Humbucker, single coils, hum, and maybe inductance audio loops

Gear & Tools Talk
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I did an interesting (well to me at least) test today with various coil configurations on various guitars and basses. It was triggered by a couple of the tech team members at church telling me that single coils were problematic with the installed hearing induction loop. I think the single coils split on my PRS, into effects and a high headroom fender amp is probably the sweet spot for the type of stuff we play.

Based on my own experience with having played my Jazz bass there numerous times as well as my Rick a couple of times and guitar once, I thought they were probably being too general. Along the lines of “well some single coils might be a problem, but not all”. There is some electro magnetic interference (EMI) in my music room, such that if I only use one of the coils on my jazz I will get 50cycle hum, but if blended 50/50 there isn’t any.

So I did a bit of research, then ran the test. The results quietest to noisiest were:

Jazz Bass - 50 /50 neck bridge blend; equal with my G&L L2000 in passive mode (any combination of the 2 humbuckers). No hum from either of them.

PRS 24-08 SE electric guitar, any combination of humbuckers (a tiny amount of 50Hz hum)

PRS 24-08 SE, single coils in any combination ( slightly more than the humbuckers, but still hardly any).

Jazz bass from about 75/25 favouring either pickup.

Rickenbacker 4003 bass. Quite noisy compared to the others. (To be honest I hadn’t really noticed it being noisy before doing the test). I could reduce noise by reducing the volume of the bridge pick up.

My thoughts on why

Theses are based on a bit of physics, a bit less electronics knowledge, a good dollop of sceptical internet research and experience.

The L2000 has (I think) symmetrical coils in each of the humbuckers. By symmetrical I mean the magnets have opposite polarity, and the coils are wound the same but in the opposite direction (it seems like this term is understood in internet pick up world). This symmetry is hum cancelling. (I had to run the test in passive mode as I was getting a high pitched whistle from the active modes - but it wasn’t 50Hz hum so not really relevant to the test)

The jazz bass (a fretless Sire V7) I assume has symmetrical coils, so when run together at 50/50 they are hum cancelling.

The PRS has (I assume) assymetrical coils I.e. they are wound differently to each other in each humbucker. This is probably to get the desired sound in both humbucker mode and single coil mode. I think in the single coil mode there may still be some of the impact of the other coil, maybe trying to keep a similar output to the humbucker mode. This has the additional benefit of giving some hum cancelling.

The Rickenbacker has single coils wound very differently to each other (I.e. assymetrical). The bridge pup has considerably higher output than the neck pup.

I’ve played all 4 instruments in church, including the PRS in single coil mode without problems, even when I’ve been stood close to the main area of inductance loop concern. I think I’ve enough info that I can have an informed discussion with the techies such that they will hopefully understand that not all single coils are created equal and that configuration and how the player uses them makes a difference.

I’m keen to hear your thoughts.

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Some stuff to think about:

When you were listening to noise, was there any change in the amp or amp settings?
Were the guitars in the exact same place each time?
What kind of noise are you hearing?
Do you have a way to look under the stage or in a nearby wall (as appropriate) for the troublesome place?

In general, the terms applied here don’t make sense to an electrical engineer, so I am making some guesses as to what is meant.

For your pickups, often the bridge and neck are wound differently. The model number on that PRS will tell if they are different - check their web site and see the specs on that model. Winding a little differently is often done to make up the difference between being at the bridge and at the neck. It can help tame or bring out volume or tone changes based on the position the pickup is to the string vibrational anchor (bridge).

It is also possible to alter the winding spacing to control the tone. There is a little capacitance between every winding and spacing it out in various ways can change that. single coils often have a peak in their response and that could be where the problem is. HB usually are a bit flatter and also have their peak and rolloff further out in frequency until you start to roll the tone down, but that doesn’t generate much if any peak.

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@sequences Michael, thanks for the response. It won’t be the 1st time a Chemical Engineer has written something that doesn’t make total sense to Electrical Engineer (it’s not even the 1st time this particular Chemical Engineer has done that).:grinning_face:

No, I kept them constant. I was trying to carry out a fair test.

That was my intent. I had to get instruments on and off the wall, so my feet probably moved a few inches but not much. I started off in the same orientation (the one with the loudest hum) with each guitar; turning my body through 90 degrees, such that the pick-ups were perpendicular to the original orientation, reduced the hum.

A hum - I assume 50cycle hum (60Hz in the US). And it sounded like what people claim is 50cycle hum on various guitar / bass internet channels.

