Principleof High Frequency Circuit

 

 

 

 

ses, this is not

critical, as the

large output

voltage

01 the

microphone

The capsule

of a RF condenser microphone

presents,

contrary

to

combined

with

its low output

impedance

provides

a large signalto

low frequency circuits, a low

impedance

output.

Instead of the

high

noise

ratio. Care should

be taken, however, that no multiple ground

polarization

voltage

normally

required,

a high

frequency

capsule

circuits

are formed when

the

microphones

are mounted

on tripods

needs only

a high

frequency

voltage of about10

volts, which is

ete.

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

 

 

capsule impedance

leads to a high performance

reliability

 

Connection

to microphone
inputs with
high sensitivity

of the microphones.

 

 

 

 

 

 

 

If the unit being used has a very high input sensitivity, i. e. when it is

 

 

 

 

 

 

 

 

 

Powering
and Connection

 

 

 

 

 

 

normally intended for use with dynamic microphones, it can be

 

 

 

 

 

 

necessary to reduce the output voltage from the microphone by

 

 

 

 

 

 

 

 

 

Sennheiser electronic introduced AB powering, which was then

means 01 a voltage divider, which should be built into the micro-

standardised In OIN 45595. As with dynamic microphones, only

phone cable atthe amplifier input. By this means the large signal

two wires are required to connect the microphone when this power-

on the microphone cable is maintained up to just belore the ampli-

ing system is being used. The operating current is fed along the

fier, which results In an increased signalto noise ratio.

 

~same wires as the audio frequency signal, so thatthe circuitry in the

microphone does not have to be connected to earth. Because of

,j

Connection to mixer and sound recording equipment with

 

this earth free technique the highest possible values of immunity

 

powering facilities

 

from noise or disturbance are achieved.

 

 

 

If an appropriate voltage source is available the condenser micro-

The connection of Sennheiser condenser microphones and

 

 

phone can be powered directly. The voltage should be 12 volts::t 2

dynamic microphones as weil is carried out using the principle of

 

 

volt. It should be so stabilised and filtered, thatthe unweighted

 

voltage matching. The advantages of this system are that neither

 

 

 

noise voltage is less than 5 f1V and thatthe weighted noise compo-

impedance variations of the microphone output nor of the amplifier

 

 

nents are less than 2 f1V. The current consumption 01the mlcro-

input exercise a noticeable influence on the total frequency

 

 

phone is approximately 6 mA. According to the OIN standard the

response. The source impedance of the Sennheiser condenser

 

 

resistors should be 2 x 180 Q. This means thatthe voltage drop

microphones with AB powering is so low (approx. 8 Q at 1000 Hz)

 

 

across the resistors is approx. 2 V.

 

that an amplifier input with an impedance of at least 600 Q will be

 

 

 

 

 

suitable. This is usual in the majority 01 cases. However, if the input

 

 

 

impedance is smaller than 600 Q, a resistor 01 appropriate value

 

 

 

should be placed in series with the microphone so that it "sees" at

 

 

 

least 600 Q. The voltage division caused by this series resistor

 

 

 

must of course be considered. The same method can be used

 

 

 

when a highter output impedance 01the microphones is

 

 

 

demanded. In this case again aseries resistor can be used to

 

,n_:r-nnn__,

 

provide correct matching.

 

,---

Sennheiser condenser microphones

produce

relatively

large output

I

I

I

I

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

I

I

I

I

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

I

 

I

I

Interference signals

can

be disregarded. Also

the internal

noise pro-

I

I

I

I

Juced by the microphone

does not

contribute

to the total

noise

:nnL-mm-:

 

3vel. The microphones are lilled with high Irequency filters, whicn

Balanced

 

;nsure that no high Irequency signals from the microphone can

 

A-B powering

3ffectthe

external

circuitry, and also

thatthe

microphone

itsell

is

motected Irom high Irequency disturbance.

It is, therefore,

not

 

according to OIN45 595

I.ecessary, even under the most difficult conditions, to take special

 

 

['recautions such as double screening of the cables or the provi-

 

 

on of high Irequency filters.

 

 

 

 

 

 

 

 

 

. mnhelser condenser microphones are polarised according to OIN

,---r-_m--:

.',3ndard i. e. when

pressure

signal

strikes

the

capsule

from the

, ,nt, pin

1 (pin 2

for

MKH

406

TU 3)

goe5 positive with

relerence

to

1

,

1

1

p',l3. This should be considered when the amplifier input plug is

1

1

1

I

being wired.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1

1

 

 

 

 

 

 

 

 

 

 

 

 

1

1

 

 

 

 

 

 

 

 

 

 

 

 

I

1

 

 

 

 

 

 

 

 

 

 

 

 

:__nL

n--1

\ '==~ I b

==r~'

1

:

I

 

I

1

 

1809

1800 :

1

,__-

12VCJS

3600 +12V

NF

+'c-

Connection to balanced, floating microphones inputs

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

amplilier via a powering adapter MZA 16 T or the power supply unit MZA 16 T.

Connection to unbalanced microphone inputs

In many cases, lor example most tape recorders, the input socket is unbalanced. In this case one pin 01 the balanced microphone output has to be earthed (preferably pin 3). When using the power supply unit MZN 16 T an unbalanced operation only is possible after a modification 01the power supply unit. Apart Irom cases where the microphone is being used lor prolessional studio purpo-

 

 

 

 

-12V

(--',---7""

,

a 360Q

NF

,

,

 

 

,

,

I

 

~

 

 

 

 

\-:-Z:==-=-"r) b

Unbalanced AB powenng

8

9