I want to use an H9 with both inputs, where input 2 will only receive signal when the tuner is on (using a programmable switcher) but with one output in mono.
Will there be any effect on the sound considering I have something connected to input 2 but with no actual guitar signal when playing ?
I think there will be. The H9 will detect that something is plugged into the second jack and configure its algorithms to run in stereo mode but there won't be a stereo signal…
I don't think so. Hopefully, my colleague, Nick, will chime in to verify that. By the way I posted a classification of the algorithms by whether they're dual mono, stereo summed to mono, or true stereo on the gearpage a while back: