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 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).