Just to be sure, from the back of the Art tube pac, you are running a TRS cable from the unbalanced 1/4" output of the Art to the 1/4" balanced input (center of the XLR) of the IPR. Since this has worked, I assume that there are no issues in doing this. Sometimes you need a 1/4" unbalanced to balanced cable. You can run from the Art's balanced output XLR connector to the mixer. You were plugged into the left hand side at the back of the Art, not the right which is an input.
When running just from the Art to the IPR, it would be better to use an XLR cable. The connection is better and you are running balanced to balanced. The specs are typically different for 1/4" and XLR inputs and outputs. They have different impedances and different signal levels. In general, if you can, go XLR to XLR.
A hum at the mixer would indicate that the ground needs to be lifted, pin-1 on cable connected to the Art's output XLR disconnected. Some mixers have a switch for this, otherwise you can use a ground lift patch cable. This breaks a ground loop and eliminates the hum.
Official Ampeg Portaflex Club #89
Last edited by beans-on-toast : 01-13-2013 at 10:15 AM.