Fender SRA 400 Administrator Guide

(Professional Sound Reinforcement Amplifier)
OPERATION INSTRUCTION MANUAL
MANUAL NO. 017386

COPYRIGHT© 1979 CBS MUSICAL INSTRUMENTS. A DIVISION OF CBS INC. LtTHO U.S.A.

SRA 400
STEREO POWER AMPLIFIER
OPERATION INSTRUCTION MANUAL
BY
PHYSICAL DIMENSIONS (APPROXIMATE, FOR SHIPPING PURPOSES)
Weight
Width
Depth
Height
U.S. System
43 pounds
19 inches
17.3 inches
5.25 inches
Metric System
19.5 kg
48.3 cm
44.0 cm
13.3 cm
P.O. BOX 4137 • 1300 EAST VALENCIA DRIVE, FULLERTON, CALIFORNIA 92634
NOTE: See accompanying limited warranty folder.

TABLE OF CONTENTS
PAGE
Introduction .iv
SECTION I
SRA 400 FRONT PANEL .1
Input Attenuators .1
Circuit Breaker/Power Switch .1
Power Output Displays .1
SRA 400 REAR PANEL
Channel 1 Input .1
Channel 2 Input .1
Channel 1 Output .1
Channel 2 Output .1
Channel 1 Output Fuse . 2
Channel 2 Output Fuse .2
Mode Switch .2
Fan .2
PAGE
SECTION II
SETTING UP THE SYSTEM . 3
Sound System Connections .3
Rack Mounting Instructions .3
Speaker Connection .3
Stereo Program Connection .3
Monophonic Connection .4
Monophonic/Monitor Connection .4
Stereo Bi-amplified Connections .4
Monophonic Bi-amplified Connection .4
Bridged Output Connection .4
SECTION III
Sound System Connections .5-
Preliminary Operating Sequence .
SRA 400 General Specifications .
LIST OF FIGURES
FIGURE DESCRIPTION PAGE
1 Front Panel Functions .1
2 Rear Panel Connections .2
3 Typical Stereo Program Connection .5
4 Two Channel Output from Single Source (Mono) .5
5 Monophonic Program/Monitor Connection .6
6 Stereo Bi-amplified connection, #1 6
7 Stereo Bi-amplified Connection, #2 . 7
8 Monophonic Bi-amplified Connection .7
9 Bridged Output Connection .8
iii
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INTRODUCTION
The Fender SRA 400 is a 200 watts per channel solid state stereo power
amplifier designed for sound reinforcement application. It is designed
for standard 19" rack mounting, and ruggedly constructed to withstand
the physical abuse encountered in road travel. Aten segment, fast acting
LED bar graph display indicates output power delivered to the load for
each channel. The SRA 400 incorporates detented input attenuators
with 22 steps, calibrated to indicate amplifier gain in dBV. These input
attenuators allow for predictable and repeatable set-ups, accurate input
sensitivity adjustments, and precise channel tracking. Each channel
employs fully complementary circuitry throughout. Sixteen 250 watt
power transistors are mounted on a massive tunnel heatsink with over
6000 square centimeters of cooling surface. A two speed thermally
switched fan forces air from the rear of the unit through the tunnel, and
out the front panel. A mode switch allows the operator to easily select
stereo, mono, or bridged modes of operation.
The SRA 400 features protective circuitry such as fast action speaker
fuses, power supply fuses, primary electromagnetic circuit breaker,
over- temperature sensing, and output transistor commutating diodes,
making it practically abuse proof. The following pages of this manual
detail the functions of the various controls and jacks, and the use of the
SRA 400 in a professional sound system.
BEFORE ATTEMPTING TO USE THE UNIT, FAMILIARIZE YOURSELF
WITH THE INFORMATION CONTAINED IN THIS MANUAL.

