Re: Shielding... no, Grounding Question

Benj:

As always, thanks for the thoughtful response. But per my original post:

I believe you forgot to put "thoughtful" in quotes (giving it the
meaning "insane") :)

- The control cavity has been fully shielded with copper foil.

excellent.

- The cover has also been shielded with copper foil.
- The c.c. foil was spot-soldered, and extends over the top of the cavity to
contact the cover's foil.

Yes. That's the way.

- All pickup coils have been wrapped with copper foil, per StewMac's
instructions. The foil was "notched" to ensure it didn't contact the wire
where it goes from the windings to the solder points.

Wrapping with foil is the same as coating pickup cavity with foil.
Usually you want to put insulator under the solder points rather than
cutting away shielding. But still the notch shouldn't be any big
problem.

- Shielded wire has been run from both pickups to the control cavity.

OK. And of course you DID connect the copper pickup wrapping to shield
of the pickup wires, right? Plus the copper shield of the pickup wires
IS connected to the cavity copper. Right?

- The wires' shielding was soldered to the coils and to the control cavity shielding.

PLUS the copper pickup wrapping!

- Original ground wires from the pots were removed to eliminate ground
loops. Continuity was checked.

Good plan. All ground wires going to copper shield should go to ONE
point where they make contact with the copper. Usually best place is at
the jack. But you should have run ground wires form the grounds on the
pots (which probably were soldered to the covers of the pots) to your
single ground point near the jack.

- The bridge ground wire was removed.

Should make no difference and is not needed if shielding is working!

- All components' ground wires, including the jack's ground wire, are now
soldered to a single eyelet that's screwed into the side of the control
cavity.

Good enough! (continuity check between eyelet and copper, right?)

All due respect, I don't see how this can be a "shielding" problem. Case in
point: I own two other basses, one passive and one active (the bass in
question is active). Neither is shielded *at all.* Using the same amp, with
the same cord, in the same room, neither of them produces this buzz.

This is good because it pretty much shows the cord is OK and the hum is
not in the amp.

It pretty much HAS to be a shielding problem SOMEWHERE! That is unless
your bass has some source of hum feeding into it like say lights or
phantom power or a power cord draped over the neck or something. The
fact that the hum goes down when you touch a ground says that something
somewhere HAS to be pickup up hum in a capacitive manner. Just for fun
run a temporary wire from some ground point (like under the cavity lid)
to a piece of copper foil and just put it over the top of the pickups.
Not to play but just to see if hum is getting in that way.

You need to look to make sure that the shield of the pickup wire
(assuming the shield is "ground" on the pickup does not float. In other
words it has to got to ground. If the pickups have EACH lead being a
shielded wire then the pickup can float but the shields all must be
connected to ground and the pickup foil.

Once you've got your shielding box TOTALLY enclosing everything,
touching ground screws or other things should have zero effect on hum
level!

Hence my puzzlement and frustration.

The rule DOES work! Put a jack on a totally closed aluminum box and
plug in your cord and I DEFY you to get any hum into the amp! [do note
however the wire shielding is not 100% perfect and with effort one CAN
get hum through cord shielding. But I doubt that could be your problem.


You said you checked continuity. But be sure that it's there. Check
from jack metal to copper shield. From copper cavity to copper pickup
wrapping. From control ground side pot connections (typically going to
metal pot covers) to copper cavity lining. The problem can't be the
shielding rule. The problem HAS to be something isn't wired right.
Double check your jack to make sure the terminal going to the threaded
part is going to ground and the tab that goes to the part that rubs on
the tip goes to the output circuit. This job you've done SHOULD be
working better than anything you've ever seen! That it's not must mean
that somewhere, somehow, a part of the circuit has found it's way
outside the shield. It CAN'T be anything else! Holding the bass away
from you and slowly rubbing your hand over the bass like say over the
back can help find the place the hum is leaking in sometimes. Is it an
active bass? Is the battery also shielded? I don't know. If you have
done everything you've said exactly correct and haven't made a mistake,
then your job is getting pretty close to where you get out the shakers
and the jingles that go around your ankles and start using magic to fix
it!

PS. As for the rest of you braying asses, PISS OFF! John and I are
talking.

Benj

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