Why would a guitar amplifier emit a loud humming sound whenever you touch your thumb to the tip of the phone plug?
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Answer

This is normal on guitar amplifiers because of the very small signal from the guitar pickup one will need a high gain pre amplifier to boost the signal to drive te main amplifier, if you touch the tip of the phone plug you are actually feeding a 50Hz or 60Hz signal that is picket up by your body that act as an antenne for the magnetic fields from the 50 or 60Hz mains, that is then amplified by the preamp to a large enough signal to drive the main amp.

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First answer by ID1257162463. Last edit by Chrismicro. Contributor trust: 113 [recommend contributor]. Question popularity: 23 [recommend question]

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Why is your guitar humming?  Why is the sound on the drum different from that of the guitar?  Why does your guitar amplifier emit a loud humming sound whenever you touch your thumb to the tip of the phone plug?