SECTION I
SRA 400 FRONT AND REAR PANELS
SRA 400 FRONT PANEL
Input Attenuators (Fig. 1 - Item 1)
Each of these two calibrated stepped input at¬
tenuators lowers the input signal level to its respec¬
tive channel, ahead of amplification stages. The gain
of the amplifier is indicated in dBV. The 0 VU CAL
position indicates the calibrated setting at which O
VU (1.23 volts RMS) will drive the amplifier to full
power.
CIRCUIT BREAKER/POWER SWITCH
(Fig. 1 - Item 2)
This combination Circuit Breaker/Power Switch con¬
trols AC power to the SRA 400 unit. The internal
lamp glows green when the power is turned on.
The circuit breaker will shut off AC power in the
event of amplifier overload.
POWER OUTPUT DISPLAYS (Fig. 1 - Item 3)
The ten segment LED bar graph displays indicate
power delivered to the load for each channel. These
electronic displays respond quicker than ordinary
mechanical VU meters, and thus allow accurate
monitoring of program peaks. The displays are cali¬
brated to indicate decibels below rated power (200
watts into 4 ohms, 100 watts into 8 ohms). The dis¬
plays are color coded, with the red LED indicating
full power.
SRA 400 REAR PANEL
CHANNEL 1 INPUT (Fig. 2 - Item 1)
CHANNEL 2 INPUT (Fig. 2 - Item 2)
These phone jacks on each channel are unbalanced
and are used to connect an external signal such as
that from the output of a mixer, to the respective
power amplifier input channel.
CHANNEL 1 OUTPUT (Fig. 2 - Item 3)
CHANNEL 2 OUTPUT (Fig. 2 - Item 4)
For operator convenience, a standard phone jack
and a banana jack, wired in parallel, are provided as
output connectors for each channel. They are used
to connect each speaker enclosure to its respective
channel.The total impedance of the speaker in each
channel should not be less than 4 ohms.
1

CHANNEL 1 OUTPUT FUSE (Fig. 2 - Item 5)
CHANNEL 2 OUTPUT FUSE (Fig. 2 - Item 6)
These fuses are connected in series with their re¬
spective speaker jacks. They protect the speakers in
the event of amplifier failure, and prevent damage to
the amplifier caused by driving low impedance
loads. Each fuse is rated at 6 amperes, 250 volts, and
should be replaced only with one of the same rating
and type (Littlefuse, catalog number 312006, or
equivalent).
MODE SWITCH (Fig. 2 - Item 7)
This switch selects one of the following amplifier
modes of operation.
Stereo : Normal dual channel operation.
Mono: Connects the inputs of both channels to¬
gether. In this mode a signal input to channel 1 is also
input to channel 2. This mode eliminates the use of a
“Y” cord in monophonic sound applications.
Bridged: Converts the SRA 400 into a single chan¬
nel 400 watt amplifier. The input is applied to channel
1, and the input of channel 2 should NOT be used.
The gain is controlled by the channel 1 input at¬
tenuator. The load is connected across the red
banana terminals. Minimum load is 8 ohms. Opera¬
tion into smaller loads will trigger the protective cir¬
cuitry and cause the amplifier to shut off.
FAN (Fig. 2 - Item 8)
This fan cools the tunnel heatsink and power transis¬
tors of the SRA 400 while in operation. To insure
adequate airflow be sure that the fan opening is not
blocked during operation. An internal thermostat au¬
tomatically switches the fan to high speed when the
heatsink temperature rises above 60°C (140°F).
FIGURE 2 — Rear Panel
2

SECTION II
SETTING UP THE SYSTEM
SOUND SYSTEM CONNECTIONS
The SRA 400 is a stereo (two channel) amplifier and
special care must be taken in setting it up. The unit
contains two channels of power amplification, and
offers some special connections which may be ad¬
vantageous under certain conditions. The normal
set-up and some of the special connections are de¬
tailed in this section.
RACK MOUNTING FOR SRA 400
The SRA 400 can be used as a stand alone unit, or if
preferred, can be mounted with other equipment in a
standard 19” (48.3cm) rack. If rack mounting is de¬
sired, it may be necessary to remove the plastic feet
from the bottom of the amplifier. Unscrew them with a
Phillips head screwdriver. After removing the feet,
re-install the screws into the chassis. In addition to
mounting the amp by its front panel, it is recom¬
mended that the rear of the amp be securely sup¬
ported in the rack. For installation in portable racks,
rear support is mandatory.
SPEAKER CONNECTION
Each output channel of the SRA 400 is designed for a
minimum total load impedance of 4 ohms. If the total
impedance of the speakers on either channel output
is less than 4 ohms the amplifier will be overloaded
and cause the corresponding channel’s speaker
fuse to blow. For example: at high volume, overload
might occur if two 4 ohm speakers were plugged into
one channel’s pair of output jacks (a parallel connec¬
tion resulting in a load impedance of 2 ohms). Con¬
nect the speakers to the power amplifer using #18
AWG or larger unshielded wire. ‘‘Zip Cord” is suitable
for this purpose. For long runs of speaker cable (over
25 feet),#16 AWG or larger wire is recommended.
While use of a shielded guitar cable to connect the
speakers will not damage the equipment, a loss of
volume or damage to the shielded cable may result.
Choose only high quality Va" phone or banana plugs,
and check the cables for possible short-circuits; an
internal short-circuit or a cracked phone plug in¬
sulator might blow a fuse in the power amplifer.
STEREO PROGRAM CONNECTION (Fig. 3)
The conventional stereo program system set-up is
illustrated in Figure 3. In this connection the program
outputs of a conventional stereo mixer are fed to the
corresponding channel inputs of the SRA 400.
Channel outputs of the SRA 400 are then connected
to their corresponding speakers.
3

