Let me elaborate a little more: the amp is quiet up until 1/2 volume, then the buzz starts and gets louder and higher pitched as you increase towards full volume. And again, this is WITHOUT the speaker being plugged in. When the speaker IS plugged in there is slight hum which I expect, and when I make contact with an installed instrument CABLE I get the feedback I would expect, but plugging in an instrument itself produces no sound nor hum.