For my first project I took an onboard preamp out of a bass and put it into a stompbox so I could use it with other basses.

Here's a diagram from the manufacturer:
http://sadowsky.com/media/download/wiring_diagrams/preamp_w iring.pdf

See how the 9v neg connects to the ouput "ring"? Is that right?

Electrically, verified with a continuity check, the ring is the same as all the negatives in the circuit.

I did use a 9v power supply, not a battery.

The preamp works but I get some noise, could it be a ground loop?

And ideas would be welcomed!

thanks

want type of box are you using, abs, metal etc...

It's aluminum.

Also, I tested 3 different 9v power supplies and they were putting out between 11-13 volts......?

Maybe that's the problem?

[Edited on 2/26/2008 by jongor]

You don't want that, it will burn up the circuit. Not sure why a 9v rated power supply would read 11-13v

Hi Jongor and Brian!The connection from the negative side of the battery or power supply to the "ring" of the jack is common practice but if you are building the preamp as a stompbox you should do it on the input jack.Use a stereojack as inputjack and connect the neg. side to the ring.When you plug in your guitarcord(which has a monoplug) it will connect the minus to ground(which is what you want it to do). For outputjack use a standard monojack.The reason your power supplies put out more than 9 volt is because they are unregulated . The voltage will vary depending on how much current your stompbox will draw .Obviously yours draw very little current.If you use a battery instead and the hum disappear you will know that the power supply is the culprit which gives you a choice of A:use a 9 volt battery or B:use a regulated power supply and finally C:add more filtering to the supply you already have.