Adcom GFP-345 User manual

HIGH DEFINITION
PREAMPLIFIER

INTRODUCTION
Please read thoroughly these operating instructions for the GFP-345 before connecting or attempting to operate this unit
For your own benefit, follow all the instructions in this manual and save it for future reference.
The ADCOM GFP-345 is a result of a thorough examination and reevaluation 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.
I^ in fh 3 at '° n i nd ° per ‘* ,,onof the GFP-345 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
I!*®^ 3 S?« t 0dei ! d L a J!f r c « e h ' 9hly innovative internal designs and circuit topologies of both the "Reference
Standard GFP-565 and GFP-555H 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-555II have been built into the GFP-345.
The power supply and low impedance outputs were designed to preserve music dynamics. The amplification staqes
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
precl ude 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
This should insure stable, dependable operation and long, trouble-free life.
moderate cost.
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.
• AM capacitors are state-of-the-art electrolytics and film capacitors with very low ESR and unsurpassed sonic purity
This design feature provides an audible benefit, the lowest possible distortion of music signals.
• Overdesigned mu-metal-shielded power transformer for better regulation. This transformer design eliminates stray
hum fie ds for lowest noise and provides undiminished voltage to circuits for best performance under any demands
• Precision programmable regulators for stabilized, constant DC voltages, regardless of load. This type of requlator
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
hrOOmn At ifmirn
• Amplifiers are operated in pure Class-A mode to insure lowest distortion
the level control.
regardless of the signal level or setting of
• 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.
* I W th Se , , f°'?^ t "2^ TPUTS LAB ar ® direct ‘ coupled - The V Provide a signal in the most straightforward, simplest
patn. OUTPUTS NORM are capacitor-coupled using precision, high-grade film capacitors for power amps which
can not accept ultra-wide bandwidth inputs.
1

• 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.
• *f Pe °^ tpu,s {10 ° ohms) to P erf ectly interface with any type of tape recorder. This technique allows
^ recorder - including DAT and DCC. and insures the best recording characteristics
independently of the cable used and the load 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.
• H. r ° n ,H Pa : e, .; SWitChab,e proc l essor l0 °P' Sh ortens 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 mov.ng-co.l 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.
• J-°^‘ ,mpedance - RIAA-equalization network. This unique network insures the lowest achievable noise level in a
pnono preamp.
UNPACKING THE GFP-345
ariu r wn^rr:nnni the 'T^ it ^ as 1 car « ,ul| y inspected 'or physical imperfections and electrical performance as
fnsure a orolct fS2S« « VCo " tro, - ™ S- al °"9 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
poss i b Hty oTt^a n s do rtet km damn no TZT al ! p acking materials as the Y are intended to reduce to a minimum the
^ a ^ . 6 pr0dUC ' ever need t0 ^ shipped again. In the unlikely event damage has
damage <UnbeiJSiat^ * ^ ' m y and request the name of ,he carrier so tha » a written claim to cover shipping
RIGHT TO A CLAIM AGAINST A PUBLIC CARRIER CAN BE FORFEITED IF THE CARRIER IS NOT NOTIFIPn
^cdc^i! 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 vou keen
should SrbeSS? 9 ? T h radiators or h ot-airducts, and provide reasonable ventilation. The GFP-345
p ' acad w,t . h 0,her heat-producing components in a cabinet or enclosure lacking free air flow. If placed
the component hea, ' producmg component ’ such 33 a power amplifier, please allow a minimum of three Inches between
For use in professional installations, the GFP-345 may be mounted in a standard 19-inch
rack-mount adaptors available through ADCOM dealers.
rack using the optional RM-3
CONNECTING THE GFP-345
7 m d S pe " d ° n the quality of the ' nterc onnection of both the preamplifier and its
associated equ£ment. All the input- and output-signal connections should be made only with hiqh-aualitv low-loss
audio cables. LEFT CHANNEL and RIGHT CHANNEL inputs and outputs are cleaHy labelled on the r2r panel
2

NOTE
WHENEVER CONNECTIONS TO OR 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 wire, if supplied with your
turntable, to the GND Q terminal. The GND Q terminal can also be used to connect the chassis of the GFP-345 directly
to the center screw of your AC wall 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 low-
output-level phonograph cartridges (see section PHONO (PHO-8Q2A OPTION) © following).
NOTE
Although the GNO Q 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 in 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.
AUX 1 ©
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) ©
To use an analog disc turntable with the GFP-345 requires installation of the optional PHO-802A 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 pre^
preamplifier (sometimes referred to as a "head-amp''), or step-up transformer must have these auxiliary devices
connected before 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 was 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 © 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 of the GFP-345 to facilitate installation of the PHO-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.
3

