/DCCM
HIGH DEFINITION
PREAMPLIFIER
GFP-345
INTRODUCTION
Piease read thoroughly these operating instructions forthe G FP-345 before connecting or attempting to operate this unit.
For your own benefit, foHow alt the instructions in this manual and save it tor future reference.
The ADCOM GFP-345 is a result of a thorough examination and réévaluation of all factors affecting the sonic performance
of preamplifiers. A great deal of care was taken to insure that the audio performance of the GFP-345 could be maintained
for years to come by the selection of top-quality components and circuit topologies. The result is a preamplifier which is
as musical-sounding as, and which preserves the dynamic contrasts of, an original performance.
The installation and operation of the GFP-346 are described in the following pages. We sincerely hope you will value and
enjoy the considerable attention we have given its design and construction. This manual has been written to help you
understand the correct operation of the GFP-345, Please read it carefully to fully comprehend all its features and functions
and thereby derive the maximum performance from its use in your system.
FEATURES GFP-345
The GFP-345 is modeled after the highly innovative internal designs and circuit topologies of both the "Reference
Standard” GFP-565 and GFP-555D preamplifiers — accordingly, it is setting new standards for products in its price
category.
Many of the most significant performance characteristics of the GFP-565 and GFP-555D have been built into the GFP-345.
The power supply and low impedance outputs were designed to preserve music dynamics. The amplification stages
employ direct-coupled, custom-designed, linear-gain amplifiers operating in full Class A to insure the minimum
distortion and low-noise required for digital-source material. Buffered tape outputs insure input-signal integrity, and
preclude interference with the main-source signal in the preamplifier's circuits when digital or cassette tape recorders are
connected (even when these are not operating).
The optional phono preamplifier {available as a plug-in board: the PHO-802A) delivers the quietest obtainable
performance with unmatched record-equalization accuracy and lowest distortion. Operating in full class A, its
unrestricted dynamics and musical accuracy are delivered at surprisingly modest cost.
The GFP-345 contains the highest-quality components; never before available in a component of such moderate cost.
This should insure stable, dependable operation and long, trouble-free life.
• Low-impedance power supply for best regulation and optimal circuit performance. This type of design insures that
music dynamics are delivered through the preamplifier without compression.
• Thick power-supply traces on printed circuit board for minimal losses and improved voltage stability. This
technique insures constant voltage to all the circuitry, regardless of volume or dynamic demands of the music.
• All capacitors are state-of-the-art electrolytics and film capacitors with very low ESR and unsurpassed sonic purity.
This design feature provides an audible tenefit, the lowest possible distortion of music signals.
• Overdesigned mu-metal-$hielded power transformer for better regulation. This transformer design eliminates stray
hum fields for lowest noise and provides undiminished voltage to circuits for best performance under any demands
for level.
• Precision, programmable regulators for stabilized, constant DC voltages, regardless of load. This type of regulator
insures stable operation of all circuits regardless of the dynamic demands of the music being played.
• Amplifier stages use ADCOM premium-grade ICs selected for their linear operation and sonic quality. These linear
amplifiers insure extremely low noise, low distortion and low DC offset for best performance with either set of
preamp outputs.
• Amplifiers are operated in pure Class-A mode to insure lowest distortion regardless of the signal level or setting of
the level control.
• Entire signal path is direct-coupled from input to output. Direct coupling minimizes the number of components
signal must go through, preventing degradation of the music.
• Two sets of outputs: OUTPUTS LAB are direct-coupled. They provide a signal in the most straightforward, simplest
path. OUTPUTS NORM are capacitor-coupled using precision, high-grade film capacitors for power amps which
can not accept ultra-wide bandwidth inputs.
•
• Low-output-impedance {100 ohms) from both sets of outputs to reduce interaction of connecting cables and other
equipment and preserve music dynamic contrasts.
• Five sets of inputs, front panel controlled, including TAPE IN; six sets if the EXTERNAL PROCESSOR IN jacks are
used also as an auxiliary input.
