Infinity 255a User Manual

®

50w x 4 + 200W x 1

255a

ST

BR

HP

FLAT

LP

.25V

9V

G
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N

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.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

HP

FLAT

LP

FRONT LP

EXT

INT

EXT

ST

BR

SUBWOOFER

FRONT REAR

50W X 4

+

200W CLASS D

DIGITAL SUBWOOFER

AMPLIFIER

O
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P
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C
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255a 5-Ch Power Amplifier

Owner’s Manual

Installation Guide

DECLARATION OF CONFORMITY

We, Infinity Systems A/S

Kongevejen 194B

DK-3460 Birkerød

DENMARK

declare in own responsibility, that the product described in this

owner’s manual is in compliance with technical standards

EN 55013/A12/8.1994 and EN 55020/12.1994.

Steen Michaelsen
Infinity Systems A/S
Birkerød. DENMARK. 3/97

KAPPA 255A POWER AMPLIFIER

The Kappa 255a is a member of Infinity’s new Kappa series
of mobile power amplifiers. Housed within the sleek,
extruded aluminum frame, you’ll find five channels of
amplification – four for full-range, midrange, or high­frequency reproduction and a 200 watt class-D channel to
efficiently power a subwoofer. This unique “hybrid”
amplifier features a flexible integrated crossover so you can
easily configure the Kappa 255a for a front, rear, and
constant bass system, or for a three-way system with
separate midbass or tweeters.

ABOUT THE WARRANTY...

You’ve selected a premium product that offers superior
performance and advanced materials, resulting from over
25 years of car audio design.This Infinity product is made
with our ongoing dedication to creating the best consumer
audio products possible. As a result, you can expect your
new Kappa Power Amplifier to provide you with many
years of listening enjoyment.

All Infinity Automotive Products carry a limited parts and
labor warranty (see the enclosed warranty card), so retain

KAPPA 255A AMPLIFIER FEATURES...

The Kappa 255a is a 5-channel power amplifier that offers

the bill of sale to protect your purchase and to aid us with
any service-related questions you may have.

full-range stereo and bridged-mono operation on four
analog channels and band-limited mono operation on a
class-D channel for subwoofer applications. The front/rear
amplifiers are rated at 50 watts (rms) per channel into a 4­ohm load, while the subwoofer channel is rated at 200 watts
(rms) into a 4-ohm load. In bridged-mono configurations,
front and rear amplifiers can deliver up to 150 watts (rms)
for the same load. The Kappa 255a also features:

• 2-ohm operation, rated at 75 watts (rms) per channel for
front and rear channels and 300 watts (rms) for the
subwoofer channel

• Bridge/stereo switches for fast system setup

• Built-in 12 dB-per-octave electronic crossovers, variable
from 32 to 320 Hz, with an “x15” front-channel switch (to
increase the frequency range from 480 Hz to 4.8 kHz)

ABOUT THIS MANUAL...

To attain maximum amplifier performance, we encourage
you to read the remaining pages before installing and
operating your new Infinity Kappa Power Amplifier.
Especially review the Applications section (on the next two
pages) for ideas on designing a system. Also, save these
instructions for future reference.

IMPORTANT: Installation of automotive stereo com­ponents can require extensive experience in performing a
variety of electrical, and mechanical procedures. Although
these instructions explain how to install a Kappa Power
Amplifier in a general sense, they do not show the exact
installation methods for your particular vehicle. If you do
not have the experience, do not attempt the installation
yourself; instead ask your Authorized Infinity Car Audio
Dealer about professional installation options.

• Dynamic Bass Optimizer™ (DBO) 12 dB-per-octave
subsonic filter with variable frequency (20 to 80 Hz) and
Q for enhancing subwoofer low frequencies while
conserving amplifier power

• Front and rear channels, individually selectable as high­pass, low-pass, or through-pass

• External switch for subwoofer inputs allows direct
connection to source units with subwoofer outputs

• Amplifier input sensitivity controls to match a wide
range of input signal levels from 250 mV to 9 V

• Five protection levels guard against over-voltage, under­voltage, over-power, over-temperature, and over-current
situations

• 2-color LED array indicates green when power is on and

TABLE OF CONTENTS...

