Humbucker is humming, what to do?

[K-Frog]

I put in a big chrome humbucker in my 51 P copy, similar to what you would find in the Squier VM tele bass, and I have an atrocious hum going on. It's not playable this way.
It's a simple 2 conductor pickup, I wired it back to the volume pot just like the original. I pulled the bridge to verify proper bridge ground and everything looks good there.

What else can i check or do?

 

[SGD Lutherie]

Is the ground from the back of the volume pot connected to the output jack? It sounds like you are missing a ground connection.

Also, is it a hum, or a high pitched buzz (like the kind that goes away when you touch the strings)?

 

[K-Frog]

Not sure on that ground connection, but I'll check it this evening.
It's a big fat humming that won't quit for nothing.

 

[SGD Lutherie]

You have a missing ground. Make sure there is a ground wire from that pot to the output jack's ground.

 

[K-Frog]

All necessary grounds appear to be in place. Everything is grounded to the back of the volume pot (pickup, output jack, bridge ground, tone pot jumper)



What next? Could it be a problem with the humbucker?

Here's the pickup

 

[SGD Lutherie]

Do you get any sound from the pickup?

 

[K-Frog]

Yeah, sounds fine except for the continual hum.

 

[SGD Lutherie]

Try this, get a spare piece of wire, and touch it to the pickup's pole piece screws and to the output jack ground, and see if the hum stops.

 

[K-Frog]

I will try that. What will it mean if it stops humming, or what if it doesn't?

 

[SGD Lutherie]

I will try that. What will it mean if it stops humming, or what if it doesn't?

It would mean the ground connection from the pickup is bad, or that the metal parts are not grounded.

 

[Bass4LifeRS]

If a humbucker is humming, then buck the humm!

 

[K-Frog]

no change when i used a jumper from a couple of the pole piece screws to the output jack.

 

[SGD Lutherie]

Without being able to see the pickup, all I can suggest is to check all the solder connections again.

As a test try connecting the pickup right to an output jack and see if it still hums.

 

[David Jayne]

I suspect the coils are wired in parallel, and that one coil is open.

 

[K-Frog]

Without being able to see the pickup, all I can suggest is to check all the solder connections again.

As a test try connecting the pickup right to an output jack and see if it still hums.

ah yes, such a simple test to rule out everything but the pickup. I'm embarased that I didn't think of it. I've done it before for similar reasons, but it escaped me this time.

 

[K-Frog]

I suspect the coils are wired in parallel, and that one coil is open.

I figured they were wired in series, due to the 30K spec, but I don't know that.

I can check that as well since the pickup wiring is exposed/accessible.

 

[SGD Lutherie]

They are wired in series.

If you got a reading of 15K that would indicate that one coil was shorted at the series connection, which is taped up.

Did you actually take a reading of the pickup?

 

[K-Frog]

I thought I did when I got it, reading around 28.something K, but I really don't recall now. Again, something easily checked.
Now I can't wait to leave work and go home and check it, not just because it's Friday either.

 

[K-Frog]

29.68K ohms measured

I connected the pup straight to the jack and it still hums.

I've added a pic of the wiring arrangement. I had to remove the base plate to show it well.

 

[SGD Lutherie]

One thing I notice there is the magnet on the left has the white paint showing, which is north. The magnet on the other side doesn't show white paint, so that would be south. This is wrong. All the magnets have to face the same pole towards that metal blade they are touching on this type of pickup.

So you would want the white paint showing on every magnet, so they would have the non painted side touching the steel blade for every magnet, and the white paint would be showing on every magnet. This way all the south poles are touching the blade.

This could be why it's humming, because it's not functioning as a sidewinder style humbucker.

Are the magnets loose? Or are they glued on? Did any of them come lose when you took the cover off?