• Low-impedance tape outputs (100 ohms) to perfectly interface with any type of tape recorder. This technique allows
the preamp to mate with any type recorder, including DAT and DCC, and insures the best recording characteristics
independently of the cable used and the toad impedance of the tape recorder inputs.
• Buffered tape outputs to preserve input-source-signal integrity and preclude "loading" of the signal-source
components and distortion. Buffering prevents the degradation of the source signal caused by most tape recorders
when they are connected to the tape outputs. The buffers insure that the integrity of the internal signal path will not
be affected by the tape recorder used.
• Front-panel-switchable processor loop. Shortens the signal path by switching the processor in and out of the circuit
directly on the main circuit board. Allows the processor to be removed totally from the circuit when not needed.
• All high-grade construction parts including 1%, Roederstein metal-film resistors and all metallized-film, precision
capacitors throughout. These components helps the GFP-345 achieve lower noise levels and lower signal
degradation than preamps selling for many times its price.
• Extremely-low-noise, optional phono preamplifier board (PHO-802A) with virtually zero RIAA error, optimized for
high-output moving-coil and moving-magnet cartridges plus direct-coupled signal output for maximum bass
impact and dynamic response. These features will provide the flattest, lowest-noise, lowest-distortion response
from a phono cartridge and musically satisfying reproduction from any vinyl record.
• Low-impedance, RIAA-equalization network. This unique network insures the lowest achievable noise level in a
phono preamp.
UNPACKING THE GFP-345
Before each GFP-345 left the factory, it was carefully inspected for physical imperfections and electrical performance as
a routine part of AOCOM’s systematic Quality Control. This, along with full operational and mechanical testing, should
insure a product flawless in both appearance and performance. After you have unpacked the GFP-345, inspect it for
physical damage. Save the shipping carton and all packing materials as they are intended to reduce to a minimum the
possibility of transportation damage, should the product ever need to be shipped again. In the unlikely ëyent damage has
occurred, notify your dealer immediately and request the name of the carrier so that a written claim to cover shipping
damage can be initiated.
THE RIGHT TO A CLAIM AGAINST A PUBLIC CARRIER CAN BE FORFEITED IF THE CARRIER IS NOT NOTIFIED
PROMPTLY IN WRITING AND IF THE SHIPPING CARTON AND PACKING MATERIALS ARE NOT AVAILABLE FOR
INSPECTION BY THE CARRIER. SAVE ALL PACKING MATERIALS UNTIL THE CLAIM HAS BEEN SETTLED.
INSTALLING THE GFP-345
Although the GFP-345 does not generate much heat, you will help insure its long-term, trouble-free operation if you keep
it away from external sources of heat, such as radiators or hot-air ducts, and provide reasonable ventilation. The GFP-345
should never be placed with other heat-producing components in a cabinet or enclosure lacking free air flow. If placed
near or above any heat-producing component, such as a power amplifier, please allow a minimum of three inches between
the components.
For use in professional installations, the GFP-345 may be mounted in a standard 19-inch rack using the optional RM-3
rack-mount adaptors available through ACCOM dealers.
CONNECTING THE GFP-345
The performance of the GFP-345 will depend on the quality of the interconnection of both the preamplifier and its
associated equipment. All the input- and output-signal connections should be made only with high-quality, low-loss
audio cables. LEFT CHANNEL and RIGHT CHANNEL inputs and outputs are cleaHy labelled on the rear panel.
NOTE
WHENEVER CONNECTIONS TO OB FROM THE GFP-345 ARE BEING MADE, BE CERTAIN ALL
ASSOCIATED COMPONENTS ARE TURNED OFF.
GND O
Ground connection to chassis is provided primarily to connect phonograph (turntable) ground terminals. Most turntables
are supplied with a separate ground wire to help eliminate hum. Connect the separate ground wjre, if supplied with your
turntable, to the GND O terminal. The GND O terminal can also be used to connect the chassis of the GFP-345 directly
to the center screw of your AC wait outlet or other good "earth” connection such as a water pipe or radiator. This earth
connection may be useful in areas of high RF interference, and may help to minimize noise particularly when playing lowoutpuHevel phonograph cartridges (see section PHONO (PHO-802A OPTION) 0 following).
