Pickup coil shielding?

[Cutty]

I'm thinking of shielding my single coil jazz bass 4 string pickups using copper shielding foil,however i have read that this causes a loss of high frequency,could anyone who has done this, comment please,thankyou.

 

[SGD Lutherie]

To prevent treble loss, don't wrap the copper foil all the way around the pickup. Leave a small gap. You can start to wrap the foil and put a piece of masking or PVC taper over the start of the wrap so the ends don't touch. The reason for this is because you do not want a closed conductive loop, or single turn, around the pickup.

So just prevent the two ends from touching somehow.

Also remember to ground the foil, but don't solder a ground wire to it when it is wrapped around the pickup, or you might damage the pickup. Solder a ground wire to the finish end before it is stuck down.

Lastly, don't expect the shielding to get rid of hum. It will help with the more high pitched buzz you get through. Shielding is effective on electrical field noise. The hum you hear in single coil pickups is magnetic field noise.

 

[Cutty]

That's fantastic advice,thankyou.

 

[David Jayne]

To prevent treble loss, don't wrap the copper foil all the way around the pickup. Leave a small gap.

Could you please explain? How would wrapping all the way around cause treble loss? Wouldn't painting a pickup route completely with shielding paint, or using foil all the way around it cause the same problem?

 

[SGD Lutherie]

Could you please explain? How would wrapping all the way around cause treble loss? Wouldn't painting a pickup route completely with shielding paint, or using foil all the way around it cause the same problem?

The foil forms a closed conductive loop around the pickup. When a conductor is in the presence of a changing magnetic field, it causes small currents to flow in the conductor. This is of course how a pickup works in the first place. But the loop creates its own magnetic field that's opposed to the field from the pickup's magnet, and this causes a loss in high frequencies. It might not be drastic, but you would probably hear it.

Metal pickup covers do the same thing. Shielding in the pickup cavities is probably not close enough to the coil to matter.

Conductive paint has a resistance to it, and it's also not forming a loop. So it shouldn't be an issue.

As an example, you can see the way Duncan applied the foil shielding to this Music Man pickup. They didn't wrap it around the coil, they went over the sides and left the ends open and didn't touch on the top. The ceramic magnet is glued to the foil.

 

[bassbenj]

Could you please explain? How would wrapping all the way around cause treble loss? Wouldn't painting a pickup route completely with shielding paint, or using foil all the way around it cause the same problem?

He's talking about putting a loop of copper right around the outside of the coil or worse over the top of the pickup. That makes the coil act like a transformer with a shorted turn (the copper loop) that cuts volume and can kill high frequencies. However when shielding a cavity that is far enough away from the coil that the effect is minimal. Also grounding pole pieces is important because they are conductive and can inject hum right into the coil if you touch them. For some reason some makers never bother to ground them.

But with J pickups hum that can be stopped with shielding can be heard when both pickups are on full. When you turn one of them off you get "single coil hum" which cannot be stopped with a copper shield. It takes a "humbucker" pickup to do that like Fender's "noiseless" J pickups.

 

[BackToTheGroove]

Man I love TB.
This is exactly what I wanted to know today while shielding a JTB401.
Thank you.

 

[SGD Lutherie]

Man I love TB.
This is exactly what I wanted to know today while shielding a JTB401.
Thank you.

Hi, I had gotten your email but you found this before I had a chance to get back to you.

 

[BackToTheGroove]

Yes, and thanks again.
Question: the cavity is shielded now with copper, and the bottom of the pickup has the poles exposed. Should I have something between them and the copper'd cavity?

 

[SGD Lutherie]

Yes, and thanks again.
Question: the cavity is shielded now with copper, and the bottom of the pickup has the poles exposed. Should I have something between them and the copper'd cavity?

You should ground the poles on the pickup. The easiest way is to stick some copper foil with conductive adhesive to the bobbin of the pickup, and solder a ground wire to the foil.

The problem however is that often the pickup has been either wax potted, and sometimes the flatwork is dipped in lacquer before it is wound, so you might not get a good connection to the magnets/poles. But you can try scraping them with a razor blade if they are lacquered.

 

[BackToTheGroove]

Job complete: Silent single coil P bass! Even with the horn turned up and right up to the amp. Incredible then vs now.

And the direct p'up to jack output is like having a new bass. E string is so defined now; way more and clearer output with just the right amount of brightness added for the DR flats I have on.

Great DIY upgrade if anyone is considering it. Thanks to the many TB threads for the know-how.

 

[SUBass]

And the direct p'up to jack output is like having a new bass.

If I recall right, there was a Nikki Sixx signature Thunderbird that had an On/Off switch as the only control. I'm not a Thunderbird guy, but the brief exposure I had with that instrument left an impression on me.

I've done the pickup to the jack thing a few times in the past. Sonically it's a great thing. I always miss the utility of having a volume control though.