RB-1090Stereo Power Amplifier
Input Signal Connections
The RB-1090 gives you a choice of two dif- ferent kinds of input connections — conven- tional unbalanced RCA type connections (such as found on nearly all audio equip- ment) or balanced XLR-type connections for use with some high-end preamps or digital processors featuring this lower noise con- nection.
Input Selector Switch 
A toggle switch in the middle of the RB-1090’s rear panel selects which type of input sig- nal to use. The operation of this switch is self-evident. Put the switch in the unbalanced position when you are using the RCA-type inputs. Put the switch in the balanced posi- tion when using XLR-type connections.
NOTE: To prevent loud potentially damag- ing noises, make sure the amplifier is turned off when you make any signal con- nections.
RCA Inputs (unbalanced) 
See Figure 2
When a component with RCA connectors
–such as a preamplifier or surround sound processor – supplies signals to the RB-1090, the RCA-type phono plug inputs should be used.
Select high quality audio interconnect cables. Connect the left channel output of your preamp to the left channel UNBALANCED IN- PUT on the RB-1090. Connect the other cable to the right channel UNBALANCED INPUT. Make sure that the input selector switch is in the
UNBALANCED position.
XLR Inputs (balanced) 
See Figure 3
If you are using one of the high-end pream- plifiers or processors with low-noise balanced signal outputs to drive your RB-1090, you may choose to use these low-noise XLR-type connections. See your authorized Rotel dealer for the appropriate cables.
Connect the left channel output of your preamp to the left channel BALANCED INPUT on the RB-1090. When properly seated, the connector should click into the connection.
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Connect the other cable to the right chan- nel BALANCED INPUT. Make sure that the IN-
PUT SELECTOR SWITCH is in the balanced posi-
tion.
Speakers
The RB-1090 has two sets of SPEAKER CON- NECTORS for each channel. These can be used to connect two pairs of loudspeakers, or to connect one pair of loudspeakers with bi- wire connections.
Speaker Selection
The nominal impedance of the loudspeaker(s) connected to the RB-1090 should be at least 4 ohms. When driving multiple pairs of speak- ers in parallel configuration, the effective im- pedance 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, select speakers with a nominal 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-1090. See your authorized Rotel dealer if you have any questions.
Speaker Wire Selection
Use insulated two-conductor stranded wire to connect the RB-1090 to the speakers. The size and quality of the wire can have an au- dible effect on the performance of the sys- tem. Standard speaker wire will work, but can result in lower output or diminished bass response, particularly over longer distances. In general, 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 appropriate cables for your system.
Polarity and Phasing
The polarity – the positive/negative orien- tation of the connections – for every speaker and amplifier connection must be consistent so all the speakers will be in phase. If the polarity of one connection is mistakenly re- versed, 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 in- sulation with different color conductors (cop- per and silver). There may be polarity indi- cations printed on the insulation. Identify the positive and negative conductors and be con- sistent with every speaker and amplifier con- nection.
Connecting the Speakers 
See Figure 2
The RB-1090 has two pairs of color coded binding posts per channel. These can be used to connect two pairs of loudspeakers by con- necting one pair to the first speaker and the second pair to the other speaker. Alterna- tively, they may be used for bi-wire connec- tions by connecting one pair to the high-fre- quency input on the speaker and the other pair to the low-frequency speaker input.
These SPEAKER CONNECTORS accept bare wire, connector lugs, or dual banana type con- nectors (except in the European Community countries where their use is not permitted).
Route the wire from the RB-1090 to the speak- ers. Give yourself enough slack so you can move the components enough to allow ac-
cess to the SPEAKER CONNECTORS.
If you are using dual banana plugs, connect them to the wires and then plug into the backs of the SPEAKER CONNECTORS. The collars of the
SPEAKER CONNECTORS should be screwed in
all the way (clockwise).
If you are using terminal lugs, connect them to the wires. If you are attaching bare wires directly to the SPEAKER CONNECTORS, separate the wire conductors and strip back the in- sulation from the end of each conductor. Be careful not to cut into the wire strands. Un- screw (turn counterclockwise) the SPEAKER CONNECTOR collars. Place the connector lug around the shaft, or insert the bundled wire into the hole in the shaft. Turn the collars clock- wise to clamp the connector lug or wire firmly in place.
NOTE: Be sure there are no loose wire strands that could touch adjacent wires or connectors.
