Grateful Dead Music Forum

A place to talk about the music of the Grateful Dead 

 #127802  by b1jsph
 Sat May 11, 2013 11:26 am
Sorry if this has been addressed somewhere already, but..., I spent 1hr searching and couldn't find it if it does. My question concerns the wiring of the guitar cables used in an OBEL with an active (9 volt) UGB.

I understand the effects cable. Stereo TRS end at Guitar into two mono cables for effects send & return.

I'm not quite sure how the guitar out to amp cable is wired. I have heard that the guitar end is TRS and the AMP end is mono TS. Somehow, TRS plugged in guitar turns on 9 volt, unplugged, 9 volt stops drawing power?

Is this correct and..., if so, how exactly is this cable wired. Just TS to TS and on the TRS plug the ring isn't wired?

What happens if you run a regular mono cable from guitar to amp? Does UGB still become active when a mono plug goes into the guitar jack?
 #127849  by milobender
 Sun May 12, 2013 7:57 am
Go to and you can see the schematic for how the battery is connected and disconnected by the stereo jack for the main out from the guitar... The cable you use for the guitar main out is mono, with a mono plug, not stereo (just the effects loop is a stereo cable). You'll see in the schematic how it works.
 #127853  by BDI
 Sun May 12, 2013 9:20 am
^^That's the best site for any Garcia-related wiring questions. It's just like Milo said- both jacks are stereo, but only the OBEL cable (either "Y" or to junction box) is TRS. The out guitar>amp cable is a regular mono/TS.

 #127855  by myoung6923
 Sun May 12, 2013 10:00 am
The cable itself is a regular mono cable on both ends. The trick is, the JACK is a TRS jack. You just wire the negative to the ring and the sleeve, so that when the mono plug is in it, the sleeve bridges the ring and the sleeve of the jack and completes the negative side, which engages the battery. This way, the battery disengages when not in use.