Adcom GFA 555 amp upgrades

Hi. I own an Adcom GFA 555 amp, and I'm wondering if its practical to upgrade the amp to the standards of the Adcom GFA 555 series II (or better). Love the power and flexibility of this amp, as it powers my 4 ohm Kef Reference 103/4 towers with ease, but you know how it is, we audio junkies are always trying to squeeze a bit more fidelity out of our gear. Many thanks! -David
You might want to call Musical Concepts. They specialize in Adcom Mods plus more. Been around for many years and have gotten some very good reviews.
Joe Nies
My dad got a gfa 555 years ago and it was the one that originally gave me my Audiophile epiphany. He still uses it and it's going strong. I don't know if you'd really gain anything by going to the series 2 though. What about that one designed by Nelson Pass (I can't remember the model)
The old 555 is a decent amp but I wouldn't do a factory upgrade, as you'd be better off selling what you have & buying the different version.

If you really, really want to hang on to this amp & price isn't your main concern, you can get someone like Musical Concepts to mod it.
Musical Concepts modified my GFA555 many years ago with great results. I eventually gave it to my nephew who loves it. John at Musical Concepts told me that the Mark 2 version was warmer and more laid back but had less resolution and weaker bass, so he thought it was not an improvement over the mark 1, although some people might like that sound. The question is whether it is cost effective to do a complete mod/upgrade on such an old design, when you can buy a better amp for the price of a complete mod/upgrade. That is unless there is something about the GFA555 you really like and would like to keep but just improve upon.
I had a Mark I and Mark II. I had the Mark II modded by Musical Concepts since it was a later model. Much improvement. However after much comparision I found the original unmodded Mark I to my preference.
you'd probably be better selling the mark 1 and buying the 555 mk2s on the used market if you want an Adcom with a larger supply. But even then the 555 mk2 is not optimal.
Hi, just bought a used Adcom GFA 555. I believe it's the original model. Mark 1 is it?  Does this amp have an impedance switch on it, or does it just adjust impedance according to the speaker load? My first time going with 4 ohm speakers. Thanks.
No sir, there is no impedance switch.  That's for weaker amps or girlie receivers that have no jam.  It'll be fine with your 4 ohm speakers.

On the other hand, you might want to consider the age of the 555.  Shine a light inside the amp to see if there are any bulging or leaking caps, as a 30+ year old amp can develop issues.
If you are truly a fan of what Nelson did with Adcom,  the 5802 is by far the best sounding Adcom amp.... Keeps that Adcom flavor, but more refined.  
I was an Adcom dealer long ago, I agree the 5802 was by far their best amp. It had that “French dark roast” character of the rest of the line but with a refinement not in the others. I think Audio Amateur had a regulator board that improved the 555 in much the same direction as the 5802, but never heard a “triple nickel” with it installed.
My first experience in high end audio 25+ yrs ago was an Adcom CD player, Preamp and a 100 w per channel Adcom and 200 w per channel Adcom bi-amping a pair of Definitive Technologies BP 20's it was an amazing sound for the money. I still use it today for stereo in my home office 25 yrs later no regrets no need to upgrade.  I'm currently building a home theater in our new home & old habits die hard. I Auditioned some  Sandy Grosse creations the Golden Ear Triton 1 and surround speakers for our 9 channel surround ATOMS system. Already purchased the last OPPO UDP 205 I could find & 4 Goldenear Invisa 650 ceiling speakers.  I've been consider ADCOM again for AMPS but it seems they have fallen behind in development compared to other brands. Any feedback regarding the multi channel ADCOM amps such as the GFA-7605, 7607, 7705 and 7707 would be appreciated. I understand the 7705 and 7707 need a forklift basically to carry and will run hot and make the power meeting spin like a ceiling fan.  Considering other better options any recommendations?  
The 555 is one of those pieces of hi fi that are just about perfect.  I'd leave it alone.. Nelson knew what he was doing when he designed it and if modding is a must that is the man I would talk too.