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Pickup screws causing microphonics with Bartolini 9SU's

B

BobaMosfett

Sep 12, 2003
380
235
Haarlem, Netherlands
#1
Hi all,

For a while I was under the impression that my newly bought bass had microphonic Bartolini J-pickups. Yesterday my tech installed new (identical) pups, wich were definitely ok - outside the bass. Once installed, the same problems occured. And the old ones were dead silent when tested outside the bass. We were stumped at first, but when testing different options (tapping different components etc), the pups were ok in the bass without screws, but even when inserting screws they were not.
In the end, we covered the top part of the screws that are touching the pickups in tape to isolate them from the pickups, wich helps a great deal.

So my questions to you people are:
Has anyone else encounterd this with Bartolinis, or other pickups wich are of one piece (you know, not with a separate cover)?
And, do non-magnetic screws exist, like plastic, or aluminum, that could be used to mount pickups?

Thanks!
Ray
 
#2
Maybe not related to your problem, but ...

I had an issue with the pickups making a clicking noise when I played. This I found was because I depressed the pickups slightly with my thumb when plucking the string (I rest the thumb on the pickup) and it was then pushed back against the screw head by the foam under the pickup, making a click I could hear amplified. I solved this by changing the foam to a stiffer kind so the pickups don't move.
 
#3
Can't say that I've encountered this on either of my two basses with Bartolini soapbar pickups, but then again it's not something I was looking for. Will have to test that out later. There are many types of non-ferrous screws available such as aluminum and titanium. Brass and nylon screws are more widely available, you should be able to find them at your local hardware store. Let us know how it turns out.

Jeff
 
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#5
jeffmensch said:
Can't say that I've encountered this on either of my two basses with Bartolini soapbar pickups, but then again it's not something I was looking for. Will have to test that out later. There are many types of non-metallic screws available such as aluminum and titanium. Brass and nylon screws are more widely available. You should be able to find them at your local hardware store. Let us know how it turns out.

Jeff
Click to expand...


I believe the term you were looking for was non-ferrous instead of non- metallic. All of those metals are still conductive so I don't think it will solve this problem.
 
#12
Hopkins said:
I believe the term you were looking for was non-ferrous instead of non- metallic. All of those metals are still conductive so I don't think it will solve this problem.
Click to expand...

Yes, you're right (fixed my post). My impression was that the screws were picking up some of the magnetic field, but this would be very unusual. The nylon screws are non-conductive, which would help if it is an issue with contact to the wiring harness.
 
#13
BobaMosfett said:
I'm not sure if I was clear; there is no noise, but microphonics. By wich I mean that tapping the body or pickups, or even scraping them with a fingernail, is heard through the amp. Loudly...
Click to expand...
After looking up the specs for the 9SU pickups I noticed a couple things. They are epoxy potted to reduced microphonics, which you've tested by tapping them outside the bass. The four mounting screws are located physically close to the coil (as they are for most jazz type pickups).

How's this for a working theory? Tapping on the body is causing the mounting screws to vibrate and induce a current in the coil the same way it would pick up string vibration. By taping up the top of the mounting screws the effect was not so much to electrically insulate them but to reduce how much they move. If this is the case, adding enough tape to completely immobilize them should greatly reduce the problem. Assuming that works, then changing the screws to a non-ferrous type such as brass or nylon should completely eliminate the issue. Thoughts?
 
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#14
Yes, that's exactly what I'm thinking. But if that's the case, this problem should always occur, at least with these pickups and when using ferrous screws.
So why isn't Bartolini recommending using non- ferrous screws then? Or using some sort of isolation between the screws and the pickup?
Like someone said earlier, this is a weird problem...

Oh, by the way, taping the screw also prevents it touching the pickup. This idea happened when there were no microphonics when the pickup was in the bass without screws, but when a screw was inserted this was very audible.
 
#15
Good question. To my knowledge Bartolini does not include screws with their pickup so you would think they would at least recommend which type to use. The only thing I see in their FAQs is to add wax paste to the screw hole, likely to lubricate the hole. See section 5 in their pickup FAQs.
Invalid Link Removed

Perhaps the screw mounting holes in your bass are a bit more loose than is typical. This could happen if the pickups have been replaced a couple times or if the new mounting screws are slightly smaller in diameter. You could try installing a couple screws into the pickup cavity, without the actual pickup, and do a 'wiggle test' on them. If they feel a bit floppy then glueing dowels into the old holes and drilling new smaller holes would correct that.
 
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#16
BobaMosfett said:
Yes, that's exactly what I'm thinking. But if that's the case, this problem should always occur, at least with these pickups and when using ferrous screws.
So why isn't Bartolini recommending using non- ferrous screws then? Or using some sort of isolation between the screws and the pickup?
Like someone said earlier, this is a weird problem...

Oh, by the way, taping the screw also prevents it touching the pickup. This idea happened when there were no microphonics when the pickup was in the bass without screws, but when a screw was inserted this was very audible.
Click to expand...

They probably don't recommend using non-ferrous screws because it is rarely a problem. I have used numerous 9J1 sets and never had that problem.
 
#18
BobaMosfett said:
So my questions to you people are:
Has anyone else encounterd this with Bartolinis, or other pickups wich are of one piece (you know, not with a separate cover)?
And, do non-magnetic screws exist, like plastic, or aluminum, that could be used to mount pickups?

Thanks!
Ray
Click to expand...

I just tried an experiment.

I held a steel screw horizontally above the pole on my strat (close but not touching).
Scraping by nail along the threads, the noise was quite loud. Then I tried the same thing with a brass screw.
Huge difference, much quieter.

So if it is the screw vibrating, brass screws may solve the problem. Bartolini uses ceramic magnets I believe,
and the magnet might be very close to the screw (unlike alnico poles).

I don't think you will find nylons screw in wood screw form, and brass would be more durable
than aluminum.

If it is some type of wierd electrical noise, it is easy to test: touch the screw very slowly so you don't disturb
it mechanically. If the noise is still there and as loud, it is electrical, maybe ungrounded shielding paint or
something. It does sound like it's microphonic though.

-
 
#19
If the pickup is microphonic when it's installed in the bass, and it isn't microphonic when tested on the bench, then the problem is with the mounting. What's happening is the pickup is mechanically wiggling when it's mounted on the bass. That's what microphonics is: You tap on the bass, and the pickup wiggles in place, in relation to the strings. That creates a signal, because of the relative motion between the pickup and the strings. This wiggling can be very small; you may not be able to see the motion. A quick test is to hold the pickup still with your fingers, and tap on the bass. Does that stop the problem?

The fix is to mount the pickup more solidly, to stop it from wiggling. The simple way is to put a block of fairly stiff foam rubber in the cavity under the pickup. Or heavier springs over the screws. Or silicone rubber tubing. Or fit strips of felt between the sides of the pickup and the cavity. It depends on the installation. You just need to stop it from moving around.
 

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