CD Q
Iia!»r et .hl SK iaCkS '?l 0r USe W j th a Com P act Disc ( CD > P'ayer Or other similar high-level signal source, such as a tape
approximatet/ 22 OOOohrlT 3 P ' ayer ’ ° r vide °- cassette record e r (^R). The load impedance of this input is
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 taoe
Playe ' 0rO,herSiml,ar signal source. The load impedance of,his input
AUX2 0
T Vided f ?: any ° thef high-level source you may have available such as a tape player, an additional
CD & Sp°ut C ° P 3yer ° r h6r S ' m ' 3r h ' 9h ' level source - The load impedance of this input is identical to that of the
TAPE IN O
Ibolfthe c a nO inmi ann! iC Xh n Sensitiv ‘ ,y and electd cal characteristics to the CD O inputs and the comments made
tbe , C ? ® ," puts app ' y ; These may be used not on| y ,or 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 Payback ofprerecorded tapes, plug the left and right outputs of your tape machine labelled “tape
nulh In hP TA U pFMn2 e ffi . k G |aCk f USin9 3 S6t ° f Sood-q^ty, low-loss audio cables. To select playback of tape
pd ® b " f P M S N P s *' ,ch on the ,ront P anel of ,he GFP-345. Whenever the TAPE MON © is activated the LED
directly above it will glow. Also, whenever the TAPE MON © switch is pushed in the INPUT © selector will be
disconnected from the circuit. That is, whatever source has been selected through the INPUT © selector will be
SKTSF frdm th ® c,rcu,,s of the GFP * 345 and will be supplanted by the source, or tape recorder, plugged into the
TAPE IN Q jacks on the rear panel of the preamplifier.
TAPE OUT O
'^ biph ® v ®^ i " pdt is 3 ®'® cted via ,h « INPUT © selector knob will appear at the TAPE OUT O jacks. It should be pointed
ou , that re 9 ard| ess of the positionthe TAPE MON © switch is in, whatever source is selected via the INPUT © selector
All 8 T X PE OUT ° iaCkS - TheTAPE M0N ° SWitCh only CO " trols the P^y^ckcircuitsof theGFP-345^
tapp unSffifc? h .• If y ° U are rn °7 ,0nn9 3 recordin 2 which is being made on a tape or cassette machine, by using the
TAPE MON © function, you must leave the INPUT © selector on the source selected for recording or the recording
thr^nLT^nnT P e H r ,n P .h e ; ' S ’ , he changing of SOurce selection through the INPUT © selector switch will interrupt
T 9 ,ed tP the tape or cassette recorder via the TAPE OUT O jacks. To hook-up the TAPE OUT Q to your
cassette or tape recorder, connect the right and left jacks on the cassette or tape recorder labelled “line in" or “record in"
L6FT CHA ,T EL and RIGHT CHANNEL TAPE OUT o jacks on the rear panel on the GF^is It
recording P ° r,ant ^ Y ° U ^ ° n Y high " quallty ’ low * loss interconnecting cables in order not to degrade the quality of the
NOTE
T ^| PE ?!^ T ® circuds are actively “buffered" in order to insure that the signal within the circuitry of the GFP-
345 will not be compromised regardless of whether the tape recorder is in use or not. Therefore, you can listen
‘J® source which, yot.are recording without fear of deg rading 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 ©/ EXTERNAL PROCESSOR OUT ©
J, h '® -"Puts and outputs is provided for use with any "signalprocessor" such as an equalizer, time-delay unit.
EEfTT* d6 ^ er : ® T he ^^NAL PROCESSOR IN 0 / EXTERNAL PROCESSOR OUT © jacks are
selected and controlled by the front-panel button labelled EXT PROC ©. Pushina in the EXT PROC © button will
connect whatever processor is plugged into the EXTERNAL PROCESSOR IN ©/EXTERNAL PROCESSOR OUT
to C TCU'try of the GFP-345. Whenever the EXT PROC © button is pushed In. activating this circuit, the red
li^F^FRNAi 1 ppnr r Ji* as, " B ] h ® 0(7 PROC ® button will disconnect the EXTERNAL PROCESSOR IN
St PROr® L hMn° CES ^ OR ^ U h T ® jacks from the circuitry of the preamplifier It is important to note that when the
EXT PROC © button is released, both sets of jacks (EXTERNAL PROCESSOR IN ©/EXTERNAL PROCESSOR OUT ©)
E*?" 0 ?* removed ,rom ,he circui,r V of Preamplifier (and, so, consequently whatever processor is plugged into
these jacks) to prevent any possible degradation of the signal selected through the INPUT © selector switch.
4