Applications ..................................................3

orange when protection is activated

• Industrial-grade, gold-plated, “pre-wire and plug-in”

System Expansion...........................................4

connectors for an easy-to-install high-quality interface

• Transparent control cover to deter tampering yet provide
a clear view of installation settings

• Built-in automotive type fuses to protect the amplifier

• Unibloc™ chassis provides improved heat-sink capacity
and exceptional RFI shielding characteristics

Precautions And Notes .....................................5

Installation ...................................................6

Troubleshooting..............................................8

2 – Infinity Kappa 255a Power Amplifier

R

– ––

+ ++

L

R

– –

+ +

L

KAPPA 255a

(front panel)

KAPPA 255a

(rear panel)

REM

–

R

+–+

L

SUBWOOFER 1 and 2
are common outputs
and are supplied as
a convenience for
dual-subwoofer
applications

Subwoofer

LR

-

+

+

-

+

-

RRLF

+

-

RF

+

-

ST

BR

HP

FLAT

LP

.25V

9V

G
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C
R
O
S
S
O
V
E
R

.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

FRONT LP

EXT

INT
EXT

ST

BR

SUBWOOFER

FRONT REAR

O
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T
P
U
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C
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S
O
V
E
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D
B
O

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O
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HP

FLAT

LP

x1

x15

Set Switches As Shown

(set controls for your system plan)

Set to EXT for
source unit with
subwoofer outputs

KAPPA 255a

(top panel)

R

– ––

+ ++

L

R

– –

+ +

L

KAPPA 255a

(front panel)

KAPPA 255a

(rear panel)

REM

–

R

+–+

L

+

-

+

-

LF

Tweeter

+

-

RF

Tweeter

RR
Mid

LR
Mid

+

-

+

-

Subwoofer

(4 Ω min.)

Subwoofer

(4 Ω min.)

+

-

ST

BR

HP

FLAT

LP

.25V

9V

G
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O
V
E
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.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

FRONT LP

EXT

INT

EXT

ST

BR

SUBWOOFER

FRONT REAR

O
U
T
P
U
T

C
R
O
S
S
O
V
E
R

D
B
O

X
O
V
E
R

HP

FLAT

LP

x1

x15

Set Switches As Shown

(set controls for your system plan)

Set to EXT for
source unit with
subwoofer outputs

FRONT LP creates
bandpass when rear
output is set to HP

KAPPA 255a

(top panel)

APPLICATIONS

Enclosed are several diagrams to help you plan your own
system installation. Figures 1 through 3 (on pages 3 and 4)
show how to configure the Kappa 255a to drive front and
rear speakers and a subwoofer, tweeters and midrange
speakers and a pair of subwoofers, and a tweeter/midrange
component set, midbass speakers, and a subwoofer.

Figure 1. This wiring diagram shows
a Kappa 255a amplifier driving front
and rear pairs of full-range speakers
and a single subwoofer.

For system expansion, see Figure 4 on the next page.

NOTE: For simplicity, Figures 1 through 4 do not show power,
remote, and input connections.

Figure 2. This wiring diagram shows a
Kappa 255a amplifier driving a pair of
tweeters, a pair of midrange speakers,
and a pair of subwoofers (4 Ω minimum).

Owner’s Manual/Installation Guide – 3

APPLICATIONS (continued)

R

– ––

+ ++

L

R

– –

+ +

L

KAPPA 255a

(front panel)

KAPPA 255a

(rear panel)

REM

–

R

+–+

L

SUBWOOFER 1 and 2
are common outputs
and are supplied as
a convenience for
dual-subwoofer
applications

Subwoofer

-

+

+

-

+

-

L

Plate

+

-

R

Plate

R
Midbass

L
Midbass

+

-

ST

BR

HP

FLAT

LP

.25V

9V

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C
R
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S
O

V

E
R

.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

FRONT LP

EXT

INT

EXT

ST

BR

SUBWOOFER

FRONT REAR

O
U
T
P
U
T

C
R
O
S
S
O
V
E
R

D
B
O

X
O
V
E
R

HP

FLAT

LP

x1

x15

Set Switches As Shown

(set controls for your system plan)

Set to EXT for
source unit with
subwoofer outputs

FRONT LP creates
bandpass when rear
output is set to HP

KAPPA 255a

(top panel)

To Front L/R
Tweeters

To L/R
Midrange
Speakers

To L/R
Midbass
Speakers

To Rear L/R
Speakers

To Subwoofer(s)

Front L/R Inputs

(from Source Unit)

Subwoofer Inputs

(from Source Unit)

Rear L/R Inputs

(from Source Unit)

L/R Outputs

(Low-Pass)

