Beschrijving

Enormous power at an affordable price is what this amp is all about. A pure class A/B power unit, driven in parallel to deliver 450 watts/channel into 8 ohms with impeccable quality.

While developing the new GFA-585se, every single part was put under the microscope to create a better & upgraded version of what is already considered a great component in audio industry.

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
loudspeaker load.

To achieve the above, 14 pairs of specially selected TO-3-type, metal-cased bipolar output
transistors are used in the GFA-585se in a triple-Darlington configuration of its driver and
output stages. The safe operating area of these transistors, along with their circuit topology,
insures very efficient power delivery to reactive loads, regardless of the phase angle of
voltage and current. Many protections & current-limiting circuitry is used in the GFA-585se
which could grade the safety.
The power supply in the GFA-585se has enormous reserve power capability with an
extremely large transformer feeding a storage bank of 132,800uF of filter capacitance. The
transformer itself was designed for extremely good regulation, insuring stable voltages
regardless of the power demands from the amplifier. Its higher efficiency was insured by
using a toroidal design. Additionally, thermal and dynamic tracking of the bias for the tripleDarlington 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.

All internal point-to-point wiring is OFC and the highest-grade parts, consistent with their
application and voltage requirement, have been used in its construction. In especially critical
circuits, the finest quality film capacitors have been used. Among its other design
improvements are the following:
 18,800uF individual power supplier for input stage & pre driver stage
 PP.PS.MPE.MPP.MPBM plastic capacitors inside
 132,800uF NICHICON gold series filter for power output stage
 DC Servo and OMRON 20 Amp speaker relay protection circuits
 ELNA silk capacitors
 Precision TVR for bias adjustment
 28 beta-matched TO 3 output transistors
 1.7kVA shield cover toroid power transformer
 6U chassis & rear carry handles
 25 Amps NTC Resistor for surge killer & auto delay time shunt relay function
 Larger outside double heatsinks of each channel for greater heat dissipation and better
temperature and dynamic bias tracking. Greater thermal stability is thereby insured.
 High-quality, gold-plated brass RCA input jacks
 Acrylic cover with 24K gold plate heavy speaker terminal
 2 Distortion(L.R), thermal and limit (overload) indicator LEDs on front panel
 DC voltage protection circuit
3
 Auto audio signal “on” & 5V-12V DC trigger “on” 3.5ᶲ jack
 DC 12V 100mA 3.5ᶲ output jack for trigger other devices