NOTE
Although the GND O connection is probably the best place at which to connect your system to a good earth
ground, it should be pointed out that only one connection to an earth ground is to be made iri any system.
Otherwise what is commonly known as a “ground-loop" will be caused and hum and noise may increase
sufficiently to become a nuisance. In any system, only one ground connection can be made to earth. If one of
your components is supplied with a three-prong AC connector which is plugged into the AC wall outlet, earth
connection will be made through this plug and additional ground connections are not recommended. Similarly,
if the system’s units are mounted in a rack and ground connection between chassis is made through the rack
mounting, special techniques must be undertaken to minimize ground-loops and subsequent noise, A detailed
discussion of ground-loops with methods for their elimination is beyond the scope of this manual.
AUX1 О
This set of input jacks is for use with a high-level signal source, such as a tape player, the audio signal from a video-disc
player, or video-cassette recorder (VCR). The load impedance of this input is approximately 22,000 ohms. This input can
also be converted for use with an analog disc turntable if the optional PHO-802A board is installed onto the main PCB of
the GFP-345. This is a procedure best left to your dealer, or ADCOM authorized service personnel. It is not recommended
you undertake the installation of the PHO-802A board within the GFP-345 yourself.
PHONO (PHO-802A OPTION) О
To use an analog disc turntable with the GFP-345 requires installation of the optional РНО-в02А phono preamp board
onto the main PCB of the GFP-345. Once the PHO-802A board is installed, the input jacks marked AUX 1 © are then
usable with any high-output moving-coil or moving-magnet phono cartridge. These two standard RCA jacks will accept
all common RCA plugs, one for each channel, left and the right, usually supplied at the ends of the turntable’s cables.
LEFT CHANNEL and RIGHT CHANNEL inputs are clearly labelled and their routing, even when the PHO-802A board is
installed, will remain left and right as indicated. Determine the exact color coding or markings on your turntable's cables
for left and right channels in order to insure the correct connections. The PHO-802A circuit is designed to accept the
signal from any high-output moving-coil, moving-magnet, induced-magnet, moving-iron or variable-reluctance car
tridge, the output from which is rated at 2.2 mV/cm or higher. The PHO-802A-input electrical impedance characteristics
are the standard 47,000 ohms with lOOpF shunt capacitance. ADCOM high-output moving-coil cartridges, for example,
are ideally suited for use with this phono preamplifier. Low-output moving-coil cartridges which normally require a prepreamplifier (sometimes referred to as a "head-amp”), or step-up transformer must have these auxiliary devices
connected l>efore the RCA jacks feeding the input to the PHO-802A board. A pre-preamplifier, or step-up transformer
provides the additional gain required by very-low-output moving- coil cartridges to operate with a standard preamplifier
circuit. A pre-amplifier, or step-up transformer, is not necessary and must not be used with high-output moving-coil
cartridges or moving-magnet, induced-magnet, etc. cartridges. If you are uncertain as to which type of cartridge you will
be using, please consult the instruction manual or specification sheet which wés included with your cartridge, or contact
the dealer from whom you purchased the cartridge, or the cartridge manufacturer.
Some turntables are supplied with a separate ground wire, which must be connected to ground, to reduce hum. If the
turntable is provided with this separate ground wire simply connect it to the GND О screw on the rear panel of the
GFP-345 directly to the left of the AUX 1 inputs (now converted to PHONO),
There are simplified instructions on the main PCB oftheGFP-345to facilitate installation of thePHO-802A board. Detailed
instructions are also supplied in the section INSTALLING THE PHO-802A BOARD IN THE GFP-345 at the end of this
manual.
CD O
This set of input jacks is for use with a Compact Disc (CD) player or other similar high-level signal source, such as a tape
player, the audio signal from a video-disc player, or video-cassette recorder (VCR). The load impedance of this Input is
approximately 22,000 ohms.