To connect the processor, equalizer or surround-sound decoder, etc., to the GFP-345 always use high-quality low-loss
PROCESSOR OUT © £2? °V^ *** P [°f SSO I , ab *" ed "‘"P*" Hn*n". or "source- into the EXTERNAL
Ph ° UT ® k , th ® r ear pane 0f lhe GFP ‘ 345 ' observing the left and right labelling on both sets of jacks
PRnrpstqnR iw rfi h n S,9n .t processor marked “output, "out" or "line-out" to the GFP-345 jacks labelled EXTERNAL
Fp^°"-M e K^hese connections have been effected simply pushing in the EXT PROC © button on the front
panel of the GFP-345 will bring the processor into the circuit.
NOTE
11 n0 processor is plugged into the EXTERNAL PROCESSOR IN © and EXTERNAL
PROCESSOR OUT © 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
® * n £ SOund wil1 be heard throu 9h the s y s,em - Whenever a signal processor is not being
used, the EXT PROC © button should always be in the out position.
! v ^r, r ' n ° P rocessor is connected to the EXTERNAL PROCESSOR IN ©and
Kt PRnr L flft R ? C .f SS .? R OUT 0 jacks, to use the EXT PROC © button as a mute function. By pressing in the
relMMd ° ® bU * ® S ' 9 W 66 m,errupted until ,he EXT PROC © button once again, pushed in and
3. Normally, the GFP-345 does not invert polarity; that is, if a positive-going signal is present at any of its inputs,
or^^^ 8 i t i V f^Sl n9 signal at the ou,puts - However, if a signal processor is connected to the
EXTERNAL PROCESSOR IN © and EXTERNAL PROCESSOR OUT © jacks, and its circuitry inverts polarity
the signals present at the OUTPUTS NORM © and OUTPUTS LAB © 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 © button), so long as the processor was
designed with an absolute gam 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 carl
d© enectea.
5 It is also possible to employ the EXTERNAL PROCESSOR IN © jacks as an additional set of inputs, since
Sf5£55' a pRn t ^2S , rl^f«- U, l ry * before j beLEVEL © and BALANCE © controls. If you wish to use the
S ^ R N ® ,acks 88 an add,tional lf1 P ut . simply plug the signal source into the EXTERNAL
PROCESSOR IN ©jacks as you would any of the other inputs (CD ©, TUNER ©. etc.) and select that source
by pushing In the EXT PROC © button. Whatever other selection of sources has been made through the INPUT
p selector wiM be disconnected and the source plugged into the EXTERNAL PROCESSOR IN © jacks will then
be fed through the circuits of the GFP-345 and out of the OUTPUTS NORM © and OUTPUTS LAB ©
5

Whatever processor is connected to the EXTERNAL PROCESSOR IN O and EXTERNAL PROCESSOR OUT O jacks
ro'Tnhfh! i acks - l f V ou wj sh to insert an equalizer into the tape recorder circuits this must
be done through the specific TAPE IN © and TAPE OUT © 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
FXTFRNAI °pinr^nSl^n n n T te(i ' simi,arly ' because of the design of the circuitry in the GFP-345. and when the
TA QC , S S0R IN ® )acks are used an additional high-level input, this individual signal will not appear at the
TAPE OUT © jacks, nor can it be selected through the INPUT © selector Therefore, tape recordings cannot be made
of the signa source Pegged into the EXTERNAL PROCESSOR © jacks. To return to usual operation of the preamplifier
push and release the EXT PROC © button and the operation of all the switches and selectors will return to normal and
the source plugged into the EXTERNAL PROCESSOR IN © 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-limited signal which does not extend to DC. Although these capacitivelv-
coupled outputs do restrict, somewhat, the extremely low frequencies, around 5 Hz or 10 Hz, it does not, in any way
sonic detedoration ° f ^ S ' 9nal fr ° m ,he preampli,ier Great care was taken in the selection of capacitors to preclude any
™ £ tpUtS ,0 V ° Ur POWer arnplifier ' sim P'y 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 hiqh
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. y
OUTPUTS LAB ©
Tha ? U J« PUTS L ^ B ® . ,s direct-coupled, with no capacitors, and was designed to provide an output voltaqe ideally
ma c ed for operation with the ADCOM brand of amplifiers. !t 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
l ™ uwii° W h| t0 . D ? (d J[’ e ?’ C Urren,) ' There,ore ' '* 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
wo 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. You 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
°J P ? ™ er am P |lfiers up to the 200-watt-per-channel 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).
UNSWITCHED © OUTLET
The UNSWITCHED © outlet can supply the AC power requirements of any accessory source used with the GFP-345,
f^ a S r a ? P P ^ yer anal °9 The AC 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 mam power switch ©. The total power drawn through the UNSWITCHED © outlet must never exceed 800 watts.
6

