3 Applications
This PA stereo amplifier is especially designed
for applications on stage and in the discotheque.
It can be used in stereo operation or in mono
bridge operation. Extensive protective circuits
protect the amplifier and the speakers connected.
Two powerful, temperature-controlled fans pro-
vide the necessary cooling of the amplifier.
4 Placing the Amplifier
The amplifier is provided for insertion into a rack
for units with a width of 482 mm (19″), but it can
also be used as a tabletop unit. In each case air
must be allowed to flow freely through all venti-
lation slots so that a sufficient cooling of the
amplifier is ensured.
4.1 Rack installation
For rack mounting 2 rs (rack spaces) = 89 mm
are required. Above the amplifier one rack space
should be left unoccupied for the air supply. The
heated air blown out by the amplifier to the rear
and to the sides must be able to dissipate from
the rack, otherwise a heat accumulation will
occur in the rack which may not only damage the
amplifier but also other units in the rack. In case
the heat is not dissipated sufficiently, insert a fan
unit into the rack.
To prevent top-heaviness of the rack, the
amplifier must be inserted in the lower part of the
rack. To ensure a safe fixing, the front panel
alone is not sufficient. In addition, the unit must
be fastened at the rear side or be supported by
means of lateral rails or a bottom plate.
5 Connections
Prior to connecting units or changing existing
connections, switch off the amplifier and the
units to be connected.
1) Connect the output of a preamplifier or a
mixer to the 6.3 mm jacks INPUTS (7) or the
XLR jacks (6). The jacks are designed for
balanced signals; the pin configuration is
shown in fig. 2. For connection of sources
with unbalanced signals 2-pole 6.3 mm plugs
may be used or adapters with the XLR con-
tacts 1 and 3 bridged.
The input signal should have line level. For
rated power of the amplifier an input signal of
1.3 V (STA-225) or 1.2 V (STA-235) is required
as a minimum.
For bridge operation only connect the
input of the left channel L-CH.
As the XLR jacks and the 6.3 mm jacks of
the same input are directly connected in each
case, they can also be used for passing on
the signal e. g. to an additional amplifier.
2) The maximum output power is reached in
stereo operation when connecting 4 Ω speak-
ers (minimum admissible load impedance). It
is also possible to connect 8 Ω speakers,
however, in this case the output power will
slightly be decreased. In bridge operation the
maximum output power will be reached with
an 8 Ω speaker (minimum admissible load
impedance in bridge operation). The required
power rating (P
MIN
) of the speakers is listed in
the table fig. 3.
For
stereo operation
connect the speak-
ers to the speaker jacks (12, 13), pin configu-
ration of the plug see fig. 2, or to the screw
terminals (11).
After inserting a speaker plug into the jack,
turn the plug clockwise until it locks into
place. For removing it later, retract the latch
lock at the plug and turn the plug counter-
clockwise.
If the screw terminals are used, ensure
that the cable ends are not stripped too far
and that no bare wires protrude (hazard of
contact and short circuit).
When connecting the speakers, pay atten-
tion to the same polarity of all speakers.
For
bridge operation
connect the positive
pole of the speaker to the positive terminal
(11) of the left output L-CH and the negative
pole of the speaker to the positive terminal of
the right output R-CH (11). (By signal inver-
sion in bridge operation, the positive terminal
of the right output becomes the negative
connection for the speaker.) The speaker
can alternatively also be connected to the
speaker jack BRIDGE (14) [pin configuration
of the plug
fig. 2].
Table fig. 3 also shows possibilities of con-
nection for several speakers to one output. In
each case it is stated which power rating
(P
MIN
) each speaker must have as a mini-
mum with the corresponding impedance (Z).
When interconnecting several speakers, spe-
cial attention has to be paid to the correct
connection of the positive and negative ter-
minals.
Important:
The total impedance at each out-
put must not fall below 4 Ω in stereo operation
and must not fall below 8 Ω in bridge opera-
tion!
3) Connect the mains cable to the mains jack
(15) and the mains plug to a socket (230 V~ /
50 Hz).
6 Operation
6.1 Selecting the operating mode
Select the desired operating mode STEREO
/
BRIDGE with the switch MODE (9).
Stereo operation
– “
STEREO
”
In stereo operation, both channels are operated
independently of each other.
Bridge operation
– “
BRIDGE
”
The bridge operation serves to obtain a higher
power at one speaker. For this purpose both
amplifier channels are combined to a mono
amplifier: The input signal at the left channel is
sent to the right channel additionally in an
inverted way. Thus, the voltage at the output is
doubled if the speaker is connected for bridge
operation, as described in chapter 5. A signal at
the right input is ignored. The volume is adjusted
with the left control L-CH.
6.2 Switching on / off
To prevent loud switching noise always switch
on the power amplifier in an amplifier system
after all other units and switch it off as the first
unit after operation. Prior to switching on, turn
the volume controls (1) to the left stop “MIN”.
Switch on the amplifier with the switch
POWER (5). After the welcome, first the display
(3) shortly shows the adjustments of the operat-
ing mode, the limiter and the input attenuation
(fig. 5) and then changes to the standard operat-
ing indication (fig. 4). After switching-on, the
LEDs PROTECT (2) light up for a short time.
During this time the switch-on delay for the pro-
tection of the speakers is active.
6.3 Adjusting the level
Control the output of the mixer or preamplifier to
its rated level (0 dB) or the highest undistorted
output signal. Turn up the controls (1) so far until
the maximum desired volume is reached. The
attenuation “
ATTEN
” of the input signal by the
controls is shown on the display (3) both numer-
ically (i) and graphically (j) for a few seconds
after changing the adjustment. Then the display
is changed to the standard indication again
(fig. 4). The LEDs SIGNAL, -20 dB and -10 dB
(2) and a vertical bar (e) on the display show the
output level.
If the display shows
CLIP ON
or if a CLIP
LED (2) lights up, the input is overloaded. In this
case turn back the corresponding control (1).
In addition, an automatic level limitation may
be switched on with the switch LIMITER (10)
[
chapter 7].
6.4 Power indication
The standard indication during operation (fig. 4)
shows the output power of both speaker outputs
in the first line (a). This value has been calcu-
lated according to the output voltage measured
and a load impedance assumed. The specified
load impedance is always 8 Ω after switching on
the amplifier.
If 4 Ω speakers are connected, press the
button LOAD 4/ 8 OHM (4) to adapt the calcula-
tion. The display now shows
OUT 4Ω
(k) and the
power is calculated for a load impedance of 4 Ω.
To switch back, press the button repeatedly until
OUT 8Ω
is shown. The display switches back to
standard indication a few seconds after pressing
the last button.
Note:
The power indicated is not effective in
bridge operation.
6.5 Groundlift switch
If an interfering hum noise can be heard without
a music signal, a ground loop may be the reason
for this. Ground loops may occur if two units
have contact both via the signal ground and via
the earthed conductor of the power supply or a
conductive connection of the housings in the
rack. To separate the ground loop thus occur-
ring, set the switch GROUNDLIFT (8) to position
LIFT.
CAUTION
Never adjust the amplifier to a
very high volume. Permanent high
volumes may damage your hear-
ing! The human ear will get accus-
tomed to high volumes which do
not seem to be that high any more
after some time. Therefore, do not
further increase a high volume
after getting used to it.
8
GB