Front L/R Inputs

KAPPA 52a

KAPPA 52a

KAPPA 255a

50w x 4 + 200W x 1

255a

ST

BR

HP

FLAT

LP

.25V

9V

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S
O
V
E
R

.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

HP
FLAT

LP

FRONT LP

EXT

INT

EXT

ST

BR

SUBWOOFER

FRONT REAR

50W X 4

+

200W CLASS D

DIGITAL SUBWOOFER

AMPLIFIER

O
U
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C
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S
O
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x1

x15

SUBWOOFER

REAR
INPUT

FRONT LP

EXT

ST

BR

HP

FLAT

LP

O
U
T
P
U
T

C
R
O
S
S
O
V
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FRONT

x1

x15

ST

BR

HP

FLAT

LP

O
U
T
P
U
T

REAR

SUB
INPUT

INT
EXT

Figure 3. This wiring diagram shows a
Kappa 255a amplifier driving a front
set of tweeter/midrange components, a
rear pair of midbass speakers, and a
single subwoofer.

SYSTEM EXPANSION

Figure 4. In this expanded
system, a Kappa 52a
drives a front pair of
tweeters. The 52a’s low­pass outputs feed a Kappa
255a to drive stereo pairs
of midrange and midbass
speakers. An external
subwoofer signal feeds the
Kappa 255a to drive the
subwoofer(s). Another
Kappa 52a drives a rear
pair of speakers from the
source unit’s rear outputs.

4 – Infinity Kappa 255a Power Amplifier

+–

Battery

Fuses

LF

RF

LR

RR

SUB

Kappa 255a
Amplifier

POWER and

REMOTE Cables

Chassis

Ground

Chassis
Ground

Chassis

Ground

Source
Unit

Ignition

SPEAKER Cables

AUDIO Cables

PRECAUTIONS AND NOTES

• The Kappa 255a has five levels of circuit protection that
monitor the amplifier and will shut it down if the
electrical system voltage drops below 10 Vdc or exceeds

15.5 Vdc, temperatures are above 194° F (90° C), short
circuits occur, or current draw exceeds product
specifications. For best performance, check the intended
mounting site to make sure the operating environment
does not create conditions that will trigger circuit
protection.

• Prior to installation, turn off all audio systems and other
electrical devices. Also disconnect the (–) negative lead
from the vehicle’s battery.

• At the installation site, locate and make a note of all fuel
lines, hydraulic brake lines, and electrical wiring. Use
extreme caution when cutting or drilling in and around
these areas.

• Use the amplifier as a mounting template to mark
locations for the mounting holes.

• Check clearances on both sides of a planned mounting
surface before drilling any holes or installing any screws.
Remember that mounting screws can extend up to an
inch behind the surface.

• Always wear protective eyewear when using tools.

• The Kappa 255a uses gold-plated, industrial-grade
Weco® plug-in connectors for power and speaker wiring.
Because of precision tolerances, do not insert the
connectors into the amplifier without pre-wiring them
first. Once the wires are fastened in each shell, they
provide additional gripping area for easy connector
removal.

• When routing cables, keep input signal cables away from
power cables and output speaker wires, as shown in
Figure 5 (below).

• When making connections, make sure that each
connection is clean and properly secured. Observe the
polarity markings on the front and rear panels. Refer to
the application drawings (Figures 1 through 3 on pages 3
and 4) to set up the amplifier for operation of various
configurations.

• If the amplifier’s fuses need replacement, use only
the same rating and type as replacements. Do not
substitute another kind.

Figure 5. To minimize possible noise pickup, use this suggested cable
routing scheme to plan your amplifier installation.

Owner’s Manual/Installation Guide – 5

KAPPA 255a WIRING CONNECTIONS

(front panel)

KAPPA 255a WIRING CONNECTIONS

(rear panel)

R L

INSTALLATION

The Kappa 255a is easy to install. For optimum
performance, we recommend using high-quality, twisted­pair shielded RCA audio cables and 14-gauge or larger
speaker wire. Also, you’ll need a minimum of 10-gauge
stranded copper wire (e.g., red and black jackets) for the
power connections. Use 18-gauge (e.g., blue jacket) wire for
remote turn-on.

Depending on your total system plan, allow for adequate
time and the possibility of overnight storage of your vehicle,
since it may take more than one day to complete the
installation.

PARTS LIST...

Examine and verify that the package includes the following
items:

• (1) Kappa 255a Power Amplifier

• (2) Spare ATC fast-blow fuses (40 A)

• (1) Control cover with (2) machine screws

• (1) Weco 5-pin audio connector

• (2) Weco 4-pin audio connectors

• (1) Weco 2-pin power connector

• (4) #8 mounting screws

MOUNTING THE AMPLIFIER...

