Once you turn the unit on, set the smaller Gain control knob so its green LED is lit but without flashing red LEDs, you're ready to advance the bigger Volume control to whatever volume level you require.
I found the sound to be marvelous (even though it has to be mono) and there is a lot of volume level available--louder than I can take.
I tested using both modes. I fed a mono mix from Pro Tools as a +4dB line level signal and I also connected my left small speaker's cable from my power amp to Sound Tap. Both ways worked flawlessly.
Sound Tap is housed in a rugged metal box with a threaded 3/8-inch European mounting nut underneath it so it can mount on a mic stand. It is built first class with dual, quick-change 9V battery holders, all metal control knobs and switches and finished in chip-resistant paint.
So I am highly recommended Sound Tap and I'm sure live sound/stage pros will pickup on it immediately and add it to their kit. Why didn't I think of this!!
Read Barry's full Sound Tap article here.