IRP PA 225 User manual

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Installations Manual
Model Number of
channels Power per channel
4 Ohm
Power
per channel
8 Ohm
Power
Bridge Mode
two channels
Power 70.7 /
100V
per channel
PA 225 225 W 18 W 50 W
PA 250 250 W 35 W 100 W
PA 425 425 W 18 W 50 W
PA 450 450 W 35 W 100 W
PA 225T 225 W
PA 250T 250 W
PA 425T 425 W
PA 450T 450 W
PA-225T / PA-250T / PA-425T / PA-450T with internal 70.7/100V constant voltage transformers, models PA
225 and PA 250 are two-channel versions, models PA 425 and PA 450 are four-channel versions.
Features
Dual Channel / Four Channels / Bridgeable, 4 Channels in 1 RU (PA 425, PA 450)
Convection Cooling
Short-circuit Protection, 115/230V 50/60Hz Operation
Power Band Limited
High Impedance, Bridging, Electronic, Balanced Inputs
Channel Clipping, LED Indicators, LED Signal Presence Indicators
Removable, screw-clamp Connectors
Lightweight, compact Design, rugged, all metal Chassis for maximum RFI and EMI Protection

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
© IRP professional sound products L.P. All Rights Reserved.
IRP reserves specification privileges Information in this manual is subject to change without notice or obligation.
Declarations of Conformity
IRP hereby declares that this product is in accordance with the following standards:
EMC Regulation 89/336/EEC (Electromagnetic Compatibility)
EN-55013 (Radio Disturbance, Emission
EN-55020 (Electromagnetic immunity)
Caution
To reduce the risk of electrical shock, do not remove the cover. There are no user serviceable parts inside, refer
all servicing to qualified personnel. Replace fuses only with same type. Avoid damaging the AC plug or cord. It
can potentially causing a shock hazard. The unit should only be connected to an AC power supply of the correct
voltage.
To reduce the risk of fire or electrical shock, do not expose this appliance to rain or moisture. Do not use this
unit in damp areas or near water.
The amplifier must be adapted slowly to extreme temperature changes. These extreme changes can cause
moisture development inside the amplifier that can cause failure and /or electrical shock.
Though the amplifiers from IRP are quite simple to operate and are covered by a solid steel chassis, improper
use can be dangerous.
NEVER isolate the ground of the AC power cord (the non-fused earthed protective conductor) to eliminate
noise-problems.
Always use safe operating techniques! Incompetent and improper servicing can void the warranty.
Description
The IRP PA-Series Power Amplifiers are comprised of building-block modules. Each power amplifier module is
constructed as a ½ of 1-RU device. Consequently, each dual channel (bridgeable to one mono channel)
amplifier occupies only ½ of 1-RU. Two such modules mounted in a single (1.75 x 19 inch) rack space can
provide four (4) audio output channels, 2 monaural (bridged) outputs or combination thereof.
The ‘T’ version of these power amplifiers incorporate a built-in, internal mounted, constant voltage output
transformer capable of driving either a 70.7 or 100 volt transmission line.
The building-block concept of the IRP PA-Series amplifiers provides the capability, with minimum
wiring configuration, to drive selected output channels at constant voltage while simultaneously
operating other channel(s) at voice coil impedances.

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Getting Started
Unpacking
Upon unpacking, please inspect the amplifier. If you find any damage, notify your supplier immediately. Be sure
to save the carton and all packing materials in case you have to send the product to the supplier. Please use
only the original factory packing. If the shipment carton is unavailable, contact IRP professional sound products
L.P. to obtain a replacement.
Installation
The amplifiers will mount in standard 19-inch racks having sufficient depth. The height of the amplifier is one
rack unit (RU). Please keep attention that enough cooling is provided. The amplifier has no internal active
cooling system (fan etc.). The cooling provided by the heat sink of the amplifier is sufficient, if the amplifier is
installed in a vented rack.
Power Connection
The power amplifier must be connected only with the attached three-wire safety power cord with protective
conductor (non-fused earthed conductor).
This amplifier is made for use with the mains voltage labeled on the back of the amplifier only. Check the label
on the back panel of the amplifier for the appropriate voltage. Make sure the voltage of your mains outlet is
correct.
The power voltage is factory set as labeled on the back panel and can be changed by switching the main
voltage on the back site of the amplifier and changing the fuses as labeled. Damage caused by connecting the
amplifier to improper AC voltage voids the warranty.
Always turn off and disconnect the amplifier from the mains voltage before making any audio connections. As a
precaution, turn the audio attenuators on the front panel down during powering up.
The power fuses are located on the back panel of the amplifier and can be accessed from the outside. Use only
the appropriate fuses as labeled.
After properly mounting and connecting the AC cord and the audio connections, the unit can be switched on.

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Amplifier PA-225 / PA-250
Control Elements and Indicators
1
5
4
3
4
5
6
2
1 -level control for channel 1 and for bridge mode
2-level control for channel 2
3 -switch for two-channel or bridge mode
4 -overload indicator -red LED
5 -connected audio signal -green LED
6 -power indicator -green LED
Level Control
The audio level can be controlled for all channels individually. Using two amplifier blocks in bridge mode, only
the level control for channel one is active.
The potentiometers are flat bushing mount potentiometers. As an option the amplifier can be ordered with
potentiometers with knobs.
Bridge Mode
If the Bridge Mode switch is set to BRIDGE, the amplifier will deliver the following power:
PA-225 1x 50 Watts at 8 Ohms
PA-250 1x 100 Watts at 8 Ohms
CLIP Indicator
If the audio signal is insufficiently high, the red CLIP LED will lit up.
SIGNAL Indicator
The SIGNAL LED indicates, that audio signal is connected to the amplifier’s input.

