GAI-Tronics PMA-300 User manual

Pub.: 42004-667L2A
GAI-Tronics Corporation P.O. Box 1060, Reading, PA 19607-1060 USA
610-777-1374 n800-492-1212 nFax: 610-775-6540
GAI-TRONICS CORPORATION
Model PMA-300
300 Watt Central Amplifier
TABLE OF CONTENTS
Confidentiality Notice ..................................................................................................................1
General Information....................................................................................................................1
Product Overview.................................................................................................................................1
System Requirements and Limitations................................................................................................1
Features and Functions........................................................................................................................1
Important Safety Instructions..............................................................................................................2
Description of Major Components ......................................................................................................3
Internal Components ......................................................................................................................................... 3
External Components ........................................................................................................................................ 4
Block Diagram ......................................................................................................................................5
Speakers ................................................................................................................................................5
Speaker Wiring Guidelines................................................................................................................................ 6
Installation ...................................................................................................................................6
Speaker Out Connection ......................................................................................................................8
Bridging of Amplifier Speaker Output Connection ...........................................................................9
Operation....................................................................................................................................10
Maintenance...............................................................................................................................11
External and Internal Adjustment ....................................................................................................11
Troubleshooting..................................................................................................................................11
Specifications .............................................................................................................................12
Replacement Parts..............................................................................................................................13

Pub.: 42004-667L2A
GAI-Tronics Corporation P.O. Box 1060, Reading, PA 19607-1060 USA
610-777-1374 n800-492-1212 nFax: 610-775-6540
Model PMA-300
300 Watt Central Amplifier
Confidentiality Notice
This manual is provided solely as an operational, installation, and maintenance guide and contains
sensitive business and technical information which is confidential and proprietary to GAI-Tronics.
GAI-Tronics retains all intellectual property and other rights in or to the information contained herein,
and such information may only be used in connection with the operation of your GAI-Tronics product or
system. This manual may not be disclosed in any form, in whole or in part, directly or indirectly, to any
third party.
General Information
Product Overview
The Model PMA Series products are
industrial rack–mountable public address
power amplifiers. This manual describes the
installation, operation, and maintenance of the
300 W amplifier.
System Requirements and
Limitations
The Model PMA-300 is a 300 Watt Central
Amplifier designed to use speakers with
variable-impedance, line matching
transformers that are made to match the
selected output voltage of the amplifier.
Features and Functions
•Internal power supply with soft-start
•Front panel status indicators
•Compact 19-inch rack mount design (3U)
•Rear mounted Speaker Output connections for 70V (Class 2) OR 100V (Class 1).
•Easy interconnection to system cabling via keyed connectors
•Dual Mic input connector for ease of connecting multiple amplifier inputs in a parallel configuration
•Electronic protection against speaker output short-circuits and overload
Figure 1. PMA-300 Outline Diagram

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Important Safety Instructions
WARNING When using this product, these basic safety precautions should always
be followed to reduce the risk of fire, electrical shock, and/or injury to persons:
1. Read these instructions.
2. Keep these instructions.
3. Heed all warnings.
4. Follow all instructions.
5. Do not use this apparatus near water.
6. Clean only with a dry cloth.
7. Do not block any ventilation openings. Install in accordance with the manufacturer’s instructions.
8. Do not install near any heat sources such as radiators, heat registers, stoves, or other apparatus
(including amplifiers) that produce heat.
9. Do not defeat the safety purpose of the polarized or grounding-type plug. A polarized plug has two
blades with one wider that the other. A grounding-type plug has two blades and a third grounding
prong. The wide blade or the third prong are provided for your safety. If the provided plug does not
fit into your outlet, consult an electrician for replacement of the obsolete outlet.
10. Protect the power cord from being walked on or pinched particularly at plugs, convenience
receptacles, and the point where they exit from the apparatus.
11. Only use attachments/accessories specified by the manufacturer.
12. Use only with the cart, stand, tripod, bracket, or table specified by the manufacturer, or sold with the
apparatus. When a cart is used, use caution when moving the cart/apparatus combination to avoid
injury from tip-over.
13. Refer all servicing to qualified service personnel. Servicing is required when the apparatus has been
damaged in any way, such as power-supply cord or plug is damaged, liquid has been spilled or
objects have fallen into the apparatus, the apparatus has been exposed to rain or moisture, does not
operate normally, or has been dropped.

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Description of Major Components
This assembly includes external components accessible to the user as well as internal components or
subassemblies.
Internal Components
The assembly contains the following components or subassemblies. Please refer to Figure 2 below for a
top view with the cover removed.
•Chassis
•Amplifier Heat-sink Assembly
•Power Supply (10272) PCBA
•Amplifier (10270) PCBA
•Monitor (10271) PCBA
•AC Power Input Transformer
•Audio Output Transformer
Figure 2. Component Subassembly Detail

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External Components
The Model PMA-300 Power Amplifier’s front panel includes the following components. Refer to Figure
3 below.
•POWER: This rocker switch controls the main ac power to the amplifier.
•Status Indicator Panel: The status panel is a series of 14 LEDs that indicate the overall status of the
amplifier along with various fault indications.
Refer to Figure 4 for the amplifier’s rear panel diagram for the locations of the following connectors:
•DUAL LINE IN
•DUAL MONITOR OUT
•SPEAKER OUT
•I/O PORT
•ACV IN
•AC PRIMARY LINE FUSE LOCATED WITHIN THE LINE FILTER / IEC CONNECTOR.
Figure 3. PMA-300 Amplifier - Front View
Figure 4. PMA-300 Amplifier – Rear Panel

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Block Diagram
The block diagram for the PMA-300 Amplifier is shown below:
Speakers
The individual speaker’s power level is determined by the tap settings on the proper V-matched line
matching transformer. Use of these transformers allows the speakers to be placed at long distances from
the amplifier without significant power loss. The number of speakers for a central amplifier system is
limited to the power available from the central amplifier.
The sum of the speaker power settings MUST NOT exceed the total power available from the amplifier.
For an example, a 300-watt central amplifier can drive approximately 40 speakers with drivers tapped at
7.5 watts each.
Figure 5. PMA-300 Block Diagram

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Speaker Wiring Guidelines
Cable distance should be kept as short as possible to reduce power loss. The following chart illustrates
the correlation between four typical wire sizes and the distance that speakers with integral drivers or horns
with separate drivers can be placed from the central amplifier for a -1 dB loss (-20% power).
Speaker Wiring Guidelines For 300 Watt Central Amplifiers
Wire Size
Central
Amp Line
Voltage 18 AWG (0.82mm2)16 AWG (1.31mm2)14 AWG (2.08mm2)12 AWG (3.31mm2)
100 V Line 319 feet (97 m) 509 feet (155.1 m) 810 feet (246.8 m) 1,289 feet (392.8 m)
70.7 V Line 162 feet (49.3 m) 257 feet (78.3 m) 409 feet (124.6 m) 650 feet (198m)
Installation
WARNING Please follow below recommendations / instructions for installation.
CAUTION These installation instructions are for use by qualified service
personnel only. To reduce the risk of electric shock, DO NOT perform any servicing other
than that contained in the operating instructions unless you are qualified to do so.
1. Ensure that the installation conforms with all applicable local electrical codes.
2. Avoid running input and output signal cabling near high voltage/high electromagnetic sources.
3. When the SPEAKER OUT voltage connection being used is 100V, the amplifier’s Speaker Out
wiring MUST conform to Class 1 wiring specification. When the SPEAKER OUT voltage
connection being used is 70V, Class 2 wiring specification is acceptable.
DANGER Do not install in a hazardous area.
4. Use in safe, non classified, non hazardous areas only.
5. The total power distribution to the speakers MUST NOT exceed the amplifier’s rated output wattage.
Rack Mount Installation
The power amplifier is designed to be mounted in a standard 19-inch equipment rack ONLY. Place the
amplifier in the desired rack location and secure with appropriate rack mounting hardware
(customer-supplied).
Due to the weight of the unit, supporting rails (customer supplied) mounted inside the equipment rack
MUST be used for adequate support of amplifier; however, do not block the heatsink fans preventing
adequate air circulation. Please refer to the equipment rack manufacturer for the appropriate support rails
to use.

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Ventilation
The amplifier creates heat during operation. Although the amount of heat generated varies depending on
various factors, the unit should be positioned to allow for natural convection air flow to prevent excessive
temperature rise.
If additional amplifiers or other heat producing equipment is installed within the enclosure rack, ensure
that the ambient temperature near the amplifiers does not exceed ~50ºC during normal operation by
installing adequate rack ventilation fans.
Note: If, during normal operation, the ambient temperature exceeds ~50ºC inside the equipment rack,
increase the spacing distance between the amplifiers and equipment and install suitable equipment rack
fans to reduce cabinet’s ambient to below ~ 50ºC.
Audio Line Input Connection
The LINE IN connection is designed to mate with a 3-pin male, XLR-style connector. It can be
connected into either of the two parallel XLR receptacles located on the rear of the amp. Connect the
audio (+) to pin 2 and audio (-) to pin 3 of XLR plug.
The second XLR receptacle can be used to connect the line-in audio signal to additional amplifiers in
parallel, if needed. Connect the audio (+) to pin 2 of each amp and audio (-) to pin 3 of each amp.
Minimum recommended wire gauge is 18 AWG. See Figure 6 below.
Figure 6. LINE IN Connection

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Speaker Out Connection
The amplifier’s SPEAKER OUT connection uses a keyed, positive-locking Neutrik® SPEAKONTM
connector, which eliminates the possibility of vibrating loose. The ‘keyed’ feature prevents
misconnection to similar style connectors on the amplifier’s rear panel. The amplifier contains a 70V out
and a 100V out connection depending on your constant voltage speaker system.
Notes:
•Use only one of the SPEAKER OUT connections at a time.
•If using the 100V out connection, only CLASS 1 wiring specification is acceptable.
•If using the 70V out connection, CLASS 2 wiring specification is acceptable.
Connect the speakers as follows:
1. To properly terminate to the system speaker cable, use the enclosed SPEAKON™ connector (blue
body), which is supplied with the unit.
2. Determine which SPEAKER OUT voltage, 70.7V or 100V, is required for your constant voltage
speaker system.
3. Determine the desired wire gauge per the Speaker Wire Guidelines chart on page 6.
4. Determine the correct clamping strain relief depending on your cable’s diameter.
5. For 100V Speaker Systems: Connect the audio (+) wire to pin 1 (+) and audio (-) wire to pin 1 (-)
(markings are embossed on body of connector) and tighten securely.
Note: Terminals 2 (+) and 2 (-) are not used. Refer to Figure 4 for connector location.
6. For 70.7V Speaker Systems: Connect the audio (+) wire to pin 2 (+) and audio (-) wire to pin 2 (-)
(markings are embossed on body of connector) and tighten securely.
Note: Terminals 1 (+) and 1 (-) are not used. Refer to Figure 4 for connector location.
Speaker System’s Voltage
Output Needed Corresponding Load Impedance (ohm) for 300W (Full output)
100 V 33.4 ohm
70.7 V 16.7 ohm

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Bridging of Amplifier Speaker Output Connection
If the distributed speaker system requires more than 300 watts out, bridging of multiple amplifiers’
speaker out connections in a parallel configuration is needed. The maximum total output power can be
increased in multiples of 300 watts. This is done by connecting the output of each amp required together
in parallel. See chart below and Figure 7 for some examples.
Parallel Configuration Example Chart
Speaker System’s
Constant Voltage Value:
(as designed)
Total System Output
Wattage Needed: (in
watts)
# of PMA-300
amplifiers (300 watt
ea.) required:
100V 500 2
100 V 650 3
70.7V 350 2
70.7V 250 1
The following is a general formula to assist in determining # of amplifiers needed:
____ (Total wattage required)/300 (max. wattage per amp) = _____# of amplifiers needed
(If fraction, round up to next whole number)
When wiring multiple amplifiers’ SPEAKER OUT connections in a PARALLEL configuration, ensure
that the Speaker Out (+) of one amp is connected to the Speaker Out (+) of the second amp and the
Speaker Out (-) of one amp is connected to the Speaker Out (-) of the second amp, etc. Each amplifier
must use the same SPEAKER OUT voltage selection, either 70.7V or 100V connection. Refer to Figure
7 for more details.
Contact GAI-Tronics’ Field Service Department at 800-492-1212 inside the USA or 610-777-1374
outside the USA for further information and assistance.
Figure 7. Bridging of Amplifiers

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Operation
This section describes the simple operation of the Model PMA-300 Power Amplifier.
1. Push the front panel main ac POWER rocker switch to the “ON” position.
2. With no unit adjustments required, apply the appropriate audio signal applied to LINE IN.
3. The audio signal is amplified and is heard in the speakers.
Front Panel Status Indicators
The front panel status indicators show the user, at a glance, the following operating status conditions of
the amplifier:
Function Description
ON Illuminates BLUE when the internal power supply circuitry supplies are OK and
functioning when the power switch is ON.
DC Illuminates YELLOW when external AUX power (48 V dc) is applied, if equipped.
OHEAT Illuminates RED when the amplifier’s heatsink thermostat has opened due to excessive
heat. (approximately 75-80ºC).
FUSE Illuminates RED when the internal main bus voltage fuse (F1) opens on the Power
Supply PCBA.
OLOAD Illuminates RED when the Speaker Out signal has exceeded 300 watts.
ALARM Illuminates RED when an ALARM condition exists such as main bus voltage fuse (F1)
opens, or OHEAT occurs.
OUTPUT
PEAK Illuminates RED when the Speaker Out signal starts to exceed 300 watts.
7 SEGMENT
BAR GRAPH Illuminates in 3 dB increments depending upon the OUTPUT signal level.
Range is –18 dB to 0 dB, as related to 300 watts (full out).

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Maintenance
External and Internal Adjustment
There are no external or internal user-adjustments required.
Troubleshooting
Problem Possible Cause Possible Solution
No ac power present. 1. Check applicable power connections
and for presence of correct voltage.
2. Check ac primary fuse located in the
IEC power connector housing.
CAUTION: Replace ONLY with
same type/value fuse.
No front panel Power ON
indications.
Blown low volt power supply
fuse (F3). Check low volt power supply fuse (F3) located on CS10272 Power Supply PCBA
inside.
CAUTION: Replace ONLY with same
type/value fuse.
No audio out, plus FUSE
and ALARM LEDs are on. Blown dc bus fuse (F1) Check main dc bus fuse (F1) located on CS10272 Power Supply PCBA inside.
CAUTION: Replace ONLY with same
type/value fuse.
No audio out, OHEAT LED
and ALARM LED are on. Amplifier’s heatsink thermostat is
activated, probably due to lack of
proper ventilation.
1. Allow unit to cool down, thermostat
will automatically reset itself.
2. Add or increase ventilation for more
effective cooling within the rack.
Audio out is very low. Possible low resistance or shorted
wiring across the LINE IN audio,
or across SPEAKER OUT audio.
Check/correct speaker system wiring.
Excessive audio out signal
distortion, plus PEAK and
OLOAD LEDs are ON.
Above normal audio input drive
level. Reduce input drive signal accordingly.
Excessive
static/electromagnetic
interference
Input and/or output signal cables
are routed too close to high
voltage/high electromagnetic
sources
1. Re-route cables away from high
voltage/high electromagnetic sources.
2. Use shielded cables.

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Specifications
Electrical:
Supply Voltage:................................................208 V ac +10%,-0%, (208 V ac, 60 Hz nominal), 50/60 Hz
Power consumed (@ nominal V in):
Idle / Rated Output...............................................................................30 VA.; 20 W / 790 VA; 530 W
Output Power:..............................................300 WRMS continuous @ TA= 24ºC with adequate ventilation.
..............................................................De-rate to ~10 WRMS continuous @ TA= 50ºC @ nominal V ac in
Output Peak Power:...................................................................................................430 WRMS (t=100 mS)
Output Voltage:...................................................................................................... 70.7VRMS ac; 100VRMS ac
THD @ rated output & nominal Vin: .................................................................................1.5 % maximum
Frequency Response: (At rated output)................................................................. 50 Hz-17.5 kHz +0/-3dB
Hum/Noise below rated output:.........................................................................................-70 dB minimum
Input Sensitivity for rated output:..............................................................~775 mVRMS (Balanced Z Input)
Input Impedance............................(Balanced - Between Pin 2 {Hi} & Pin 3 {Low}) 15 K ohm (nominal)
Phase linearity: .........................................................................................................+/-35º (100-10000 Hz)
Damping factor:.................................................................................................>10 @ 1 kHz >3 @ 19 kHz
Start-up Delay Time: ....................................................................................................2 seconds (nominal)
Internal Thermal Protection {mounted to heatsink}:.................................................. 75ºC (167ºF) nominal
Temperature range: Operating:..................................................................... 0 to +50ºC (+32ºF to +122ºF)
Storage:.....................................................................-10 to +60ºC (+14ºF to +140ºF)
Humidity: .................................................................................................Non-condensing, 85% maximum
General:
External Controls
Front:..................................................................................................................AC Main POWER Switch
Rear:.............................................................................................................................................................
Front Panel LED indicators: ........... Power ON; DC in; OHEAT; internal main dc bus FUSE failure (F1);
output OLOAD; output PEAK; ALARM; watt output (dB scale) seven segment
LED bar graph.
AC Primary fuse: (accessible externally from inside of rear panel’s IEC power connection)
Model PMA-300 (208 V ac):..................................................... T6.3A, Time-lag Slo Blo (5 x 20 mm)
Internal Fuses:
Low Voltage Power Supply:.....................................................F3 T1A, Time-lag Slo Blo (5 x 20 mm)
Audio Output Stage:...............................................................F1 T16A, Time-lag Slo Blo (5 x 20 mm)
External Connections (Rear):
AC in:............................................................................................................IEC 320 (male) connector
Audio In:......................................................................Dual (feed-thru) 3-pin XLR (female) connector
Audio Out: ................................Two SPEAKON™ (70.7 V ac and 100 V ac) by Neutrik® connectors
Monitor bus: (Reserved for special applications) ............. Dual gold-plated RCA™-style (female) jack
I/O port: (Reserved for special applications)............................................D sub 9-pin (male) connector
Enclosure:............................................................................................................ 16 gauge cold-rolled steel
Finish: Front:......................................................................................................................................Black
Rear:.......................................................................................................................................Black

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Front panel: ..........................................................................................................5/32 inch thick aluminum
Overall Unit Dimensions:..................5.2 H x 17.125 W x 14 D inches (132 mm x 435 mm x 356 mm)
(Designed for mounting in standard 19-inch equipment rack) (3U standard 19-inch rack)
Front Panel Dimensions:...................................................... 5.2 H x 19 W inches (132 mm x 483 mm)
Supplied accessories:
One (1) SPEAKONTM by Neutrik® Mating Plug for SPEAKER OUT connection
Unit Weight:.....................................................................................................................49 lbs. (22.23 kg)
Replacement Parts
Model Number Description
21932-001 Speaker Output Connector (SPEAKON™) by Neutrik®
51809-020 Fuses – AC Primary Main T6.3A (pack of 10)
51809-021 Fuses – Low Voltage Power Supply T1A (pack of 10)
51809-022 Fuses – Audio DC Bus T16A (pack of 10)