Hum increases as volume drops on new Sheraton wiring, help please?

[Dave]

In the schematic, there are direct ground wires connecting the cases of the pots to each other, from volume to tone then to the tone and volume of the other set of pots. If any of these are missing, you lose the ground chain between the pots. And as Daneman said, carefully check the polarity of the wires to the output jack.

 

I'd verify the polarity of the pickup wires, also. One is ground and the other is hot. Look at the data sheet that came with the pickups. Here's an interesting link where this is explained. The guy goes through actually MAKING a humbucking pickup.

 

http://europa.spaceports.com/~fishbake/buck/humbuck2.htm

 

There's also a ground wire from the ground lug on the selector switch to each volume pot case and to the ground side of the output jack. Another check would be to make sure that you have a ground wire from the case of the pots to the bridge. This is where the strings become grounded.

 

Connect an ohmmeter to the ground side of the output jack and check for continuity to each pot case. The lug where the capacitor is connected to the volume control is also connected to the volume pot case, check this. The connection from the pot case to the lug where the capacitor is connected is actually where the ground reference for the output signal is established. If this is missing, you will have serious grounding issues. The wire I'm talking about is a little arc to the left of the capacitor that connects the lug to the pot case. If you get buzz when you turn down the volume control, I'd bet this is the problem. When you turn down the volume control, you are sending the signal more and more to ground as you turn the pot. If this wire is omitted, you have no ground reference and you end up with an open circuit, much like a guitar cord plugged into an amp and not into the guitar. It becomes an antenna.

[Dave]

With the standard wiring method' date=' where the volumes will short each other out at zero, the guitar's output (and the amp's input) is grounded at '0'.

 

[img']http://www.marantatech.com/Graphix/normal.gif[/img]

 

The 'independent' wiring method leaves the guitar's output 'floating' when the volumes are turned down.

 

 

...I could see how the latter method could be noisy.

 

In either diagram, the pickup sees a ground path when its respective volume control is turned down. In the second, where the pickup is connected at the variable lug instead of the common wire to the output, there is isolation between the pickups, but the signal for the respective pickup is still grounded individually when its volume is turned down. In the second case, the pickups can be turned off individually. In the first, either volume control affects the other and they become additive in their effect.

 

 

Good contribution to the thread, RotcanX. This is a good explanation as to why some guitars volume controls affect both pickups when in the dual pickup selection position and others do not.

[vomer]

Dave, you could be right with your diagnosis, but the loom I was building for my Sheraton has been reduced to its components now. I've ordered some extra braided cable and will attempt to build a loom for the Sherry based on my EA250 wiring. (Which works fine!)

[vomer]

Took me a while to get around to this but it's finished now. I never did discover why I couldn't make the first wiring scheme I tried work. I've copied the all-braided cable wiring from my EA250, and I built it fixed on a template made from a cardboard box lid, so there was no chance of any shorts while testing. It's now back in the guitar and it all works OK!

 

I'm going to start another thread about the process of changing the Sheraton wiring.