TUNER O
Although this pair of inputs is provided for your tuner, they may be used with any other high-level source such as a tape
player, an additional Compact Disc (CD) player or other similar high-level signal source. The load impedance of this input
is identical to that of the CD e input.
AUX 2 O
This pair of inputs is provided for any other high-level source you may have available such as a tape player, an additional
Conmact Disc (CD) player or other similar high-level source. The load impedance of this input is identical to that of the
CD O input.
TAPE IN O
This set of tape inputs is identical in sensitivity and electrical characteristics to the CD e inputs and the comments made
about the CD O inputs apply. These may be used not only for cassette or other audio tape recorders (such as DAT or
DCC), but also with any high-level signal source such as a VCR's audio outputs, etc.
If you desire simple playback of prerecorded tapes, plug the left and right outputs of your tape machine labelled “tape
out” or "line out” into the TAPE IN O jacks using a set of good-quality, low-loss audio cables. To select playback of tape,
push in the TAPE MON O switch on the front panel of the GFF^345. Whenever the TAPE MON O is activated the LED
directly above it will glow. Also, whenever the TAPE MON ® switch is pushed in the INPUT O selector will be
disconnected from the circuit. That is, whatever source has been selected through the INPUT 0 selector will be
disconnected from the circuits of the GFP-345 and will be supplanted by the source, or tape recorder, plugged into the
TAPE IN O jacks on the rear panel of the preamplifier.
TAPE OUT O
Whichever input is selected via the INPUT 0 selector knob will appear at the TAPE OUT O jacks. It should be pointed
out that regardless of the position the TAPE MON 0 switch is in, whatever source is selected via the INPUT 0 selector
will still appear at the TAPE OUT O jacks. The TAPE MON 0 switch only controls the playback circuits of the GFP-345.
Also, please note that if you are monitoring a recording which is being made on a tape or cassette machine, by using the
TAPE MON 0 function, you must leave the INPUT
process will be interrupted: that is, the changing of source selection through the INPUT 0 selector switch will interrupt
the signal being fed to the tape or cassette recorder via the TAPE OUT e jacks. To hook-up the TAPE OUT o to your
cassette or tape recorder, connect the right and left jacks on the cassette or tape recorder labelled “line in" or "record in"
to the corresponding LEFT CHANNEL and RIGHT CHANNEL TAPE OUT O jacks on the rear panel on the GFP-345. It
is very important that you use only high-quality, low-loss interconnecting cables in order not to degrade the quality of the
recording.
0 selector on the source selected for recording or the recording
NOTE
The TAPE OUT О circuits are actively “buffered" in order to insure that the signal with in the ci rcuitry of the GFP345 will not be compromised regardless of whether the tape recorder is in use or not. Therefore, you can listen
to the source which you are recording without fear of degrading the signal either in the recording or the listening
mode. In addition, the buffered outputs will prevent the normal degradation that tape recorder inputs cause an
audio signal in a preamplifier when the tape recorder circuits are turned off and not in operation.
EXTERNAL PROCESSOR IN O/ EXTERNAL PROCESSOR OUT O
This set of inputs and outputs is provided for use with any "signalprocessor" such as an equalizer, time-delay unit,
surround-sound decoder, etc. The EXTERNAL PROCESSOR IN © / EXTERNAL PROCESSOR OUT © jacks are
selected and controlled by the front-panel button iabelled EXT PROC 0. Pushing in the EXT PROC 0 button will
connect whatever processor is plugged into the EXTERNAL PROCESSOR IN ©/EXTERNAL PROCESSOR OUT
e jacks to the circuitry of the GFP-345. Whenever the EXT PROC 0 button is pushed In, activating this circuit, the red
LED above it will glow. Pushing and releasing the EXT PROC 0 button will disconnect the EXTERNAL PROCESSOR IN
O/EXTERNAL PROCESSOR OUT 0 jacks from the circuitry of the preamplifier. It is important to note that when the
EXT PROC 0 button is released, both sets of jacks (EXTERNAL PROCESSOR IN ©/EXTERNAL PROCESSOR OUT ©)
are electrically removed from the circuitry of the preamplifier (and, so, consequently whatever processor is plugged into
these jacks) to prevent any possible degradation of the signal selected through the INPUT 0 selector switch.
