Adcom GFA-555II Amplifier- Serviced

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General:
Large 200w amplifier with excellent build quality and sound. Serviced in house and functioning beautifully.

From Adcom:
The Adcom GFA-555 represents the most advanced thinking in audio amplifier design. At 200 watts per channel, it offers exceptional value and superior performance at a reasonable price.

SkyFi Cosmetic Notes:
The top cover has some scratches and scuffs. There are also some light dings on the other surfaces. The faceplate is very clean.

SkyFi Technical Notes:
This amplifier was serviced in house. We replaced the four electrolytic capacitors on the driver board and added heat sinks to the TO-220 diver transistors. The bias was set to service manual specification. DC offset is stable and within +/- 10mV of zero.

Brand Background:
ADCOM started in the 70s. Our first offering wasn’t amplifiers but phono cartridges. They were no ordinary cartridges; however, they were extraordinarily musical "moving coil" designs that extracted a lot of information from a record groove. These products were so successful that other companies asked us to begin making cartridges for them, too! And so, we became a manufacturer!

Early Electronics... ADCOM's first electronic product, the groundbreaking GFA-1 power amplifier, appeared in December 1979. It was substantially more powerful than most of its competition at 200 watts per channel and was one of the first "high current" designs available. . Again, it was an affordable and standout performer. Critical response was phenomenal and the GFA-1 became the "hot ticket" amplifier of its day, as did the successor GFA-1A.

Ownership:
Second Owner

Connections:
5 way speaker binding posts, RCA inputs, captive power cord.

General Sound:
Neutral sound with little to no coloration

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Just the Unit

Packing:
Will be packed using our highly developed in-house process and custom packing materials.Specs:
Power output: 200 watts per channel into 8Ω (stereo), 600 watts into 8Ω (mono)
Frequency response: 10Hz to 20kHz
Total harmonic distortion: 0.04%
Damping factor: 800
Gain: 27 dB
Input sensitivity: 1.75V
Signal to noise ratio: 110dB
Semiconductors: 42 x transistors, 2 x zener diodes, 13 x diodes, 2 x IC, 2 x diode bridges

Dimensions:
7.3 x 17 x 12.2"

Weight:
35.3 lbs.

Approximate Age:
1985

Link to Manual:
Click Here

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - Speaker Cables - Better

Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect the PCBs for discoloration from resistors or transistors that may have been running hot. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a controlled power on sequence using a Sencore safety analyzer to monitor current draw in real time. Once the amplifier is determined to be safe to operate, we connect it to full AC mains for function and power testing. We connect the speaker outputs of the amplifier to a Sencore PA81 Power Analyzer which acts as a dummy load, DC offset monitor, and oscilloscope interface. We start with a low level 1 KHz test signal at the amplifier's input and slowly increase its amplitude while monitoring the output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping.

At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance. If the device under test has both balanced and single ended inputs they are both tested at this time.

We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier's frequency response characteristics.

This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench, we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum. This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when the unit has fully come up to temperature.