I have several Adcom GFA 555's and I must say I enjoy them alot. I have them running my Infinity RS KAPPA 9's. These are very difficult speakers to run for several reasons: Very low sensitivity (89db for evry one watt for one meter), The impedence is very inconsistant in the expanded mode (.8 to 4 ohms), In the normal mode they are (1 to 4 ohms). I have had my amps to an impedence as low as .5 ohms for an extensive period of time. I have only blown a rail fuse once. (1812 overature was palying while the amp was in a .5 ohm load, Then came the cannon Blast and pop went the fuse)
The sound quality of these amps is very impressive. I have owned everything from McIntosh to Krell and this stands very class and even surpasses the performance of the higher priced amps. Thanks Adcom for the outstanding, Bulletproof, great sounding product.

I've owned this amp for over 8 years. While it will not compare to likes of Classe or Bryston it is also half the cost. I have found this amp to be a workhorse. I currently have it connected to some older Infinity Reference Studio speakers which present a demanding 4 ohm load and are extremely power hungry. If you are looking for an audio enthusiast power I would recommend Adcom. If you are considering the jump to audiophile and the associated cost then Classe would be my choice.When considering price and performance this amp is 5 stars. On performance alone 4 stars. Consider the rating 4.5 stars.

I bought this GFA555 in 1990 and it is still performing wonderfully. The sound it produces is detailed, and transparent. I've used it to power full range Polk Audio SDA's and a 12" home sub I made myself. This amp is bulletproof! I know there are better amps on the market, but yer name would have to be Rover to hear the difference. Used GFA555's can be found occasionally found for very reasonable prices occasionally on auction on-line sites such as E-Bay. If your lucky enough to see one, BUY IT! One final observation, Adcom used to use TO-3Bi-polar transistors on these amps and has since switched to those little chicklette MosFets. Whats up with that??????

Depth and control

none

I have had this amp for quite a while now driving my Maggie MGII Cs. This amp has always provided depth, control and provided a wide soundstage.

I have always been impressed with this amp. Now that I am changing my speakers to the JM Labs 905 and Velodyne HGS-12 combo, I am anxiously anticipating the sound.

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luxman amps

Strictly a Little League Amplifier. I'm driving a pair of Magnepan Q1.5r's that I'd sooner sell my first born then part with. Although the speakers sound excellent, I know I'm gonna get a lot more mileage out of upgrading to an Aragon 8008 st, or Bryston 4, maybe a smaller classe'. I've got the speakers bi-wired with monster cable, and bi-wired at the amp end as well. I auditioned the Aragon 8002 on Saturday on the Maggie Q1.6R's and was blown away!! I can't wait to upgrade!!!!

Unbelievable power, crisp, distinct sounds

capacitor burbs after shoutdown, apparently its ok, just different from what i'm used too

i purchased this gfa-555 amp and a gfp-500 tuner/preamp off ebay after i decided to split my current Audio/video system. i have Phase-Tech 7t fronts and was using Klipsch hersey's for rears. Well just for fun i hooked up the phase tech's to the adcom and WOW, the sound was incredible. these speakers never sounded like this when i had them on my Sony str-1015.
i haven't hooked the klipsch to the adcom yet, but i'm sure the sound will be awesome. I would highly reccommend the gfa-555 for anyone looking to listen to music the way it was intended!!!!

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none of this quality and power, pror to this i was using a sony str-1015

VERY low impedance capability

Annoyingly loud on/off thump-click

This is very good subwoofer amplifier, and at the super low prices on ebay you just can't pass it up for this purpose. It is currently driving a 2.8 ohm nominal load in stereo and even at relatively high power levels the amp remains perfectly stable and retains excellent dynamics and low distortion. Unit does get a bit warmer than I think is appropriate after sustained(more than an hour) high power use. I am going to purchase 2 fans to mount to the heatsinks to provide better cooling. I am overall very happy with this beast, and at 2.8 ohms it puts out almost 400 watts/channel so I do think that qualifies it as a beast! I have not nor do I intend to use this on my JM Lab mains so this review only pertains to it's slave use as a sub amp. FYI, the subs I am using are two 10" Kicker Solo Baric S10c 2 ohm subwoofers, actively crossed at 80 hz with the towers. Oddly enough, in a well damped ported enclosure tuned to 25hz these sound as realistic as any high end subwoofer I have heard even in the 2k mark, and in the brute force area--they measured 138 db max at 34hz in a 12x11x7'2" plaster/lathe walled room. It would appear they have amazing dynamic range ability, I do see why these were marketed as car audio SPL woofers, it does not even look possible for two 10" speakers to reach such high levels. My ears were actually in pain, a bit of overkill if I must say so. Too bad I'll never have use for more than 115 db of that at any point. I did manage to get the clipping LEDs on the amps to flicker for like 1/10th of a second while testing max SPL. I do find that a much better value is to be had by picking out certain car audio sub raw drivers. My personal favorites are the PPI carbon fiber cone(approx. 300-350 each) but they do not have the ability to go very low because of high free-air resonance and I listen to alot of newage which just does not sound good without a flat response to at least 30hz or so. The solobarics(10"-approx. 220-250/each)(older round version(c and d series)) sound the second best IMO and go very low in a ported enclosure. Do not even consider the newest versions that are square, these forgoe quality with higher SPL ability. Sound too undefined/coarse for any serious audiophile to ever consider. The high end Focal car audio subs sound even more amazing, but at 600 dollars for a single 13" that is sort of defeating the purpose of a DYI sub.

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Pioneer Elite, Denon, Onkyo, etc.

Well built, a work horse, sounds great

none

I've had my GFA-555II since 1990 and it's still working great. Never once, have I had any problem with it. I use it to drive my B&W Matrix 802 speakers. These speakers require alot of power to drive, but the 555II never failed me. The sound is very natural. I can listen to music or anything else for that matter without fatigue. I'm sure there are better amps out there, but not one that can produce audiophile quality sound for 1/3 the cost.

Power

For the price none.

I recently purchased a GFA555 and a Parasound HCA THX 1500A at the same time to compare which one I would like to run my Monitor Audio Silver 9i's in my home theater set up. Both amps run similar power with a slight edge to the Parasound 205 versus 200. First of all these amps sound nothing alike. The Adcom is a brighter then the Parasound. I found both amps would drive my speakers with ease. The long and the short of it is I kept the Parasound but for the money the Adcom is an excellent amp that is capable of running any speaker. I found both amps to be excellent and kept the Parasound because I liked the warmer sound and the fact that it meets THX power requirements.

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Parasound HCA THX 1500A

Musically, a very capable amplifier, however, I don't know
what it's original price is. Mine has the nice heavy duty metal covered transistors, so I think it's the better of the
versions put out

Very poor bass control

For an Adcom, not too bad...usually Adcoms' kill my ears
Using it in stereo with a pair of Dynaudio Audience 5's
should bring out lots of bass, however, there seems to be a large abscence (even comparing it to the 50WPC micro power drive!) However, it's not a bad amp, but nothing to write home about.

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McCormack Micro Power Drive, Mccormack DNA.05 DLX
ADS R4 receiver