Sound card microphone

Most sound card microphone inputs require a minimum signal level of at least 10 millivolts, but some older 8-bit cards need as much as 100 millivolts. The typical impedance of the PC soundcard microphone input is in order of 1 to 20 kohms (can vary from card to card). The microphone type which works best with computer sound cards is the electret microphone.
Sound card microphone - schematic

Sound Blaster soundcards (SB16, SB32, AWE32, AWE64 or Live) from Creative Labs have a 3. 5mm (1/8 inch) pink stereo jack for the microphone input, with the following pinout: Note: Most soundcards will wire the positive DC bias voltage to the ring, but a small number of non-standard soundcards can have the bias voltage wired to the tip. A few cards have a jumper which enables or disables the power to the microphone jack. If the jumper is put on, the bias voltage ( +5V through a few kiloohm resistor) is wired to the tip. Newer mainboards with stereo microphone support will provide the bias voltage for both the tip and ring. The approximate schematic of a Sound Blaster microphone input circuitry shows that the +5V voltage on the connector is heavily current limited. The card`s voltage might not be exactly 5V, but it is usually something between 3 and 5 volts when no microphone is connected. The electret microphone is the cheapest omnidirectional microphone you can buy. Very sensitive, durable, extremely compact in size, electret mics are used in many applications where a small and inexpensive microphone with reasonably good performance is needed. You can find them in almost every stereo equipment, in consumer video cameras, mobile phones and so on. The electret is a modified version of the classic capacitor microphone, which exploits changes in capacitance due to mechanical vibrations to produce a small voltage proportional...

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