Issue building jkokura's Test Rig

[soonerrob]

Hey guys,

Wondering if someone can spot where Ive gone wrong... I'm stumped.

I just finished my test rig and can't figure out why this is happening... I feel like its a stupid simple issue that I'm looking right past..



OK... So I have a GREEN wire going from the ground of the DC jack to the sleeve of the jack to its right (output) and a RED wire on the outer lug of the DC jack that goes to my RED alligator clip. I have a BLACK wire along with my audio probe on the TIP of the jack to the right (output). I have my WHITE Alligator clip on the sleeve of the input jack and my YELLOW alligator clip on the tip of the input jack.






I rigged a 9v battery clip to a DC plug which seems to test out correctly.






However, when I plug in the battery, clip the red wire to my red multimeter probe and touch the black MM probe to the sleeve of the jack to the right I get negative voltage.



Yet, when I hookup my test rig backwards to my MM, I get positive voltage..



Please tell me I'm not as stupid as I feel right now...

thanks

Rob

[gtr2]

It's because your 9V input plug from the battery is center positive.  It should be center negative for your testing rig.  Most circuits use center neg, there are exceptions such as some fuzzes etc...

Josh

[soonerrob]

I see... Would an acceptable fix then be to swap the wires from the battery to the DC plug?

[gtr2]

Yes, you could.  Im guessing that battery adapter thing came with a pp2.

Or you could just use a standard neg center wall wart.

Josh

[soonerrob]

thank you.  i swapped the wires. I thought about swapping them initially, but I still would have gone crazy wondering why this happened.. thanks for the info, I learned something from this..

I bought the plug at radio shack.. I wanted to be able to use a battery when i didnt have a proper wall wart available.

thanks again.