Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #132943  by Searing75
 Sat Oct 05, 2013 11:36 am
Sorry, I misread that. It's 9.3 v from the battery and the power source I use (the one spot). Although, when I measure from the tip of the jack in the guitar to ground, it reads -9.3v??? Negative??

I have tried different switches, so I do not believe that to be the problem.

Thanks all for the help!!! But, let me know about the whole negative reading from the 1/8th jack in the guitar.

 #132944  by waldo041
 Sat Oct 05, 2013 12:39 pm
If you flip the black probe onto the tip and the red probe onto the ground you should read 9.3v. If this is the case you have reversed the polarity and quite possibly have fried the preamps opamp. Your one spots center pin is negative and the shield is positive. You will need to rewire the plug for the power jack to the guitar so that the positive is on the tip and the negative is on the ground. You have the equivalent of putting a 9volt battery in backwards. If you powered this with the polarity reversed as it is, you most likely now have a bad preamp.

You did say that your other guitar is wired identical to this one but i am not sure why your other guitar would work with the positive feeding to ground, something has got to be different with it?

 #132945  by Searing75
 Sat Oct 05, 2013 3:10 pm
Yup. Fried the opamp. The other guitar was wired to receive the backwards power from the onespot, the new one was not. Put in the CB1 I have and it worked. Thanks Waldo. Now I need to part out the fried opamp, and repair it to use in my old guitar. Smallbear, here I come.