Tone Pot Wiring Help?

freebeer · #1 03-04-2013, 08:38 PM

Alright...I'll spare you all the details but the short story is that the instrument has a nasty hum/buzz when you are too close to the TV/monitor, florescent light, etc. The current pickups are Bartolini p-bass pickups. This instrument is shielded to high heaven and I had a great local luthier check it out. I have swapped pickups, added ferrite beads, and still battling most the hum (the beads seemed to help a little).

When the tone pot is down the hum is gone. I'm beginning to wonder if I am just screwed and this is the nature of this beast but perhaps there is something just basically wrong...

Can anyone verify that the tone pot wiring here is correct? Also, any suggestions are appreciated...

Forgive my horrid drawing...I did it in about 2.2 seconds flat...

The ground/shield side of the pickups are on the copper foil shielding.

line6man · #2 03-04-2013, 08:43 PM

The wiring is correct.

The bass gets quiet when the tone control is rolled down, because the tone control reduces high frequencies by decreasing the impedance at high frequencies. That's normal.

freebeer · #3 03-04-2013, 08:44 PM

So am I out of luck? I have other instruments that are dead silent in the same location...

line6man · #4 03-04-2013, 08:54 PM

Quote:

Originally Posted by freebeer

So am I out of luck? I have other instruments that are dead silent in the same location...

This sounds like a magnetic field noise issue, rather than an electrical noise issue that shielding would take care of.

Is the bridge grounded properly, and all ground points electrically continuous?

freebeer · #5 03-04-2013, 08:58 PM

Yep. Really went over that with a fine tooth comb (and my Fluke multimeter).

I cannot find any ground contact that shuts it up. Extremely frustrating. There is more to the story though...it's got a piezo bridge (Bartolini MPB2 buffer) and then out of there the mag pickups are wired as shown from a DPDT switch. When the piezo's are selected it's dead quiet. When the mags are selected I buzz like mad.

I've used Bartolini pre's in the past with no issues.

line6man · #6 03-04-2013, 09:14 PM

Quote:

Originally Posted by freebeer

Yep. Really went over that with a fine tooth comb (and my Fluke multimeter).

I cannot find any ground contact that shuts it up. Extremely frustrating. There is more to the story though...it's got a piezo bridge (Bartolini MPB2 buffer) and then out of there the mag pickups are wired as shown from a DPDT switch. When the piezo's are selected it's dead quiet. When the mags are selected I buzz like mad.

I've used Bartolini pre's in the past with no issues.

Piezo bridges are not inductive and do not have any electromagnetic properties, thus, they don't respond to emissions from magnetic sources.