Adcom GFA-555 or 555-II?

[chadbang]

I'm suddenly in need of lost of power and Adcom amps always represents a good price-to-wattage ratio (Plus they're quality units, my GFA535 has been running non-stop for 10 years!).

Does anyone know of any preferences for choosing a Adcom GFA-555 or a GFA-555-II? I'll do some research, but I thought might find a quicker answer here. Thanks!

 

[Tedrick]

The original '555 is said to have better bass and to sound a little harder or drier in the treble. The Mk II was tweaked to make the treble a little smoother and less 'edgy,' but supposedly is just a touch softer in the bass. I have a Mk II that I used with Infinity RS-IIb's and have been very happy with its sound. It took a Forte amp that cost 2-3x the Adcom (when new) to knock the Mk II off its perch.

Be aware that, due to age, the output caps in these will need to be checked out by a competent tech and likely replaced. If these caps go south, they will leak on the PCB beneath them and cause problems, including some bad ones that can take out your speakers. But properly checked and serviced, these are both solidly built, good performing and sounding amps that can drive even very difficult speakers.

 

[SoCal Sam]

PCB mounted main filters is bad design. Also no speaker relay so Tedrick is right to caution about this amp taking out speakers.

 

[visiman]

How old before they go south? And how often should I look? I have never taken the cover off and have had it a few years.

 

[rroobbcc]

I own a whole slew of Adcom amps including both the GFA-555 and GFA-555II. My experience with the sound of these two amps is exactly as Tedrick describes it. When making a recommendation to someone deciding between the two I always stress that the person consider the character of the speakers they will be using.

For example, the 555II would be the better choice for most vintage Infinities. The EMIT tweeters of the older Infinities work better with this amp's smoother top end, while the sealed enclosures provide tight well controlled bass despite the amps slightly looser control. The triple-darlington output stage of the 555II is also a better match for the typically difficult impedance loads of the older Infinities.

Similiarly I found the original 555 a better match to my previously owned B&W DM602 S3s. The brighter top-end of the 555 worked better with the more muted output of the tweeters in the 602 S3s, while the 555s tighter bass control tightened up the bass output of the speaker's small woofer and ported enclosure.

Hopefully that helps you make decision between the two.

BTW, I have always understood the failing capacitor problem to be an issue with 565 and 585, but not the either of the 555s. I don't worry much about having no speaker protection circuit and relay. When powerful amps go bad, there is always a risk to the speaker regardless of fancy circuits.

Rob

 

[chadbang]

Thank you very much for your responses. That is exactly the knowledge I needed. I'd like to tame a little top end on my speakers, so the Mark II it is, if I go with the GFA-555.

PS. Failing capacitors are extremely painful. I had a Harman Kardon Citation 22 take out a pair of MIrages I loved. I was so pissed, I chucked the Citation 22 on the sidewalk in L.A., literally. I always felt bad because someone probably thought they had hit the goldmine when they found it. I didn't think about it until later that I should have put a "WARNING" sign on that g-d amp. Never thought much of it anyway, it had died twice on me before.