Fender Mexican Jazz Bass- Static and Hum

[jbyrdmb]

Hey guys, I was hoping you could shine some light on an issue I’m having with my 2005 MiM Jazz bass. I recently bought some Fender vintage 74’ pickups to put in and the swap went relatively easily, but since then I’ve been getting an occasional hum that’s not like ordinary single coil hum. It goes away when I touch the bridge/strings/knobs (anything grounded). 

I thought it could be bad wiring on the old pots, so I bought 3 new pots and rewired the electronics. Low and behold, the hum was still there. I’ve plugged my Stratocaster in and no hum, tried multiple instrument cables, no difference. So I’ve deducted it’s not due to my amp or cables.

I’m racking my brain over what it could be, shielding issue? Bad pickups? Any advice would be appreciated!

[geoham]

Sounds quite weird indeed. The fact it's going away when you touch the strings etc would suggest an issue somewhere with earth wiring, but the fact you've replaced the pots would hopefully suggest otherwise, unless you made the same error twice. It's probably worth checking against a wiring diagram to be 100% certain, and possibly confirming a good solid bridge earth connection. 

Here's some things I'd try...

• Try in a different room. I had an issue once, where if my active Lakland was plugged into an amp which was plugged in to a socket in the same room as a powerline adapter, i'd get all sorts of weird noises. Only this bass in this exact scenario. I know folk have had similar experiences where problems only occur in certain rooms.
• If there's a pickup at fault, I'd expect it to just be one - unless you are exceptionally unlucky. So, does the hum occur with one or both pickups? I'd first test by just using the volume pots, then try removing the suspect pickup from the circuit entirely and running it in isolation to confirm.
• Check you don't have any pots, wiring etc touching the inside of the control cavity - it's probably got conductive paint on it as shielding.
• If you have a multimeter, measure the resistance between various earth points - like between the bridge and the back of a pot. It should be as close to zero as possible. Anything that gives a value significantly greater than just touching the two points together should be investigated.
• Also use a multimeter to check the DC resistance of the pickups, a quick Google suggests the following values for your pickups: Neck: 8.3K, Bridge: 7.8K. I wouldn't be worried about a small difference here, just anything significant like half or double the expected value.

Good luck!

George

Edited May 12, 2020 by geoham

[ejor31]

It sounds like a shielding issue. It is an easy and inexpensive fix. I had the same issue with a Jazz Bass. Take out the pickups and desolder their wires at pots. Get a small pot of shielding paint, some adhesive copper foil and three tiny screws. Before we start remember ALL shielding MUST be earthed onto a control pot.

Shielding and its  earthing are in addition to the existing circuitry of your guitar. 

Using sandpaper abrade both pickup and control cavities so that paint will stick. Apply one coat and let it cure for 24 hours.

Apply a second coat only then and let it cure also for 24 hours.

Shield the rear of the pick guard for 3cm  around its pickup cavity. Use conductive copper foil for this.

Run a wire ( strip off plastic from a piece of guitar or mains wire, the only requirement being that there is a contact with pick guard shielding) up from the base of the neck pickup cavity to contact the rear of the pick guard. Screw this wire into the bottom of the cavity. From the same screw run a wire through the neck pickup wire channel and screw into bottom of control cavity. Use a tiny screw to avoid it going through the back of your bass!!! 
 

Now in the same way run a wire from the control cavity screw through the bridge pickup channel and screw into bottom of the channel.  Also be sure to run a plastic coated wire from the this screw to a control pot surface. 
 

You have now created an electrical circuit between the pick guard, both pickup cavities and control cavity. Remember your bridge must remain earthed..  Resolder pickups to respective pots.

If you do the work described carefully the hiss/hum will be eliminated. The sound of the bass will be in no way affected. Good luck with it!
 

 

 

[ClassicVibes]

Definitely a shielding issue. Get some copper tape underneath your pickups and in your control cavity. 

[Dov65]

Just received some 74's this afternoon and theres 2 brass shielding plates included in the box, i was just asking about these this morning as i've already got a pair....i'll post them to you if you want cheers D

[Oopsdabassist]

Check the earth wire connection between the underside of the bridge and the loom, I bet its that!

[ClassicVibes]

1 hour ago, Oopsdabassist said:

Check the earth wire connection between the underside of the bridge and the loom, I bet its that!

But when he touches the strings, the bass goes silent so I'm pretty sure it's not a grounding issue.

[Oopsdabassist]

Yup it is, when you touch the strings its grounding through you, hum goes away.

[ClassicVibes]

19 hours ago, Oopsdabassist said:

Yup it is, when you touch the strings its grounding through you, hum goes away.

If it was a real grounding issue, the hum would be very loud and make the bass unplayable so it's not that. By touching the strings to make the hum disappear means that the grounding is fine. The problem is poor shielding which emphasises the hum. 

[KiOgon]

FYI:

https://www.notreble.com/buzz/2015/04/15/solving-bass-hum-problems-grounding-vs-shielding/

[Oopsdabassist]

Just seen this, thanks John, always learning I am! 👍