Guardian Telecom Inc. Installation & Operation
TBA Models
Page 9
The Push to Talk (PTT) switches may be of a suitable rating for use in hazardous areas, or connected
through an approved intrinsically safe barrier.
Any application of equipment into a hazardous area must be approved by the appropriate authority.
The speakers used may be of a suitable rating for use in hazardous areas. The speakers used with the
system may or may not be approved, check the labels on the speakers for ratings.
Follow all local codes and requirements when installing the TBA Intercom System.
The TBA does not have a weatherproof or drip-proof rating, and is not protected for prolonged
exposure to high humidity and salt fog.
6. Installation Instructions
The Talk Back Amplifier (TBA) is an audio amplifier that has been designed to operate in a commercial
setting. In order to obtain the best results, use shielded cable and follow the instructions below.
6.1. TBA Enclosure
The TBA enclosure houses the Printed Wiring Board Assembly (PWBA) within a steel enclosure
that has a removable top cover. A wiring diagram is on the inside of the cover. The enclosure may
be placed on a flat surface, mounted in an equipment rack or otherwise securely mounted.
The TBA enclosure can dissipate up to 110 watts with all of the speaker amplifiers outputting
maximum energy. There must be adequate heat conduction so that the enclosure does not exceed
20 deg above ambient with 110 watts dissipation. An air flow caused by convection with a 1 inch
gap to surrounding side walls is normally adequate. If in doubt, test the temperature rise using a
heater of 100 watts in the case and measure the resultant temperature after 1 hour.
The TBA enclosure top panel may be removed by unfastening the six screws. Once the top panel
has been removed, access to 120 volts AC is provided; therefore the service personnel should be
qualified to work with electrical equipment.
The TBA amplifier enclosure is painted and uses stainless steel hardware internally. The
components within the enclosure are not waterproof or corrosion resistant so the enclosure should
not be used in a corrosive or contaminated environment.
6.2. AC Supply
The Talk Back Amplifier uses 120 VAC at 60 Hz with a maximum of 1 amp continuous current for
energy supply. Note that the inrush current may be up to 10 amps for a fraction of a second.
There is an inrush surge reduction circuit that reduces the capacitive charging surge on power-on.
This circuit can be evaluated for inrush surge reduction if there is a problem with the external 120
volt power current surge capability.
6.2.1. 230 VAC operation
A 230 VAC to 24 VAC transformer can be special ordered for the TBA. The input voltage
labeling and serial number label must be changed or marked to indicate this change. The front
panel Power ON indicator must also be changed for 230 VAC operation.
6.2.2. DC Supply Options
The use of a separate DC supply for 27 to 35 volts (0.5 amps maximum) is possible to replace
the internal supply of the TBA logic and preamplifier sections for supply to J22 pins 1 and 3.
The negative ground connection is available at J22 pin 3 and positive is attached to J22 pin 1.
The use of a separate 30 to 70 volt supply (10 amps maximum) can be applied separately for
the audio power amplifiers if the jumper on J22 pin 1 to 2 is removed. The negative ground
connection is available at J22 pin 3. If this option is used, the internal transformer for 8 to 325
Ohms is to be removed and the amplifier will drive the 70 volt line directly.
Note that the DC supply generated within the TBA is “floating” with respect to the chassis
ground. Verify that the negative at J22 pin 3 (PWBA ground) has a low voltage and low audio
frequency noise with respect to chassis ground if there is noise present on the Talk Back
Amplifier system.
