Hum problem of a 60s SG Special

[simon3142]

I wonder if anyone can help with a hum problem on an early 60s SG special with P90 pickups.

 

I posted this on the vintage form but then I realised this might be a better place.

 

The problem is recent and I first noticed it after swapping the bridge.

 

It was an uncompensated wrap around bridge that just slides into the mounting posts. I tried out a cheap “pattern” compensated bridge but I didn't like the result and swapped the original back immediately. There was no unscrewing or disconnections involved so I don't see how this could be related unless the wiring got shaken up although I didn't touch it.

 

The guitar has two types of hum

1) a low level mains hum which goes away with the pickup selector in the central position – as expected.

2) A much louder buzzy hum which is stays even with the pickup selector central. This is the one that is bothering me.

 

The hum goes away if I touch the strings or any earthed part of the wiring such as the back of a pot or screening braid. It gets louder if I touch the insulation on the "live" wire from a pickup.

 

The hum is affected by the volume controls in an odd way. It reaches a peak at about ¾ volume and then its becomes more buzzy or treble as though the volume is partially acting as a tone control.

 

The wiring is original apart from an earth wire to the socket which fell off and I connected it to the earth on the switch long before this problem started.

 

There is no problem with another guitar (strat) using the same same cable and amp.

 

 

Added: I don't see any sign of a wire to ground the bridge, I wondered if it is in the pick up cavity but I haven't looked there yet.

[retrorod]

You should see it from the control cavity.

[stein]

If the hum goes away when you touch the bridge (and thus the strings), that is correct. You should be good.

 

P-90's hum much more than Strat pups. That;s normal. I would say it should be about twice as loud.

[simon3142]

If the hum goes away when you touch the bridge (and thus the strings), that is correct. You should be good.

 

P-90's hum much more than Strat pups. That;s normal. I would say it should be about twice as loud.

 

Ah, that's interesting I assumed that they would be similar.

 

AS I originally mentioned, there are two type of hum - The low level mains hum that remains when the strings are touched but is greatly reduced when the pickup selector is central.

 

And the louder buzzy hum which is not affected by the pickup selector but goes way when ground is touched.

 

I had assumed the the low level hum was the P90 hum and the other was a ground problem.