Using a metal pickguard to reduce pickup noise

[skycruiser]

A quick demo showing how single coil buzzing can be reduced by having a somewhat thick metal plate surrounding or covering (quite close) to the pickup. The pickup in the video goes straight to a jack, then cable to Ampeg combo.



I have had trouble with multiple single-coil basses and pickups over the last few years. They were all noisy as shown in the video. I have done all types of shielding and grounding and none of it has any effect on this particular type of interference. The only solution I have found, besides switching to NC pickups, is to use a metal plate around the pickup.

Of course the best solution is to find the source of the noise and kill it. But that won't help you if you run into this problem on a gig. It is definitely a location/environment related thing because I have taken my noisy bass other places with no issues.

I don't plan to own another bass with single coils without either a metal pickguard surrounding them or some sort of removable plate that can be installed when I run into noise.

 

[XLunacy]

What is the blue plate thing? Aluminium plate covered with tape?
Why is the aluminium pickguard doing something, but not the aluminium foil? Is it only aluminium?
Since the pickguard is not grounded, why is the noise still attenuated? Is the EM noise simply "reflected" back or something like that?
Would the noise have been reduced further had the pickguard been grounded?
Do you get better noise reduction by placing another plate under the pickup?

 

[Dadum]

How about using conductive paint on the interior side of a plastic pick guard? It is easier to make than creating an aluminum pickguard.

 

[skycruiser]

What is the blue plate thing? Aluminium plate covered with tape?
Why is the aluminium pickguard doing something, but not the aluminium foil? Is it only aluminium?
Since the pickguard is not grounded, why is the noise still attenuated? Is the EM noise simply "reflected" back or something like that?
Would the noise have been reduced further had the pickguard been grounded?
Do you get better noise reduction by placing another plate under the pickup?

I should have described the blue plate. It is 0.05" thick copper plate, similar thickness as the aluminum pickguard. This is what I'm using temporarily to shield my bridge pickup, and it is covered with tape so I won't scratch the bass and pickup when I take it on and off. Copper is much easier to cut and shape than aluminum.

In my experimenting, I didn't find noticeable difference between a grounded and non-grounded plate (pickguard). I don't ground the blue tape covered copper plate when I use it, and it does a great job cutting the noise in that pickup.

I just checked and placing a thick plate under the pickup has a similar effect.

I also tried putting the pickup in a plastic bag and completely covering it with foil. This had no impact on this noise. I then lowered the thick plate as shown in the video and the noise is reduced. So again, it is the proximity of a thick plate that is reducing the noise.

The video shows that this isn't a simple shielding effect that you can get with thin foil. Thickness is required. My working theory is this is an EM wave attenuation effect. The magnitude of EM waves are attenuated as they pass through conductors, and the amount of attenuation (reduction) depends on the thickness, and if I recall correctly, the frequency of the radiation. But if this is what is happening, it is not clear to me why it still works when the pickup is protruding through a hold in the plate. You might think it needs to be fully covered. It is possible the physical size of the waves is large (several inches) so attenuating them around the pickup effectively attenuates the signal that reaches the coil. This is all speculation, but it is the only effect I have come across that depends on conductor thickness.

 

[Dadum]

The aluminum has some practical shielding effect due to the “Lenz effect.” The aluminum plate is probably not pure aluminum (alloy properties are different than pure aluminum) whereas the aluminum foil is probably pure aluminum (and very soft). Also, thicker plates have a stronger effect (check out discussion in link). Also, pure aluminum in motion against a magnetic field can create electrical currents and thus magnetism. Some Lenz effect could be what is happening.

Here someone discusses a positive experience with EMI shielding with an aluminum alloy plate.

Magnetic shielding with aluminum

Maybe this gives a path to investigate on how an ungrounded metal plate is helpful. Especially since aluminum and copper are not “magnetic” (regular magnets don’t stick to them).

I don’t know much but I’m just pointing to a possible connection.

 

[Dadum]

An interesting EMI test would be using thinner magnet material such as low cost zinc plated metal.

But, this could hurt the pickup performance due to disturbing the normal magnetic interaction between pickup and strings though. Just wondering about it. It could be a magnetic mute in some ways similar to a foam one for those who want a blunted sound.

 

[skycruiser]

The aluminum has some practical shielding effect due to the “Lenz effect.” The aluminum plate is probably not pure aluminum (alloy properties are different than pure aluminum) whereas the aluminum foil is probably pure aluminum (and very soft). Also, thicker plates have a stronger effect (check out discussion in link). Also, pure aluminum in motion against a magnetic field can create electrical currents and thus magnetism. Some Lenz effect could be what is happening.

