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Connections: Chapter 2
14 RA150/300/500 Reference Manual
Warning: Be sure that the AC power is off prior
to connecting or disconnecting any signal
wiring.
The input circuits of the Alesis amplifiers are
electronically balanced. They may be fed from
either symmetrical (“balanced”) or unbalanced
sources. On the RA300 and RA 500, there are two
combination XLR/1/4” (6.3 mm) jacks provided,
one for each channel.
Figure 3. Balanced wiring of an XLR input
connector.
Figure 4. Unbalanced wiring of an XLR input
connector.
Figure 5. Balanced wiring of a 1/4” (6.3 mm) three-
wire phone plug.
Figure 6. Unbalanced wiring of a 1/4” (6.3 mm)
three-wire phone plug
All input wiring should be done with shielded
cable.
To use an unbalanced source with an
Alesis amplifier:
Connect the High (+) signal wire as shown in Table
1 and connect the shield wire to both the Low (–)
and Audio Ground input connections. See Figures
4 and 6. If a two-wire (tip and sleeve only) phone
plug is used for an unbalanced input, the sleeve of
the plug will automatically connect the Low and
Audio Ground connections together inside the
amplifier.
Long input cable runs, particularly in areas with
high electrical interference, should be done with
symmetrical (“balanced”) configuration, if possible,
to lessen the possibility of interference being picked
up by the cables.
Only one input jack of a channel should be used at a
time: don't use the 1/4"/XLR input jack and phono
input jack simultaneously. Do not plug two
different sources into the same amplifier channel.
While this will not harm the amplifier, the sources
may interfere with each other causing distortion.