Sennheiser SK 1006 User Manual download pdf (Page 7)

TECHNICAL NOTES

High Frequency Circuit

The capsule 01 a RF condenser microphone presents, contrary to

low Irequency circuits, a low impedance output. Instead 01 the high

polarization voltage normally required, a high Irequency capsule

needs only a high Irequency voltage 01 about 10 volts, which is pro-

duced bya built-in low noise oscillator (8 MHz). The low capsule

impedance leads to a high performance reliability 01 the microphones.

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 led along the same

wires as the audio Irequency signal, so that the circuitry in the micro-

phone does not have to be connected to earth. Because 01these

earth Iree techniques the highest possible values of immunity Irom

noise or disturbance are achieved.

The connection 01 Sennheiser condenser microphones and dynamic

microphones as weil is carried out using the principle 01 voltage

matching. The advantages 01 this system are that neither impedance

variations 01 the microphone output nor of the amplilier input exer-

eise a noticeable influence on the total frequency response. The

source impedance of the Sennheiser condenser microphones with

A-B powering is so low (approx. 8 n at 1000 Hz) that an amplilier

input with an impedance of at least 400 n will be suitable.

Senn heiser condenser microphones produce relatively large output

voltages, these can be up to 1 volt with maximum sound pressure

levels. This has the advantage that even with long cables induced

interference signals can be disregarded. Also the internal noise pro-

duced by the microphone does not contribute to the total noise

level. The microphones are litted with high frequency filters, which

ensure that no high frequency signals from the microphone can al-

lect the external circuitry, and also that the microphone itsell is pro-

tected from high frequency disturbance. It is, therelore, not necess-

ary, even under the most difficult conditions, to take special pre-

cautions such as double screening 01the cables or the provision of

high frequency lilters.

Sennheiser condenser microphones are polarised according to DIN

standard i. e. when apressure signal strikes the capsule from the

front, Pin 1 goes positive with reference to Pin 3. This should be

considered when the amplilier input plug is being wired.

Connection to Amplifiers with balanced Inputs

In this case the microphone is simply connected to the input of an

amplifier via a battery adapter or the power supply MZN 16 T.

Connection to Amplifiers with unbalanced Inputs

In many cases, for example most tape recorders, the input socket

is unbalanced. In this case one side of the balanced microphone

output has to be earthed. Apart lrom cases where the microphone

is being used for professional studio purposes, this is not critical, as

the large output voltage of the microphone combined with its low

output impedance provides a large signal to noise ratio. Care should

be taken, however, that no multiple ground circuits are formed when

the.microphones are mounted on tripods etc.

Connection to Amplifiers with High Input Sensitivity

In the amplifier being used has a very high input sensitivity, i.e. when

it is normally intended for use with dynamic microphones, it can be

necessary to reduce the output voltage from the microphone by

means of a voltage divider. This should be built into the microphone

cable at the amplifier input. By this means the large signal on the

microphone cable is maintained up to just before the amplifier, which

helps to increase the signal to noise ratio.

Connection to Amplifiers with Defined Input Impedances

Sennheiser studio condenser microphones can be connected directly

to all amplifiers whose input impedance is larger than 400 n. This is

usual inthe majorityofcases. However, if the input impedance is smaller

than 400 n, a resistor of appropriate value should be placed in series

with the microphone so that it "sees" at least 400 n. The voltage

division caused by this series resistor must 01 course be considered.

The same method can be used when a higher output impedance of

the microphone is demanded. In this case again aseries resistor can

be used to provide correct matching.

Connection to Amplifiers with Powering Facilities

If an appropriate voltage source is available in the amplifier the con-

denser microphone can be powered directly. The voltage should be

12 volts :t 2 volt. It should be so stabilised and filtered, that the un-

weighted noise voltage is less than 5 /LV and that the weighted noise

components are less than 2 /LV. The current consumption 01the

microphone is approximately 6 mA. According to the DIN standard

the feed resistors should be 2 x 180 n. This means that approx. 2

volts are lost across the resistors.

,n-T-_nnn,

1 1

:n__L_nn___'

A-B powering

according to DIN 45595

";:r

1800 , , Cn

,-uT--_n---,

1 1

1 I

1 1

: Ln nl

,"',_n7--\ a 360Q

1 1 I ,

, , , 1

\""' '.IJ b

A-B powering unbalanced connection

360Q +12V

+'C-

-12V

f:;:-

1 2 3 4 5 6 7 8 9 10 11 12

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Sennheiser SK 1006 User Manual Page 7

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