To connect the processor, equalizer or surround-sound decoder, etc., to the GFP-345 always use high-quality low-loss
audio cables. Plug the jacks on the signal processor labelled "input", "in”, "line-in", or “source” into the EXTERNAL
PROCESSOR OUT O jacks on the rear panel of the GFP-345, observing the left and right labelling on both sets of jacks.
Plug the jacks on the signal processor marked “output, “out" or "line-out" to the GFP-345 jacks labelled EXTERNAL
PROCESSOR IN ©. Once these connections have been effected simply pushing In the EXT PROC © button on the front
panel of the GFP-345 will bring the processor info the circuit.
NOTE
1. Please be advised that if no processor is plugged into the EXTERNAL PROCESSOR IN O and EXTERNAL
PROCESSOR OUT O jacks, and the EXT PROC ® button is pushed in, all the inputs of the GFP-345 will be
disconnected and no output signal will be present at either the OUTPUTS NORM ® or the OUTPUTS LAB
o and, consequently, no sound will be heard through the system. Whenever a signal processor is not being
used, the EXT PROC ® button should always be in the out position.
2. However, it is possible when no processor is connected to the EXTERNAL PROCESSOR IN O and
EXTERNAL PROCESSOR OUT O jacks, to use the EXT PROC ® button as a mute function. By pressing In the
EXT PROC 0 button the signal will be interrupted until the EXT PROC ® button is, once again, pushed in and
released.
3. Normally, the GFP-345 does not invert polarity; that is, if a positive-going signal is present at any of its inputs,
it will appear as a positive-going signal at the outputs. However, if a signal processor is connected to the
EXTERNAL PROCESSOR IN O and EXTERNAL PROCESSOR OUT O jacks, and its circuitry inverts polarity,
the signals present at the OUTPUTS NORM © and OUTPUTS LAB O will also be inverted in polarity (check
the Instruction Manual of your signal processor to determine if it does or does not invert polarity).
4. Usually, there should be no appreciable level difference whenever a signal processor is connected into or out
of the circuitry of the GFP-345 (through the use of the EXT PROC 0 button), so long as the processor was
designed with an absolute gain of 1 and adequate input and output impedances to fulfill this function. If a level
difference can be detected when switching a processor in and out of the circuit, and this is disturbing to you,
please contact the manufacturer of the processor you are using to see if a correction of this level difference cari
be effected.
5. It is also possible to employ the EXTERNAL PROCESSOR IN О jacks as an additional set of Inputs, since
these jacks are located, in the circuitry, before the LEVEL 0 and BALANCE 0 controls. If you wish to use the
EXTERNAL PROCESSOR IN О jacks as an additional input, simply plug the signal source into the EXTERNAL
PROCESSOR IN О jacks as wu would any of the other inputs (CD O, TUNER O. etc.) and select that source
^ pushing In the EXT PROC
0 selector will bedisconnected and the source plugged into the EXTERNAL PROCESSOR IN О jacks will then
be fed through the circuits of the GFP-345 and out of the OUTPUTS NORM ©.and OUTPUTS LAB ©
0 button. Whatever other selection of sources has been made through the INPUT
Whatever processor is connected to the EXTERNAL PROCESSOR IN О and EXTERNAL PROCESSOR OUT 0 jacks
will not be operative at the TAPE OUT 0 jacks. If you wish to insert an equalizer into the tape recorder circuits this must
be done through the specific TAPE IN О and TAPE OUT О jacks along with the particular recorder. In such an instance,
this processor will not operate on any other source selected through the INPUT ® selector but will operate only on the
tape loop to which it has been connected. Similarly, because of the design of the circuitry in the GFP-345, and when the
EXTERNAL PROCESSOR IN О jacks are used an additional high-level input, this individual signal will not appear at the
TAPE OUT О jacks, nor can it be selected through the INPUT © selector. Therefore, tape recordings cannot be made
of the signal source plugged into the EXTERNAL PROCESSOR О jacks. To return to usual operation of the preamplifier,
push and release the EXT PROC 0 button and the operation of all the switches and selectors will return to normal and
the source plugged into the EXTERNAL PROCESSOR IN О jacks will be disconnected from the circuitry of the GFP-345.
