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INTERFERENCE on cavity cover
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=38662		 Page 1 of 1
Author:  herry tze [ Tue Dec 25, 2012 2:47 am ]
Post subject:  INTERFERENCE on cavity cover
Hello, I need help my problem as seen on my pictures.
This is my first Electric Upright Bass, I built from Motolla Libellula EUB Plan, 35 scale 4/4
And I use Piezo Under Saddle Pickup, I built from coax (from Experiment Musical), and the PreAmp I bought from Walter Cafe PZP-1.
there is some sound interference when I put my hand on the top of PreAmp cavity cover, all inner cavity I shielded with bronze foil from StewMac.
I've check the groung of pot and the ground of jack connected with the shielding, is that the problem?
And what should I do.. thank's and I will soon post the picture of this guitar...
And Merry Christmas to all of you... pizza

edit post: picture pickup (and that is PreAmp): I've release the battery ground (black wire) and move to the one other pin of the jack (medium tall) because that was no signal when I do as seen on that picture.. thank's and sorry for this info
Author:  senunkan [ Tue Dec 25, 2012 6:28 am ]
Post subject:  Re: INTERFERENCE on cavity cover
I supposed you meant ground humming noise when you are referring to "interference".
If that's the case, you might have to check the way you ground the signal.
For a grounding to be effective, the grounding point must be, as far as possible, a single point ground.
If connected to a wide area ground or multi-point grounding, there is a chance of ground noise current which cause the humming.
Author:  Quine [ Tue Dec 25, 2012 8:58 am ]
Post subject:  Re: INTERFERENCE on cavity cover
It only happens when you touch the preamp cover? You must be creating a second ground by touching it (grounded through you). Find a way to connect the cover to the main ground point. Or change it to wood or plastic that is not conductive
Author:  SteveSmith [ Tue Dec 25, 2012 9:58 am ]
Post subject:  Re: INTERFERENCE on cavity cover
For the shielding to be effective it must be grounded. The covers will probably ground ok to the cavities when they are screwed down as long as you have copper to copper contact. The control cavity is grounded by the pot but it looks like the preamp cavity shielding is not connected to anything. If you haven't already, solder a wire to the preamp-cavity copper and connect it to your central grounding point on the back of the pot, (the ground on the preamp would be my second choice). I would leave the copper on the covers, if the copper is oxidized where the cover and cavity make contact then they won't make good electrical contact; the eraser on a regular old wooden pencil is perfect for cleaning the copper so you get good connectivity between cover and cavity.
Author:  herry tze [ Wed Dec 26, 2012 8:50 pm ]
Post subject:  Re: INTERFERENCE on cavity cover
thank's all of you,.. Yeah, that's ground humming noise,
Quine, the cover made from wood but I covered with copper shielding too in it, and the noise just on the preamp cavity.
Steve, the preamp cavity shielding is not connected to anything, I 'll try it, leave the shielding cover and solder a wire to the preamp-cavity copper and connect it to my central grounding point on the back of the pot. bliss
thank's all Eat Drink
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