Please refer to the illustrated Fly Handbook for the full story. Over tightening the Balance Wheel can cause the spring to break and possibly damage the guitar. When I use the stereo cable and separate amps for the magnetic and piezo pickups I hear a pretty serious hum. You have what is known as a ground loop. This isn t the fault of the guitar or the amp.
Ground loops can occur whenever two pieces of electronic equipment are connected.
Use a Direct Box with a ground lift to isolate the two amps. Plug the Magnetic end of the Y cable into one amp, and the Piezo end into the Direct Box. Plug the Direct Box s output into a balanced input on the second amp. When you move up to heavier strings you also need to move up to the matching heavier Flat Spring. Using a spring size that is smaller than the string gauge may cause the spring to break and damage the guitar.