Adcom GFP-345 Manual page 9

INPUT © SELECTOR
This rotary selector lets you choose any input connected to the GFP-345 and feed it. through the circuitry of the GFP-345,
to both the OUTPUTS NORM © and OUTPUTS LAB © jacks and, then, through your amplifier and loudspeakers The
INPUT © selector will also feed the signal you choose to the TAPE OUT O jacks on the rear panel of the preamplifier.
AI1 on the front panel of the GFP-345 will affect the signal present at the OUTPUTS NORM © and OUTPUTS
LAB © jacks. Please note that some of these controls will not affect the signal present at the TAPE OUT © jacks.
TAPE MON ©
The TAPE MON © switch selects the TAPE IN © jacks on the rear panel of the GFP-345. This switch is meant to provide
you with the capability of "monitoring" a recording you are making on a tape machine which is provided with 3-heads (that
is, an erase head, record head and separate playback head). With 2-head machines, DAT recorders and DCC machines,
itwill permit you to verify that thereis a signal being fed to the tape recorder and through its circuits into the TAPE IN
© jacks. Whenever the TAPE MON © switch is pushed in, the red LED above this switch will glow and the signal selected
by the INPUT © selector will be disconnected from the amplification circuits of the GFP-345. Please note that whatever
source is selected via the INPUT © selector will still appear at the TAPE OUT Q jacks.
EXTPROC©
Pushing in this switch connects the EXTERNAL PROCESSOR IN © and EXTERNAL PROCESSOR OUT © jacks on the
rear panel of the GFP-345. Please refer to the section EXTERNAL PROCESSOR IN © /EXTERNAL PROCESSOR OUT
© above for a complete explanation of the function of this circuit. Whenever the EXT PROC © switch is in the red LED
above this switch will glow. Please note that whenever the EXT PROC © switch is in the out position, whatever processor
is connected to the EXTERNAL PROCESSOR IN © /EXTERNAL PROCESSOR OUT © jacks will be completely
disconnected from the circuit to prevent any possible degradation of the signal being amplified by the GFP-345.
MONO ©
Pushingin this switch mixes the left- and right-channel signals. This combined signal is then fed to both OUTPUTS
NORM © and OUTPUTS LAB © jacks. The mono switch does not insert switch contacts in series with the signal path
but simply parallels the left and right channels. The MONO © switch is useful in reducing FM noise and distortion on
weak stations, or when playing older analog mono recordings, or in checking relative phasing of your loudspeakers It is
also useful when setting the channel balance of your loudspeakers using the BALANCE ©' control.
CONTOUR ©
The CONTOUR circuit in the GFP-345 differs markedly from conventional loudness compensation circuits. Recent
studies show that conventional circuits overcompensate for natural low- and high-frequency hearing reduction at low
signal levels. The studies of Robinson and Dadson of Harvard University have provided guidelines for a newer and more
accurate curve for loudness compensation. In our judgement, a subtle boost of low frequencies (in the 20-100Hz range)
and no boost at high frequencies, provides the ideal musical balance for listening at low to moderate levels. The effects
of the circuit gradually diminish as the volume level is increased (that is, when the LEVEL © control is turned clockwise)
Pushing in the CONTOUR © switch activates this function. Whenever the CONTOUR © switch is in the out position
the CONTOUR circuit will be disconnected from the circuitry of the GFP-345.
BALANCE ©
The BALANCE © control permits you to adjust the level of the left channel versus the right channel and vice-versa.
Turning the control counterclockwise will reduce the level of the right channel. Turning it clockwise will reduce the level
of the left channel. At the maximum counterclockwise position, only the left channel will operate. Conversely, at the
maximum clockwise position, only the right channel will operate. In most cases the proper setting of the BALANCE
© control will be at or near its 12 o'clock position.
To adjust for optimum balance between channels, it is easiest to use a tuber tuned to a station in which the announcer is
speaking. This will almost alwaysbe a mono signal. Place yourself in your normal listening position and adjust, or have
someone adjust, the BALANCE © control until the announcer appears to be centered between the two speakers. This
method will compensate for almost all the variations within your system, and the room, and is the easiest of all methods
to use.
Ifvour system does not include a tuner, the nextbest way is to select a CD, push in the MONO © button, place the INPUT
© selector on CD and adjust the BALANCE © control as described above.
Once the correct setting is chosen, it will need to be changed only to compensate for unequal signal levels from an outside
music source, such as a cassette, disc, etc.
LEVEL ©
This rotary control sets the level at the OUTPUTS NORM © and OUTPUTS LAB © and, consequently, the level heard
through the amplifier and loudspeakers. Turning this control clockwise will raise the level of the signal chosen via the
INPUT © selector. Turning the control counterclockwise will reduce the level of the signal. Normally, when used with
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