Here someone discusses a positive experience with EMI shielding with an aluminum alloy plate.

Magnetic shielding with aluminum

Maybe this gives a path to investigate on how an ungrounded metal plate is helpful. Especially since aluminum and copper are not “magnetic” (regular magnets don’t stick to them).

I don’t know much but I’m just pointing to a possible connection.

Thanks for your input. Interesting information. I am having a little trouble imagining how a Lenz Effect type of interaction might occur here because there is no varying magnetic field. When you have a fully built up guitar and you pluck the strings, then you have a varying magnetic field as the magnetized strings vibrate. In the video above, there are no strings and the pickup is just sitting on the floor.

 

[sunbeast]

A plate like this interrupts the electromagnetic waves, but will also affect the tone of the pickup significantly via eddy currents as it affects the magnetic field of the pickup itself in a similar fashion (aluminum and copper would have different affects, with the copper I would think a stronger one), particularly when placed around the coil vs underneath it. Eddy currents effectively lower the amplitude of the resonant peak of the pickup making it darker (similar tonal effect to adding a ton of loading resistance to the electronics, but with some unique lossy artifacts before the cutoff as well).

To me humcancelling pickups are a better compromise as you retain a strong resonant peak, generally it is just a bit lower in frequency and mains hum is virtually eliminated.

Something to try though is to cut a notch all the way through your copper plate so that it no longer makes a full uninterrupted path around the pickup coil- doing this should eliminate a lot of the eddy current losses to the pickup coil, though the aluminum material should be noticeably better if it is also notched. Not sure how this might affect the shielding though as these waves would be on a different plane.

 

[skycruiser]

A plate like this interrupts the electromagnetic waves, but will also affect the tone of the pickup significantly via eddy currents as it affects the magnetic field of the pickup itself in a similar fashion (aluminum and copper would have different affects, with the copper I would think a stronger one), particularly when placed around the coil vs underneath it. Eddy currents effectively lower the amplitude of the resonant peak of the pickup making it darker (similar tonal effect to adding a ton of loading resistance to the electronics, but with some unique lossy artifacts before the cutoff as well).

To me humcancelling pickups are a better compromise as you retain a strong resonant peak, generally it is just a bit lower in frequency and mains hum is virtually eliminated.

Something to try though is to cut a notch all the way through your copper plate so that it no longer makes a full uninterrupted path around the pickup coil- doing this should eliminate a lot of the eddy current losses to the pickup coil, though the aluminum material should be noticeably better if it is also notched. Not sure how this might affect the shielding though as these waves would be on a different plane.

Good suggestion sunbeast. I will definitely give this a try - see if the plate needs to be a complete circuit around the pickup or not. I suspect it does not need to be since putting the plate near but not around it has a similar effect. This test would provide an interesting clue though. I'll have to pick up another copper plate to do this test - don't want to ruin my "working" plate that I have now.

I really need to look into what you are saying about eddy currents affecting the tone because honestly I cannot discern even the slightest change in tone when I put the plate on my bridge pickup. The noise goes away but nothing else seems to change. People have been using aluminum pickguards for decades and, maybe I missed it, but I haven't seen much discussion about concern for these pickguards affecting tone. The entire series of Squier 40th anniversary basses and guitars use aluminum pickguards for example. But to test this some sort of audio spectrum analysis would need to be done and unless this can be done in my DAW software (Audacity), I'm not really equipped to do it. Audibly though, I detect no tonal change when using the aluminum pickguard and the copper bridge plate that I added.

Edit: After some googling and reading, there is talk on various forums about the effects of metal pickguards on tone. Maybe a higher frequency effect that might not affect bass so much. Hard to say. Not noticeable to me - and I have tried HC pickups which, to my ear, did sound significantly different and "dark". I really hated the ones I have tried, though I accept there may be others that sound great.

 

[sunbeast]

Good suggestion sunbeast. I will definitely give this a try - see if the plate needs to be a complete circuit around the pickup or not. I suspect it does not need to be since putting the plate near but not around it has a similar effect. This test would provide an interesting clue though. I'll have to pick up another copper plate to do this test - don't want to ruin my "working" plate that I have now.

