Power. Ability to run for long periods at high levels with no complaints. Yes, they do thump when turned on. But if you have never listened to music live, so does the equipment of the pros.

I'm in the process of soldering the grounds and replacing the cords on my amps. If this is a weakness, I guess this is it.

I bought the amp used from ebay. It was my first step up from "mid fi" I since bought another one in preperation for some larger speakers. I use a 555II preamp also. Yes, it has awesome power, we all know that. My Infinity rs 5001's come alive with this amp. If there's a weakness in this system, it's the speakers. Yet I can detect a 3d soundstage even with the small speakers. The amp works effortlessly to provide this. It does get warm when driven at high levels, but if you get a muffin fan and rheostat to slow it down to sub sonic speeds, the amp stays very cool even when driven hard with my DVD player. The way I see it, the amp is superior in all ways to our hearing on paper and in life. While I have not listened to Krells, or Mark Levinsons and such, to compare, I think that in the price range of these amps I cannot see anything else that even compares. My friends are now buying Adcom amps to start their systems "again" after listening to my 555II system. Being a mechanic, I very well know the difference in quality of things. I also know that at some point it becomes nonsense. It all boils down to how much money you got and how much you want to spend. These things are a steal. Watch ebay and see how long these last. They are gone in a snap almost without exception.

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Harman Kardon PM 660 of years past.

Amazing power, including a capacitance reserve I have yet to even come close to fully exploit. Great value, durability and nice looks. Bridging a pair of these provides an electrical force that borders on insanity.

Getting harder to find, as most people who own them realize they one of the finest 2nd room, true 2-channel (seperate power supplies for each channel) hifi power amps that don't require a big new, investment... they're being retired as opposed to resold. I guess that's not a weakness, aye?

My first real hifi purchase, I can't say enough about how much it helped me learn to appreciate quality, well-recorded music. The effortlessness and ease that this amp simultaneously reproduced the more subtle details and huge transients provided me with one my most dramatic audiophile epiphanies. Quality big iron is worth every penny. I have since moved on to a pair of Citation 7.1's, and while better in most everyway, they only act to remind me of the incredible value the Adcom 555 II's provide. These classic amps will impress all but the most discriminating ear, and are bult like tanks - they should provide you almost infinate long term stabilty.

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Various Rotels, a Parasound and a large array of sh-- solid state recievers from the big chain stores.

Clear Highs, good mids, and strong controled bass. Lots of power and the avaibilty to bridge and change ohems (very flex per application)

None other that kind of ugly but it does make it look tuff

WOW!!! I was pushing a set of JBL S312 with a yamaha htr-5280 (110 X 5) and it just sounded like something was missing. Sure it sounded good but there was that depth missing to the music not there. So I stopped at a speciality store and the sales man introduced me to the Adcom line, he told though if i want the max for my buck to try and find a used adcom gfa-555 mkII. So i went home, got online and checked out what other people had to say about the amp and for the most part most people were pleased with it. I found one in the paper in mint condition and bought it for $400. Brought it home and hooked it up and wow what a difference. I'm no pro at this stuff but i do know what i'm doing. I hooked the amp up with Monster Cable Reference RCAs and a set of Monster Z-Series to my mains. The music is great. When i first thought about upgrading i wasn't sure whether i would hear a difference going from 110watt to 200watt but there was a huge difference. I would say it didn't effect my highs as much as it affected the bass and mids. I bought the JBLs but were to the point that i figured they just didn't have what i was looking for but after putting this amp on it the JBLs are staying. Adcom definity has something special in this amp.

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Yamaha, JBL, Bose, Mission, Denon, Polk

Tremendous power and agility, the Adcom 555 Mark II is one of the most durable and musical amps from its era, and a bargain at its used price of about $400.(which hasn''t changed in the past 10 years).

Oddly, I have occasionally found speakers with which the Adcom simply did not work. I suspect this is the reason that it sometimes gets a bad review. When it doesn''t match, it''s awful! When it does, you can''t buy anything for this price that comes close.

