Phantom-powered / T-powered
- balanced, very low-impedance output
- can be used with
very long cables (several hundred meters)
- can be used
with Active Accessories for miniaturization and special
applications
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CMC 6
(12 V and 48 V phantom powering) |
CMC 5
(48 V phantom powering) |
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CMC 3
(12 V phantom powering) |
CMC 4
(12 V parallel powering) |
The chief task of a CMC microphone amplifier is to convert
the extremely high-impedance signal from the capsule to a
very low-impedance one suitable for transmission through
a microphone cable. Several versions are available which
differ only in their powering, connectors, output levels
and surface finishes. They all feature a symmetrical class-A
output stage with neither coupling condensers nor an output
transformer. This design helps them to achieve extremely
low distortion and light physical weight, while their very
low output impedance helps make them insensitive to electrical
interference.
On the choice of amplifier type:
If a recording device has balanced inputs but lacks phantom
powering, it may be possible to add 12 Volt powering rather
easily by using a supply voltage that is already present
internally. In most cases 48 Volts would need to be generated
with a voltage multiplier circuit, which is more difficult
to implement. That is why we recommend the CMC 6, which
works with both 12 V and 48 V phantom powering so long
as the relevant standard is followed.
If it is certain that 48 Volt phantom powering will be available
in all foreseeable recording situations, the CMC 5 should
be fully satisfactory. In addition to the CMC 6's dual-voltage
circuitry versus the CMC 5's single-voltage circuitry, the
two amplifiers differ in their response at the very bottom
of the audio frequency range. The CMC 5 rolls off below 30
Hz, while with digital recording in mind, the CMC 6 is essentially
flat to 20 Hz.
The CMC 3 is designed for 12 Volt phantom powering. If necessary
it can also be driven from certain 48 Volt phantom supplies,
but it will draw significantly more current than a CMC 5
or CMC 6 without offering any particular advantage for doing
so (a CMC 3 draws 11 mA at 48 V).
The CMC 4 works only with 12 Volt parallel powering (“T-feed“),
which is rarely encountered nowadays except in video and
film sound.
Special Versions
Please note: The two amplifiers in a stereo pair of microphones
should always be of the same type.
CMC 6 Ug"xt" – the 40 kHz
Version
This version is indicated by the letters “xt“ engraved
on the microphone's output socket as shown at left. It extends
the frequency response of the axially addressed Colette capsules
beyond 40 kHz.
CMC “+5dB”
(Formerly marked with a blue dot.)
The sensitivity of a microphone using this type of microphone
amplifier is 5 dB higher. The signal-to-noise ratio of
the microphone itself remains nearly unchanged. The maximum
sound pressure level the microphone can then accept is
reduced by 5 dB.
The risk of overloading the input of the following device
when high sound pressure levels are encountered is also increased.
This version might be chosen in order to raise the microphone's
signals above the noise level of the equipment to which it
will be connected, and/or for working with sounds that occur
mainly at low levels.
CMC “linear”
(Formerly marked with a dash.)
CMC microphone amplifiers normally have a gradual rolloff
below 30 Hz (20 Hz in the CMC 6) to guard against infrasonic
disturbances from various sources such as air movement
and vibration. However, when using pressure (omnidirectional)
transducers, particularly with digital recording, it can
be desirable to pick up frequencies below 20 Hz without
attenuation. The special technology of the CMC microphone
amplifiers makes this possible; on request we can deliver
microphone amplifiers with response that is flat to as
low as 3 Hz.
Caution must be advised with respect to infrasonics, however.
Since pressure transducers can pick up very low frequencies,
ventilation systems in large spaces (churches, concert halls)
can create a problem. With pressure gradient transducers
the risk is even greater. They are far less sensitive to
very low frequency sound, but respond much more strongly
to unwanted low-frequency stimuli such as air currents and
solid-borne noise. Although such signals may be below the
audible range of frequencies, they can overload electronic
circuitry and produce severe distortion.
Included accessory with every CMC microphone amplifier:
polished wood case for two microphones
A note of caution: The current required by the SCHOEPS class “A“ output
circuit falls well within the limit of 10 mA set by the prevailing
standard (DIN EN 61938, July 97, formerly DIN IEC 268-15
and DIN 45 596). However, certain commercially available
power supplies, preamplifiers, and mixing desks – mostly
older, but some more recent – may fail to meet this
standard. Such units may not be able to power SCHOEPS microphones
adequately, especially where headroom at high SPL is desired.
Where doubt exists, equipment should be checked to verify
its suitability for professional work with SCHOEPS microphones.
The PHS 48 accessory test plug can be helpful in testing
equipment quickly and easily to see whether it is compatible
with SCHOEPS 48 Volt phantom-powered microphones. |
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