Tony - this comment: "Whenever I combine piano channels in a stereo to mono adapter" is the problem with the thin sound of the Yamaha. Don't do this, plain and simple.

This will cross-feed the individual outputs from your Yamaha into each other- and while it's probably designed to handle this, it's just bad practice to drive one output channel from a different output channel. You will get some unintended phase cancellation as well as potentially causing damage to the output stages of the Yamaha. Mac can give you the electrical engineering details, but this is not the way to force a mono signal. As Mac pointed out, if you want mono out of the keyboard, use the forced left mono output from the keyboard itself (Left channel for your CP33). That shouldn't sound thin at all. You should be able to run that into one of the mono input channels on the Behringer without issue.

Best wishes and sounds like a good gig. If it's in the Lakeland area, I may look you up sometime when I visit my mom and dad.

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