I also play with a mic on my tenor neck. I plug into a small mixer to control the volume. The mixer is 4 channel and is about 4"x6" and sits on the floor.
If I bring a keyboard to a gig the mixer sits on it and I have volume control of the sax, keyboard and vocal mic. before it gets sent to the PA.
If I bring a keyboard to a gig the mixer sits on it and I have volume control of the sax, keyboard and vocal mic. before it gets sent to the PA.