OUTPUTS NORM ©
The OUTPUTS NORM © are capacitively coupled using very-high-grade metallized film capacitors. It is ideal for use
with power amplifiers which require a bandwith-Mmited signal which does not extend to DC. Although these capacitively-
coupled outputs do restrict, somewhat, the extremely low frequencies, around 5 Hz or 10 Hz, it does not, in any way,
degrade the quality of the signal from the preamplifier. Great care was taken in the selection of capacitors to preclude any
sonic deterioration.
To connect these outputs to your power amplifier, simply interconnect the LEFT CHANNEL and RIGHT CHANNEL
OUTPUTS NORM © jacks to the corresponding left and right input jacks on the amplifier. To preserve the extremely high
quality of the circuitry in the GFP-345, it is recommended that you use as high a quality cable as possible to make this
interconnection.
NOTE
Both the OUTPUTS NORM © and the OUTPUTS LAB © may be used simultaneously should you wish to
bi-amp your speakers, or drive more than one amplifier. When using both of these outputs simultaneously, there
will be no “loading” effects on the preamplifier.
OUTPUTS LAB 0
The OUTPUTS LAB © is direct-coupled, with no capacitors, and was designed to provide an output voltage ideally
matched for operation with the ADCOM brand of amplifiers. It can be used, however, to drive almost any power amplifier
presently available with input sensitivities ranging from below 500mV (0,5V) to well above 2.0V. To connect this output to
your power amplifier, please follow the instructions in the section above OUTPUTS NORM ©.
It should be pointed out that, since the OUTPUT LABS © is direct-coupled, it is an extremely broadband circuit which
responds down to DC (direct current). Therefore, it requires that your power amplifier (if it is not an ADCOM-brand
amplifier) be able to handle this extremely broadband signal.
NOTE
Although the GFP-345 was designed primarily for use with stereo power amplifiers, it can operate just as well with
two mono power amplifiers. When two mono amplifiers are used for stereophonic reproduction, it is strongly
suggested that they be a matched pair with respect to brand, model, input sensitivity and power output.
SWITCHED © OUTLET
The SWITCHED © outlet is controlled by the power switch © on the front panel of the GFP-345. 'ibu may plug the AC
line cord of your power amplifier, or any other accessory, which you want to turn on and off with the power switch © of
the GFP-345 into these outlets. The current-carrying capacity of the switch © Is sufficient to handle the inrush current
of power amplifiers up to the 200-watt-per-channei class. It is not recommended that very-large-power amplifiers, above
the 200-watt class, be plugged into these outlets (see NOTE below following UNSWITCHED © outlet).
UNSWITCHEO © OUTLET
The UNSWITCHED © outlet can supply the AC power requirements of any accessory source used with the GFP-345,
such as a CD player or analog turntable. The ^ line cord of the accessory may be plugged into this outlet. The
UNSWITCHED © outlet is not controlled by the power switch © on the front panel of the GFP-345, and power will
always be available at this outlet so long as the GFP-345 is plugged into an energized wall outlet, regardless of the position
of the main power switch ©. The total power drawn through the UNSWITCHED © outlet must never exceed dcio watts.
NOTE
Most electronic or electrical devices state the maximum power drawn by the device on a plate, or label, on the rear
panel of the unit, near the AC line cord which supplies power to the unit. If is a good idea to check these
requirements before plugging an amplifier into either the UNSWITCHED outlet or the SWITCHED o outlet.
Most large-power amplifiers should be plugged directly into an AC wall outlet.
AC FUSE O
The AC line fuse protects the circuits of the GFP-345. This fuse should be replaced only with a fuse of the same current
value, type and rating as that supplied with the preamplifier. The correct fuse type, current value and rating is printed
directly above the AC FUSE socket on the rear panel of the GFP-345, Replacements with fuses of higher value and/
or different rating and/or type will not protect the GFP-345 circuits, may void the Warranty and may cause a fire hazard.
