The Tri-Vista 300 does have an internal switch. Actually, there are 2 little dip switches toward the back once you have removed the 18+ screws that hold on the top of the case. This tortuous procedure is evidently necessary, according to the US importer, because Musical Fidelity thinks we're too stupid to do this without the assistance of a dealer, and if we were allowed to switch back and forth willy-nilly between MC & MM, we would surely ruin the thing. I believe the factory default is MM. I had to remove the lid to change to MC.
Whether throwing these switches will help your hum is another story. Probably because I have a cable box hooked up to mine and a bunch of audio and video cables are tangled behind my system, I have a ground loop, but it only manifests itself on digital, specifically if I use the external digital input on my Tri-Vista SACD. I cured it by floating the ground. I know - rivers running backward, human sacrifice, cats and dogs living together - but so far no one has died. There may be another way to ground your TT. Perhaps the more technically inclined can help you out.