I really need to look into what you are saying about eddy currents affecting the tone because honestly I cannot discern even the slightest change in tone when I put the plate on my bridge pickup. The noise goes away but nothing else seems to change. People have been using aluminum pickguards for decades and, maybe I missed it, but I haven't seen much discussion about concern for these pickguards affecting tone. The entire series of Squier 40th anniversary basses and guitars use aluminum pickguards for example. But to test this some sort of audio spectrum analysis would need to be done and unless this can be done in my DAW software (Audacity), I'm not really equipped to do it. Audibly though, I detect no tonal change when using the aluminum pickguard and the copper bridge plate that I added.

Do a search for “eddy currents aluminum guitar” or just “eddy currents guitar” and you will find TONS of posts on guitar forums about this issue. It is certainly more noticeable with guitar as you are mostly affecting the high-frequency response characteristics, whether a bassist would be bothered about it the same way will be dependent on te kinds of tones you use (I like bright/clear piano-type top end, which is why I use mostly single coil instruments to begin with). The type of metal used in the bridge is a big part of the different sound of Telecaster bridge pickup tones for example, or the use of metal pickup covers of different materials and designs (the design of the distinctive Gretsch Filtertron pickup cover was made specifically to minimize eddy current losses), and of course relevant here, the classic anodized Fender metal pickguard.

I’ve experimented with modifying Rickenbacker and Telecaster pickup covers to good effect as well.

Actually measuring these effects scientifically requires a rig that can drive the pickup without strings in order to measure frequency response of the coils objectively, so for most people it relies on subjective hearing tests. If it sounds good to you and works for your application, then there is no reason to stop!

Here’s a cool experiment a guy did measuring the frequency-response effects of copper loops put in different places in and around the perimeter of pickup coils for some related research: http://kenwillmott.com/blog/wp-content/uploads/2016/11/Pickup_Cover_Geometry.pdf

For me, single-coil hum is rarely a deal-killer in a live environment. It is higher RFI noise that can truly be bothersome and proper shielding usually takes care of that in most but the worst of venues. RFI can be an issue with humbuckers too, just something we all have to deal with on occasion!

 

[skycruiser]

Do a search for “eddy currents aluminum guitar” or just “eddy currents guitar” and you will find TONS of posts on guitar forums about this issue. It is certainly more noticeable with guitar as you are mostly affecting the high-frequency response characteristics, whether a bassist would be bothered about it the same way will be dependent on te kinds of tones you use (I like bright/clear piano-type top end, which is why I use mostly single coil instruments to begin with). The type of metal used in the bridge is a big part of the different sound of Telecaster bridge pickup tones for example, or the use of metal pickup covers of different materials and designs (the design of the distinctive Gretsch Filtertron pickup cover was made specifically to minimize eddy current losses), and of course relevant here, the classic anodized Fender metal pickguard.

I’ve experimented with modifying Rickenbacker and Telecaster pickup covers to good effect as well.

Actually measuring these effects scientifically requires a rig that can drive the pickup without strings in order to measure frequency response of the coils objectively, so for most people it relies on subjective hearing tests. If it sounds good to you and works for your application, then there is no reason to stop!

Here’s a cool experiment a guy did measuring the frequency-response effects of copper loops put in different places in and around the perimeter of pickup coils for some related research: http://kenwillmott.com/blog/wp-content/uploads/2016/11/Pickup_Cover_Geometry.pdf

For me, single-coil hum is rarely a deal-killer in a live environment. It is higher RFI noise that can truly be bothersome and proper shielding usually takes care of that in most but the worst of venues. RFI can be an issue with humbuckers too, just something we all have to deal with on occasion!

I was editing the previous post as you posted this - but yeah I will continue reading through the stuff out there online. However, I have not yet come across any discussion about using the metal pickguards to reduce RFI related noise, which appears to be what is happening with my experiments. And in my experience, foil shielding does absolutely nothing for this buzzing noise. The only thing I have found to suppress this noise is the thick metal plate (or HC pickups).

Maybe you could toss a copper plate with a cut-out in your gig bag and take it along on gigs. Next time you run into one of these noisy venues, as an experiment, put the plate on and see if it kills the noise or not. In my experience, it is a night-and-day effect.

 

[skycruiser]

Interesting information here. So this is not a new concept and people are marketing metal pickguards to reduce high frequency noise.

Metal Pickguard Info

 

[skycruiser]

One correction - the blue tape covered plate is 0.025" thick, not 0.05" thick.

 

[totalnoob]

A quick demo showing how single coil buzzing can be reduced by having a somewhat thick metal plate surrounding or covering (quite close) to the pickup. The pickup in the video goes straight to a jack, then cable to Ampeg combo.



