Electret mike - connection to plug

[atferrari]

I soldered the red/white wires to the mike's +/- terminals and the shield to the metalic housing.



A) At the plug end, the (-) and the shield were soldered together going to the common of the preamp. Is this reasonable?

B) Found the shielded plastic-jacketed bipolar cable quite hard to bend. Could I use single shielded wire (red only plus shield), soldering the shield to the housing and negative terminal? I do not see any difference since in both cases signal is unbalanced.

C) Used it to test on the bench my just-built pre + filter + amp. It seems to work but I hear some hum (most probably 50 Hz from mains). Should I do something else on the mike + wire + plug or could I expect that a metalic enclosure could cure it?

Thanks for any reply / comments.

 

[Audioguru]

There are two different kinds of electret mics:
1) 2-wires. It has a signal output wire and a 0V shield wire. The signal wire is shielded by the 0V shield wire that also connects to the metal housing of the mic.

2) 3-wires (sold at Radio Shack). It has a positive power supply wire (red), a signal output wire (white) and a 0V shield wire. The signal wire is shielded by the 0V shield wire. I do not know if the shield wire connects to its metal housing.

If the preamp is built on a solderless breadboard then the many rows of contacts and jumper wires are antennas that pick up mains hum and all kinds of interference.