Linear Input Signal Source
Connect a linear input signal source (e.g., computer, DVD player, tuner) to the preamplifier or mixer.
Successively unplug each source and check if the noise disappears.
Identify which signal source introduces the noise into the system.
Connect the computer's power supply to the same outlet as the preamplifier or try a different computer for testing.
Address potential differences causing noise by using an audio isolator between the computer and preamplifier.
Share the same power source for the computer and preamplifier or remove the computer's power supply ground wire.
If tuner noise persists, turn off the tuner's power and improve signal reception with an outdoor antenna.
Microphone Input Signal Source
Unplug each microphone signal input line (wired or wireless) one by one.
Check if speakers still have noise after unplugging each microphone.
Identify which microphone introduces noise into the system.
If wireless microphones cause interference, adjust frequencies or consider using a different frequency band.
Address wireless microphone receiver grounding issues; separate from the rack and isolate if needed.
For wired microphones, replace excessively long cables with shorter ones. Use high-quality shielded cables for long runs.
Consider adding an audio isolator between the microphone cable and preamplifier.
Power Amplifier or Preamplifier
With no audio source connected, have only one signal line between the preamplifier and power amplifier.
If noise persists, unplug the signal line and check if the speakers still have noise.
If noise disappears when the signal line is unplugged, the issue is with the preamplifier. Test with another preamplifier and repair or replace if needed.
If noise persists, the problem lies with the power amplifier. Substitute with another amplifier for testing and repair or replace if necessary.