Strat build from scratch-Question about potential eddy current losses using solid copper pickguard

[SoulFetish]

I'm getting my unfinished strat body this week, and I'm starting to put together the supplies I need (ie, grain filler, hardware, knobs, etc.) for the project. For the aesthetic, I'm thinking of going with a with a white finish on the body, and etched solid copper pickguard showing a modest patina. A nicely beveled solid copper pickguard, would look fantastic when paired with the right wood finishes, and would be difficult to replicate with a different material and faux type appearance, without looking cheap.
Other than what will almost certainly be more money than I want to spend on a pickguard, the main concern is how the copper plane might introduce eddy current losses that could affect the pickup's expected resonance. What effects might I expect from using copper as a pickguard material? Also, would the construction style of the pickup make a difference in what kind of influence the copper pickguard might have?

For instance, I'm becoming more and more of a fan of the Bill Lawrence SmCo noiseless pickups. I think they sound very good, and I think it's a clever design. I already have a set that came stock in my other strat, so I might try something else. If I were to go with another noiseless type of pickup that fits into a single coil footprint, I would probably go with a Zexcoil set; and I've always liked the sound of Jason Lollar's traditionally wound single coils, if I were to go that route. So, it's probably down to those three types of pickups, if that helps direct anyone's answers.

[Leo_Gnardo]

Sounds like a kool project & looking forward to pics & sound bites of the finished product. I wouldn't sweat eddy current losses due to a copper pickguard. Plenty of guitars have copper shielding, including the back of pickguards on Strats and siimilar instruments. Do they have eddy current losses? Hm... hard to tell. One would have to do before/after comparisons. But I reckon if your copper (or brass, iron, aluminum, etc) is not in close proximity to the magnets, like in a backing plate right behind, or a cover over the magnets/coils then it's no worries. My 2 pence worth, if that. Let's hear the pickup builders, engineers & scientists sound off on this.

[Helmholtz]

A solid copper pickguard will have strong Eddy losses especially with SCs. Even a thin aluminum sheet has audible effect on treble response.

As the PG closely surrounds the PUs, you have maximum coupling and Eddy currents - much more than with shielding foil.
The PU and the surrounding copper PG can be seen as a (loosely coupled) transformer with a shorted secondary.
The lower the resistance of the pickguard (= shorted single secondary turn), the more losses you get.

If you have an LCR meter, you can see the Q-factor of the inductance drop when placing the PU on a copper or aluminum plate. This shows the Eddy losses.
In a copper PG the effect is even stronger.


BTW, unprotected copper would tend to look ugly over time by surface corrosion.

[xtian]

BTW, unprotected copper would tend to look ugly over time by surface corrosion.

Or beautiful, depending on your aesthetic...

[Helmholtz]

Or beautiful, depending on your aesthetic...

Well, if you like black fingerprints..

[Antigua]

I'm getting my unfinished strat body this week, and I'm starting to put together the supplies I need (ie, grain filler, hardware, knobs, etc.) for the project. For the aesthetic, I'm thinking of going with a with a white finish on the body, and etched solid copper pickguard showing a modest patina. A nicely beveled solid copper pickguard, would look fantastic when paired with the right wood finishes, and would be difficult to replicate with a different material and faux type appearance, without looking cheap.
Other than what will almost certainly be more money than I want to spend on a pickguard, the main concern is how the copper plane might introduce eddy current losses that could affect the pickup's expected resonance. What effects might I expect from using copper as a pickguard material? Also, would the construction style of the pickup make a difference in what kind of influence the copper pickguard might have?

For instance, I'm becoming more and more of a fan of the Bill Lawrence SmCo noiseless pickups. I think they sound very good, and I think it's a clever design. I already have a set that came stock in my other strat, so I might try something else. If I were to go with another noiseless type of pickup that fits into a single coil footprint, I would probably go with a Zexcoil set; and I've always liked the sound of Jason Lollar's traditionally wound single coils, if I were to go that route. So, it's probably down to those three types of pickups, if that helps direct anyone's answers.

I did some relevant testing if you google "Eddy currents in relation to an aluminum Tele pickguard" it will turn up. The amplitude at resonance dropped by about 3dBV, without load, which means that with load, the losses are negligible, with a rather thick aluminum pick guard. I believe the losses were too great for the same reason they're not that great with a Telecaster bridge plate; the conductive loop is not very close to the coil, and it only intersect with the magnetic field on one plane, the plane of the pick guard, where as a cover or the pole pieces intersect with it in three dimensions. But if you wanted to feel better about having any losses, using 500k pots instead of 250k would win back whatever was lost to eddy currents.

