Problems with noise in condenser microphone.

[janeriksen]

What causes the humming noise from these microphones? Even if I only use a battery on the preamplifier, the noise will not dissapear. Is this noise caused in the preamplifier or is it general to these kind of microphones? Are there any differences between cheap and more expensive microphones?
The noise dissapear if I lower the voltage to under 2V, but that also reduce the effect very much.
Are there anybody here who can help me with this problem?

 

[Compositepro]

Humming is almost always due to picking-up 50 or 60 cycle signal from nearby power lines. The microphone and all low level signal lines need to be properly shielded from electromagnetic interference.

 

[Strong]

There should be no hum in microphone or preamplifier. I assume you are using an electret type of condenser microphone. These can require up to 40 volts phantom power. Be sure the preamplifier provides the correct voltage to the microphone and for most sound and vibration measurement instruments, be sure the instrument is AC-coupled to remove DC. You would have to provide a lot more details for specific help on this problem.

Walt