Foam under bridge pickup?

[Switch]

Ok, so I'm a guitarist, and I'm helping fix up one of our bass players basses. It's a Yamaha 5-string, seems pretty nice. Anyway, I took it apart to check it all out and get it working, and there's a strip of foam under the J-pickup. I figure this is normal cause it's mounted to the body, but what's odd (maybe) is this...

 

There's a piece of of what looks like copper or something conductive on one side of the foam strip. There's a wire running from that to ground. I'm guessing maybe the strip is supposed to be face down, so it's touching the (possibly conductive) paint of the cavity?

 

The P-pickups have foam under them too, but it's glued or something to the pickups themselves, the one on the J isn't. On the wire which connects the 2 pups, it goes thru a little eyelet thing which is screwed into the body, maybe this is also done for grounding?

 

So yeah, what's the deal with the conductive strip on the foam?

 

And also, is it safe/ok to put another strip of, say, mousepad under the pickups for a little more output and/or better coupling to the body?

[MrJoshua]

Sounds like shielding. Unnecessary on the P-pups as they're humbucking, but the single-coil probably wants as much noise-reduction help as it can get.

[Craig Vecchione]

Shielding helps both single-coil and humbucking...it helps block RF. Humbuckers can still pick up RF signals.

 

There is no reason to add more foam. Coupling isn't an issue at all, because these pickups 'read' the changing magnetic field cause by the moving strings....they don't pick up any acoustic energy from the body at all. They would sound exactly the same if they weren't even touching the body. The only thing that matters is the distance from the strings and relative position along the strings.

[takeout]

 

Originally posted by Craigv ...Coupling isn't an issue at all, because these pickups 'read' the changing magnetic field cause by the moving strings....they don't pick up any acoustic energy from the body at all. They would sound exactly the same if they weren't even touching the body. The only thing that matters is the distance from the strings and relative position along the strings.

Um... not entirely true.

 

There is a noticeable difference if a pickup is screwed down directly to the wood rather than being padded with foam or springs, mainly if the pickup has any sort of microphonic tendencies (i.e. overwound or not wax potted). I've done a lot of experimentation with one of my guitarist's axes, and we've both noticed it. It's a certain "acousticness" that gets added. I don't have any scientific explanation - just empirical observation.

 

It is subtle, but definitely exists. At any rate, adding more foam would only decouple the pickup from the body vibrations even more than at present.

[Craig Vecchione]

microphonic pickup = bad pickup

 

Adding foam to a pickup that's microphonic could go either way depending on the properties of the foam.

 

Unless the foam's gone bad, it's usually best to leave things alone unless you're just curious and are able to restore whatever you did back to 'normal' should something go horribly wrong:)

[takeout]

 

Originally posted by Craigv microphonic pickup = bad pickup

There are a plethora of Tele players that would disagree.

 

Plus, you forgot "overwound" - surprising coming from a fellow Ric player.

[MrJoshua]

Transferring body vibrations to the pickups cause them to vibrate, which changes the way the strings are vibrating in relation to the pickups. So it will make a difference in how the bass sounds. Maybe not a huge difference, but a difference.