Hum from Yamaha Bass

[Luckydog]

Hi, I’m helping my son’s friend who wants his passive Yamaha bass with a lower setup. Not sure what model, but its a passive PJ.

It had nickel plated rounds of some type, no silks, prob 45-105. Took off old strings, rough cleaned it, put on some DR Hi Beams 45-100, did rough setup, noted that there is some hum. I figured its either 60 cycle or ground hum (I know squat about electronics). I had just finished shielding another bass, so went ahead and shielded the pickup cavities of the Yamaha.

I intended to shield the control cavity, but it looked to me like a too-tough job, requiring janking around the wires and solder joints.

I don’t know whether I had accomplished anything with the pickup cavity shielding, so plug it in, and sure enough- hmmmmmm. Sounds like ground hum, but what do I know. I had previously removed the bridge and noted there is a ground wire there under it. As typical, the hum is louder when not touching strings or bridge or instrument jack, but quite audible still when touching strings etc. Is it likely the pickups themselves are naturally that noisy? Do you notice anything in the pics that looks like a ground problem? Any advice is appreciated!

Luckydog

 

[Matt Liebenau]

If the bridge pickup is a single coil, and I think the stock one was, it’s going to have some 60 cycle hum. Did you connect the shielding in the pickup cavities to a ground point in the control cavity? Back of a pot, sleeve terminal on the output jack. If not it’s doing nothing to reduce the hum and could be making it worse.

 

[Luckydog]

If the bridge pickup is a single coil, and I think the stock one was, it’s going to have some 60 cycle hum. Did you connect the shielding in the pickup cavities to a ground point in the control cavity? Back of a pot, sleeve terminal on the output jack. If not it’s doing nothing to reduce the hum and could be making it worse.

Ahh, no I did not. Thank you. So would you suggest I solder a wire onto the shielding tape, run it through the channel with the rest of the pickup wires to control cavity, and solder that end to the back of any pot?

 

[SharpCat]

I think you’re gonna need to shield the control cavity too. Should be easier if you gently unbolt and pull back the pots to make room. Can also get some shield paint (MG Chemicals brand) if desired.

 

[Luckydog]

I think you’re gonna need to shield the control cavity too. Should be easier if you gently unbolt and pull back the pots to make room. Can also get some shield paint (MG Chemicals brand) if desired.

Good advice, thanks. I was hoping not to, but it makes perfect sense that it needs to be done, and loosening the pots is likely to help. I had read somewhere that the shielding paint is less effective than copper tape, so I probably will do the tape.

 

[Matt Liebenau]

Ahh, no I did not. Thank you. So would you suggest I solder a wire onto the shielding tape, run it through the channel with the rest of the pickup wires to control cavity, and solder that end to the back of any pot?

Yes, you can solder a wire to the tape and solder the other end to a potentiometer back. Like sharpcat said, you need to shield the control cavity to be effective. Don’t forget to connect that shielding to ground.

 

[Luckydog]

Yes, you can solder a wire to the tape and solder the other end to a potentiometer back. Like sharpcat said, you need to shield the control cavity to be effective. Don’t forget to connect that shielding to ground.

Got it, thank you!

 

[Luckydog]

Now I’m trying to access the control cavity. Can’t see any set screws on these knobs and don’t want to just yank them and break something. Is there maybe a secret to this type of knob?

Doesnt appear to be accessible from the pot side either-

 

[maturanesa]

Jazz + P doesnt cancell hum

 

[Riff Ranger]

I have a budget Yamaha RBX260F, very similar, but a few generations earlier, with only the split coil pickup. Even with only a single hum-canceling pickup, it produced A LOT of extraneous noise before I had a proper shielding job done. I probably know even less about electronics than you claim to but it seems likely that you can rule out 60-cycle hum as your primary culprit.

Yamaha has never skimped on build quality to my knowledge, so when they’ve produced budget instruments, they’ve had to cut corners elsewhere. Even so, I’ve encountered this problem on some not-budget instruments, such as my Ibanez RB820. In some settings, the extraneous noise was impossible to ignore but the same shielding treatment took care of that.

 

[SharpCat]

Now I’m trying to access the control cavity. Can’t see any set screws on these knobs and don’t want to just yank them and break something. Is there maybe a secret to this type of knob?
View attachment 7357465

Doesnt appear to be accessible from the pot side either-

View attachment 7357466

No set screw, you gotta pull/pry off. Gently wiggle side to side while pulling. I don’t think you could use a pry tool without marring the top.

 

[Luckydog]

No set screw, you gotta pull/pry off. Gently wiggle side to side while pulling. I don’t think you could use a pry tool without marring the top.

Thank you sharpcat!

 

[Krakmann]

Salud!

I love my Yamaha BB734a, but two sound guys protested about hum from it and the culprit was the noisy J bridge pickup. I finally replaced it with a Sadowsky noiseless one. Perfect since then.

 

[toughluck]

Number the pots and unscrew them. They're held in by just a hex nut.
Once you remove the pots and push them aside, it becomes easy. I did it on my own P+J (noname German "Vision" brand):

T

Thread 'Installed EMG GZR P+J pickups and electronics in my old Vision bass!'

May 27, 2025

(I'm not sure if it's the right sub-forum, please move the thread if it's not)

I have an older Vision P+J guitar that I don't use since I got my Harley Benton. It was a gift from my dad who was a bassist in his day, and who wanted me to try out the bass.

It's extremely basic, but it actually has a lot going for it: it's fairly light, it has a nice neck profile, it doesn't have any problems with the neck straightness or anything, so I kept it as a backup, but never really needed it.

It had one big problem, however. The electronics and the pickups were simply dreadful, especially the J...

• toughluck
• Replies: 9
• Forum: Pickups & Electronics [BG]

• 

 

[TeeSee]

Thank you sharpcat!

Those knobs look very close to the surface of the guitar so putting anything like a tool between them is going to ruin the finish.
Normally I'd say use the old boot lace trick under the knob but I doubt you'd get a bootlace between the underside of the knob. If you have some sturdy fishing line or nylon cord try to see whether that will get under and wrap the other end round a stick to give you something to pull on, try to gently pull up until there is daylight. Hopefully you can work it loose with fingers after that but if it's still tight then put a protective cloth on the surface and use a metal teaspoon bowl end with the lip of the spoon bowl under the knob and the bottom of the bowl as it's fulcrum. very gently prise at different points while turning the knob to ensure it starts to lift off square.
Failing that as it's not a super expensive guitar you could make the knobs sacrificial in a way and buy a cheap set off amazon to put back on.
Either way you will be now be able to access the pot nuts and remove the pots and jack out to give yourself some space for shielding the control cavity.
Remember to solder wires from the pickup cavities shielding to the control cavity shielding and obviously don't forget your bridge ground.

Off topic but kinda useful, I always secure the bridge ground underneath the bridge with a small piece of copper tape which stops the wire from disappearing into the hole and also giving a bit more surface area to the wire/bridge interface. Some folks also shield the bottom of the control cavity cover as well as long as there is a bit of overlap in CC shielding that will make with the underside.

Question, when you first had the guitar did you notice the hum before you started work? If it was already present, then shielding will help but it won't be the panacea for all evils as you also have single coil pickups.
If the hum has become more noticeable then the shielding will help but also pay attention to your bridge ground too and just check continuity of said wire has full integrity, if dodgy then replace.

 

[toughluck]

No shoelaces needed, I've never seen a pot knob get stuck on a shaft.

There are only four types of pot knobs.

First type are smooth pot shafts and smooth pot knobs with a locking screw. You can identify them easily by looking for a small hex socketed screw in the side of the knob. If you loosen the locking screw, you can remove the knob. It's as simple as that.

Second type are knurled pot shafts and corresponding knurled pot knobs. They are a simple push-on type and are held only by friction. If there's no locking screw in the side of the knob, you can try pulling on the knob to remove it.

Third type are smooth pot shafts with a screwdriver slot and a pot knob that has a corresponding blade. They're a pain to install, but they won't become loose and won't go dead. I haven't seen them on a factory installed guitar.

The rarest kind (I've never seen one on a guitar, I've never seen one in a guitar parts shop, either) is a screw-on type where you screw the cap on by rotating it clockwise, then screwing it in the extreme right position. Removing it is the opposite, rotate CCW and then twist to unlock.
You would typically hold the bottom of the pot or it would have a screwdriver slot to keep the shaft in place to prevent it from rotating.
I'm only mentioning this type because for all we know, Yamaha could have gone that route and if all else fails, this remains something to try.

 

[TeeSee]

No shoelaces needed, I've never seen a pot knob get stuck on a shaft.

I'll take your word for it. I, however have lacked your good fortune on at least a couple of occasions especially when the good idea fairy visits the previous owner with a tube of glue.

 

[toughluck]

Oh...

Good idea fairy — shoot on sight.

 

[Luckydog]

Salud!

I love my Yamaha BB734a, but two sound guys protested about hum from it and the culprit was the noisy J bridge pickup. I finally replaced it with a Sadowsky noiseless one. Perfect since then.

I think I have a set of Sadowsky jazz pups sitting in a box from years ago. Its been so long, I cant recall if they are SC or HB, or 4 or 5 string. Prob from early/mid 90’s. Good info, thanks.

 

[Luckydog]

Number the pots and unscrew them. They're held in by just a hex nut.
Once you remove the pots and push them aside, it becomes easy. I did it on my own P+J (noname German "Vision" brand):

T

Thread 'Installed EMG GZR P+J pickups and electronics in my old Vision bass!'

May 27, 2025

(I'm not sure if it's the right sub-forum, please move the thread if it's not)

I have an older Vision P+J guitar that I don't use since I got my Harley Benton. It was a gift from my dad who was a bassist in his day, and who wanted me to try out the bass.

It's extremely basic, but it actually has a lot going for it: it's fairly light, it has a nice neck profile, it doesn't have any problems with the neck straightness or anything, so I kept it as a backup, but never really needed it.

It had one big problem, however. The electronics and the pickups were simply dreadful, especially the J...

• toughluck
• Replies: 9
• Forum: Pickups & Electronics [BG]

• 

Do you mean after I remove the knobs? I would also need to unsolder pot wires, before unscrewing the pot, right?