OT: are pickups antenna's?

[chi_boy]

I was googling for tone witching options for my Strat and came across the below article.  I've never heard of this, but there is a part of me that believes it could be true.  He makes a persuasive argument for the unconnected pickups adding noise to the signal.  I'm really tempted to give this a shot. 

Does anyone have any experience with this type of pickup arrangement?

Cheers
George


[url]http://urthman.jsent.biz/music/silence.html[\url]

[jefe]

Too bad he doesn't have any diagrams up yet. I'm having trouble following just the text, and not sure what exactly he's re-wiring.

I've been playing around with shielding & star grounding, so I'd be very interested in more details. In my research, I have read that pickups do basically act like antennas - can't remember where I read it at the moment.

[Papa_lazerous]

all I know is I get zero noise from my single coils, so it seems redundant to me whatever the theory or mojo behind it.  I dont have any fancy screening just good quality pickups and nice grounding

[Mark Hammer]

Pickups ARE antennae.  That is why humbuckers were necessary.  The pickup coil serves as a sensing device for that which disturbs the magnetic field, but it also serves as an antenna for sources of EMI and RFI that are distant as well.  The humbucker configuration involves permitting the audio signal being sensed to be summed by the two coils, but the extra-musical signal sensed by the coil in its other role as antenna to be cancelled out.

Many players have what are referred to as "dummy coils" on their instruments.  These are essentially pickups without magnets in them.  As such, they provide only the antenna function, and not the string-sensing function.  I've made and installed them, and they work.  The limitation is that, like any antenna, good cancellation would involve both coils picking up the same common noise in equal proportions, which would necessitate them being close by each other and oriented the same way.  That poses challenges to a 3-pickup instrument like a Strat.  More recently, John Suhr came up with a nifty system that involved embedding a very broad coil on the back cover plate that goes over the tremolo springs.  As such, this essentially overlaps the position of all 3 pickups, so it is capable of sensing the same noise that each pickup coil is.  I've tried one out, and it works well.  Stand right beside your amp head, and you pick up some hum, but generally it reduces noise by a considerable amount.

Now, does a coil that is connected on only one end act like an antenna?  It can.  Not as much of a contributor to noise as a fully connected coil, but I assume it can play some minor role.  After all, one can easily "boost reception" on portable radio/TV receivers by simply hanging a single wire off the screw terminal, without connecting the other end.

Will the suggested cure work?  Can't say, but it is worth a try.

[chi_boy]

Pickups ARE antennae. 

Will the suggested cure work?  Can't say, but it is worth a try.

Mark,

Coming from you, I'll take that as a sound endorsement of the need to experiment.  I have a Strat that has been in line for a pickup change for a long time.  I think I will have to play with the wiring some to see if I can hear a difference. 

Now, does a coil that is connected on only one end act like an antenna?  It can.  Not as much of a contributor to noise as a fully connected coil, but I assume it can play some minor role.  After all, one can easily "boost reception" on portable radio/TV receivers by simply hanging a single wire off the screw terminal, without connecting the other end.

But how would one know the true source of the noise?  If I modify a set of pickups to add dummy coils, how would I know if the benefit of quieter pickups is due to silencing the pickup I am playing, or silencing the other 2 pickups that are connected only by a ground wire?  It would be nice to know if someone has already done this, but it would seem the only way to know for sure would be to wire all 3 pickups with toggles to allow switching of the hot and ground sides individually.  The player could then turn the pickups on both with and without the grounds connected and listen for a difference. 

[ashcat_lt]

I find this a little suspect, myself.  If what he posits is true, then shielding in general would not work.  We all know (and can prove) that we pickup up more noise if we use an unshielded cable between guitar and amp.  We all know that circuits tend to be a bit noisier on the breadboard than they will be once mounted inside a metal enclosure.  I'm pretty sure this works only because the shield is connected to the "ground" of the circuit.  That's the same point where your pickup ground (or signal return, if you prefer) wires are connected. 

Seems to me like if he was correct about this then shielding in general would make things worse, no?


BTW - Why are the tone pots general wired this way?  Because the original switching scheme did not include any combination settings.  It was a DP3T switch with 3 positions.  That and it saved them a cap.

[Ripdivot]

Also he is not exactly correct about the guitar having a floating ground. If your amplifier's input jack ground side is connected to the amp chassis (which is grounded) the "common" in the guitar is also grounded via the guitar cable. I know some amps have isolated input jacks but this is not always the case.

[Paul Perry (Frostwave)]

There's RF from radio stations etc.
There's RF from power line spikes, harmonics of 50Hz (or in the US 60Hz) 50, 100, 150, ..all the way up.
There's alternating magnetic fields from the amp, and from the house wiring.
There's RF from every switchmode power supply in the house - because they are all made in China & nobody REALLY tests them, they just put the CE sticker on.

Every one of these sources is asking for a different approach.
The humbucker fixes the magnetic field.

Looking at the post referred to, I think the guy is just getting a bit of modulated RF out, and possibly filtering out some 50 or 100Hz by dicking around with the caps. I don't think he has discovered the philosopher's stone by any means.

