Simple phase reverse box...

[hairyandy]

Hey all,

I'm in need of a schemo or layout to implement R.G.'s polarity reverse circuit.  I'm on the road and need to electronically flip the phase on one channel of a guitar amp that is out of phase with the other amp in the rig.  Unfortunately, the amps are under the staging so I can't physically get to them to swap speaker leads during a show.  Plus that wouldn't be very pro of me.   

Any help would be appreciated,

[hairyandy]

Anyone?  I've read the polarity reverser article at geofex (http://www.geofex.com/Article_Folders/polarity_reverser/polarity_reverser.htm) but I'm unsure of the opamp and component values.  I just need to make a quick and dirty box that can flip the phase via a switch.

Thanks,

[spudulike]

Andy -

  Get the schem for the Runoffgroove Splitter-Blender here.

   Use the section U2A and take the output straight off the 10uF cap.
   Remember the Vref v-divider though

[R.G.]

The opamp can be any opamp you can get easily. I like TL072's because they are a combination of available, cheap, and good. Note that if you use a dual like the TL072, you'll need to use only one half - pin 1,2,3 being one half, pins 5,6,7 being the other.

R1, 2,3 can be 10K to 220K, all the same whatever value you pick. Pick your value based on whatever the signal impedance is that drives the thing. If you have some active device like a preamp out or an effect output driving it, use 10K's. If it's a guitar, use 100K or 220K. You could use the other half of the opamp as a buffer, and that's actually a pretty good idea. Make Rbias large, maybe 510K. Not shown but necessary is a bias supply, which can be two 10K resistors in series from +9 to ground, with the center bypassed to ground by a 10uF cap. The bypassed center is where the bias resistor connects.

[hairyandy]

Thanks a lot guys!  As always, this place rocks...

[Paul Perry (Frostwave)]

Suprised nobody menioned the single transistor solution: (right hand side schem)
http://ourworld.compuserve.com/homepages/g_knott/elect234.htm

though I would use a transformer solution (passive).

[Gladmarr]

...or just an isolation transformer with a 1:1 ratio and reversed polarity on the secondary.  Okay, more dough than a transistor circuit, but way fewer parts!   

Okay, I should read all the way through before I post.  I just saw Paul's last line that beats me to it...   

[Paul Perry (Frostwave)]

Actually, YOU beat ME, gladmarr, becuse i was thinking a transformer with an earthed centre tap on the output, wiht a SPST switch to choose phase. Whereas your isolation tranny is probably easier to find & there are plenty of DPDT switches! Hell, get a 3PDT switch from Aron or Steve & have an indicator as well