Adcom GFA-565, User Manual

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Should you wish to verify that your loudspeakers are in-phase, once connections to the
amplifier have been made, play a recording of solo voice with single-instrument
accompaniment, at normal volume, with the preamplifier's mode switch in the mono or A+B
position. Stand about three feet in front of the loudspeakers and exactly between them. If
your loudspeakers are in-phase, the voice and accompanying instrument will appear to
originate from a point directly in front of you and exact localization will be fairly easy. If you
now move a foot or two to the left and the right of your previous position, the singer and
instrumentalist will still appear to come from a point directly in front of you. If your
loudspeakers are out-of-phase, the image of the performers will be imprecise and difficult to
pinpoint. Depending on the room, the image may appear to be coming from behind you, or
the sound will seem to surround you, and, as you move left and right from your center
position, the origin of the sound will seem to change instantaneously.
Should your connections have resulted in an out-of-phase condition, simply reverse the
leads on one of the loudspeakers; that is, switch the wire connected to the positive input
terminal of the loudspeaker to the negative terminal of the loudspeaker and vice-versa.
Repeat the listening test with the mono signal to make sure you are correct in your initial
evaluation. If you can now achieve a precise and stable image of the singer and instrument
between the two speakers, make that connection to the speaker permanent.
STEREO/BRIDGED MONO INPUT/OUTPUT
The GFA-565 can be used as a very powerful mono amplifier to drive 8-ohm impedance
loudspeakers when in its "bridged" mode. No modification to the amplifier is necessary for
operation in the bridged mode, nor are any additional accessories required. However, you
will need two GFA-565 for stereophonic reproduction, if you are using them in the bridged
mono mode.
To set the amplifier in bridged mono operation, flip the STEREO/BRIDGED MONO INPUT.
switch into the BRIDGED MONO INPUT position. When in the bridged mono mode, input to
the amplifier is made only through the LEFT INPUT RCA jack. The connection to the RIGHT
INPUT jack should be removed since the right-channel input portion of the amplifier is
inoperative.
Only a single loudspeaker is to be connected to the GFA-565 when in the bridged mono
mode. Please note that connections made to the loudspeaker from the GFA-565, when used
in the bridged mono mode, are different from those made when the amplifier is used in the
stereo mode. The LEFT RED output binding-post terminal (labeled BRIDGED MONO