Schoeps CMC 3U, Руководство пользователя, Страница: 6 / 24

SCHOEPS
GmbH · Spitalstr. 20 · D-76227 Karlsruhe (Durlach) · Tel: +49 721 943 20-0 · Fax: +49 721 943 2050
www.schoeps.de · mailbox@schoeps.de
Phantom Powering
Microphone Amplifiers
6
If possible, an unbalanced input should be bal-
anced with a high-quality microphone input
transformer. That will also allow the signal leads
from the microphone to be balanced, for best
rejection of interference.
If such an arrangement is not possible, how-
ever, a CMC microphone may be operated in
unbalanced mode by taking the signal from
pin 2 via a coupling condenser with a value as
shown in Figure 2 above. The signal from pin 3
must be left unconnected; do not short it to
ground. This ”unbalancing act” must occur
between the power supply and the preamplifier
input, however, since naturally all three pins
of the microphone must still connect to its
phantom or parallel power supply.
+ phase
- phase
2 (4)
3 (5)
microphone
1
screen
cable
powering
R
S
U
S
input
R
S
P48: U
S
= 48 V ± 4 V; R
S
= 6,8 k W *,
I
max.
= 10 mA
P12: U
S
= 12V ± 1V; R
S
= 680 W *,
I
max.
= 15 mA
I
/2
I
/2
I
+ phase
- phase
2 (4)
3 (5)
microphone
1
screen
cable
powering
R
S
U
S
input
R
S
R R
C
C
* see note in the text concerning tolerances
with XLR-5
(stereo microphones)
Fig. 2
To add phantom powering
to a balanced, grounded,
transformerless input, capa -
citors must be inserted into
the signal lines and polariza-
tion resistors provided as
shown.
*
*
*
Fig. 1
Input with transformer
(or balanced, floating trans-
formerless input)
XLR-3-
connector
XLR-3
connector
XLR-3-
connector
cable
Ohms
Ohms
* recommended values:
C: 100
μ
F, 63V; R: 22k
Ω
, 1%
** Tolerance ca. 5%; precise
matching is not critical.
Fig. 3
Parallel powering;
with parallel powering there is low-impedance
DC across pins 2 and 3. This can damage
dynamic microphones, especially ribbons.
z.B.
10 kOhm
**
**
R
*
be checked to verify its suitability for profes-
sional work with
SCHOEPS
microphones. On
page 8 a method is described for checking a
phantom supply quickly and easily.
For P12 the standard allows a current of
15 mA. A
SCHOEPS
CMC 3 will draw 11 mA
while a CMC 6 needs 8 mA at 12 Volts.
Fig. 2 shows a bal an ced but groun ded am -
pli fier in put. In this case eit her a trans for mer
(see fig. 1) or ad di tio nal ca pa ci tors ha ve to be
in ser ted in the au dio li ne.
Unbalanced Operation
Unbalanced operation of CMC microphone
amplifiers is not recommended; both noise and
vulnerability to interference will be increased.
shield
shield
shield