I have had trouble with multiple single-coil basses and pickups over the last few years. They were all noisy as shown in the video. I have done all types of shielding and grounding and none of it has any effect on this particular type of interference. The only solution I have found, besides switching to NC pickups, is to use a metal plate around the pickup.

Of course the best solution is to find the source of the noise and kill it. But that won't help you if you run into this problem on a gig. It is definitely a location/environment related thing because I have taken my noisy bass other places with no issues.

I don't plan to own another bass with single coils without either a metal pickguard surrounding them or some sort of removable plate that can be installed when I run into noise.

This is akin to winding a single, really thick wire short circuitt around your J-pickup. It does have an effect on the output and frequency response of the pickup.

 

[sunbeast]

I was editing the previous post as you posted this - but yeah I will continue reading through the stuff out there online. However, I have not yet come across any discussion about using the metal pickguards to reduce RFI related noise, which appears to be what is happening with my experiments. And in my experience, foil shielding does absolutely nothing for this buzzing noise. The only thing I have found to suppress this noise is the thick metal plate (or HC pickups).

Maybe you could toss a copper plate with a cut-out in your gig bag and take it along on gigs. Next time you run into one of these noisy venues, as an experiment, put the plate on and see if it kills the noise or not. In my experience, it is a night-and-day effect.

Grounded thin copper shielding foil (or aluminum to a lesser degree) will shield against high-frequency noise which to me is the main problem on a gig and can come from countless sources (fluorescent lights, computer/radio equipment, phones, etc). Low frequency noise (like 60hz/120hz/180hz mains hum typical of single-coil pickups) requires a much thicker material to shield against as it will pass right through thin foils. I think the main offenders for most of us are the harmonics (120hz, 180hz and up in multiples of 60hz) and I think some of those midrange harmonics is what you are effectively shielding against in your video (you can still hear low frequency hum underneath but the midrange harmonics are lowered greatly). If you ground either of those plates you will also have some shielding against high-frequency RFI noise, though fully shielding the cavities will be even better for this.

 

[sunbeast]

Interesting information here. So this is not a new concept and people are marketing metal pickguards to reduce high frequency noise.

Metal Pickguard Info

Yeah not a new thing, but also not an attractive solution for many guitarists because of "Reason #2" listed on that site: it will change the tone of single-coil pickups due to induced eddy currents (they refer to it as "smoothing", while many of us might instead call it "dulling"- that opinion is all subjective of course)

 

[skycruiser]

EDIT: Sorry need to take a closer look at this. A lot of that upper area noise is handling noise - picking up the pickguard etc.

Why I think this not 60-cycle related noise that is being cut by the plate:

The major signal reduction (in the time frame 8 to 11 seconds when the plate is first placed over the pickup in the video), is the yellow stuff above around 3000Hz. That upper area becomes very clear when the cover is in place. The lower "hum" related things persist throughout (lower part of chart).

 

[skycruiser]

This is akin to winding a single, really thick wire short circuitt around your J-pickup. It does have an effect on the output and frequency response of the pickup.

I will try this tonight and see if it has a similar effect. The thickest wire I have is 14 or maybe 12-gauge single copper - basically house electrical wiring type of wire. How thick do you think is needed to have this effect?

 

[totalnoob]

I will try this tonight and see if it has a similar effect. The thickest wire I have is 14 or maybe 12-gauge single copper - basically house electrical wiring type of wire. How thick do you think is needed to have this effect?

I am not sure if we're understanding each other. I am saying that this aluminum plate is topologically and physically identical to a single loop of thick wire around the j-pickup, short circuited. A transformer where the primary is the pickup's copper winding, the secondary a thick aluminium short-circuited wire. This has a big effect on the pickup's output and frequency response.

 

[skycruiser]

I am not sure if we're understanding each other. I am saying that this aluminum plate is topologically and physically identical to a single loop of thick wire around the j-pickup, short circuited. A transformer where the primary is the pickup's copper winding, the secondary a thick aluminium short-circuited wire. This has a big effect on the pickup's output and frequency response.

Thanks, gotcha, I understand.
In my experience with these plates, I do not detect a big effect on the pickup's output and/or frequency response, or any noticeable effect for that matter. So based on my experience, I would not agree with that. Maybe I don't have the sensitivity to hear the difference. I can hear dramatic differences when I change strings and pickups. But nothing at all when I install one of these plates. And it's not like I have to take the bass apart to do it. I can insert the bridge plate almost without disturbing string vibration. I will try to do a recording or video of that.