How to reduce feedback
* When playing through an amp, place the amp behind you and to the left so your body blocks the feedback. Or place the amp in front of you, close to the audience. Then the audience will hear a louder sound, without you having to turn up the volume so much.
* Use a preamp that has a feedback notch filter, such as the Zoom A3.
* Try to play a little louder and turn down your amp to compensate.
* If the feedback is a low tone, turn down the bass (low-frequency EQ) on your amp a little at a time until feedback stops.
* If the feedback is a high squeal, turn down the treble (high-frequency EQ) on your amp a little at a time until feedback stops.
* If you have a pickup, mix it with the microphone to get a louder sound.
* If you have a pickup, send its signal only to the monitor speakers, and send the mic signal only to the house speakers. Here's how: In your mixer's pickup channel, turn up the monitor send and turn down the fader. In your mixer's mic channel, turn down the monitor send and turn up the fader. The audience will hear the natural acoustic sound of your mic, and you will hear the pickup in your floor monitors, with no feedback.
* Use in-ear monitors instead of floor monitor speakers. The Behringer MA400 headphone amp is a one-person solution.
* If your amp is near a wall or on the floor, that can exaggerate low frequencies (bass) and cause feedback. Try placing the amp on a chair, and further from the walls.
* If your instrument is facing a wall, sound reflections off that wall can get into the mic and cause feedback. Try to play into an open space. Also, don't face directly into a monitor speaker -- aim a little away from the monitor speaker.
* Ask the sound tech to turn on, in their mixer, a highpass filter (low-cut filter) around 75 Hz to 200 Hz. That will prevent feedback at very low frequencies without affecting the sound of your instrument.
* Mandolin only: Try mounting the mic inside an f-hole instead of outside, and turn down the bass to compensate.
* Banjo only: Try mounting the mic inside on the dowel rod, and turn down the bass to compensate.