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. It is a good idea to check these
requirements before plugging an amplifier into either the UNSWITCHED © outlet or the SWITCHED © outlet.
Most large-power amplifiers should be plugged directly into an AC wall outlet.
AC FUSE ©
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 thatsupplied 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 ACcord and plug, suitable to your particular area or country, to provide
AC power to operate the GFP-345 circuits and energize the SWITCHED © and UNSWITCHED © outlets. The AC line
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 of the GFP-345 will be grounded to “earth”. If a 3-prong plug is not available
m 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 of the GFP-345 and to the SWITCHED © outlet on the
rear panel of the GFP-345. Whenever the GFP-345 is energized, the red LED © will glow. Push the top of the rocker switch
to energize the GFP-345. Push the bottom of the rocker switch to turn the unit off.
7

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
8

f“ d r P " f,erS .! ndSP ° akerS hav ' ng med,ljrn -to-low sensitivities, the position o< this control will beat its normal 1230
to -I . 30 O clock position. There are many factors which will affect the position of the LEVEL © control for any qiven
listening level. 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
USe i? 3nd plu " ed ' n, ° the GFP-345 (cassette machines, tape recorder. CD player, etc.); the modulation
, 9 7*7* J. y yourtuner; etc - The Position of the LEVEL © control is a relative indication to permit
/ l evel ^ ttmg agam and a 9 ain - 1 1 is n °> an absolute indication of how much power the amplifier
9 * th f peakers or how Powerful” a system is. It is quite possible, with different component systems, to have
° utpi f ,rom an am P |d| ef, and sound level from the speakers, but with different LEVEL © control settings
nnjrnu 50 qu :l e C ? mm l ° n t0 have t0 set the LEVEL © contro1 to a different position, when switching from
“ i- { % CD } X ° a "°’ her (SUCh as a cassette machine), to achieve the same, or approximate volume level from the
' h' ar y ' ‘flT®'’ 6 "' FM and AM stat 'ons received by your tuner may require adjustment of the LEVEL
of music it broadcasts °" ^ am ° Unt ° f aud '° “ l,m,,,n 9" and “compression" used by the particular station and/or the type
NOTE
For the reasons described above, it is good practice to lower the LEVEL © control before changing the INPUT
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 be fully operable throughout its complete rotation.
CARING FOR YOUR GFR-345
I 5660 l aken by ADC( ? M t0 assure thal y° ur preamplifier is as flawless in appearance as it is electronically.
pane ' ls a heavy-gauge, high-grade, anodized-aluminum extrusion, bead-blasted for durability. The bottom
Should Iprlm H P C .° ver and rear panel are of heavy-gauge steel, both painted and baked. If the front panel, top or sides
detergent solution V ° rf,n9erprmted ' ,he y can be cleaned with a soft, lintless cloth, slightly dampened with a very mild
NOTE
DO NOT SPRAY OR USE LIQUIDS OF ANY KIND ON THE
SURFACES OF THE GFPv345.
SERVICING
3 "'‘if Service Department to answer questions pertinent to any difficulties you encounter in the
ZT Ztir Un,t f y ? U encounter Problems obtaining advice or resolving your problems locally, please contact us
we mai rofervm, . r ® co "\ mendat ' on ; lf y° ur 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 08816
U.S.A.
^»n d rlT,° re 6Xped ' ent *° C ° ntaCt US Via f3X ' ,he numb€r is (908-390-9152). Please include a return fax number
9

INSTALLING THE PHO-802A BOARD IN THE GFP-345
ImITIS' 802A * Ph0 ?? pre , amp b ° ard re P' aces the standard AUX 1 © input. Any high-leve! source connected to the
AUX 1 © input must be relocated to one of the other high-level inputs not already in use. The AUX 1 © 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. . cn must
1. Begin installation by unplugging the GFP-345 power cord from the AC wall outlet and remove its cover by unscrewinq
the six Phil 1 1 ps-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 Bt, B2 and B3 on the main PCB of the GFP-345 at the middle, raised portion, and fold awav the
cut ends to insure that the ends do not touch each other. 1
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-pin connectors so that the corresponding Til and T12 sockets and 5-pin connectors mate properly and the larqe
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 PCS 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
L°j^r" P CBand alS ° aCt as spacers for ,he ph °- 802A board. They are essential to prevent shorting between the
PHO-802A board and the main GFP-345 PCB.
8. 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.
1. There are two PHONO labels supplied with both the GFP-345 (in the plastic bag containing the instruction manual
e c i‘ a " d a, f° !i the Packaging of the PHO-802A board. Affix one PHONO label on the front panel over the AUX 1 label
at the INPUT © 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 © so
that now it read PHONO. Although this is not absolutely necessary, it will simplify identification of the now-PHONO
input to the GFP-345.
10