Channel High Power

Adcom 5500 2 Channel Power Amplifier

Adcom 5500 2 Channel Power Amplifier
Adcom 5500 2 Channel Power Amplifier
Adcom 5500 2 Channel Power Amplifier
Adcom 5500 2 Channel Power Amplifier
Adcom 5500 2 Channel Power Amplifier

Adcom 5500 2 Channel Power Amplifier    Adcom 5500 2 Channel Power Amplifier

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. 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. 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. All audio elements of the amplifier are Power Mosfets Even the input transistors are power devices, capable of as much as 2 amps of current by themselves. The transconductance characteristic of Mosfets 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 Mosfets are sonically superior to the Bipolar transistor, delivering all of the muscle of Bipolar circuitry with the sweeter qualities found in tube equipment. Most high end amplifiers have at least 5 successive gain stages associated with their signal path. 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. The output Mosfets 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.

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.

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. 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.

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. 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. 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 output: 200 watts per channel into 8? Frequency response: 10 Hz to 20 kHz.

Total harmonic distortion: 0.02%. Signal to noise ratio: 100 dB. Dimensions: 7" x 17" x 13.75 (178 x 432 x 349mm). Weight: 57 lbs (25.9kg).


Adcom 5500 2 Channel Power Amplifier    Adcom 5500 2 Channel Power Amplifier