- If the microphone is a handheld or gooseneck style with an internal preamplifier that requires phantom power (because a battery cannot be accommodated), it cannot be connected directly to the computer. These microphones must be connected to a dedicated phantom power supply or a microphone mixer that has this feature; the output of the power supply or mixer is then connected to the input of the computer using the same method as for a dynamic mic.

- If the microphone is a lavalier (tie-clip), headworn, or other type with a separate tube- or box-style preamplifier that requires phantom power, it may be possible to bypass the preamplifier and connect the microphone capsule directly to the computer audio input. This is only an option if the computer mic input provides the proper bias voltage.

(WARNING: This is a highly technical approach, and requires that you understand basic electronics and are comfortable with soldering. Mistakes may permanently damage the microphone, and the modifications described here will almost certainly void the manufacturer’s warranty. Consult the microphone manufacturer before proceeding.)

Adapting Condenser Mics to Operate on Voltage from the Sound Card
Most condenser microphone capsules can be operated on the bias voltage that is supplied by computer’s mic input. Bias voltage is usually between 3 and 9 volts dc; some microphones can operate on a range of voltages, while others require a specific voltage. To operate a condenser microphone (without its preamplifier) directly from the bias voltage supplied by the computer requires replacement or modification of the cable that connected the microphone to its preamp.

It is critical to know both the requirements of the microphone and the wiring scheme and amount of bias voltage available from the computer input. Specifically, you must know if the cable that connected the condenser microphone to its preamplifier is a one conductor shielded cable or a two conductor shielded cable. If this cannot be determined, you cannot proceed further. Keep in mind that signal level and electrical impedance are still important. For more information on the difference between bias voltage and phantom power and their functions in condenser microphones, see the Shure applications bulletin Phantom Power and Bias Voltage: Is There A Difference

It is more common to find condenser mics using two conductor shielded cable, where one conductor is used to carry the audio signal and the other carries the dc power. The shield is used as the ground, and should be connected to the Sleeve of the miniplug. The bias conductor should be connected to the Ring, and the audio conductor to the Tip of the miniplug.

If your condenser microphone uses only one conductor shielded cable, the conductor carries both the audio signal and the bias voltage at the same time. In this case you must add some circuitry to separate the audio signal from the bias voltage. It involves a resistor and a capacitor and will fit inside of most miniplug connectors that can be disassembled. Again, it is advisable to contact the microphone manufacturer to make sure that this will work with your particular microphone.

Typical wiring scheme for microphones with separate conductors for audio and bias voltage.