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Speaker Connection
Speaker Selection
We recommend using loudspeakers with a nominal impedance of
4 ohms or higher with the RB-985 MKII. You should exercise some
caution in driving multiple pairs of speakers in parallel configura-
tion, because the effective impedance the amplifier sees is cut in
half. For example, when driving two pair of 8 ohm speakers, the
amplifier sees a 4 ohm load. When driving multiple speakers in
parallel, it is recommended that you select speakers with a nomi-
nal impedance of 8 ohms or higher. Speaker impedance ratings
are less than precise. In practice, very few loudspeakers will
present any problems for the RB-985 MKII. See your authorized
Rotel dealer if you have any questions.
Speaker Wire Selection
Use insulated two-conductor stranded wire to connect the RB-985
MKII to the speakers. The size and quality of the wire can have an
audible effect on the performance of the system. Standard
speaker wire will work, but can result in lower output or dimin-
ished bass response, particularly over longer distances. In gen-
eral, heavier wire will improve the sound. For best performance,
you may want to consider special high-quality speaker cables.
Your authorized Rotel dealer can help in the selection of appropri-
ate cables for your system.
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 iden-
tify the two conductors. There may be ribs or a stripe on the insu-
lation of one conductor. The wire may have clear insulation with
different color conductors (copper and silver). There may be po-
larity indications printed on the insulation. Identify the positive
and negative conductors and be consistent with every speaker
and amplifier connection.
Speaker Connection
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The RB-985 MKII has five pairs of color coded binding posts on
the back panel. These connectors accept bare wire, connector
lugs, or dual banana type connectors (except in the European
Community countries where their use is not permitted).
The negative connectors for all the channels are black. The posi-
tive connectors for the right front and surround speakers are red.
The positive connectors for the left front and surround speakers
are blue. The positive connector for the center speaker is green.
Most likely, you will never see this protection circuitry in action.
However, should a faulty condition arise, the amplifier will stop
playing and an 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 circuitry activates because of a fault
condition such as shorted speaker wires, or inadequate ventila-
tion leading to an overheating condition. In very rare cases, highly
reactive 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 retailer for assistance in troubleshooting.
Input Signal Connection
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[See Figure 2 for wiring illustration.]
The RB-985 MKII has conventional RCA type input connectors, the
type found on nearly all audio equipment.
Note: Do not connect inputs to both the RCA and DB25 inputs.
(See the following section.) Use one or the other.
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.
Use high quality audio interconnect cables. Connect the various
outputs of your preamplifier or signal processor to the corre-
sponding inputs of the RB-985 MKII . Check these connections
carefully to be sure there are no incorrect connections.
DB25 Connector Input
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The RB-985 MKII is also equiped with a DB25 type input. This input
is typically only used in professionally-installed custom systems.
The DB25 input duplicates the function of the five RCA inputs. For
information regarding how to use this input, contact your nearest
authorized Rotel service center.
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