Installed a JB and ended up with a lot of hum- Ideas?

[zionstrat]

Workign in a PRS HSH today- We replaced a dead bridge pickup with a JB, but when we got into the cavity, it was clear that the switch was bad-

We had a 4 pole 5 way at available and wired as follows:


Good news, is that we get the proper combinations:
1. JB
2 JB and Neck
3. Center single
4 Neck split + center
5. Neck

However, it is extremely hummy in all positions, much like the times I have inverted a ground somewhere.

With that in mind, the 5 way isn't grounded, but I essentially replaced the old switch which also wasn't grounded.

I don't think the problem has anything to do with the JB since hum occurs in all positions. It also seems unlikely that I am dealing with 2 bad switches.

I'm hoping one of you will take a look, tell me I was just at it too long today and that there is an obvious fix.

Thanks in advance for any and all ideas-
Zstrat

 

[Clint 55]

Re: Installed a JB and ended up with a lot of hum- Ideas?

the 5 way isn't grounded

Yep, that's the main cause of noise, leaving out components from your ground circuit. If you get noise, don't assume something's broke until you make sure everythings right: ground all your components with a wire, get your bridge (and body) connected to ground, and make sure all your solder joints are good.

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

Thanks Clint-
I really was concerned about 5 way grounding- I have seen rotors where the pup ground is part of switching- The fact that I have seen pup ground switching and that the previous 5 way didn't work got me looking online, but I couldn't find anything that fit this build-

But if not a design problem, yep, there's lots of joints to check-
Much appreciated-
M

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

Hmmm, now I am starting to question myself regarding switching the ground-

Here's a schematic for standard PRS pups with this switch- Although we're aiming for totally different combinations, they are switching the ground-

For my build, I thought I could run pup grounds directly to ground, but am I missing something about this switch? Do pup grounds have to be switched for some reason?

Thanks again for any input!

 

[Clint 55]

Re: Installed a JB and ended up with a lot of hum- Ideas?

You're right, it looks like at least the switch is grounded by the main ground from the jack. The neck pickup ground lead isn't connected to the main ground, but I assume it's supposed to be like that for the switching. Other things to consider are bad solder joints, the bridge (and body) connected to the ground circuit, and shielding.

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

Thanks Clint-

The only time I switch a pup ground lead is to isolate that coil for phase reversal, etc and that is what I imagined was taking place in their schematic. As far as actually grounding the switch, there isn't a ground lug or a way to ground the switch body that I can see.

I tried an alligator from the switch frame to ground- didn't help-

Still wondering if there is something fundamentally wrong with my design and contacting stew-mac to see if they have ideas.

 

[Stuartg]

Re: Installed a JB and ended up with a lot of hum- Ideas?

You say Green to ground in the diagram. I assume you have also grounded the screen wire from the pickup ?
You can phase switch with the green and do stuff but the cable screen should go to ground, preferably as close to the jack as possible (VOL in your case)

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

You say Green to ground in the diagram. I assume you have also grounded the screen wire from the pickup ?
You can phase switch with the green and do stuff but the cable screen should go to ground, preferably as close to the jack as possible (VOL in your case)

Good eye Stuart-
Yes the shields are grounded, but I reused old wiring and the shields are grounding much farther down the path- I will revisit the patient this afternoon and I was planning on doing a total rewire and will definitely address shields and let you know the outcome-

Much appreciated-
Z

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

I replaced 90% of the original wiring and now all is good!

Thanks for input from you guys and special thanks to Stewart Mac! I sent them the diagram and thy confirmed that the design was solid, which made it easy to put in the extra T&E to pull the old wiring.

That is superb customer support for a 10.99 switch, so let's give them support for the bigger stuff as well-

Thanks again and much peace to all-
ZStrat/Mickey

 

[Adieu]

Re: Installed a JB and ended up with a lot of hum- Ideas?

Bad solder job?

 

[zionstrat]

Re: Installed a JB and ended up with a lot of hum- Ideas?

Bad solder job?

The old wiring was a rats nest and I realized the old wiring had to go when I started probing around while connected to an amp- just pushing on the old wiring created big noise- It was essentially a badly grounded antenna (no cavity shielding).

Classic case where our estimate should have covered replacing all old wiring, but you never know until you get into the cavity and the challenge is that the luthier who gives me work doesn't want to do a lot of up front testing before quotes-

I think this makes the case for a little change in the process-

Thanks to all for great questions and feedback.
ZS