1
INTRODUCTION
Please read thoroughly these operating instructions for the GFA-585se before connecting or
attempting to operate it. The installation and operation of the GFA-585se 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 GFA-585se. Please read it carefully to fully comprehend all its
features and functions and thereby derive maximum performance from its use in your system.
It is a good idea to keep this manual handy for future reference.
PREFACE
WARNING
The GFA-585se is a very powerful amplifier capable of delivering very large peaks into low
impedances, exceeding 50 amperes per channel. Therefore, be certain to exercise
extreme
caution when making connections to and from the amplifier.
Always make
certain that the amplifier is disconnected from the AC outlet, and its large filter
capacitors are discharged.
Please note that the power supply capacitors can take more
than
12 minutes
to discharge
. Failure to observe this precaution may result in damage
to the loudspeakers and/or blowing of the amplifier's AC RAIL FUSES, conditions
which are NOT covered by the warranty.
The GFA-585se amplifier 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 little known fact is that amplifiers which
measure extremely well on the test bench into a resistive load may not develop the same
amount of power into a loudspeaker. Depending on the amplifier's design, sometimes as little
as one third of the power which the amplifier develops into a resistor is delivered to a speaker
load. Also, the distortion level measured when the amplifier is driving a resistive load is
degraded. in some cases quite substantially, when driving the loudspeaker. It is, however,
very difficult to measure the performance of an amplifier into a loudspeaker. One reason why
this information is not widely known is because during such high-power tests, destruction of
the loudspeaker is often the result. In order to determine the performance of the GFA-585se,
ADCOM developed a "computer model" of a "difficult" loudspeaker load. A computer model
"mimics" the reactance of the very difficult speaker and duplicates the actual phase angles
of the voltage and current throughout the entire audio range. In this manner, high-power
testing of amplifier parameters could be undertaken without repetitive destruction of the
