Lectrosonics Inc UH400E Manuel D’Utilisation

7

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 protects the supply if the supply current is ac-

cidentally shorted to ground and also keeps the micro-

phone from being attenuated by the power supply. The 

UH400A 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 arrange-

ment the UH400A 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.
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 most 

likely be destroyed. Lectrosonics makes an adapter, 

MCA5X, that will adapt our standard TA5F 5 pin mi-

crophones to the UH400A. This adapter also provides 

protection against excessive phantom voltage. If volt-

ages higher than 5 Volts are applied to the adapter, a 

Zener diode 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 protec-

tion circuit into the XLR to prevent accidental destruc-

tion of the lavaliere. 

Frequency Select Switches

Two 16 position rotary switches adjust the operating 

frequency and are also used for setting Compatibility 

Modes.

The 1.6 MHz is a coarse adjustment and the 100 kHz 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.

Input Jack

Standard 3-pin Switchcraft XLR type with locking collar.  

Pin 2 is signal, pin 3 is a floating signal ground, and pin 

1 is case ground (see schematic below). 

Modulation LEDs

The Modulation LEDs 

indicate the proper setting 

of the MIC LEVEL control. 

There are two bicolor modu-

lation LEDs that can light 

either red or green depend-

ing on the amount of gain 

applied.  The transmitter 

should be set so that both 

LEDs glow green, with the 

-20 LED occasionally blink-

ing red.

Less than -20 dB 

Off 

Off

-20 dB to -10 dB  

Green 

Off

-10 dB to +0 dB 

Green  

Green

+0 dB to +10 dB 

Red 

Green

Greater than +10 dB  

Red 

Red

Input Signal Level

LEDs on the panel next to 

the input coupler display the 

modulation level for proper 

input gain adjustment.

Input Gain Adjustment

The rotary control on the 

recessed panel adjusts the 

gain over a 43 dB range to 

set the proper modulation.

1

2

3

+5V / +18V / +48V

4.7uf

1uh

1uh

1uh

To Mic
Preamp

1000

I

100 pf

511

1000

PHTM

NO PHTM

PWR OFF

LEVEL

15V

48

V

5V