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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 perfor-
mance 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 micro-
phone 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
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