NOTE
Before checking or replacing a blown fuse, make certain you UNPLUG THE POWER COR D FROM THE AC WALL
OUTLET TO PREVENT POSSIBLE ELECTRICAL SHOCK.
POWER ©SOCKET
The POWER © socket permits connection of an AC cord and plug, suitableto your particular area or country, to provide
AC power to operate the GFP-345 circuits and energize the SWITCHED © and UNSWITCHED ® outlets. The AC tine
cord should be plugged into any standard wall outlet providing the correct operating voltage. To determine the voltage
for which the GFP-345 has been set, check the voltage listing on the upper right-hand corner of the GFP-345’s rear panel.
NOTE
The GFP-345's POWER © socket is “polarized" and its lower, center pin is grounded as required by many
standards and safety organizations. If at all possible, make certain that there is a matching, 3-prong plug on the
end of the AC cord so that the chassis ofthe GFP-345 will be grounded to “earth”. If a 3-prong plug is not available
in your area, or in your specific circumstances, experiment with the “phasing", or reversing, of the AC plug to
achieve minimal hum in your system and minimal noise as well.
CONTROLLING THE GFP-345
Please refer to the diagram of the front panel of the GFP-345 to identify all the controls and their functions.
AC POWER SWITCH © ©
The "rocker” AC power switch © controls power to the circuits ofthe GFP-345 and to the SWITCHED © outlet on the
rear panel of the GFP-345. Wheneverthe GFP-345 is energized, the red LED© wiii glow. Push the top of the rockerswitch
to energize the GFP-345. Push the bottom of the rocker switch to turn the unit off.
INPUT © SELECTOR
This rotary selector lets you chooseany input connected to the GFP-345 and feed it, through the circuitry of theGFP-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 © jacks on the rear panel of the preamplifier.
All the controls on the front panel oftheGFP-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 theGFP-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,
it will permit you to verify that there is a signal being fed to the tape recorder and through its circuits into the TAPE IN
O jacks. Whenever the TAPE MON © switch is pushed in, the red LEO above this switch will glowand 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 © jacks.
EXTPROC©
Pushing in this switch connects the EXTERNAL PROCESSOR IN O 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 EXTPROC © switch isin 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 ©
Pushing in 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 Oadson 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 disconriected 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 useatiiher tuned to a station in which the announcer is
speaking. This will almost always be 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.
I Wour system does not include a tuner, the next best way is to select a CD, push in the MONO'
© 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.
button, place the INPUT
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
standard amplifiers and speakers having medium-to-low sensitivities, the position of thiscontroi wiil beat its normai 12:30
to 1:30 o'clock position. There are many factors which will affect the position of the LEVEL control for any given
iistening levei. Among these are; the specific sensitivity of the power amplifier for maximum output; the sensitivity (or
"efficiency") of the speakers being used; the size of the room in which the speakers are located; the output levels of the
sources being used and plugged into the GFP-345 (cassette machines, tape recorder, CD piayer, etc.): the moduiation
ievei of the station being received by yourtuner; etc. The position of the LEVEL ® controi isareiative indication to permit
you to return to a simiiar level setting again and again. It is not an absolute indication of how much power the amplifier
is delivering to the speakers or "how powerful” a system is. It is quite possibie, with different component systems, to have
the same power output from an amplifier, and sound level from the speakers, but with different LEVEL © control settings
of the GFP-345, It is also quite common to have to set the LEVEL ® control to a different position, when switching from
one source (say CD) to another (such as a cassette machine), to achieve the same, or approximate volume level from the
loudspeakers. Similarly, different FM and AM stations received by your tuner may require adjustment of the LEVEL
® control depending ontheamount of audio "limiting" and “compression" used by the particular station and/or the type
of music it broadcasts.
NOTE
For the reasons described above, it is good practice to lower the LEVEL i
o selector to a different source.
