Schoeps MSTC 64 Ug User Manual download pdf (Page 13)

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Powering

English

Powering

The MSTC 64 Ug is electrically active and

requires operating current. This will most

often be supplied by the inputs of a mixer,

preamplifier (such as the SCHOEPS VMS 5U

shown on Fig. 1) or recorder that has suitable

microphone powering built in. Otherwise, a

stand-alone microphone power supply of

proper type can be used.

Like most modern, solid-state professional

microphones, the CCM also uses a standard-

ized powering scheme known as “phantom

powering.” Most recording equipment offers

a 48-Volt supply for such microphones. Some

equipment, however, provides a 12-Volt sup-

ply for phantom powering, or can readily be

modified for such a supply. The SCHOEPS CCM

compact microphones series can work with

either voltage. The current remains the same

for both options. The output level, i.e. maxi-

mum sound pressure level, is 6dB lower when

running on a 12V phantom power supply.

Please note that the MSTC 64 is designed

to work with standard 12-Volt or standard 48-

Volt phantom powering. It is therefore no ”12

- to - 48 Volt” microphone. Any input to

which it is connected must implement one of

those two standard phantom powering meth-

ods, which means that not only must the sup-

ply voltage meet the standard, but the resis-

tors must be correct as well.

Our microphones are developed and tested

with power supplies that conform to the

require ments of this standard. Proper opera-

tion with non-standard power supplies cannot

be guaranteed. Circuit arrangements that

deviate from the standard can cause opera-

tional problems (i.e. distortion or even gaps in

the signal), particularly at high sound pressure

levels or in the presence of strong wind noise.

Such problems may often seem to defy analysis

until their real cause is discovered.

You can find out more about phantom

power supplies below.

Phan tom po we ring to stan dard

DIN EN 61938

For a condenser microphone correct powering

is essential. There have been various myths

and misunderstandings about it. Authoritative

information is contained in the standards doc-

uments, but few people have access to them

which is why we are offering this detailed

explanation.

Phantom powering is designed to be ”invis-

ible” and harmless to balanced microphones

which were not specifically designed to use it;

this includes most balanced, professional

dynamic and ribbon microphones, as well as

condenser microphones that use vacuum-tube

circuitry. Exceptions are quite rare. The only

likely cases in which standard phantom power-

ing will endanger a balanced microphone (e.g.

a ribbon) are if a microphone cable, con nector

or adapter is defective or wired in a non-stan-

dard way, such that one modulation lead of the

microphone is shorted to ground at DC while

the powering is on. If a microphone is con-

nected to such a cable with the powering

turned on, impulse current will flow through

its coil or ribbon, possibly causing damage.

Fig. 1 shows the only valid 48 V and 12 V

phan tom powering circuit (abbreviations: P48

and P12) that can be realized with resistors as

opposed to a center-tapped input transformer.

This illustration is based on the international

standard document EN 61938 of 1997.

The permissible tolerance of the feed resistor

values as such is ±20%. However, the difference

between the resistors of any one pair should

be less than 0.4% (i.e. 27 Ohms for 48-Volt

phantom powering with 6.8 kOhm). This

close matching is necessary to maintain ade-

quate impedance balance for the sake of com-

mon mode rejection. It also avoids the flow of

Fig. 1

VMS 5 U microphone preamplifier

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Schoeps MSTC 64 Ug User Manual Page 13

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