I recently got a Yamaha 8 track cassette. In the manual, they indicated that the guitar should be connected to a 'guitar processor' and then into the deck. What is a guitar processor? I plug the guitar into an amp and then come through a jack in the back of the amp to the deck, but the sound is not so good and it picks up the hum of the amp. The more instruments I record this way increases the hum. How do I record clean sounding guitar with reverb?