Return to Main-Page

Problems with pins 4/5 Shorting

It has come up over and over again. A recurring problem unique to single-ear headsets equipped with 5-pin XLR connectors.
Which pin should the one earpiece solder to? The answer to this queastion can vary depending on several factors including
system design and the manufacure of the equipment that the headset is plugging into.

Equipment will often have the ability to alter their configurations to service a wide range of user's needs. That might
include connectors for both 4-pin and 5-pin headsets, and the ability route signals to left, right or both ears.
What is significant here is that the Headset not bear the burden of altering the performance of the equipment because
this can lead to unpredictible performance for the individual user and expand to other users as well.

In the case of the RTS BP-325, the most common and simutaneously destructive condition to find is a 5-pin headset
with pins 4 and 5 tied together. Shorting together the pins in the headset causes the earpiece amplifier outputs to
also short together. This, in turn, causes the earpiece amplifiers to draw excessive current from the beltpack's internal
power circuits which drastically changes the impedance and maximum audio level of the intercom channel. This manifets in the
form of extreme levels of distortion and completely unintellagible audio for all users on that channel

The proper method of accomodating the need to hear both channels in a single ear headset is to set the internal jumpers
in the beltpack to the MONO position.

It is important to note that in other types of equipment, it is possible that with pins 4 and 5 tied together, no unwanted side
effects could occur. That is no excuse for allowing a headset, with such potential for damage, to float around a facility or production
truck. Go the extra mile and investigate completely the ramafications of such a modification and persue alternative alterations to
accomodate the needs of the users.

Typical Pinout from RTS BP-325 Portable User Station

RTS BP-325 STEREO Headset Connector
pin #UseColor The Microphone Input is unbalanced, making
the "mic signal low" actually signal ground. The circuit design supports a balanced condition by cutting a trace on the PCB but should only be used with headsets that have balanced wiring.
1mic signal lowShield/Low
2mic signal high 
3ear signal low 
4ear signal left 
5ear signal right 

RTS BP-325 MONO Headset Connector
pin #UseColor notes
1mic signal lowShield/Low
2mic signal high 
3ear signal low 
4ear signal high 

Return to

Copyright 2006 - Technical Audio Solutions