[SoulFetish]

BTW, unprotected copper would tend to look ugly over time by surface corrosion.

It certainly could look ugly. But a controlled treatment of annealing and turquoise colored oxide finish on a pickguard with an etched paisley or scroll design would look killer. When I got the effect where I wanted it, I would need a way of treating it, to preserve the desired look.

I would use the technique subtly, and allow the nice turquoise build up in the etched groves, but here are some examples of oxide and




It will look killer.

[SoulFetish]

I did some relevant testing if you google "Eddy currents in relation to an aluminum Tele pickguard" it will turn up. The amplitude at resonance dropped by about 3dBV, without load, which means that with load, the losses are negligible, with a rather thick aluminum pick guard. I believe the losses were too great for the same reason they're not that great with a Telecaster bridge plate; the conductive loop is not very close to the coil, and it only intersect with the magnetic field on one plane, the plane of the pick guard, where as a cover or the pole pieces intersect with it in three dimensions. But if you wanted to feel better about having any losses, using 500k pots instead of 250k would win back whatever was lost to eddy currents.

I'm definitely going to look at your research. Great idea on the option of using 500k pots to recover losses from damping of the resonant peaks. I wish I'd thought of it.
Appreciate the info!

edit: by the way, I just found that page on guitarnuts2. Is that your tele? LOVE the look of that guitar, by the way.
I'll have to do a build log of this strat as I start getting into it.

[Helmholtz]

Some years ago I experimented with pieces of different thickness sheet aluminum having PU cutouts, that could be placed (and taped) over the PUs of a strat on top of the PG.


Audible treble loss started at 0.01" and increased with thickness of the sheets.

[Antigua]

I'm definitely going to look at your research. Great idea on the option of using 500k pots to recover losses from damping of the resonant peaks. I wish I'd thought of it.
Appreciate the info!

I think the summary I gave might be all there is to say about my own testing, but I wanted to show that I really did have "findings" to speak to. I'd actually suggest reading this moreso https://kenwillmott.com/blog/archives/246 , "Undercover Pickups" on kenwillmott.com, it's a more expertly written document about eddy currents. If you were to put cuts in the pickguard between the pickup holes using a fine kerf saw, it would eliminate the eddy currents entirely, but my testing indicated that it's not even worth the trouble. On the other hand, cutting covers, especially brass covers, can render them magnetically transparent.

[Fluoroscope 5000]

The eddy current effects of metals around the pickups aren't necessarily the same electrically as electrodynamically (if that's the correct term). While one study showed a ~2dB loss in an electrical signal above 2kHz with a (paramagnetic) Aluminum pickguard, the loss from the electrodynamically created eddy currents interacting with the direct magnetic string vibrations was not presented. Bill Lawrence claimed a 0.015~0.03" thick Aluminum shield affects the upper-mids without affecting the highs. The electrical signal loss from such a thin shield should be inaudible -- maybe ~1/4dB? The results of my b4 and after recordings with Al shielding coincide with those claims: Sweeter upper-mid sound and no audible high-end loss. He also claimed that a ~1/4" Al shield would virtually eliminate 60Hz hum, but would drop the output by ~6dB. I would then conclude that the Al thickness electrodynamically cancels the upper-midrange first, and increases in bandwidth with the Al thickness. The coil mass & shape and the field strength of the poles may affect the result.

I think a (diamagnetic) Cu pickguard electrodynamically reduces the high-end without affecting the midrange, so it's sort of the opposite effect. 1 or 2 500k pots should help, but that may also increase the 3-3.5kHz harshness and still have some 4kHz+ loss. I agree that Copper looks awesome, but I'd find a plastic (or wooden) pickguard with a color pattern you like and use 1 or 2 GFS Al pickguard shields for some upper-mid softening if you want.

I'd try the Zexcoil 'Z-core' set. Zexcoils have a few other advantages over typical single-coil designs wound with 42AWG wire. The thinner gauge wire used gives them stronger note fundamentals from increased coil density, so they are warmer, and the high end is a bit smoother and more open. They also have individually wound string voicing. I assume that means fatter plain string timbre and brighter wound string timbre. The Vintage Hot set is a good choice for versatility. They are essentially flat in response i.e no mid-dip. Install a Wilde "Q-Filter" if you want a variable mid-dip (I love mine). $34+ shipping may be a bit much for such a simple passive device, but you won't get the silent operation and high-end extension from a simple iron core coil wound to the same inductance.