P-Bass pickup change = hum

[Gustav]

Hi.
I finally got around to switching the pickups in my old P-bass. Some guy put in some actives when the originals broke some years ago, and I havent been happy with the sound since, so I ordered a new set of fender pickups a few months ago.

Now- The bass sounds awsome again, but I am getting a hum. I couldnt just follow the wiring that was already in the electronics, cuz that was active, and different from the instructions that came with the new pickups.

It doesnt hum when the tone control is dialed alll the way to dark, only when its turned to bright, and I can get rid of the hum by connecting a wire from the volume control to the strings.

I think the problem is where I put the ground wires shown on the schematic for the new pickups. They just say ground to and ground from, and I actually dont know where that is. I think those were the lines connected to the battery before.

Any advice on this ?

Gustav

 

[jrmintz]

Gustav,

Fenders have a ground wire that runs from the control cavity to the underside of the bridge. It sounds like yours is not making contact somewhere. If you take off the bridge you'll see the routing for it - it's not soldered, just held there by pressure (in the old basses anyway). It probably got yanked out and not replaced at some point. Just run a wire through the hole to a ground point in the control cavity.

:thumb:

 

[OldHouseScott]

If someone put active pickups in, it was probably removed. I know EMG's literature specifies that the ground wire be removed when installing their (active) guitar pickups.

HTH,

 

[NewYorkDave]

A better, safer alternative to grounding the bridge is to shield the inner cavities of the bass and the underside of the pickguard with copper foil, connected to the low side of the circuit.

 

[Gus]

P bass pickups should be humbucking. Do you have the two coils phased correctly?

I often twist the two wire that go the control cavity. Twisting can often help with hum.

 

[Guest]

The hum can be from various sources, but grounding properly will get rid of it. Start with regrounding the bridge. A wire runs from the control cavity to the underside of the bridge. Make sure it has good contact.

Second, as was mentioned above, shield the cavity and underside of pickups with copper foil and ground this.

Third, as was also mentioned previously, twist your wires it they are not shielded. These steps will get rid of that hum and protect you from noise in most any venue.

 

[jensenmann]

If anything helps throw that beast out of the window (but give me a call before ).



Jens :green:

 

[Neeno]

[quote author="NewYorkDave"]A better, safer alternative to grounding the bridge is to shield the inner cavities of the bass and the underside of the pickguard with copper foil, connected to the low side of the circuit.[/quote]

My father uses a kind of graphite varnish... easy to apply and good conductance...

 

[Gustav]

[quote author="Neeno"][quote author="NewYorkDave"]A better, safer alternative to grounding the bridge is to shield the inner cavities of the bass and the underside of the pickguard with copper foil, connected to the low side of the circuit.[/quote]

My father uses a kind of graphite varnish... easy to apply and good conductance...[/quote]

agh...was happy to read the first post, but not so happy about the one about removing the ground wire thing when installing actives (and who in their right mind would do such a thing ? )

Theres actually some tinfoil on the inside of the pickguard already, and I had the ground to and from going to that, but....

Ill pop it open again next week and take a look and print this thread. Thanks a lot guys. Aside from the hum it really does sound awsome again. Reminds me why I bought the thing in the first place...those actives were horrible, and the tech who did it should be beaten up.

Gustav

 

[jensenmann]

When I worked in a luthier´s shop years ago I remember a guy who wanted an Alembic PU and electronics in his ´62 Precision. Well.... he got what he paid for, but we were wondering why he wanted it. The instrument sounded incredible with original PUs (and sounded still good with the replacements) but the original sound was way better. It´s a matter of taste and depending on kind of trendyness, whatever. I met the guy a year ago and he told me that he had again the PUs changed into original Version and now he loves it even more. Sometimes you have to go through certain things to find your way....
cheers
Jens

 

[Scodiddly]

There are some webpages around on "proper" bridge grounding. What I've seen (but not tried myself) is a setup where there's a capacitor between the bridge and the electronics, with enough capacitance to pass RF and other noise, but not enough to pass AC. Theory being you could prevent shocks from bad amp grounding.

The other thing to look out for is that the split-coil Precision pickup is actually a humbucker... the two sections should be wired out of phase with each other. Because they cover different strings you don't get any audible phase problems, but you do get overall noise cancellation. Shield the cavities and you get single-coil sound with humbucker quiet.

 

[Gus]

People

If a split pickup P bass is wired right you should not need any shielding. For guitars and bass when you need shielding make sure the whole thing is single point ground and that the shield is only connected to the same point.

 

[Scodiddly]

[quote author="Gus"]People

If a split pickup P bass is wired right you should not need any shielding. For guitars and bass when you need shielding make sure the whole thing is single point ground and that the shield is only connected to the same point.[/quote]

Still need shielding around the controls, though.