hum cancel.
 
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