Maximum Bang for the Buck. I''ve used the 555 Mk. II for more than 10 years, both as a stand-alone and as the bass amp in bi-wired systems. You could think of it as the "poor man''s" Krell. It''s interesting that the used price for this amp hasn''t dropped significantly in the last decade, proving its worth and desirability for a wide range of systems.

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Muse stereo and monoblock amps; NAD; B&K; Eagle 2a.

power

No detail, no soundstaging, no imaging, flat sounding with no excitment.

What can you say? I have had this unit for about 10 months. It has power, and that''s about all! Terrible soundstage, smeared detail, the music sounds like it has a blanket over it! Great amp for people who don''t have an audio ear. As long as you don''t compare the amp to anything else, it does not sound bad. I did''t realize how bad it sounded until I replaced it with an Aragon. If you want good sound, bypass this audio fiasco and pursue something else!

cheap and reasonable sound

I connected 555 II with exposure 17 and EPOS 11 and audioquest indigo biwire cable CD marant 6000 OSE with Kinble PBJ .They are good matching with small band , folk , some audio phile CD like mary black, amanda mcbroom , jim croce , crytal gayle.

powerfull bass great highs built like a tank

none that i could think of

i had this amp for almost 10-yrs,within the last yr i had purchased the sister pre-amp. thought about new equiptment,but this still rocks ilove it and would recomend to anyone on a budget who loves two channel sound

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before i found adcom,used dennon and kenwood,no comparison.i love my adcom setup,would only move up to the gfa5802

Definition

None

I have two of these amps Mono powering Acustat 2+2's (these speakers are such power hogs 200 watts per chanel was not enough).

I previewed many 7-8 Amps priced up to $1800 and could not find anything that was as clear and detailed as this amp.

I am confused at the mediocre reviews here. There might be better out there but it will cost you over 2 grand...

Used these go for $450 tops... great deal... they were $1,000 new 92'- 95'

If someone knows what amp sounds better for $450 for 200 watts a chanel let me know... I would be first to give it a try...

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Phase Linear Dual 500, Carver 200 Watt Per chanel

Huge power reserve and low end

harsh brittle treble, forward mids

A bargain amp that will put out trmendous power but has a very foreward sound, expecially with my Adcom GFP 565 pre-amp.( the 565 has perhaps the best and most quiet phono section ever made, the preamp itself is very neutral and quite revealing) Low volume listening is very good, but when you turn it up the shrillness is more than you can stand. I've used this for over 5 years and had a 555 before that, I am looking for a better amp right now, a step or two up sound wise and price wise. My first one blew out the first week, they replaced it with no arguments though. I agree with the other poster, you need to solder all clip on terminals, expecially the main ground one, and to eliminate hum in the one channel separate the internal wiring low level and ouputs away from the power supply wiring. It's a good entry level amp, but that's about it.
greg

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555 amp, which is quite similar

Big power & soundstage, high current

unforgiving of weaknesses in other components (this could be considered a strength!)

I manage a retail home theater store and hence have the opportunity to test many different amps. I also get first pick on the second hand market!
The Adcom 555MkII stood out to me at the time it became available. It suits my taste and gives the high current power that my Energy C-6 speakers demand. My major weakness until recently was the use of a Yamaha RXV-2095 receiver as the pre. I'm very happy with this receiver for movies, but now bypass it for music. Yamaha is bright at the best of times and when amplified produces very shrill and shouty mid-highs unless mellow sounding speakers are used (which the Energy are not). I'm now using a humble little NAD C320 as my pre-amp with surprisingly good results. Resolution and imaging are great, with the sound seeming to be a little more distant with other amps I've tried.
I suggest using this amp with a mid-priced pre amp with discrete circuitry (no IC's). In other words, all analogue. Furthermore, the use of a good D-A Converter from your CD player, with possibly even line a conditioner/ filter between the pre and power will certainly bring out the best in the Adcom, as I've found out. It can still be used with a digital based pre-amp/processor, with powerful results, but it will lack any kind of refinement.
The opportunity for a second unit has just come up and I'm going to buy it without hesitation. Highly recommended.

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NAD 218THX, Harman Kardon Signature 2.0, Yamaha MX-1/1000