SCHOEPS
GmbH · Spitalstr. 20 · D-76227 Karlsruhe (Durlach) · Tel: +49 721 943 20-0 · Fax: +49 721 943 2050
www.schoeps.de · [email protected]
Powering
13
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