The Kappa 255a can be mounted in virtually any location
inside the vehicle. However, make sure to keep the
amplifier away from heater vents or ducts.

1. At the chosen site, use the amplifier as a mounting
template and mark locations of the four mounting holes.

2. Drill a small pilot hole at each marked location.

3. Mount the amplifier and securely tighten the mounting
screws.

WIRING THE AMPLIFIER...

Refer to Figure 6 (below) for details of the Kappa 255a’s
front and rear panel connections.

1. For power, remote, and speaker wires, strip 1⁄4" off one
end of each jacket to reveal bare wire for insertion into
the Weco connectors.

2. Using the Weco 2-pin power connector, connect a black
wire from the nearest bare-metal chassis component to
the (–) terminal. Then, connect a red wire from the
vehicle’s +12-volt battery terminal to the (+) terminal.

3. Make sure the wires are firmly seated in the Weco 2-pin
connector and that each screw is completely tightened.
Insert the wired connector into the POWER socket (on the
amplifier’s rear panel). Press it in until it stops.

Figure 6. W iring connections for the Kappa 255a amplifier.

6 – Infinity Kappa 255a Power Amplifier

ST

BR

HP

FLAT

LP

.25V

9V

G
A
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G
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G
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M
O
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M
O
D

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O
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T
P
U

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C
R
O

S

S
O

V

E
R

.25V

9V

.25V

9V

80Hz

20Hz

320Hz

32Hz

60
Hz

Q

FREQ

REAR
INPUT

SUB
INPUT

MIN

MAX

320Hz

32Hz

320Hz

32Hz

HP

FLAT

LP

FRONT LP

EXT

INT

EXT

ST

BR

SUBWOOFER

FRONT REAR

50W X 4

+

200W CLASS D

DIGITAL SUBWOOFER

AMPLIFIER

O
U

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P

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C
R
O
S
S
O
V
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D
B
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X
O
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R

x1

x15

INSTALLATION (continued)

4. Using the Weco 5-pin connector, connect a blue wire from
the source unit’s remote connection to the REM terminal.
Depending on polarity requirements (see Figures 1
through 3 on pages 3 and 4), connect speaker wires from
the subwoofer(s) to the L and R (+ and –) terminals, as
required by your system plan.

5. Make sure the wires are firmly seated in the Weco 5-pin
connector and that each screw is completely tightened.
Insert the wired Weco 5-pin connector into the
SUBWOOFER socket (on the amplifier’s rear panel).
Press it in until it stops.

6. Using Weco 4-pin connectors, connect speaker wires from
the front and rear speakers to the amplifier. Depending
on your system plan (see Figures 1 through 3 on pages 3
and 4), match the polarities on the L and R (+ and –)
terminals.

NOTE: In 3-way applications, the rear amplifier provides
bandpass channels to drive midrange or midbass speakers.

7. Make sure the wires are firmly seated in each Weco 4­pin connector and that each screw is completely tightened.
Insert the wired Weco 4-pin connectors into the FRONT
and REAR sockets (on the amplifier’s front panel). Press
each one in until it stops.

8. Connect RCA cables from a source unit to the L/R,
FRONT/REAR INPUT jacks. If the source unit has
subwoofer outputs, also connect a pair of RCA cables from
those jacks to the SUB INPUT jacks and set the SUB
INPUT switch to EXT (see Figure 7).

SETTING THE CROSSOVERS...

1. T o use the Kappa 255a in a front/rear system, set the
CROSSOVER controls to frequencies recommended by
the speaker manufacturer (see Figure 7). If the value is
unknown, set the control midway.

2. For a 3-way system, set the OUTPUT and REAR INPUT
switches to create the appropriate bandpass filters (see
Figures 2 and 3 on pages 3 and 4).

Figure 7. Kappa 255a controls for crossover, input, output, and
DBO (Dynamic Bass Optimizer).

SETTING INPUT SENSITIVITY...

Initially, turn the front and rear input sensitivity GAIN
controls to their minimum (counter-clockwise) positions
(refer to Figure 7).

1. Reconnect the (–) negative lead to your vehicle’s battery.
Apply power to the audio system and play a favorite
music track from CD or tape.

NOTE: After the source unit is on, green LEDs (on the top
panel) will illuminate, indicating the amplifier is on. If not,
check the wiring, especially the remote connection from the
source unit. Also refer to “Troubleshooting” on the next page.

2. On the source unit, increase the volume control to
maximum position. Slowly increase the Front and Rear
GAIN controls (clockwise) towards three o’ clock and, at
the same time, listen to the quality of the reproduced
sound. At some point, you’ll hear distortion on the music
peaks. Stop the adjustment and turn it back slightly.

