C,

(v

High Frequency Circuit

The capsule of a HF condenser microphone presents, contrary to low frequency circuits, a low impedance output. Instead of the high polarization voltage normally required, a high frequency capsule needs only a high frequency voltage of about 10 volts, which is produced by a built-in crystal-oscillator (8 MHz). The low capsule impedance leads to a very small self-induced noise signal from the microphone and to a high performance reliability.

Powering and Connection

Sennheiser electronic introduced A-B

powering, which was then standardised in DIN 45595. As with dynamic microphones,

only two wires are required to connect the microphone when this powering system is being used. The operating current is fed along the same wires as the audio frequency signal, so that the circuitry in the microphone does not have to be connected to earth. Because of these earth free tech-

niques the highest possible values of im-

munity from noise or disturbance are achieved.

The connection of Sennheiser condenser

microphones and dynamic microphones as weil is carried out using the principle ofvolt- age matching. The advantages of this system are that neither impedance variations of the

microphone output nor of the amplifier input exercise a noticeable influence on the total

frequency response. The source impedance

7