Adcom GFA-555MS, Operating Instructions Manual

Page 1: ...HIGH CURRENT POWER AMPLIFIER GFA 555ms The contents of this manual are subject to change Please check our website www adcom com or www adcom usa com for the most current version Copyright 2011 Adcom LLC ...

Page 2: ...fier can drive a very broad range of loudspeakers including those with very low impedances at sustained high power levels even when the impedances are highly reactive Great care was taken to insure that distortion in the amplifier would remain extremely low particularly when driving these highly reactive loads in which the phase angles of the voltage and the current are substantially different A l...

Page 3: ...higher efficiency was insured by using a toroidal design Additionally thermal and dynamic tracking of the bias for the triple Darlington driver and output stages is provided to insure that the amplifier operates in its optimal range regardless of the length of time and the level of operation The GFA 555ms s circuitry is direct coupled internally to minimize the sonic deterioration which capacitors...

Page 4: ...rton If any number is altered or missing you should notify us immediately in order to insure that you have received a genuine ADCOM product which has not been opened mishandled or tampered with in any way UNPACKING Before your GFA 555ms left our plant it was carefully inspected for physical imperfections and tested for all electrical performance parameters as a routine part of ADCOM s systematic Q...

Page 5: ...nts on top of the GFA 555ms Not only will the heat generated by the amplifier affect the performance of equipment stacked on top of the GFA 555ms but the free flow of air through the ventilating slots provided in the chassis of the amplifier may be partially obstructed If you require that the GFA 555ms be mounted in an enclosed cabinet it is recommended that the rear panel of the cabinet be provid...

Page 6: ...sure that the performance designed into the GFA 555ms is preserved you should use the highest quality plugs and cable as are feasible There are many cables which are designed specifically for these applications and your ADCOM dealer can be of help in selecting the best cable for your application Whatever cable you finally select it should have low capacitance This is particularly important if you ...

Page 7: ...tion please refer to the section STEREO BRIDGED MONO INPUT OUTPUT In order to insure that connections to the loudspeakers are correct you must be able to identify each wire conductor of the loudspeaker cables at both ends of the cables This is relatively easy to do since most loudspeaker cables consist of two parallel stranded conductors in a flexible insulation with a coding system for wire ident...

Page 8: ... can create anomalies at ultrasonic frequencies which although inaudible can affect performance in the audible range There are different ways to connect the wiring to the RIGHT LEFT STEREO SPEAKER OUTPUTS The methods used will depend on the specific type of connectors supplied with the loudspeakers the speaker cables etc As a matter of course we prefer to use double banana plugs because it is gene...

Page 9: ...ver that when loudspeakers are paralleled the impedance presented to the amplifier is lower than the nominal impedance of each loudspeaker In other words if you parallel two 8 ohm sets of loudspeakers the resultant impedance will be 4 ohms If you parallel two sets of 4 ohm impedance loudspeakers the resultant impedance of the load will be 2 ohms If 8 ohm and 4 ohm loudspeakers are paralleled the r...

Page 10: ...dance 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 555ms 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 po...

Page 11: ...cribed above are followed exactly the GFA 555ms will be polarity correct that is it will not invert phase Any positive going signal at its input will appear as a positive going signal at the loudspeaker DC RAIL FUSES The DC RAJ L FUSES provide protection for the output stages and power supply in the event of excessive current demands from the amplifier either long term or short term If the amplifi...

Page 12: ... SUBSTITUTE FUSES WITH DIFFERENT RATINGS TIME CURRENT CURVES OR VALUES Failure to observe this precaution may cause serious damage to the amplifier circuits MAY CREATE A FIRE HAZARD AND MAY VOID YOUR WARRANTY For your convenience a replacement set of two of the correct DC RAIL FUSES is supplied with each amplifier to facilitate restoration of the amplifier to operation in the event of a blown fuse...

