Output Connections - Electro-Voice MA-1212 User Manual

The set of RCA jacks (R and L) provided on the AUX 1 and 2 inputs are
designed to match to the two outputs of the typical stereo source. The
jacks are in parallel through internal series resistors and mix both
channels. The series resistors are chosen to avoid undesirable loading
effects on the output stage of typical stereo sources.
Plug monaural high-level unbalanced sources into either the R or L
jacks.
Paging: The voice paging signal from a 600 ohm balanced audio paging
line (such as a PBX system) may be connected to the aux paging input
on the back panel.
Power Amp In: The Power Amp In jack provides direct access to the
power amplifier. It requires a line- level signal fed through a RCA type
phono plug wired with a single-conductor shielded cable.

Output Connections

The amplifier-can accommodate both Low Impedance and high
impedance constant-voltage speaker loads (25, 70.7, and 100 volt lines).
There are several considerations in the connection of a speaker or
multiple speakers to an amplifier:
1. Matching speaker impedance to the amplifier’s rated Impedance: In
general, power amplifiers deliver rated power into a rated load
impedance. Lower impedances reduce the maximum available power
available at rated distortion. Significantly lower impedances may cause
the amplifier’s protection fuses to open, especially at high volume levels.
These low impedances should be avoided.
2. Power loss in speaker wire: The impedance of the speaker connecting
wire would ideally be zero, so all of the amplifier output power can be
delivered to the speaker load. However, the impedance of a longer
speaker wire installation can become a significant proportion of the total
impedance. Thus, part of the amplifier power is lost in the wire and the
power to the load is reduced. Wire impedance is highest for the longest
wire runs and smallest wire sizes.
Table 1 shows the two wire cable (copper) lengths permissible for a
number of wire sizes and speaker impedances to avoid a loss of more
than 0.5 dB. For a 1 dB loss (basically imperceptible), double the wire
lengths. For a 2 dB loss, multiply the lengths by 4.4.
In general, note that high load impedances allow the use of longer,
smaller gauge wiring.
MA-1206 and MA-1212 User Manual
Electro-Voice
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