I’ve no idea. Note that I was doing the test in my music room. The purpose of the test was to show that different single coils will react differently to the same electromagnetic interference. This was mainly so I could have an informed discussion with the sound techs and to educate them a bit. It wasn’t an attempt to solve the issue in church (though if it helps the sound techs solve it, then great).

Agreed re bridge and neck may be wound differently and reasons for winding them differently.

I hadn’t looked at the PRS web site. Thanks for the suggestion.

Interesting. Does this mean the peak in the response curve of the pick-up may make some single coils more susceptible to some types of electro magnetic interference?

Even so, I’d guess that the hum cancelling nature of the coils would still have a big influence on the amount of hum. E.g. my jazz bass with the 2 single coils active with the blend control set to 50/50 would (I think) still cancel the hum because they are configured to be hum cancelling at a 50/50 blend; whereas the Rick (noisiest in the test I did) probably wouldn’t.

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LOL, I have made a couple really funny statements here due to not folowing the jargon properly!

Sometimes it can help to locate the source of the trouble by rotating around the length of the neck like you want to look at the fretboard and still stand straight. Gives a second axis to help you determine location if you are hunting for the source.

Yes, but it will be at the high frequency end, not down at mains hum. The inductance in the pickup and the parasitic capacitance in the windings is interacting and giving a peak just before the rolloff. I don’t see it as much in the HB plots I have seen. Not sure why. Here is an interesting writeup of someone trying to measure pickups. There are some plots near the middle that show the resonant peak.

Probably, yes. I have a guitar that does this in position 2 and 4 of the pickup switch and I can tell the hum is reduced a lot when I am working with a higher gain setup.

I designed an amp and was having some trouble with it picking up mains hum as well as higher frequency noise. I thought I had done the right design stuff to keep it quiet, but it was pretty bad. I found a handful of things with a couple that surprised me:

  1. I had a poorly shielded instrument cable out in my garage. Replacing that made a very large improvement
  2. I had a battery charger for my electric drill about 3 feet away. Unplugging it reduced the high-frequency noise
  3. I was using a flourescent light above my bench. Changing to incandescent reduced the noise more than I thought it should
  4. My anti-static mat on the bench picks up noise somehow. Raising the circuit a foot or two off the mat cleans up a lot of noise
  5. My USB charger also makes high-frequency noise. Unplugging it helped a little.
  6. Standing in bare feet on the garage concrete pickup mains hum, standing on shoes or carpet reduces it

The high-frequency noise above is likely from the switching power supply. It is a technique to get better efficiency out of a power supply and lowers the cost. It does however generate noise. You are likely to have these in many places, like USB chargers, computer power supplies, etc.

If your church stage floor is above another floor, it may be that the cable is draped over a fluorescent fixture on the lower floor. Moving to LED can help there if that is the case. Or lights off. If your stage is lit with flourescents that are somewhat close, then you are doomed until you change those to LED or incandescent.

If the equipment for the band is using power that runs near by, you can see if changing the source of the power can help by moving where the current flow is with relation to your single coil band member. For instance, if there is an extension cord near the single coil player, then move him away or change where that extension cord is plugged in so it doesn’t go by him. Same goes for in-wall wiring or in-floor wiring - you can see if moving where stuff is plugged in reduces the problem.

This next is a high-frequency problem, but it is quite strong. If I set my single coil guitar on the stand which is next to my desktop computer, then do something like play a game that uses the graphics card heavily, I’ll get data noise quite heavily out of the amp and need to go turn down the volume (guitar or amp, either will do). This only happens on single coil.

One thing you might try is see if using a wireless guitar connection helps. This will help you know if the problem is in cabling or the pickups. It could just solve the problem simply.

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Here is a better plot of the resonant peak:

if it comes thru, you should have a DiMarzio single coil compared with a common PRS HB. If not, select a pickup from the long list, then check the boxes for maybe the 10 foot low capacitance cable and the 20 foot high capacitance cable, then click the Get Pickup Info box.

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More interesting stuff Michael @sequences . Thank you.

That would be an ironic fix. When I took a 5.8GHz wireless guitar system to church, the sound guy was unhappy. He claimed it would interfere with the WiFi the preacher and service leader use to run the service.

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And it can. I’d never allow anyone to use the 2.4GHz or 5.8GHz WiFi bands for auditorium audio. Being a radio engineer, I have fought the systems part of multiple different radios in a phone and it is not easy to get right. (BT, WiFi, Cellular). A lot of the ISM band devices right next to the wifi bands are not well behaved due to no real restrictions of needing to coexist with other bands. Some engineers will do the right filtering and some will not.