[sfx1999]

I always thought that you could put a dummy coil on the same spot as the pickup and use a differential amplifier to subtract the signal of the dummy coil from the pickup to cancel the hum.

[DavidRavenMoon]

From that web site:

Therefore: when a single coil pickup is disconnected from the hot side of the circuit, but is still connected to the common side, it ceases to function as a pickup and it becomes (and behaves as) an antenna connected to the common side of the circuit; picking up the ambient noise and "magically" applying the inverse of that noise to the hot side.

That is total nonsense.  If the hot side of the pickup is disconnected.. what's left?  The common, or return side is connected to ground.  Any noise coming into that single coil, will be shunted to ground... period, the end.  Now, if you lift the ground side, and leave the hot connected.. you will get a hell of a noise.

Pickups are antennas in the sense that they do pickup electromagnetic radiation.  Humbuckers will eliminate electrical field noise, but not magnetic field noise.  Electrostatic shielding helps with the rest of the noise, but as you can clearly demonstrate by sitting in front of a computer monitor or by a light dimmer, even humbuckers and shielding wont get rid of magnetic field noise.

Single coils hum, and no amount of shielding will get totally rid of that noise.  This is because the pickup is doing what it's made to do... its picking up electrical signals.  It doesn't care if the signal is induced by the magnet/strings, or from some other source.

[DavidRavenMoon]

I always thought that you could put a dummy coil on the same spot as the pickup and use a differential amplifier to subtract the signal of the dummy coil from the pickup to cancel the hum.

Yes, you can.  That's how Alembic and EMG do it.

[ashcat_lt]

You don't really even need an amplifier to combine the signals.  Can be done completely passively.  Still won't eliminate 100% of the noise.

BTW, I took this over to THE forum for the discussion of guitar noise and wiring in general, in case you want to see what they have to say.

[DavidRavenMoon]

You don't really even need an amplifier to combine the signals.  Can be done completely passively.  Still won't eliminate 100% of the noise.

Sure, there are many stacked pickups, and passive dummy coil systems.  The reason why a summing amp might be better though, is because the dummy coil will change the tone of the string sensing coil.  One way to get around this is using a technique that DiMarzio (and others) use on the Virtual Vintage series of stacked pickups.  The bottom dummy coil has no magnets, and there is a shield between it and the top coil.  The dummy coil has extra steel slugs in its core to increase the induction, and then is wound with less turns than the to string sensing coil. They are wired in series. This helps eliminate the tonal changes from having a dummy coil in the system.

But look at EMG Strat pickups.  Actively summed stacked humbuckers, totally enclosed by a grounded brass screen acting as a Faraday cage.  Those pickups are dead quiet.

BTW, I took this over to THE forum for the discussion of guitar noise and wiring in general, in case you want to see what they have to say.

I wouldn't pay attention to anything on guitarnutz.  Most of it is misinformed nonsense IMHO.  For example, the quickest way to kill the tone on a single coil pickup is to wrap copper foil around the coil.  You are creating a closed loop, and the eddy currents produced will damp the high frequencies.  The proper way to do it is not have the two ends of the foil loop touch, either by insulating them, or leaving a gap.

[ashcat_lt]

I wouldn't pay attention to anything on guitarnutz.  Most of it is misinformed nonsense IMHO.  For example, the quickest way to kill the tone on a single coil pickup is to wrap copper foil around the coil.  You are creating a closed loop, and the eddy currents produced will damp the high frequencies.  The proper way to do it is not have the two ends of the foil loop touch, either by insulating them, or leaving a gap.

Thanks.  We are thus aware.

[DavidRavenMoon]

Thanks.  We are thus aware.

Is that why this is posted on that page you have linked?

Prepare to wrap the coil with the 1/4" copper foil tape by cutting a piece long enough to wrap once around the windings and overlap itself by 1/4".

That's not the way to do it.

[jefe]

Is that why this is posted on that page you have linked?

Prepare to wrap the coil with the 1/4" copper foil tape by cutting a piece long enough to wrap once around the windings and overlap itself by 1/4".

That's not the way to do it.

That quote is actually from another poster, referencing the instructions from the Stewmac site - which I myself have followed. It certainly didn't "kill the tone" of my p90s'. If that's not the proper way to do it, please do enlighten us on a better way to shield pickups. If most of the info on guitarnutz is misinformed, can you recommend a better site? I'm actually having trouble finding any definitive, consistent info on proper guitar shielding.

[ashcat_lt]

David actually answered that question above.  It's also answered in the thread to which I most recently linked.  Apparently the answer is to avoid wrapping the foil 100% of the way around your pickup.  Seems that leaving a small gap in the coverage provides "good enough" shielding by reducing or eliminating the capacitance issue.  I can't tell you why, nor have I tried it.

I think it bears noting that the GuitarNutz in general do not advocate wrapping the coils themselves.  Most of what we talk about when it comes to sheilding is in reference to the Quieting the Beast article, which concerns shielding the cavities inside the guitar.  This protects all the wiring and controls from interference.  It also works to partially shield the pickups themselves from RFI coming in from certain angles.