MONOPHONIC CONNECTION (Fig. 4)
This shows how a monophonic signal source such as
one program channel of a mixer, can be used to drive
both channels of the SRA 400 power amplifier in
monophonic mode. Set mode switch to mono. Con¬
nect the monophonic signal source to channel 1
input. Both channels will be driven by the input of
channel 1.
MONOPHONIC/MONITOR CONNECTION (Fig. 5)
This diagram shows that if stereo program output is
not necessary, one channel of power amplification in
the SRA 400 may be allocated to the program mate¬
rial, and the other to the monitor material. In the case
illustrated, channel 1 has been allocated to the pro¬
gram material, and channel 2 has been assigned to
the monitor material.
STEREO BI-AMPLIFIED CONNECTION (Fig. 6)
A bi-amplified system can provide increased head-
room, efficiency, damping factor, and decreased
distortion. The SRA 400 power amplifier can be in¬
corporated in bi-amplified sound systems to realize
these advantages. This diagram shows the left and
right program mixes fed to a two channel electronic
crossover, where each channel is frequency divided
into low frequencies and high frequencies. The left
program channel’s low frequency material is fed to
the SRA 400 channel 1 input, while the left program
channel’s high frequency material is fed to the SRA
400 channel 2 input. The SRA 400 channel 1 output is
connected to the high frequency driver (tweeter) of
the left bi-amplified speaker. The SRA 400 channel 2
output is connected to the low frequency driver
(woofer) of the left bi-amplified speaker. Similarly, the
right program channel’s material is processed and
eventually amplified by an additional stereo power
amplifier and fed to a right bi-amplified speaker.
STEREO BI-AMPLIFIED CONNECTION #2 (Fig. 7)
This diagram shows a second bi-amplified scheme
that is widely used. In this stereo system one power
amplifier is used to amplify only the highs, and
another amplifier to process the lows. In most popu¬
lar music low frequency material contains con¬
siderably more energy than high frequency material,
and most sound reinforcement speaker systems
have high frequency drivers which have greater ef¬
ficiencies than their associated low frequency driv¬
ers. As a result, the power amplifier chosen to amplify
the high frequency material need NOT be as power¬
ful as the one chosen to amplify the low frequency
material. In the system shown in Figure 7, the SRA
400 was chosen as the low frequency amplifier.
MONOPHONIC BI-AMPLIFIED
CONNECTION (Fig. 8)
This diagram shows how the SRA 400 can also be
used independently as a monophonic bi-amplified
system.
BRIDGED OUTPUT CONNECTION (Fig. 9)
This diagram shows how the SRA 400 can be used
as a 400 watts single channel amplifier. Set mode
switch to BRIDGED. Connect input to channel 1.
Leave channel 2 input unused. Connect 8 O load
across red banana jacks. Use of smaller loads will
cause protective circuitry to shut off amplifier.
4

SECTION III
SRA 400 STEREO POWER AMPLIFIER
SOUND SYSTEM CONNECTIONS
FIGURE 3 — Typical Stereo Program Connection
MODE SWITCH SET TO MONO
FIGURE 4 — Two Channel Output From Single Source
(Monophonic)
5