Feedback is what happens when the amplifier speaker(s) make enough sound that the vibration in the air reinforces the vibration of the strings. The stronger string vibration sends an increaased signal level to the amp, which comes out as louder sound from the speakers, which reinforces the string vibration, which sends a stronger signal to the amp...... :eek: :eek: :eek: :eek:

Some frequencies will be reinforced more strongly than others. and some parts of the system have resonnances that will build up faster than others. This is why the note that feeds-back may not be the one you 're playing. Unless you control it, this can build up to where the amp and/or the speakers burn out.

If this isn't what you're describing, it isn't feedback.

If you're talking about something else, please describe it carefully, so we can narrow down the possible causes.