IMG STAGE LINE 25.3340 Instruction Manual Download Page 9

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English

6 Operation

6.1 Selecting the operating mode

Select the desired operating mode STEREO /
BRIDGE with the switch MODE (9) .

Stereo mode

–

STEREO

In stereo mode, both channels are operated
independently of each other .

Bridge mode

–

BRIDGE

The bridge mode is designed to obtain a
higher power at a single speaker . For this pur-
pose, both amplifier channels are combined
to a mono amplifier: The input signal at the
left channel is sent to the right channel addi-
tionally in an inverted way . Thus, the voltage
at the output is doubled when the speaker
is connected for bridge mode, as described
in chapter 5 .2 . 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 ampli-
fier 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 message, the
display (3) shortly shows the adjustments
of the operating mode, the limiter and the
input attenuation (fig . 4) and then changes
to the standard operating indication (fig . 3) .
After switching-on, the LEDs PROTECT (2)
light up for a short time . During this time,
the switch-on delay for the protection of the
speakers is active .

6.3 Adjusting the level

Set the output of the mixer or preamplifier
to its rated level (0 dB) or the highest undis-
torted output signal . Turn up the controls (1)
until the maximum desired volume is reached .
When the adjustment has been changed, the
attenuation

ATTEN

of the input signal by

the controls is shown on the display (3) both
numerically (i) and graphically (j) for a few
seconds . Then the display is changed to the
standard indication again (fig . 3) . The LEDs
SIGNAL, −20 dB and −10 dB (2) and a vertical
bar (e) on the display indicate the output level .

If the display shows

CLIP ON

, the input

is overloaded . If the LIMITER LEDs light up, the

limiter circuit is active and prevents an over-
load of the amplifier (

☞

chapter 7) . In both

cases, turn back the corresponding control (1) .

CAUTION

Never adjust the amplifier to a
very high volume . Permanent
high volumes may damage
your hearing! The human ear
will get accustomed 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 .

6.4 Power indication

The standard indication during operation
(fig . 3) shows the output power of both
speaker outputs in the first line (a) . This value
has been calculated according to the out-
put 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 cal-
culation . The display now shows

OUT 4Ω

(k)

and the power is calculated for a load imped-
ance of 4 Ω . To switch back, press the button
repeatedly until

OUT 8Ω

is shown . The dis-

play switches back to standard indication a
few seconds after the last press of the button .

Note:

The power indicated is not effective in bridge

mode .

6.5 Groundlift switch

If an interfering hum noise can be heard with-
out 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 such a
ground loop, set the switch GROUNDLIFT (8)
to the position LIFT .

7 Protective Circuits

The protective circuits are provided to prevent
damage to the speakers and the amplifier .
The integrated level limiter reduces the input
signal when the limit level is reached at the
output . If the amplifier is overloaded, distor-
tions can thus be prevented which could dam-
age the speakers . With the switch LIMITER
(10), this function can be switched on and
off [indication

LIMT ON

LIMT OFF

(g)] .

Due to an additional protective circuit,

the speakers are separated from the output

of the channel concerned . If it is active, the
correspond ing red PROTECT LED (2) lights up:
1 . for a short time after switching-on

(switch-on delay)

2 . in case of overload / overheating, the indi-

cation

PROT OFF

PROT ON

on the display (3)

After cooling-down, the amplifier channel
continues its operation .

In standard mode, the display shows the tem-
perature at the power transistors separately
for both channels (d) . With higher tempera-
tures, the fan control ensures that the fan of
the channel concerned runs at higher speed .

If a PROTECT LED does not extinguish

after switching-on or after cooling-down after
an overload, the amplifier must be switched
off and the cause for the defect must be
eliminated .

8 Specifications

RMS output power

stereo at 4 Ω

stereo at 8 Ω

bridge mode at 8 Ω

2 × 350 W

2 × 250 W

700 W

Input sensitivity for

rated power at 8 Ω
Input impedance