Page 13: ...ed Since conventional household branch circuits are often limited to 15amperes when the GFA 555ms is used in conjunction with other appliances on the circuit you may find the current available for the GFA 555ms is insufficient particularly in systems using very low impedance highly reactive loudspeakers NOTE The GFA 555ms s power cord is supplied with a polarized AC plug as required by UL CSA stan...

Page 14: ... BUSSMAN ABC 12 250V LITTELFUSE 3AB314012 250V SOC CES6 12A 125V NOTE The fuses listed above and their time current blowing points have been carefully selected and thoroughly tested to deliver optimal performance while still accomplishing their protective functions Replace the AC LINE FUSE only with one of the fuses listed above DO NOT USE ANY SUBSTITUTE FUSES WITH DIFFERENT RATINGS TIME CURRENT C...

Page 15: ...Similarly if the THERMAL PROTECTION LED glows the amplifier will not produce sound even though the POWER LED may still glow Additionally the internal power transformer is provided with a thermostat which will interrupt power into the transformer if its temperature exceeds 125 C This high a temperature will seldom if ever be encountered unless the amplifier is subjected to abnormal conditions such ...

Page 16: ...activated or in extreme cases damage your loudspeakers THERMAL PROTECTION LED The GFA 555ms is provided with a thermal protection circuit which will shut down the amplifier if the temperature of either heatsinks reaches 85 C The THERMAL PROTECTION LED will light whenever the thermal protection circuit on either channel or both channels has been triggered and the amplifier is inoperative The therma...

Page 17: ...l top or sides should become dusty or fingerprinted they can be cleaned with a soft Iintless cloth slightly dampened with a very mild detergent solution or non ammonia glass cleaner NOTE DO NOT SPRAY OR USE LIQUIDS OF ANY KIND ON THE SURFACES OF THE GFA 555se DO NOT EXPOSE THE AMPLIFIER TO RAIN WATER OR MOISTURE OF ANY KIND SERVICING North America ADCOM has a Technical Service Department to answer...

Page 18: ... for service you will be instructed as to the proper procedure when you call or write UNDER NO CIRCUMSTANCES SHOULD YOUR UNIT BE SHIPPED TO US WITHOUT PRIOR AUTHORIZATION OR PACKED IN OTHER THAN ITS ORIGINAL CARTON AND FILLERS Always ship PREPAID VIA UPS FDX OR OTHER APPROVED CARRIER DO NOT SHIP VIA PARCEL POST since the packing was not designed to withstand rough Parcel Post handling FREIGHT COLL...

Page 19: ...continuous average power into 8 ohms at any frequency between 20Hz and 20kHz at less than 0 09 THD bridged IM Distortion SMPTE 1 watt to 125 watts into 8 ohms 0 009 1 watt to 200 watts into 4 ohms 0 009 IM Distortion CCIF Any Combination from 4kHz to 20kHz 125 watts into 8 ohms 0 002 200 watts into 4 ohms 0 003 THD Noise at 125 Watts into 8 Ohms 20Hz 0 004 1kHz 0 003 10kHz 0 006 20kHz 0 020 THD No...

Page 20: ... Noise Ratio A Weighted 125 watts into 8 ohms 102dB Gain 27 2dB Input Impedance 100 000 ohms Input Sensitivity 125 watts into 8 ohms 1 38V rms 1 watt into 8 ohms 123mV rms Damping Factor 20Hz to 20kHz 400 Rise Time 5kHz 90V peak to peak square wave 20 to 80 2 3us Semiconductor Complement 34 transistors 2 zener diodes 13 diodes 2 ICs 2 diode bridges Power Consumption Continuous Both Channels Driven...

Page 21: ...ced or electronically transmitted without the express written consent of Adcom LLC Adcom LLC shale not be liable for any errors contained herein or for any damages arising out of or related to this document or the information contained herein even if Adcom LLC has been advised of the possibility of such damages This document is intended for informational and instructional purposes only Adcom LLC r...

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