The design of the GFP-345 makes it usable with the gamut of power amplifiers presently available, as well with all
loudspeakers presently in use. The LEVEL control was designed to befully operable throughout its complete rotation.
control before changing the INPUT
CARING FOR YOUR GFP^5
Great care has been taken by ADCOM to assure that your preamplifier is as flawless in appearance as it is electronically.
The front panel is a heavy-gauge, high-grade, anodized-aluminum extrusion, bead-blasted for durability. The bottom
cover, chassis, top cover and rear panel are of heavy-gauge steel, both painted and baked. If the front panel, top or sides
should become dusty or fingerprinted, they can be cleaned with a soft, lintless cloth, slightly dampened with a very mild
detergent solution.
NOTE
DO NOT SPRAY OR USE LIQUIDS OF ANY KIND ON THE
SURFACES OF THE GFP-345.
SERVICING
ADCOM has a Technical Service Department to answer questions pertinent to any difficulties you encounter in the
operation of your unit. If you encounter problems obtaining advice or resolving your problems locally, please contact us
by mail or fax for a prompt recommendation. If your problem cannot be resolved directly through instructions from us,
we may refer you to an authorized representative near you for resolution.
Please address mail inquiries to:
ADCOM Service Corp.
11 Elkins Road
East Brunswick, NJ 06816
US.A.
Should you find it more expedient to contact us via fax, the number is (908-390-9152). Please include a return fax number
so that we can reply.
INSTALLING THE PHO-802A BOARD IN THE GFP-345
The PHO-802A phono preamp board replaces the standard AUX 1 O input. Any high-level source connected to the
AUX 1 O input must be relocated to orre of the other high-level inputs not already in use. The AUX 1 o input must not
subsequently be used for a high-level source unless the PHO-802A board is removed and the jumper wires, which must
be cut for use with the PHO-802A, replaced.
1. Begin installation by unplugging the GFP-345 power cord from the AC wall outlet and remove its cover by unscrewing
the six Phillips-head screws using a #2 Phillips screwdriver. The two hex-head screws securing the top cover to the
front panel must also be removed. A 2mm hex-wrench Is necessary for this operation.
2. Cut the jumper wires B1, B2 and B3 on the main PCS of the GFP-345 at the middle, raised portion, and fold away the
cut ends to insure that the ends do not touch each other.
3. Remove the top cap-nut on each of the screw studs shown in figure below and position the PHO-802A board over the
two5-pinconnectorssothatthe corresponding Til and T12socketsand 5-pin connectors mate properly and the large
upright capacitors (black, 2200uF/16V) are positioned, as shown in figure below, nearest the RCA input jacks on the
rear panel of the GFP-345. You can use the screw studs as guides,
4. Press the PHO-802A board down firmly onto the two 5-pin connectors.
5. Screw the two cap-nuts, back onto the screw studs and firmly secure the nuts onto the PC8 with a 5,5mm nut-driver
or similar tool. Please note that the bottom cap-nuts must not be removed. The bottom cap-nuts secure the screw studs
to the main PCB and also act as spacers for the PHO-802A board. They are essential to prevent shorting between the
PHO-802A board and the main GFP-345 PCB.
6. Replace the top cover on the GFP-345 making certain all the screws are tightened securely to be sure that proper
shielding of the internal circuitry of the GFP-345 is effected.
7. There are two PHONO labels supplied with both the GFP-345 {in the plastic bag containing the instruction manual,
etc.), and also in the packaging of the PHO-802A board. Affix one PHONO label on the front panel over the AUX 1 label
at the INPUT O selector so that now it will read PHONO. The AUX 1 position is the maximum counterclockwise
position of the INPUT ® selector.
8. Affix the second PHONO label over the existing type above the RCA jacks on the rear panel which reads AUX 1 O so
that now it will read PHONO. Although this is not absolutely necessary, it will simplify identification of the now-PHONO
input to the GFP-345.
CAP-NUT.
5-PIN CONNECTOR
GFP-345
MAIN PCB
PHO-802A
CAP-NUT
5-PIN CONNECTOR
INPUT SIGNALS
JACKS
10
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