SETTING DBO...

Dynamic Bass Optimizer (DBO) is a new approach to
enhancing low-frequency reproduction in a vehicle.
Conventional bass boost controls add bass at a fixed
frequency and cause the amplifier to consume considerable
power. DBO conserves valuable power at the lowest
frequencies and allows you to adjust the level and
“character” of the bass sound, instead of just the amount of
boom.

Since a subwoofer in a tuned box is given to overexcursion
below the tuned frequency, set the FREQ control below the
box’s resonant (tuned) frequency (see Figure 8 on the next
page). Power typically wasted in this region will now be
conserved and instead be available for frequencies the
enclosure will reproduce. Use the Q control to boost the
bass at the set frequency by as much as 12 dB (at MAX
position – see Figure 8 on the next page).

For sealed enclosures, use DBO to enhance the output so it
sounds more like a tuned box. This is a result of 12 dB of
rolloff being added to the enclosure’s rolloff and a flattening
of frequency response (at the curve’s knee) when Q is
boosted.

For infinite baffles, set the FREQ control to the speaker ’s
Fsvalue (to keep the subwoofer from trying to create bass
below the resonant frequency) and adjust the Q control
according to personal taste.

INSTALLING THE CONTROL COVER...

After wiring and testing the Kappa 255a amplifier, install
the control cover using the enclosed machine screws to
deter tampering and help seal out dust.

NOTE: Do not over-tighten the machine screws. Doing so may
crack the cover.

Owner’s Manual/Installation Guide – 7

®

-9

-6

-3

0

-12
20 80

Freq. (Hz)

dB

DBO FREQ Control

(adjusts cut-off

frequency)

-6

0

6

12

-12
20 80

Freq. (Hz)

dB

DBO Q Control

(adjusts boost amount

at cut-off frequency)

TROUBLESHOOTING

Use the following guide to identify symptoms and solve
problems. Make sure the vehicle’s electrical system is
working properly and power is reaching the Kappa 255a
(i.e., green LEDs on the top panel are on).

SYMPTOM LIKELY CAUSE SOLUTION

No audio Low/No Remote Check connections;

Distorted audio Input sensitivity See

Audio lacks Speakers are wired Check polarity of
“punch” with wrong polarity connections; refer to

Turn-On Voltage test turn-on voltage
Speakers are not Check wiring; use

connected or are VOM/DVM to
blown measure speaker

coil impedance

Setting Input

is not set properly Sensitivity on

previous page

Applications (pages 3
and 4)

SPECIFICATIONS

SYMPTOM LIKELY CAUSE SOLUTION

Audio cycles A protection circuit Verify the following–
off and on; is turning the electrical system is
Amber protec- amplifier off and on between
tion LEDs (on temperature is not
top panel) are on over 194°F (90°C);

no short circuits;
speaker loads are not
less than 1 ohm
(2 ohms in mono)

Audio cycles GAIN is set too high Set Input Sensitivity
off and on; correctly (see previous
Amber protection page)
LEDs (on top
panel) are on

Fuse blows Incorrect wiring or Check connections;

short circuit refer to Applications

(see pages 3 and 4)

10 ~ 15.5

Vdc;

KAPPA 255A...

Power Output, 4 ohms: 4 x 50 and 1 x 200 watts
Power Output, 2 ohms: 4 x 75 and 1 x 300 watts
Power Output, Bridged 4 ohms: 2 x 150 and 1 x 200 watts
Frequency Response: 20 Hz ~ 20 kHz
Input Sensitivity: 250 mV ~ 9 V
THD + Noise (4 ohms): 0.05 %
Signal-to-Noise: > 95 dB
Maximum Current Draw: 80 A
Dimensions (w x h x l): 23 x 23⁄16 x 81⁄2 in.

584.2 x 55.6 x 215.9 mm

Infinity constantly strives to update and improve existing products, as well as create new ones; therefore, the specifications and construction details in this and related Infinity
publications are subject to change without notice. Dynamic Bass Optimizer and Unibloc are trademarks of Infinity Systems, Inc. W eco is a registered trademark of Weco, Inc.

8 – Infinity Kappa 255a Power Amplifier

©1997, Infinity Systems, Inc., 20630 Nordhoff Street, Chatsworth, CA 9131 1, USA

VOICE [phone] • FAX [phone]

www.infinitysystems.com

Figure 8. Frequency response curves show range of Kappa 255a
DBO controls.

P/N SH1 105 Rev. 2