Lectrosonics UH400 User Manual download pdf (Page 5)

Frequency Agile Plug-on UHF Transmitter

indication immediately after being put in the unit, but will soon

discharge to the point where the LED will go red or shut down,

just like a flashlight with “dead” batteries. If the lamp fails to light,

the battery should be replaced.

PHANTOM POWER VOLTAGE SELECT SWITCH

This switch selects from three voltages when the PWR switch is

in the mid position. 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 micro-

phones. See our web site for details on finding or making the

proper adapter.

• 42 Volts for microphones that do in fact require a supply

greater than 15 Volts. (See below for a discussion of why 42

and not a “true” 48 Volts.)

For longest battery life use the minimum phantom voltage neces-

sary for the microphone. Many stage microphones regulate the

48 Volts down to 10 Volts or so internally anyway, so you might

as well use the 15 Volt setting and save some battery power. If

you are not using a microphone for the input device, turn the

phantom power off (off is the fully up position of the power

switch). The phantom power should only be used with a fully

floating, balanced device such as almost any type microphone

with a 3 pin XLR connector. If you use the phantom power with an

unbalanced device or if pins 2 or 3 are DC connected to ground,

then you will draw maximum current from the power supply. The

UH400 is fully protected against such shorts but the 9 Volt battery

will be drained at twice its 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 biasing scheme that does not

have as much voltage drop as the DIN standard. The 48 Volt DIN

standard arrangement protects against shorts and high fault

current with high resistance in the power supply feeds to pins 2

and 3. This protects the supply if the supply current is acciden-

tally shorted to ground and also keeps the microphone from

being attenuated by the power supply. The UH400 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 arrangement the UH400 can also supply more than

twice the current of competing 48 Volt plug on units and provide

4 times the current to some very high end 15 Volt microphones.

The 5 Volt setting is provided for lavaliere microphones made by

us and others. Do not power lavalieres from the 15 or 48 Volt

setting as the microphone will be most likely destroyed. Lec-

trosonics makes an adapter, MCA5X, that will adapt our standard

TA5F 5 pin microphones to the UH400. This adapter also pro-

vides protection against excessive phantom voltage. If voltages

higher than 5 Volts are applied to the adapter, a Zener will shunt

excess voltage to ground. The microphone won't work until the

voltage is correctly reduced to 5 Volts. If you have an older

lavaliere mic that was wired directly to an XLR for use with the

earlier UH200's, we strongly recommend building our protection

circuit into the XLR to prevent accidental destruction of the

lavaliere.

FREQUENCY ADJUST

These two rotary switches adjust the center frequency of the

carrier. The 1.6M is a coarse adjustment and the 100K is the fine

adjustment. Each transmitter is factory aligned at the center of

its operating range. The default position of the frequency select

switches is in the center of the transmitter’s range.

Frequency select switches, default position (8,8)

INPUT JACK

Standard 3-pin Switchcraft XLR type. Pin 2 is signal, pin 3 is a

floating signal ground, and pin 1 is case ground (see schematic

below). The UH400 is self-locking onto a standard microphone.

If severe noise is experienced when the microphone is moved

with respect to the UH400, the cause is an unbalanced con-

dition between pins 2 and 3 of the microphone.

+5V / +15V / +42V

4.7uf

1uh

To Mic

Preamp

1000

Input

Jack

Schematic

MODULATION LEDS

Indicate the proper setting of the MIC LEVEL control. There are

two bicolor modulation LEDs that can light either red or green.

“-20dB level” One modulation LED glows green and the

transmitter is 20 dB below full modulation.

“-10 dB level” Both modulation LEDs glow green and the

transmitter is close to full modulation.

“+0 dB level” The -20 LED glows red and the -10 LED

glows green. The transmitter is in slight

limiting and is fully modulated. This is

probably desirable. See the discussion below

under Input Limiter.

“+10 dB level” Both LEDs are red. The transmitter is in

limiting and you may want to reduce the

transmitter audio gain. See the discussion

below under Input Limiter.

Rio Rancho, NM – USA

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Lectrosonics UH400 User Manual Page 5

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