Three independent Pups?

[md54]

Hi,

This will seem like a daft question......but. Can you have 3 pups on the same guitar individually driving 3 different amps or P/A channels? Is it dangerous or noisy?

Sorry about my ignorance of these things!

[killemall8]

You would need 3 different input jacks.

[md54]

Thanks, yes I know that but does there have to be a common earth connection or can the pups be entirely separate?

[curtisa]

For best noise performance three separate grounds for each pickup system are required. Care should be taken to ensure none of the grounds within the guitar are mixed (hint: watch out for "sneaky" connections, such as between pot cases via the cavity shielding if the usual practice of earthing a pot case is utilised).

The ground connection to the bridge/strings and cavity shielding should be tied to only one of the three pickup grounds - shouldn't matter which one you pick.

Note that it's not electrically unsafe to mix the grounds, just that it can be a recipe for a ground loop hum between the three amps you're connecting to.

Easiset way to consider it is as three independent guitars in one common box.

[md54]

So it can be done safely and quietly!

Very much appreciate your advice (electronically dim jazz guitarist).

[curtisa]

You may get lucky by simply common-ing all the grounds together. Try it both ways (grounds split/grounds tied) to see which one works best for you. Ground loops can be sneaky buggers.

Tying all the grounds to the bridge in the guitar may be better for controlling the buzz you get by not touching the strings, but at the expense of creating the potential of a ground loop between the three amps. Separating the three pickup grounds and grounding the bridge via only one output as I suggested above will eliminate the potential for a ground loop hum, but may make two of the three pickups more prone to "hands-off-the-strings" buzz.

[Tim37]

I cant imagine there being a problem with a common ground.

[curtisa]

The problem is that the OP wants to run each output into a separate amp, each probably with its own grounded mains inlet. Normally the only way to earth via a guitar cable is via your amps' earth pin on the AC line plug, and usually results in noise-free operation. Ideally if you have multiple paths to earth then each earth location will be at the same potential. In reality this isn't the case and the difference in potential of each earth can result in current flowing between them, and is evident in audio circuits as a loud 50Hz or 60Hz hum.

If each pickup has its own earth via its own amp then no ground sharing can occur and hence no chance for a ground loop hum. As soon as you tie all the pickup earths together you've created a parallel path for each amps' earth through the pickup grounds in the guitar. Whether it actually results in hum is unpredictable and depends on many external factors - how good your amp wiring is, the quality of the guitar leads you're using, how low the impedance is of your amps earth bond, whether the amps are plugged into sockets at opposite ends of the room...

Players who like to run one guitar through multiple amps are familiar with the issue of ground loop hum. It's the same problem as running three pickups through three amps with the pickup grounds tried together. There are ways around it with careful planning of mains earthing and external ground loop isolating transformers on signal lines, but if you're building a special guitar with independent outputs it makes sense to try the low cost solution first before resorting to the expense of external fixes.

There's lots of good write-ups regarding ground loops with multiple amps. Rane did an excellent (if a bit wordy) application note on shielding and grounding in audio systems.

[Tim37]

Ok i was thinking more along the lines of getting zapped some how.