The GFA-5802 Power Amplifier
The GFA-5802 is part of a high end, high performance series of separate
components from Adcom. The other members include the GFP-750 preamp and GCD-750
single play CD unit. All three of these components were conceived as an advanced
statement of Adcom's long standing philosophy of providing exceptional
performance for the money. Actually, with these units our goal was to go beyond
Adcom's traditional "great performance at a value price" and deliver
the sonics, power, finesse, and sophistication of units costing two to three
times as much! The fact that we exceeded our own expectations is a testament to
our engineers' diligence and their unswerving dedication to these goals.
You need power to make power
In order to generate lots of output power an amplifier needs to draw even
more power from the AC wall socket (some of those "wall watts" become
heat, and some are simply "used up" by the amps circuits.) In a power
amplifier the "wall current" is modified and ultimately delivered to
the amplifier's working circuits by the input transformer, the AC to DC
rectifiers, and the power supply filter capacitors (which act like a power
reservoir, holding electrical current for the output stage till it's needed).
Collectively these critical components are known as the Power Supply.
The all important power supply
The GFA-5802's power supply incorporates a huge, donut shaped, toroidal
input transformer. The advantage of a toroidal design is it generates lower
noise and offers less resistance to current flow than standard transformer
designs. This massive transformer at the heart of the GFA-5802 means it can "pull"
enormous amounts of power from the AC line. It's also the first step on a
design path leading to an amplifier that can deliver equally large amounts of
current, into any conceivable speaker load.
After the toroidal
transformer there's a series of rectifiers which change the AC input power to
DC. These too were chosen for their ability to deliver high current, and are
almost "idling", even at the GFA-5802's full output power. Once
modified by the rectifiers, the electricity passes through to a bank of
exceptionally large filter capacitors, with over 100,000 microfarads of total
power storage. These are used to eliminate any residual noise in the voltage,
and they store the electrical energy until it's required by the amplifiers
internal circuits. They've been chosen to deliver all the reserve power possibly
necessary, even if the GFA-5802 is connected to a 1 Ohm load!
In
addition to the main transformer, the GFA-5802 includes a separate power
transformer for its input stages. This ensures that the input stages are
unaffected by large power demands made on the output section. So a big crescendo
won't adversely impact the music that comes immediately after it.
Selected MosFet transistors throughout
All the low level signal stages of the GFA-5802 use Reference Grade HexFet
transistors exclusively. HexFet's are an advanced, hybrid MosFet device known
for their superior sound quality and rugged reliability. These devices give you
the dynamic, high impact power of Bipolar transistors without any of the "brightness"
or high frequency "glare" so common with typical transistor amplifier
designs.
The output stages of the GFA-5802 (which actually have the job
of powering your loudspeakers) are made up of 32 high current MosFets (14
continuous amperes per device). These are configured in a quasi-complimentary
manner. The result is a superbly smooth, spectacular sounding output section,
with practically unlimited voltage and current capability. You simply won't find
more high quality, real, useable power unless you spend two to three times the
GFA-5802's modest price.
You've heard it before, but less is
more
By utilizing HexFet and MosFet designs throughout the GFA-5802, Adcom's
engineers were able to design short, simple signal paths. A quick glance at the
GFA-5802's elegant glass epoxy circuit boards will affirm this "less is
more" philosophy. Reducing the number of components and stages the signal
travels through by definition reduces the potential for distortion and fidelity
loss. Taking this approach even further, Adcom's engineers designed the GFA-5802
with only three active gain stages, as opposed to the 5 or more found in typical
amplifier designs. Once again, the result is improved sound, clarity, and
imaging, not to mention enhanced reliability.
The GFP-750's low voltage
gain stages are single ended Class A designs, the most neutral and accurate of
amplifier circuits. Countless hours of critical listening have confirmed the
sonic superiority of these circuits. And they're direct coupled, which
eliminates capacitor connection between stages. Since capacitors are filters by
nature, direct coupling improves signal transfer and purity.
Keepin' cool; Keepin' on Keepin' on
An important reason for using MosFet transistors in the output stage has to
do with their rugged reliability. MosFets simply aren't affected by heat the way
normal transistors are. Get the typical transistor really hot and it goes into "thermal
runaway", drawing more and more current, getting hotter and hotter until
poof; it's a gonner. MosFets on the other hand, reduce the amount of current
they conduct if they become excessively hot. So they're self-controlling and
therefore very reliable. Another advantage of this characteristic is it allows
Adcom to bias the output stage of the GFA-5802 fairly high. This makes the
GFA-5802 operate as a Class A amplifier under most normal listening conditions.
When higher power demands come along, the amplifier "switches" to
class A/B operation. So the GFA-5802 runs warm to the touch, but fear not,
because its huge external heat sinks whisk away excess heat quickly, quietly,
and efficiently.
A little extra insurance
A new, advanced protection circuit has been incorporated into the GFA-5802.
It monitors the safe operating perimeters of the amplifier, and if they're
exceeded, it protects the amplifier. This in itself is not unique, however
Adcom's protection system operates entirely outside the signal path. So
even though it offers excellent protection and peace of mind, it does so without
the slightest sonic impact!
The finishing touches
- The GFA-5802 provides both unbalanced RCA and balanced XLR input circuits.
Balanced inputs are inherently quieter and basically immune to interference,
compared to unbalanced ("RCA") inputs. Of course, the GFA-5802's
stable mates, the GFP-750 and GCD-750 have matching circuits to take advantage
of this superior balanced system configuration.
- Speaker connections are heavy duty gold plated 5-way binding posts. These
will accept heavy gauge bare or tined wires, spade lugs, and single or double "banana"
plugs. Two sets of terminals are provided for each channel, should you wish to
bi-wire your speakers.
- Finally, like all other Adcom components, the GFA-5802 features a heavy
steel chassis, an attractive extruded aluminum front panel, and a durable baked
on powder coat finish.
The GFA-5802 is a powerhouse of an amplifier, with the manners and finesse
of the most elegant audiophile components. No matter what kind of speakers you
have, we're confident that putting a GFA-5802 in your system will make a sonic
improvement. And with the money you save, you can buy lots of CDs (not to
mention other Adcom components).
 Related Products
GFP
750 Preamplifier
GCD 750 CD Player
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