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Post subject: Does shielding affect the tone of a single coil P-bass?
Posted: Tue Feb 19, 2013 8:47 pm
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Hi Everyone,
I'm new here, so before I jump into a question I'll tell you a little about myself. I'm in my late 50s and have been playing guitar/bass since the early 70s. I'm strictly an amateur and play mainly for therapeutic reasons (it's hard to worry about all the stresses in life when your trying to figure out a cool riff). :wink: I have two basses; a Mexican Reggie Hamilton and a CS '55 P-Bass NOS, both awesome basses. My amp is a Mojotone tweed Bassman that I built from a kit.

I've read a couple of posts here and have also found some great information on offsite resources (thank you BrotherDave) regarding shielding of single coil pickups and control cavities to eliminate hum. My question is, does the shielding affect the tone of a single coil pickup? I vaguely remember reading somewhere that it did. I'd like to shield the 55 P-Bass, but only if it won't negatively affect the tone. Can anyone shed some light on this?

Thanks in advance,
Nick


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Wed Feb 20, 2013 12:18 am
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Thank you for your kind words.

I'm sure someone else has a differing opinion but the advantage of PROPERLY copper shielding to ground outweighs by a landslide any negative tonal impact on any single coil solid body stringed electric instrument. I do not hear any tonal degradation on my copper shielded instruments other than they are far less susceptible to hum and RFI.

I am a huge single coil pickup fan. My very best sounding instruments are copper shielded single coil instruments. I prefer real single coil tone to the noiseless designs such as the Fender Noiseless Jazz or to the split wound first generation P-Bass replacement pickups such as the Lindy Fralin one I have. That Fralin split wound single coil replacement sounds just like a 1965 P-Bass and nothing like a 51 P-Bass. Yes the Fralin split coil pickup is absolutely noise free but I think it rips the soul right out of a first generation instrument to the point of it no longer sounding like a first generation P-Bass whatsoever. I might as well be playing a split coil P-Bass as the one with the Fralin split coil first generation pickup in it. I have a similar feeling when playing a Jazz loaded with top notch noiseless pickups. It just doesn't sound much like a Jazz Bass either.

If copper shielding to ground negatively impacted tone to any degree which I could notice then I wouldn't do it on every single coil bass I have. I have also done it on several split coil P-Basses. Why on the split coil ones? To shield the unshielded leads, other wiring and pots.

Also, if it messed up tone then copper shielding wouldn't be such a popular mod in both Strats and Teles either, because as everyone in the bass forums knows, electric Spanish guitarists are really picky about their tone too.

People who say it "messed with the tone" probably did something wrong or perhaps were so used to their instrument working as much like an RFI Theramin as it does a guitar that they actually missed the noises it made without the shielding while moving toward some RFI source like their amp.

I've noticed the same thing with the Ceramic Disc versus Paper In Oil tone capacitor debate. Some players actually miss the crunch and edge of the Ceramic Disc capacitor and put it back in after trying a cap with lower distortion. They actually miss the distortion, so to them the distortion free Paper In Oil cap sounded worse! I think that missing the noise is part of the equation in any tonal degradation argument about copper foil shielding to ground. Some electric Spanish players actually use RFI as a component to their tone. (I should not have to name any names here as examples. I think everyone knows a few.)

It is easy to get something wrong during a shielding job like damaging a pickup coil, cracking a solder joint or having the copper foil touch something it shouldn't such as the hot jack terminal....and in any of those cases then YES it absolutely will sound worse.

Now here is my stock semi-scientific explanation of "WHY COPPER SHIELDING DOES NOT EFFECT TONE IN AN ELECTRIC GUITAR." Copper isn't actually in the circuit but is merely connected to ground. Pure copper can't impact the pickup magnets either as some people claim because, as any physicist will tell you, copper is diamagnetic. Diamagnetic is a scientific term describing the magnetic property of any material that is not attracted to magnets at all. Diamagnetic elements can never be magnetized and in fact have a slight negative reaction to a magnetic field instead of a positive one, meaning they are very slightly repelled. Copper cannot be even temporarily magnetized nor can it cause a magnet to demagnetize by it's proximity or "suck out the pickup's Mojo." Copper and free space both have a magnetic relative permeability of 1, meaning copper makes no more difference to the magnetic pickup than does the air that would be there if the copper wasn't. Air also has a magnetic relative permeability of 1.

