I picked up an ART Pro Channel II off of eBay. I have it running into channel 1 of a Crown XLS 1500 via balanced XLR. However, I'm having some issues. 1. Out of the box, with normal settings, there is a bad background buzz. I played with lots of settings, bypassing the compressor, bypassing the EQ, but the buzzing persisted. Then I tried setting the "tube voltage" button to "high", and suddenly 95% of the buzzing went away. I tried swapping the tubes with a different pair of 12AX7s I had lying around, but it didn't change the problem at all. The only usable setting seems to be with the "tube voltage" set to high. The normal setting is basically unusable. I'm stumped as to what could be wrong. Maybe a tube bias problem? 2. The output level seems to be too weak to drive the Crown. If I set the preamp to just below clipping, and then set the compressor stage to just below clipping, and then crank the master output level to its highest setting, I am still unable to get the "-10db" light on my Crown XLS 1500 to light up. (My Carvin BX500 is much louder even at half-volume than this combo at full blast...) If anyone is using this setup, I'd appreciate some tips. Thanks!