Microphone amplifier

This article explains the impedance converter in condenser or electret microphones; for amplifiers for connecting microphones, see microphone preamplifier .

A microphone amplifier is an internal component of condenser and electret microphones , which is located directly behind the microphone capsule in the signal flow. Functionally, no voltage is amplified, as the name suggests, but an impedance conversion (current amplification) is carried out.

Circuit diagram: simple microphone amplifier with field effect transistor

Circuit diagram: operational amplifier as an impedance converter with a voltage gain = 1

The membrane of a condenser microphone is a very high-impedance voltage source , so it does not supply enough current to transmit the signal directly to the mixer via a cable without interference. Therefore an impedance converter is needed; this is also known as a microphone amplifier. It is not (!) A voltage amplifier (voltage gain = 1). Its sole task is to adapt the signals from the high-impedance capacitor capsule for transmission through the microphone cable and to the input of the mixer . There is an impedance conversion from the very high-resistance capacitor capsule (> 1  G Ω ) to a much lower output resistance (<200 Ω in studio technology ).

In addition, a conversion takes place in the studio technology balanced signal instead, for a can transformer or an electronic circuit can be used. The supply voltage for the impedance converter often comes from a mixer supplied by the phantom power , which mainly 48  V is.

In studio technology there is only a voltage amplifier in the microphone in exceptional cases . This also applies to electret microphones.

Otherwise the microphone preamplifier , English mic preamp called. Here, the low voltage at the microphone output (especially with dynamic microphones ) is amplified to a level that can be used to control an amplifier or a mixer. The terms microphone preamplifier (as a necessary voltage amplifier ) and microphone "amplifier" (as an impedance converter) in the microphone body are not clearly distinguished, especially in hobby technology.

See also

• Electret microphone

literature

• Siegfried Wirsum: NF tricks for the audio freak. 1st edition. Franzis Verlag, Munich 1990, ISBN 3-7723-3321-4
• R. Beckmann: Manual of PA technology, basic component practice. 2nd Edition. Elektor-Verlag, Aachen 1990, ISBN 3-921608-66-X
• Helmut Röder, Heinz Ruckriegel, Heinz Häberle: Electronics . Part 3: communications electronics. 5th edition. Verlag Europa-Lehrmittel, Wuppertal 1980, ISBN 3-8085-3225-4