Brass, which Fender used in shielding pickup base plates in some single coil and split coil bass instruments, is an alloy composed usually of at least 2 to 4% ferrous metals (principally iron & steel) which of course are magnetic materials. However in such small concentrations even the small amount of ferrous elements in the brass base plates had no tonal impact. In fact the Pre-CBS instruments with these brass base plates are among the most treasured electric instruments in the world with highly coveted tone.

Yet in spite of the physics, out there somewhere is some player who didn't like it.


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Wed Feb 20, 2013 6:52 am
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BrotherDave, I was hoping you would chime in and I can't thank you enough for the detailed response. You obviously have a lot of knowledge and real world experience on the topic and your answer is what I wanted to hear. My experience with different basses is limited (4 basses over a span of 40+ years), but I recently discovered that I too am a huge fan of single coil pickups. My '55 is by far my favorite in terms of sound; I'd just like to improve upon the noise a little.

If you don't mind, a couple of follow up questions; Do you shield the leads between the pickup and control cavity? Do you bother with shielding the recess for the output jack?


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Thu Feb 21, 2013 11:52 am
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On a first generation P-Bass I do not shield the jack cup area or the wiring channel as access is nearly impossible in these areas and I don't want to desolder anything at all. The exposure is minimal, only about 6 inches combined. The less you mess with the jack socket on these the better and in fact I don't want to disturb any existing factory solder joints at all. The new ground wire from the pickup cavity is soldered to the copper tape in the control cavity and not to the pots. Once the instrument is reassembled check continuity with a multi-meter between the copper in the pickup cavity to the bridge and to the control plate. They should all show continuity.

Additionally on a first generation P-Bass I often solder in a second ground wire to the copper shielding in the pickup cavity and route this additional wire so that it comes out the top of the cavity on the G string side and the stripped & tinned end is looped under the pickup cover screw on the G string side. This puts the pickup cover in the ground system. The real 51's did this too but it was eliminated on the 52's as being too labor intensive for the benefit. There is some benefit, just not enough to warrant taking 5 minutes per instrument and a little extra wire to do it. Some people might suggest soldering on a washer type terminal connector for the pickup cover screw to go through, however the tinned bare wire works fine and will flatten some under screw pressure to completely conceal it where a metal terminal won't squish any flatter than it already is and will leave an indention around the screw hole when removed in the future or can even cause a crack the finish. This wire can be really thin. Some people expand on this concept with an extra wire from the bridge to the bridge cover screw but I can't tell any benefit at all in doing that. Grounding the bridge cover doesn't hurt anything but I don't think it helps any either.

On a first generation P-bass there is no need to copper tape shield the back of the pickguard as it has no benefit since the pickguard doesn't surround a pickup and there are no wires under the pickguard either. A Strat or Jazz yes, but not on a first generation P-Bass.

Since the control plate is already metal on a first generation P and a Jazz there is no need to copper tape shield the back of the control plate either. I overlap the copper sheeting slightly over the lip of the control cavity so it will contact the control plate yet still be concealed when the instrument is assembled and this eliminates the need to solder an additional ground wire to the back or side of the volume pot.

A couple of final points. 1. This will not make the instrument as quiet as a split coil or humbucking instrument. It will be more immune to RFI yes, but not totally immune. 2. All the copper tape and ground wires can be removed without a trace when selling or trading or getting an appraisal.


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Sun Feb 24, 2013 12:39 am
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BrotherDave,
I really appreciate all of the fine details. This gives me the confidence I needed to tear into my new bass. All I need now is enough time to complete everything in the same day (don't want to leave a guitar/bass unstrung for any longer than absolutely necessary). I'll post results later.
Thanks again,
Nick


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Sun Feb 24, 2013 4:40 am
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That is sensible.


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Post subject: Re: Does shielding affect the tone of a single coil P-bass?
Posted: Sun Feb 24, 2013 4:44 am
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Come to think of it, it may not be necessary to actually remove the strings. You might want to loosen them just a bit, then use an appropriately sized block and prop them up just enough to remove the pickup from the pickup cavity. To the best of my memory that works on a first generation bass and then just work around the strings. I really don't think I ever removed the strings for pickup cavity shielding.


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