Protection Indicators; Stereo/Mono Mode Selection; Bridge Switch And Front Panel Bridge Led; Signal Connections - Rotel RB-951 MkII Manuel D'utilisation

RB-951 Stereo Power Amplifier
MkII

Protection Indicators

A thermal protection circuit protects the am-
plifier against potential damage in the event
of extreme or faulty operating conditions. Unlike
many designs, the RB-951
MkII
cuit is independent of the audio signal and
has no impact on sonic performance. Instead,
the protection circuit monitors the temperature
of the output devices and shuts down the am-
plifier if temperatures exceed safe limits.
In addition, the RB-951 includes overcurrent
MkII
protection which operates only when load im-
pedances drops too low. This protection is in-
dependent for the left and right channels with
separate front panel PROTECTION LEDS for
each.
Should a faulty condition arise, the amplifier
will stop playing and the PROTECTION LEDS
on the front panel will light.
If this happens, turn the amplifier off, let it cool
down for several minutes, and attempt to iden-
tify and correct the problem. When you turn
the amplifier back on, the protection circuit
will automatically reset and the PROTECTION
LEDS should go out.
In most cases, the protection circuitry activates
because of a fault condition such as shorted
speaker wires, or inadequate ventilation lead-
ing to an overheating condition. In very rare
cases, highly reactive or extremely low imped-
ance speaker loads could cause the protec-
tion circuit to engage.
Stereo/Mono Mode
Selection
The RB-951 provides three options for
MkII
Stereo or Bridged Mono operation.
• Stereo mode: Conventional 2-channel
stereo operation. Minimum speaker load:
4 ohms.
• Bridged Mono mode: Serial bridged
mode which more than doubles the am-
plifier power into a single speaker. Mini-
mum speaker load: 8 ohms.
• Parallel Mono mode: A special bridge
mode that allows the amplifier to drive
extremely low impedance speaker loads
such as might be encountered driving mul-
tiple speakers in a custom installation.
Minimum speaker load: 2 ohms.
The first two modes are selected using a rear
panel switch. The Parallel Mono mode requires
setting internal jumpers and should only be
done by a qualified technician. See the IN-
TERNAL JUMPER SETTINGS section at the end
's protection cir-
of this manual.
Bridge Switch
Panel Bridge LED
A rear panel switch selects Stereo mode or
Bridged Mono mode.
For Stereo mode: Slide the switch to the right,
use both input connectors, and connect one
speaker to each pair of speaker connectors.
The front panel LED will be extinguished.
For Bridged Mono mode: Slide the switch
to the left, use only the CH1 INPUT connec-
tion, and connect only one speaker to the two
outer speaker connectors. The front panel LED
will light to indicate Bridged Mono mode.

Signal Connections

The RB-951
input connections — unbalanced RCA type
connections as found on nearly all audio
equipment. In addition, there is a pair of SIG-
NAL OUTPUT LINK connections for passing
the unchanged input signal on to another audio
component.

RCA Inputs

See Figures 2 and 3
These RCA inputs accept audio signals from
preamplifiers or surround sound processors.
Use high quality audio interconnect cables for
best performance.
For Stereo operation, use both inputs. Con-
nect the left channel output of your preamp
to the CH 1 INPUT on the RB-951
nect the right channel of your preamp to the
CH 2 INPUT. Make sure that the BRIDGE
SWITCH is in the NORMAL STEREO position.
For Bridged Mono operation, use only
the CH1 INPUT. Connect one output channel
of your preamp to the CH 1 INPUT on the
RB-951
MkII
preamp to a second amplifier. Make sure that
the BRIDGE SWITCH selector switch is in the
BRIDGED MONO position.
and Front
provides standard conventional
MkII
. Con-
MkII
. Connect the other channel of your
10
For Parallel Mono operation, either in-
put may be used. The signal from either will
be sent to all speaker outputs.

Input Level Controls

Two recessed controls on the front panel, one
for each channel, provide input level adjust-
ments. These allow you to adjust the gain of
the amplifier to match other components in an
elaborate system. The CH 1 level control
changes the gain of the left channel; the CH
2 level control changes the right channel.
To adjust these controls, use a small, flat-blade
screwdriver. Turn the control clockwise to in-
crease gain. Turn counterclockwise to reduce
gain.
: These controls may be disabled by re-
NOTE
setting an internal jumper.

Clipping Indicators

Two front panel LEDs (one for each channel)
flash to indicate when the amplifier is "clip-
ping" or being asked to deliver more output
current than it is capable of delivering. Clip-
ping will cause distortion levels to increase.
Occasional brief clipping on the loudest mu-
sical passages is acceptable. However, sus-
tained or frequent clipping is one of the most
common causes of speaker damage and should
be avoided.
Should this occur, either reduce the overall gain
of the system by turning down the master volume
control on your preamp. Alternatively, you may
wish to permanently reduce the gain of the
amplifier using the front panel level controls
(see previous section).

Signal Output Link

This pair of RCA connections can be used to
pass the unprocessed input signals to another
audio component, for example to "daisy-chain"
an additional amplifier to drive a second set
of speakers. Any INPUT SIGNAL is also avail-
able at these LINK outputs.