Pin input jack wiring, Microphone rf bypassing, Line level signals – Lectrosonics SM User Manual

Page 12

SM Equivalent Input Circuit Wiring

10k

BIAS

MIC

BIAS SELECT

LINE IN

GND

30uF

+5 VDC

Servo Bias

Pin 4 to Pin 1 = 0 V

Pin 4 Open = 2 V

Pin 4 to Pin 2 = 4 V

30uF

500 Ohm

100 Ohm

2.7K

200 Ohm

3.3uF

100 Ohm

5-Pin Input Jack Wiring

The wiring diagrams included in this section represent

the basic wiring necessary for the most common types

of microphones and other audio inputs. Some micro

phones may require extra jumpers or a slight variation

on the diagrams shown.
It’s virtually impossible to keep completely up to date on

changes that other manufacturers make to their prod

ucts. It is possible that you may encounter a microphone

that differs from these instructions. If this occurs please

call our toll-free number listed under Service and Repair

in this manual or visit our web site at:

http://www.lectrosonics.com

The Audio Input Jack for the SM is wired as shown

below:

Audio Input Jack

To Virtual Ground

Audio Amplifier

To Limiter Control

PIN 1 Shield (ground) for positive biased electret lava

liere microphones. Shield (ground) for dynamic

microphones and line level inputs.

PIN 2 Bias voltage source for positive biased electret

lavaliere microphones.

PIN 3 Low impedance microphone level input for

dynamic microphones. Also accepts hand-held

electret microphones provided the microphone

has its own built-in battery.

PIN 4 Bias voltage selector for Pin 3. Pin 3 voltage (0, 2

or 4 volts) depends on Pin 4 connection.

Pin 4 tied to Pin 1: 0 V

Pin 4 Open:

Pin 4 to Pin 2:

2 V

4 V

PIN 5 High impedance, line level input for tape decks,

mixer outputs, musical instruments, etc.

Microphone RF Bypassing

When used on a wireless transmitter, the microphone

element is in the proximity of the RF coming from the

transmitter. The nature of electret microphones makes

them sensitive to RF, which can cause problems with

the microphone/transmitter compatibility. If the electret

microphone is not designed properly for use with wire

less transmitters, it may be necessary to install a chip

capacitor in the mic capsule or connector to block the

RF from entering the electret capsule.
Some mics require RF protection to keep the radio

signal from affecting the capsule, even though the

transmitter input circuitry is already RF bypassed (see

schematic diagram).
If the mic is wired as directed, and you are having dif

ficulty with squealing, high noise, or poor frequency

response; RF is likely to be the cause.
The best RF protection is accomplished by installing RF

bypass capacitors at the mic capsule. If this is not pos

sible, or if you are still having problems, capacitors can

be installed on the mic pins inside the TA5F connector

housing.

2 WIRE MIC

3 WIRE MIC

CAPSULE

SHIELD

AUDIO

SHIELD

AUDIO

BIAS

Alternate locations for bypass capacitors

TA5F

CONNECTOR

TA5F

CONNECTOR

Preferred locations for bypass capacitors

Install the capacitors as follows: Use 330 pF capacitors.

Capacitors are available from Lectrosonics. Please

specify the part number for the desired lead style.

Leaded capacitors: P/N 15117

Leadless capacitors: P/N SCC330P

All Lectrosonics lavaliere mics are already bypassed

and do not need any additional capacitors installed for

proper operation.

Line Level Signals

The normal hookup

for line level signals

is: Signal Hot to pin

5, Signal Gnd to pin

1 and pin 4 jumped

to pin 1. This allows

signal levels up to 6V

RMS to be applied

without limiting.
If more headroom is

needed, insert a 20 k

resistor in series with pin 5. Put this resistor inside the

TA5F connector to minimize noise pickup.

LECTROSONICS, INC.