Lectrosonics DM84 - Manual (Page 7)

DM84 Installation Guide
Rio Rancho, NM 7
Microphone Number 2:
From Specification Sheet: V
ph
(min) = 9 V
I
mic
(max.) = 2 mA
V
ph
= 15 V - (1k)(.002A)
V
ph
= 15 V - 2V = 13 V
Since the calculated Vph is greater than the Vph from
the microphone specification sheet, this is an accept-
able situation.
Audio Outputs
All outputs are a balanced differential configuration, and
include an attenuator to reduce the signal to mic level.
NOTE: Using a Line Output with digital attenuation
applied with the Control Panel to achieve Mic Level
will result in added noise.
When the DM84 output is connected to an unbalanced
input, wire it as shown here.
DM Out
+ -
Destination
+
DM Out to Unbalanced Input
(2-Wire)
Shield
DM Out
+
-
Destination
+
DM Out to Unbalanced Input
(3-Wire)
Shield
Phantom Power
The DM84 supplies +15 VDC phantom power to the
audio inputs via a programmable switch and two 2 k
resistors.
+15V
Phantom On/Off
(from Micro Controller)
Gain Control
(from Micro Controller)
0, 10, 20, 30, 40, 50 dB
RF Filter
and
AC Coupling
2k ohm 2k ohm
To CODEC
Pin 2 or 4
Pin 1 or 5
Pin 3
PGA
+
-
+
-
+
-
Chassis GND Analog GND
Programmable Gain Preamplifiers with
Software Switchable Phantom Voltage
+15 VDC
2k 2k
To
PGA
Equivalent Circuit
Phantom On/Off
However, the true phantom power available at the
microphone may be less due to voltage drop across the
microphone itself (source resistance). In some cases,
the voltage drop may be enough to result in marginal
performance.
The following formula can be used to determine how
much phantom power will be available to a particular
microphone.
V
ph
= 15 V - (1k)(I
mic
)
Where:
V
ph
= the actual voltage available at the microphone.
(Microphone specifications list this as the mini-
mum recommended phantom voltage value. To
minimize problems, the calculated Vph should
exceed this value.)
I
mic
= the current draw of the microphone. (Refer to
individual microphone specifications for this
value.)
Examples:
Microphone Number 1;
From Specification Sheet: V
ph
(min) = 11 V
I
mic
(typical) = 4 mA
V
ph
= 15 V - (1k)(.004A)
V
ph
= 15 V - 4V = 11 V
Since the calculated Vph is equal to Vph from the
microphone specification sheet, this is a marginal situ-
ation.