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POWER AMPLIFIER RB-993
Protection Circuitry Q
The RB-993 features a thermal protection circuit that protects the
amplifier against potential damage in the event of extreme or
faulty operating conditions. Unlike many designs, the RB-993's
protection circuit 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 amplifier if temperatures exceed safe limits.
Most likely, you will never see this protection circuitry in action.
However, should a faulty condition arise, the amplifier will stop
playing and the LED indicator on the front panel will light up.
If this happens, turn the amplifier off, let it cool down for several
minutes, and attempt to identify and correct the problem that
caused the protection circuitry to engage. When you turn the am¬
plifier back on, the protection circuit will automatically reset and
the indicator LED should go out.
In most cases, the protection activates because of a fault condi¬
tion such as shorted speaker wires, or inadequate ventilation
leading to an overheating condition. In very rare cases, highly re¬
active or extremely low impedance speaker loads could cause the
protection circuit to engage.
If the protection circuitry triggers repeatedly and you are unable
to isolate and correct the faulty condition, contact your Rotel au¬
dio specialty retailer for assistance in troubleshooting.
Input Signal Connections
The RB-993 gives you a choice of two different kinds of input con¬
nections — conventional "unbalanced" RCA type connections
(such as found on nearly all audio equipment) or "balanced" XLR-
type connections for use with some high-end preamps or digital
processors featuring this lower noise connection.
NOTE: You must choose one or the other type of input connection
—
not both. Do not connect both balanced and unbalanced inputs
simultaneously.
RCA Input Connections (unbalanced) O
[See Figure 2 for wiring illustration]
When a component with "RCA" connectors — such as a pream
plifier or surround sound processor — supplies signals to the
RB-993, the RCA-type phono plug inputs should be used.
NOTE: To prevent loud noises that neither you nor your speakers
will appreciate, make sure the amplifier is turned off when you
make any signal connections.
Select high quality audio interconnect cables. Connect the first
output channel of your preamp or surround processor to the
Input 1 "unbalanced" RCA-connector on the RB-993. Connect the
second output channel of your preamp to the Input 2 "unbalanced"
connector. Connect the third output channel of your preamp to the
Input 3 "unbalanced" connector on the RB-993.
XLR Input Connections (balanced) O
[See Figure 3 for wiring illustration]
If you are using one of the few high-end preamplifiers or proces¬
sors with low-noise "balanced" signal outputs to drive your
RB-993, you may choose to use special XLR-type connections.
See your audio specialist for the appropriate cables.
Connect the first output channel of your preamp to the Input 1
"balanced" XLR-connector on the RB-993. When properly seated,
the connector should "click" into the connection. Connect the sec¬
ond output channel of your preamp to the Input 2 "balanced" con¬
nector. Connect the third output channel of your preamp to the
Input 3 "balanced" connector on the RB-993.
Speakers
Speaker Selection
We recommend using loudspeakers with a nominal impedance of
4 ohms or higher with the RB-993. You should exercise some cau¬
tion in driving multiple pairs of speakers in parallel configuration,
because the effective impedance the amplifier sees is cut in half.
For example, when driving two pair of 8 ohm speakers, the ampli¬
fier sees a 4 ohm load. When driving multiple speakers in parallel,
it is recommended that you select speakers with a nominal imped¬
ance of 8 ohms or higher. Speaker impedance ratings are less
than precise. In practice, very few loudspeakers will present any
problems for the RB-993. See your Rotel audio specialist if you
have any questions.
Speaker Wire Selection
Use insulated two-conductor stranded wire to connect the RB-993
to the speakers. The size and quality of the wire can have an au¬
dible effect on the performance of the system. Standard 18 gauge
"zip cord" will work, but can result in lower output or erratic fre¬
quency response. For wire runs of 50 feet or less, we recommend
16 gauge or larger wire. For longer runs and for optimum perfor¬
mance, 12 gauge wire should be used. For best performance, you
may want to consider special high-quality audio cables. Your local
audio specialty retailer can help in the selection of speaker
cables.
Polarity and Phasing
The polarity — the positive/negative orientation of the connec¬
tions — for every speaker and amplifier connection must be con¬
sistent so all the speakers will be in phase. If the polarity of one
connection is mistakenly reversed, bass output will be very weak
and stereo imaging degraded.
All wire is marked so you can identify the two conductors. There
may be ribs or a stripe on the insulation of one conductor. The
wire may have clear insulation with different color conductors
4
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