do you think i could use a roland cube 40xl as a keyboard amp?
You could plug your keyboard into it and you would hear your keyboard, but it would be far from ideal. Guitar amps like the Roland Cube 40XL are made to deal with and accentuate the frequency response of a guitar, whereas keyboards use the full audio spectrum. Using a guitar amp has two drawbacks: 1) the amp will change the sound of your keyboard significantly. 2) the amp may not deal well with certain low frequency sounds coming from your keyboard. Depending on your keyboard patch, that could damage the loudspeaker. Also, your keyboard will not be in stereo. In a pinch, you might be able to get away with it for practice. But don't perform with it. It will sound terrible.
A keyboard has a much wider range than a guitar. If you try to play too loud while playing the low notes, you could hurt the speaker in a guitar amp. It depends on the amp and the volume. I have a Peavey Session 400 and our keyboard player used it at a gig when his own amp failed. It worked fine, but it has a 15 speaker rated for 200 watts. If you play at a low enough volume, any amp would be finebut obviously the keyboard has the capability to do damage to any guitar amp if you push it too hard. You'd be safer singing through the guitar amp. There's no way you'll hurt a keyboard amp by plugging a mic into it.we've done it in a pinch at practice.
