SCHOEPS V4 U - Handbuch (Seite 11)

SCHOEPS GmbH · Spitalstr. 20 · D-76227 Karlsruhe (Durlach) · Tel: +49 721 943 20-0 · Fax: +49 721 943 2050
www.schoeps.de · [email protected]
Phantom Powering
11
English
Phan tom Po we ring to Stan dard
DIN EN 61938
“Phantom” powering is the standard way to
power studio condenser microphones via two-
conductor, shielded cables. Both conductors
are at the same DC voltage, and exactly the
same supply current flows through both of
them. Fig. 1 shows the only valid 48 V phan-
tom powering circuit (abbreviation: P48) that
can be built using resistors as opposed to a
center-tapped input transformer. This illustra-
tion is based on the international standard
document EN 61938.
The permissible tolerance of the feed resistor
values as such is ±20%. However, the differ-
ence between the resistors of any one pair
should be less than 0.4% (i.e. 27 Ohms). This
close matching is necessary to maintain ade-
quate impedance balance, which in turn is
required for the sake of common mode rejec-
tion. It also avoids the flow of DC in an input
transformer (should one be present), which
could lead to distortion or reduced dynamic
range.
A microphone designed for 48 V phantom
powering may draw as much as 10 mA accord-
ing to the standard. The SCHOEPS V4 U will
draw only about 3.3 mA, well within this limit.
Although there is nothing particularly com-
plicated or demanding about phantom pow-
ering, there are some power supplies, pream-
plifiers, and mixing desks which fail to meet
this standard, and hence may not be able to
power SCHOEPS microphones (or other modern,
transformerless studio condenser microphones)
adequately. If in doubt, equipment should be
checked to verify its suitability for professional
work with SCHOEPS microphones. A quick
and easy way to check a phantom supply is
described on page 15.
Unbalanced Operation
You may encounter a situation in which there
is no balanced microphone input with phantom
power available, but only an unbalanced
microphone input – most likely without stan-
dard phantom powering, or perhaps with a
different microphone powering scheme.
We strongly advise against connecting the
V4 U directly to such inputs; the microphone
is not designed for such operation, and the
advantages of phantom powering (noise and
interference rejection) will be completely lost.
Instead, a high-quality microphone input
transformer could be used to turn the unbal-
anced input into a balanced one, and then
phantom powering can be supplied. This will
allow the signal leads from the microphone to
be kept balanced for best rejection of interfer-
ence.
In this case one side of the transformer’s
output should be connected to ground, and if
the unbalanced input has DC powering, the
other lead from the transformer’s output should
be connected via a capacitor, to prevent DC
from flowing through the transformer’s secondary
winding.
Fig. 1
Input with transformer
(or balanced, ungrounded
transformerless input)
+ 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 kW*, I
max.
= 10 mA
I /2
I /2
I
* Tolerance: ±20%, however, the differ-
ence between the resistors of any one pair
should be less than 0.4% (i.e. 27 Ohms)
XLR-3
Connector
Shield
Microphone
+ Phase
- Phase
Cable
Powering
Input