Bass shielding problem

[Legitcrew]

Hi everybody, I have a Yamaha bb234 which is passive pj configuration. When I turn up the tone, I get buzz/hum from the pickups. The J and P make different humming sounds but the J is way louder than the P.

After looking online and reading forums here I took it upon myself to shield the bass. I shielded the P and J pickup cavities, the electronics cavity, and ran cables from the J and P pickup cavities to the electronics cavity and used copper tape to attach the ends of the cables to the existing copper shielding.

The buzz of the P pickup is somewhat gone, it comes somewhat audible when tone is about 60%, but the J pickup is loud with tone as small as 20%, and the buzz does not go away when the strings are or are not touched.

Any suggestions?

 

[Legitcrew]

 

[Matt Liebenau]

Is the shielding connected to ground somewhere? Since the noise doesn’t go away when you touch the strings double check the bridge ground. In other words, a multimeter on ohms should read 0 when the probes are anywhere on the shielding and the sleeve terminal on the output jack. Same with the bridge. At most, you’d only want to see a few ohms.

 

[Legitcrew]

Ah one thing I didn’t do is extended the copper shielding into the cavity where the external jack is. Maybe I’ll try that and see if that does anything. The shielding is not connected to the bridge but there is a pot that is connected to the bridge. I did try solder a cable from the pot to the shielding but that made more noise.

 

[Matt Liebenau]

Ah one thing I didn’t do is extended the copper shielding into the cavity where the external jack is. Maybe I’ll try that and see if that does anything. The shielding is not connected to the bridge but there is a pot that is connected to the bridge. I did try solder a cable from the pot to the shielding but that made more noise.

Yes, all the shielding has to connect to ground somewhere. As long as the bridge has some connection to ground it should be ok.

 

[MVE]

True single coil j pickups are going to be noisy no matter how much shielding you do.

If you really want no-hum, get a noiseless j-, which are really dual coil.

 

[fourstringburn]

Yes, all shielding must connect to each other to complete what's called a Faraday cage.

The control cavity should be completely covered with 2 sided conductive foil tape with a bit of foil tape on the top edge of the cavity so the pickguard or control plate (model dependent) makes contact with it.

If your Bass has a metal control plate like a Jazz Bass, then all of the pots and input jack will ground to each other when they are snug and secure to the plate. So this control plate will bond to the cavity foil tape when secured to the Bass caging the body, control plate, and pots and other electronics from outside RFI.

If your Bass has a plastic control plate or pickguard for the pots and jack, you need to have foil tape under all the controls to get the same effect.

I only know Fender Basses but I assume others do the same. The bridge needs to be grounded to the control cavity along with any pickup cavities so a ground wire should sit under the bridge and fed thru a drilled out hole and soldered to the control cavity tape.

Foil tape should be used in the pickup cavities and a ground wire should be ran to the control cavity and soldered too if the Bass has a seperate routing for 1 or both pickups.

Take a look at how I did my Jazz Bass. You can see when all parts are assembled, all shielding is attached to each other. You can also see the bridge pickup cavity ground and bridge wires soldered to the control cavity. This Bass is dead quiet!

One mistake I made is I soldered the wire on the bridge ground to the piece of tape as you can see in the pic. This created a hard bumpy surface for the bridge to lay flat on so I cut off the soldered wire end and just let the stripped end bare wire lay flat on the foil tape and works fine now.

Also to reduce the chance for ground loops, I didn't use ground wires between each pot and input jack. The pots and jacks ground to each other via the metal control plate. The 2 ground wires from bridge and shielded bridge pickup cavity are soldered to a single point in the control cavity.

All this of course ties all grounds and shielding together when assembled.

When I remove the control plate, the Bass will buzz like crazy if plugged into the amp, as soon as I set it back on the body, it all goes away and nothing but silence!

Jazz Bass with S-1 series / parallel switch. Notice no ground wires needed between pots or on input jack.

 

[MVE]

Also, its not usually a good idea to wrap shielding directly to the pickup, as your photo appears to show.

First, you would need to cover the coil with insulating tape to ensure absolutely none of the coil wire or terminals touch the grounded shielding. - if they do, then the electricity being generated makes a short circuit to ground and never makes it to your amp to be amplified.

Second, directly shielding pickups can suck all the high-end right out of them. - I will let someone with more electrical engineering knowledge than me explain why.

There are ways to do it, I believe you need to make a little gap on one side so it doesn’t go all the way around in a loop, more like a horseshoe instead.

But good luck trying to remove that tape if you did stick it right to the coil. Be very careful. A break in the coil means… dead pickup.

 

[Cave Puppy]

I had an older version of this bass - BB424X?. That bridge pickup single coil hum drove me so insane I shielded the crap out it - didn't help much - so I replaced the pickups with EMG Geezers (had to route the bridge pup cavity a bit - that whole thing was a pain). I ended up getting rid of it. It is an issue with any of those basses no matter the price tier.