The quick question is that can I plug a microphone to a guitar or bass amp and use it properly without damaging it, instead of the original mixer-speaker combination?
You can, but it'll sound like ass.
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Yeah, you'll not ruin anything but you'll sound pretty damn funny.

Also don't use distortion, even low sensitivity mic's create a hell of a lot of feedback.
Name's Luca.

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Clue: amplifiers amplify so don't turn it on if you need quiet.
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It'll get the job done. Won't sound great. If it's jus for practice it may be good enough. If it will get long term use I'd eventually try to upgrade to a small pa or even a keyboard amp.
Originally posted by primusfan
When you crank up the gain to 10 and switch to the lead channel, it actually sounds like you are unjustifiably bombing an innocent foreign land.

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I've done this before. Nice if oyu want to sing through effects but doesn't sound "good".