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
PA-225 / PA-250 Connectors
4
4
8
SerNr.:
7
9
8
11
10
7 -electronically balanced input for channel 1 and bridge mode
8 -electronically balanced input for channel 2
9 -power output for channel 1 and 2
10 -main power connector and main fuse
11 -main voltage switch 115VAC / 230 VAC
Output:
4
8
4

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Amplifier PA-425 / PA-450
Control Elements and Indicators
1 7 9 7 3
8
8
6
5
8
8
2
7
9
7
4
1
2
1 -level control for channel 1 and for bridge mode
2 -level control for channel 2
3 -level control for channel 3
4 -level control for channel 4 and for bridge mode
5 -switch for two-channel or bridge mode for channel 1 and 2
6 -switch for two-channel or bridge mode for channel 3 and 4
7 -overload indicator -red LED
8 -connected audio signal -green LED
9 -power indicator –green LED
Level Control
The audio level can be controlled for all channels individually. Using two amplifier blocks in bridge mode, only
the level control for channel one is active.
The potentiometers are flat bushing mount potentiometers. As an option the amplifier can be ordered with
potentiometers with knobs.
Bridge Mode
If the Bridge Mode switch is set to BRIDGE, the amplifier will deliver the following power:
PA-425 2x 50 Watts at 8 Ohms
PA-450 2x 100 Watt at 8 Ohms
CLIP Indicator
If the audio signal is too high, the red CLIP LED will lit up.
SIGNAL Indicator
The SIGNAL LED indicates, that audio signal is connected to the amplifier’s input.

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
PA-425 / PA-450 Connectors
4 4
8
4
4
8
10
14
11
16
15
12
13
17
10 -electronically balanced input for channel 1 and bridge mode channel 1 and 2
11 -electronically balanced input for channel 2
12 -electronically balanced input for channel 3
13 -electronically balanced input for channel 4 and bridge mode channel 3 and 4
14 -power output for channel 1 and 2
15 -power output for channel 3 and 4
16 -main power connector and main fuse
17 -main voltage switch 115VAC / 230 VAC
Output:
4
8
4

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Grounding
The chassis ground of the amplifier is connected with the ground of the AC power cord (the non-fused earthed
protective conductor).
As soon as several devices are connected with each other in a signal chain, a ground loop is created. Ground
loops are caused when current flows from the analog ground plane of one piece of equipment to the ground
plane of another. A compensating current travels between the different devices on the shields of the audio
cables. This is mostly causing humm-problems. On the back side of the amplifier you’ll find the GROUND LIFT
switch. This switch isolates the device chassis-ground from the pin 1 of the audio connectors and interrupts any
compensating current between different devices.
NEVER isolate the ground of the AC power cord (the non-fused earthed protective conductor) to eliminate
humm-problems. This is a violation of the law and dangerous !
Decibel Explanation
A decibel is a logarithmic scale commonly used to express differences in signal levels. It is useful in audio
because it can express a wide dynamic range with relatively small numbers (or a small movement on a meter),
and it more closely matches how we perceive sound.
The measurement quoted in dB describes the ratio between the quantity of two levels, the level being measured
and a reference. The absolute quantity of the signal is not relevant. This means that decibels are always
comparing one quantity to another. For example, when we measure gain in dB, we are comparing the output
level to the input level.
To describe an absolute value, the reference point must be known.
There are different reference points defined:
-dBV represents the level compared to 1 Volt RMS. 0dBV = 1V with no reference to impedance.
-dBu represents the level compared to 0,775 Volt RMS on an unloaded, open circuit.
-dBm represents the power level compared to 1 mWatt. This is a level compared to 0,775 Volt RMS across a
600 Ohm load impedance.
1dBV equals +2.2dBu, +4dBu equals 1.23 Volt RMS, the reference level of -10dBV is the equivalent to a level of
-7.8dBu.
Headroom is a measure (usually in dB) of how much higher the peaks of a signal can be compared to the
nominal level without clipping. That is, it compares the peak level (in volts RMS) to the nominal level (in volts
RMS). The difference between the two (in dB) is the headroom.

PA 225 / 250 (T)
PA 425 / 450 (T)
two/four channel power amplifier
IRP professional sound products L.P.
1 E. Beacon Light Lane
Chester, PA 19013, USA
phone [phone]
[email protected]
Specifications:
20k. balanced
1.23 V
Phoenix screw type
0.03% at rated output
1.0% at rated output
>100
19V / microsec.
50Hz to 20kHz (+0/-3dB)
>105dB
-10 to +40°C
Phoenix screw type
Power ON LED, Signal Presence, Clip, Bridge
Mode Select, Input Level Control
110/230V, 50/60Hz
1.75” x 19” x 10” 4.45X48.3X20.54 cm
7 lbs; 3.26kg
9 lbs; 3.62kg
60Hz-20KHz(+0/3dB)
Input Impedance:
Input sensitivity:
Input connectors:
Total Harmonic Distortion:
THD: transformer versions:
Damping factor:
Slew rate:
Power Bandwidth:
Signal/Noise Ratio:
Operating temperature:
Output connectors:
Controls & Indicators:
Power requirements:
Dimensions (H x W x D):
Weight:
(transformer version):
Output Transformer Versions: