Consumer MD recorders are designed to be used with electret capacitor microphones. This type of mic uses a small foil diaphram with an electret (permanently charged) backing. This, like all capacitor microphones, has a very high output impedance, so it cannot directly drive the connecting cable. Included in the microphone capsule is a Field Effect Transistor, and the high impedance gate of the FET is a perfect match for the microphone element. A small voltage, generally 1.5 to 10V must be supplied to operate the FET. The drain current of the FET is propertional to the gate voltage, and the FET is able to drive a much lower impedance, so the high-frequency roll-off caused by the cable capacitance is negligable for normal cable of up to 100 ft. or more. Plug-in powered microphones have an unbalanced 2-wire output; stereo mics have a 3-wire output, 2 hot wires and a ground. The recorder supplies a small voltage, generally 1.5 - 2 volts DC, between each hot wire and ground, through a 2k (approximately) resistor. Phantom powered microphones have a balanced 3-wire output; stereo mics have a 5-wire output with a common ground. The mixer or recorder supplies a higher voltage, often 48 volts DC but some mics will work with as low as 9 volts, between each signal wire and ground, through matched 6.8k resistor pairs. The differences between plug-in and phantom power are: 1) Plug-in is unbalanced (ground is used as the return of the audio circuit), phantom is balanced (has individual hot, return and ground). 2) Plug-in supplies the power voltage hot = +, return/ground = -. Phantom supplies the power voltage hot and return = +, ground = -. 3) Plug-in supplies low voltage, generally 1.5 - 2 volts, whereas phantom supplies a higher voltage, often 48 volts. Plug-in and phantom power are incompatible. Plug-in is unbalanced; phatom MUST be balanced, since not only the hot but the return must carry the power voltage. ----------------------------------------------------------------- To stop getting this list send a message containing just the word "unsubscribe" to [EMAIL PROTECTED]
