ABY switcher and the HUMMMMMM !!!

OK I put together an A/B Y switcher for my guitar into two amps.

I used this schematic:
http://www.geofex.com/FX_images/spltr2.gif

and this PCB board
http://www.generalguitargadgets.com/diagrams/amp_ab_lo.gif


A terrible HUM!!! with the properly switched guitar. IS the problem.

The transformer used was also in the spec and is :
42TM018
http://www.pillarsofnein.com/diy_projects/aby_tranny.pdf

The op amp is a :
LM833


I used 2 9V batteries for +/- supply to try to isolate the problem and the hum is still there.


Any suggestions???

Thanks

-ChuckD

Does it only hum when more than one amp is connected?
Do you have the xfrmr output jacks ground (sleeve/ring) isolated from the chassis and other jacks?

Are the outputs isolated from the chassis? Sounds like you have a ground loop problem.

Cheers,
--
Don

Not sure what is causing the hum so I went out and bought a retail Hum elimnator. Which turned out to be the same exact thing I built into my switcher. Just a couple of transformers. Still has the hum.

So it may not be the ground loop thing.
Yes the jacks all are shielded from the chassis too.

outputs are floating from the secondaries as the schematic shows.

Any other ideas??

Thanks guys!

-ChuckD

And you don't get the hum when plugged straight into one amp at a time?

try connecting your gtr direct to one amp without your gizmo, and link tru an Y-adaptor to the next amp. If you also get hum this way, disconnect earth from one amp only. Then you should be fine with your AB/Y-splitter.

nothing wrong with the circuit.

Cheers,

Tony.