Lectrosonics HM - Manual (Page 11)

Digital Hybrid ® Plug-On Transmitter
Rio Rancho, NM 11
About the Phantom Power Supply
Three phantom voltages are selectable from the control
panel. The voltages are:
• 5 Volts for lavaliere microphones,
• 15 Volts for some professional mics requiring high
current and for many common stage mics that will
operate over a wide phantom Voltage range of 12 to
48 Volts. With the proper adapter, this position can
also be used with T power microphones. See our
web site for details on finding or making the proper
adapter.
• 48 Volts for microphones that do in fact require a
supply greater than 18 Volts. (See below for a dis-
cussion of why 42 and not a “true” 48 Volts.)
For longest battery life use the minimum phantom volt-
age necessary for the microphone. Many stage micro-
phones regulate the 48 Volts down to 10 Volts internally
anyway, so you might as well use the 15 Volt setting and
save some battery power. If you are not using a micro-
phone for the input device, or are using a microphone
that does not require phantom power, turn the phantom
power off.
Phantom power should only be used with a fully float-
ing, balanced device such as most microphones with
a 3-pin XLR connector. If you use the phantom power
with an unbalanced device or if pins 2 or 3 are DC con-
nected to ground, then you will draw maximum current
from the power supply. The HM is fully protected against
such shorts but the batteries will be drained at twice the
normal rate.
The transmitter can supply 4 mA at 42 Volts, 8 mA at 15
Volts, and 8 mA at 5 Volts. The 42 Volts setting actually
supplies the same voltage to a 48 Volt microphone as
the DIN standard arrangement due to a dynamic bias-
ing scheme that does not have as much voltage drop
as the DIN standard. The 48 Volt DIN standard arrange-
ment protects against shorts and high fault current with
high resistance in the power supply feeds to pins 2 and
3. This provides protection if the supply current is ac-
cidentally shorted to ground and also keeps the micro-
phone from being attenuated by the power supply.
The HM improves on those functions and is able to use
less power from the battery by using constant current
sources and current limiters. With this dynamic ar-
rangement the HM can also supply more than twice the
current of competing 48 Volt plug on units and provide
four times the current for some very high end 15 Volt
microphones.