Adcom GFA-555 MKII Amplifier- Serviced

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General:
This is the legendary Adcom GFA-555II amplifier.

The GFA-555 was quite the amp in the 1990's and one of the top selling amps of all time. It is super powerful, yet it comes in a fairly compact and lightweight package making it easy for a single person to move around and put in place. This example was clearly well cared for and is in wonderful condition.

Sure there are are plenty of 555's on the market, but most were passed around from audiophile to audiophile and got beat up in the process and over time.

While the Adcom company we knew and loved is no longer in business, prices on the top models seem to be going up as audiophiles on a budget rediscover the brand. They are simple in design and use common parts so servicing them, if the need arrises, should be an easy task performed by just about any technician. 

This amp was just serviced in-house and its ready to be enjoyed. It also Includes its original manual.

SkyFi Cosmetic Notes:
The bottom of the left heatsink has a bit of wear and slight deformation. Light cosmetic wear is present on all surfaces.

SkyFi Technical Notes:
We completed some preventative maintenance on this piece. Heatsinks were added to the large transistors on the driver board. We replaced the electrolytic capacitors on the driver board as well. Bias was set to the Adcom service manual specification.

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:
Single Owner

Connections:
RCA line Inputs, a pair of 5 way binding posts

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:
Unit and Manual

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

Dimensions:
7.3 x 17 x 12.2"

Weight:
35.3 lbs.

Approximate Age:
1990

Link to Manual:
Click Here

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

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.