I have a TC-Helicon Harmonizer GTX, which I can connect directly to an amp with no intermediate mixer. Works great. Just recently purchased a TC-Helicon Acoustic Play, set-up is similar to GTX. Only problem is that none of the harmonizer fundtions work. Can hear my guitar and my voice, but no harmonies when I try to engage the various harmonizer effects. Checked to make sure mic gain was OK, guitar input was solid, and XLR from mono (L) was securelt plugged into XLR mic input on amp. Can't get any harmonies. Tried it out with just headphone connections. Same problem. Is there a problem with the unit, or am I doing something wrong? Help!