McIntosh MC 7270 Owner'S Manual Download Page 9

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Use shielded cables to connect the signal from the

preamplifier or signal source to the power amplifier. To
minimize the possibility of hum, the shielded cables
should be of parallel construction or loosely twisted

together, located away from speaker connecting cables
and AC power cords. Be certain to use good quality

shielded cables for all interconnections. Your dealer can
advise you on the kind and length of cable that will best
suit your installation.

The appropriate length and size of loudspeaker cable for

your installation will help to preserve the quality of sound
for which the loudspeakers have been designed. If under-
size wire is use, resistance is added to the amplifier/

loudspeakers combination which adversely affects the per-

formance. Added resistance reduces the damping factor,

modifies the frequency response and reduces the power

output. Your dealer's advice will serve you best for your
installation. The cables to and from the speaker should be

of parallel construction or be loosely twisted together.
The chart shows the recommended minimum wire size
for the length of wire between the amplifier and the

loudspeakers.

SPEAKER CABLE LENGTHS
AMPLIFIER TO SPEAKER

For 4 Ohm Load

Feet

100

Meters

4.6

7.6

12.2
18.3

30.48

For 8 Ohm Load

Feet

120

200

Meters

9.1

15.2

24.4

36.6

60.0

Wire

Gauge

1 6

These speaker cable lengths represent a wire

resistance equal to 5% of the speaker impedance.

CONNECTING FOR STEREO OPERATION

Plug the left output of the preamplifier into the Left input

jack of the power amplifier. Plug the right output of the

preamplifier into the Right (Mono) input jack of the power

amplifier.

Set the MODE switch to the STEREO position.

Connect a speaker cable from the common terminal of

the left speaker to the amplifier LEFT OUTPUT terminal

strip COMmon screw. Connect another speaker cable
from the other loudspeaker terminal to the correct

speaker impedance terminal on the LEFT OUTPUT ter-
minal strip. The right channel speaker is connected in the

same manner to the RIGHT OUTPUT terminal strip.

When multiple speakers are to be connected to either

or both outputs, the combined impedance must be
calculated. The combined impedance must be connected

to the appropriate impedance tap. Use this table to aid in
selecting the correct impedance match:

Combined impedance in ohms:

Connect for:

0.8 to 1.6 1 ohm output

1.6 to 3.2 2 ohm output

3.2 to 6.4 4 ohm output

6.4 and up 8 ohm output

If the load impedance used is lower than the output im-

pedance tap, reduced power and possible distortion will
result. If the load impedance used is higher than the out-
put impedance tap, neither the quality of sound nor the

amplifier will be harmed, only the available power is

reduced. For multiple speaker operation, run separate

speaker cables from the amplifier to each speaker.

The MC 7270 will feed a constant voltage line as is often

used in background music applications, paging systems and

the like. For constant voltage of 25 volts connect output leads
to the 4 ohm connectors on each channel.

Because the crosstalk between channels is almost non

existent, each channel can be used as a separate
amplifier. (Example; use one channel for mono
background program in one area and the other channel

for paging in a separate area.)

CONNECTING FOR MONOPHONIC BRIDGE OR SINGLE

CHANNEL OPERATION

When the MC 7270 is used as a monophonic or single

channel power amplifier, the two channels are added in a

bridge configuration to produce output up to 540 watts.
For monophonic operation using the MONO-BRIDGE
mode, the amplifier can supply full power to output im-
pedances of 2, 4, 8 and 16 ohms.

Plug a shielded cable from the signal source or

preamplifier to the RIGHT (MONO) input jack only.
Change the MODE switch on the back panel of the

amplifier to the MONO-BRIDGE position. The MONO-

BRIDGE switch internally connects the output of the right

channel input amplifier to both left and right channel

power amplifiers with the phase of the left channel in-

verted to achieve bridge operation and increased power
output.

BE CERTAIN THE MC 7270 IS NEVER OPERATED WITH THE
BACK PANEL MODE SWITCH IN THE STEREO POSITION

WITH THE AMPLIFIER CONNECTED FOR MONO BRIDGE.

Operated with the MODE switch in the MONO-BRIDGE

position, the circuit subtracts the left channel from the
right channel L-R). The remaining difference signal is all

that is then fed to the speaker.