Did I screw this up?

[Rich_S]

I "permanently" installed a soundhole mag pickup in my acoustic tonight. Real simply, just the pickup, a 500K volume pot, and an endpin jack. It works - the pickup picks up, the pot make it louder and softer. The pickup is humbucking, and it's dead silent with the volume wide open. But...

As I roll the volume down, 60-cycle hum becomes audible. The guitar sound is pretty much gone by the halfway point, but the hum is at its loudest. The hum doesn't go away until the pot is nearly at zero. I've never heard a guitar hum like this at mid-volume.

I used the same kind of cable from the pickup to the pot and the pot to the jack. I'm 90% sure that I wired it right; that is, pickup hot on the top of the pot, line to the jack on the wiper. The bottom of the pot and both cables' shields are soldering to the pot case.

However, there's that 10% doubt - I might have gotten the "top" and "wiper" wires crossed since they look identical. So here's the question: Would getting those wires backwards cause the odd humming behavior?

The pot is hard to see, and I'll have to unstring the guitar and remove the pickup in order to check it. So, I'd like to be more sure of the problem before I tear it apart.

[ErikH]

I've come across this exact same situation, only in my case, I ran my acoustic pickup through a volume box and then to the amp. I have no idea why that happens and haven't been able to find an answer to it yet.

[metlking]

I had a similar problem on an HSS strat I wired up.....the volume was fine till you turned it down then it hummed.....I had the wire on the 1st lug of the volume pot switched with the 2nd. After correcting it the problem went away........perhaps this is the issue with yours?!?!?

[Rich_S]

.....the volume was fine till you turned it down then it hummed.....I had the wire on the 1st lug of the volume pot switched with the 2nd....

Yeah, that sounds like mine, but my hum goes away when the pot is all the way down. I drew a schematic of the circuit with the wires swapped, and I think the hum should get worse as the pot is turned down.

Just the same, I guess I'll have to pull it apart and check it today.

[Rich_S]

I checked my wiring - it looked right. So I cleaned up the soldering a bit, reflowed the connections, and then it didn't work at all. That, I tracked down to a failed pot. Cheap Korean jobbie I pulled from my PT a few years ago.

So, I reamed out the hole to accept a good sturdy American-style pot with a 3/8" bushing and rewired the whole mess a third time. Now it works, and I don't think I'm hearing the hum anymore. I'll check it through the PA over the weekend to be sure.

[ErikH]

Did you replace it with another 500k? Mine has a 100k in it, which is what the volume box calls for, but I might change that to 500k and test it out.

[Rich_S]

Yeah, I'm using a 500K. I don't want to lose any high-end with this pickup.

[ErikH]

Cool. I think I'll swap a 500k in to my little volume box and see what that does. I'd like to be able to use it if I can.