The article does mention shielding the pickups themselves - more as a last resort - and includes the following:

...wrapping the coils with copper will alter the tone – typically you will lose some of the high frequency bite (remember that many tele players remove the factory-equipped metal covers from their neck pickups).  This is why I don't routinely recommend wrapping the coils even though it is by far the most effective shielding.

emphasis per the OP.

[DavidRavenMoon]

Is that why this is posted on that page you have linked?

Prepare to wrap the coil with the 1/4" copper foil tape by cutting a piece long enough to wrap once around the windings and overlap itself by 1/4".

That's not the way to do it.

That quote is actually from another poster, referencing the instructions from the Stewmac site - which I myself have followed. It certainly didn't "kill the tone" of my p90s'. If that's not the proper way to do it, please do enlighten us on a better way to shield pickups. If most of the info on guitarnutz is misinformed, can you recommend a better site? I'm actually having trouble finding any definitive, consistent info on proper guitar shielding.

The article on Stew-Mac is also wrong.  That's what that particular repair person does, who probably doesn't know a lot about pickups.  The correct way to shield pickups, if you are planning on wrapping copper foil around the coil, is to leave a gap, so both ends of the foil strip do not touch, or alternately, use some electrical tape (or anything else non conductive) to prevent both ends of the loop to touch.  Then ground that loop.

The problem is when you have a closed single turn conductor around a pickup coil, you are inducing a current in that loop, just as you do in the copper magnet wire in the coil itself. When ever you have current flowing in a conductor with resistance, you also produce a corresponding magnetic field.  The field is pretty week, but it opposes the field from the pickup's magnet.  These currents are known as "eddy currents".

Pickup designer Bill Lawrence says this on his website:

http://www.billlawrence.com/Pages/Pickupology/eddy_currents.htm

Eddy currents alter sound and output of a pickup and play an important role in pickup design.

Eddy currents are induced in metals in the vicinity of an AC magnetic field, creating a secondary magnetic field which opposes the inducing magnetic field of the coil. The dimensions, conductivity and permeability of the metal, along with the frequency of the current in the coil, determine the magnitude and phase relation of the eddy currents. An internal short in a pickup coil forms a conductive loop which, also, becomes the source for internal eddy current interference.

Eddy currents can also raise the impedance in a coil, and as the AC resistance increases, the high frequencies are impeded, and the pickup gets muddy.

Its all a balancing act though.  Thinner foil will do less damage than thicker foil, and the total surface area counts.

A P-90 has a very wide and fairly shallow coil, so as it is the outer wraps of the pickup's coil are a lot farther away from the core than with some other pickups.  This could minimize the effect, or maybe you just don't hear it.

You don't see brand name pickups with copper foil wrapped around the coils.  EMG's, which are pretty damn quiet, use a very fine brass screen to totally encapsulate the pickup.  Alembic wraps their pickups in a copper braided mesh, similar to the covering on coax cables. If you look at Basslines Music Man pickups, they have the foil taped to the top and sides of the bobbin length wise, so it doesn't form a loop.

On some older pickups you see things like the holes cut in the Gretsch Filter-Tron pickup covers, and Rowe (of DeArmond-Rowe pickup fame) had a patent on a metal pickup cover that was open in the front, and had a slot cut in the side to minimize eddy currents.

[jefe]

Eddy currents can also raise the impedance in a coil, and as the AC resistance increases, the high frequencies are impeded, and the pickup gets muddy.

Its all a balancing act though.  Thinner foil will do less damage than thicker foil, and the total surface area counts.

A P-90 has a very wide and fairly shallow coil, so as it is the outer wraps of the pickup's coil are a lot farther away from the core than with some other pickups.  This could minimize the effect, or maybe you just don't hear it.

You don't see brand name pickups with copper foil wrapped around the coils.  EMG's, which are pretty damn quiet, use a very fine brass screen to totally encapsulate the pickup.  Alembic wraps their pickups in a copper braided mesh, similar to the covering on coax cables. If you look at Basslines Music Man pickups, they have the foil taped to the top and sides of the bobbin length wise, so it doesn't form a loop.

On some older pickups you see things like the holes cut in the Gretsch Filter-Tron pickup covers, and Rowe (of DeArmond-Rowe pickup fame) had a patent on a metal pickup cover that was open in the front, and had a slot cut in the side to minimize eddy currents.

Very interesting David, thank you for the info.

Now that I think about it, what I actually did was pretty much encapsulate the sides and the bottoms of the pickups - no loops (I don't think). The base of the pups are brass (?), and the copper tape that I wrapped around the coils is touching the base all around. It did alter the tone a tiny bit, but there are still plenty of highs there.

[frankclarke]

The planes of a humbucker cover touch, you could run a dremel around the edges to leave a gap . There is no need to overlap, true.
The outer coils of a pickup are usually grounded anyway, phase switches aside. So if you think shielding the outside kills the tone, install a phase switch on your single pickup guitar and enjoy.
My understanding of antenna guy is that single pickup guitars are noiseless.
The Guitarnutz system works really well. So strange to take my fingers off the ground and hear no difference.
I wrap my single coils with copper foil completely .