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Adcom GFA5500 200 Watt 2-Channel Stereo

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SKU# 349


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Adcom GFA5500 200 Watt 2-Channel Stereo

Note: Many of the design features in the GFA-5500 are virtually identical to the GFA-5800 power amplifier. The primary difference between these amplifiers is power output. The circuit topology and design concepts are virtually identical.

Completely Separate Secondary Main Power Systems. The GFA-5500 has a specially wound high power toroidal transformer which completely isolates the two channel secondary systems, not even sharing the ground connection. This eliminates ground loops and greatly reduces the possible interactions between power channels.

High Capacitance Storage
Each channel has nearly 120 Joules of energy storage, adequate for 14 kilowatts of power at 10% ripple. Under normal operation, the power supply ripple voltage is less than 1%.

Separate High Voltage Front End Supplies
The front end circuitry of each channel is supplied power by its own high voltage system - including separate transformer windings, bridge rectifiers and filter capacitors for each channel. This eliminates interaction between the early gain stages of the amplifier and the high power occurring in the output stages. The front end system is operated at a higher voltage than the output stage. This not only improves the distortion characteristic of the front end, but allows the front end to drive the output stage to its supply rails - obtaining every bit of available power to the load.

In Rush Limiting
The power supplies feature inrush limiting, which prevents the high current surges, which would normally accompany the charge cycle of the transformer and the power supply capacitors on turn-on.
Q & A
Features & Specs

Additional Information

Product ID 349
UPC 349
Brand Adcom
SKU 349
Manufacturers Part Number GFA5500
Detailed Specifications CIRCUITRY 100% MOSFET Construction
All audio elements of the amplifier are Power Mosfet Even the input
transistors are power devices, capable of as much as 2 amps of current
by themselves. The transconductance characteristic of Mosfet have a
number of advantages which are put to good use. Their high input impedance
allow for the use of an extremely simple gain path, and their negative thermal
characteristics give high thermal stability, allowing high output stage bias,
low offset voltages, and very high output current and voltage with reliable operation.
The characteristics of the Power Mosfet are sonically superior to the Bipolar transistor,
delivering all of the muscle of Bipolar circuitry with the sweeter qualities found in
tube equipment.

Ultra Simple Gain Path
Most high end amplifiers have at least 5 successive gain stages associated
with their signal path. Some have even more. The GFA-5500 achieves all of its
performance with only three. That's two stages less for the signal to travel through,
and it makes a difference.

Single Ended Class A Front End Circuitry
The front end circuitry is single ended Class A. Single ended is the purest form
of Class A operation, and yields the most pleasing sonic characteristics. It is also
the most stable class because the gain devices are biased by constant sources which
do not vary their bias under changing temperature or dynamic conditions.

Doubly Regulated Active Current Sources
The current sources in the GFA-5500 are doubly regulated for absolute stability.
This stability gives the front end circuitry the ability to ignore supply fluctuations,
noise and signals from the other channel (crosstalk). It also provides operation
which does not vary with temperature or age. The voltage references driving each
source are filtered passively, with different time constants, which allowing for
staggered turn-on of the sources, giving low turn-on thump.

Ultra Matched Devices
The output Mosfet are mated to within 2.5% of each other at the bias point,
and the input devices are matched to within 0.25%. In the output stage this
yields lower distortion and more reliable performance. Tighter tolerances also
achieves lower output impedance (higher damping factor) and higher output
currents. In the input stage, this yields lower distortion, lower DC offset voltages,
and higher thermal stability.

Ultra Low Feedback
The very simple gain path has been configured for very low amounts of feedback.
This contributes to the warm and musical quality of the sound and the high stability
of the amplifier with a wide variety of loads.

High Power Output Stage
The amplifier uses International Rectifier Hexfets exclusively in all gain stages.
The output stage uses the highest Power Mosfet types available. The output stage
of each channel is capable of withstanding transients of about 3 kilowatts.

High Current Output
Each channel uses 10 Power Mosfet output devices. These devices are each
rated to handle 20 amps of output current. This output capacity is adequate to deliver
full power into 2 ohm loads, and the amplifier is completely stable driving 1 ohm or less.

Low Impedance Performance
The amplifier does not produce significantly higher distortion readings into low
impedance loads, unlike other amplifiers on the market. Watt for watt, the distortion
into 2 ohms is only slightly higher than that into 8 ohms.

Near Class A Bias
Each channel of the amplifier is biased at about 50 watts idle current. This is
a lot, and represents near-Class A operation for most listening levels, giving
depth and ambiance to its sound. The distortion curve is monotonic,
(distortion decreases with level) and is primarily 2nd harmonic at listening levels.

Thermal and Error Warning Indicators
Each channel has a LED to indicate over temperature or excessive distortion.

Modular Channel Construction
All of the active circuitry for each channel is on a single printed circuit board
mounted on the heat sink. This assures short signal paths, accurate wiring
placement, and allows for easier servicing. Outboard heatsinks provide the
necessary air circulation to allow the output devices to operate within their
specified temperature range.

Power Rating (To FTC Requirements)
200 Watts continuous average power into 8 ohms at any frequency between
20Hz and 20kHz with both channels driven at less than 0.18% THD.

350 Watts continuous average power into 4 ohms at any frequency between
20Hz and 20kHz with both channels driven at less than 0.18% THD.

IM Distortion (SMPTE)
1 watt to 200 watts into 8 ohms.....< 0.05%
1 watt to 350 watts into 4 ohms.....< 0.05%

IM Distortion (CCIF, Any Combination from 4kHz to 20kHz)
200 watts into 8 ohms.....<0.035%
350 watts into 4 ohms.....< 0.035%

THD + Noise at 200 watts into 8 Ohms (Typical)

THD + Noise at 350 watts into 4 Ohms (Typical)

Frequency Response at 1 Watt Into 8 Ohms 10Hz to 20kHz.....+0, -0.25dB

Power Bandwidth (-3dB).....3hz to 130kHz

Dynamic Headroom into 4 Ohms.....1.7dB
Signal to Noise Ratio, A Weighted 200 watts into 8 ohms.....> 100dB


Input impedance.....49.9k ohms
Damping Factor 20Hz to 20kHz.....> 700

Rise Time 5kHz, 120V peak-to-peak square wave, 20% to 80%.....1.5uS

Power Consumption (Continuous, Both Channels Driven)
200 watts into 8 ohms .....660VA
350 watts into 4 ohms.....1165VA

Power.....115VAC 50/60Hz
Chassis Dimensions 7 (178mm) x 17 (432mm) x 13 3/4 (349mm)
Maximum Dimensions 7 1/4 (184mm) x 17 (432mm) x 14 3/4 (375mm)

Weight.....44 lbs. (20kg)
Weight Packed.....50 lbs. (23kg)