I picked up an Adcom GFA-555 II off of Ebay, which arrived today. I got it for $283 dollars, although they usually go in the $375-425 range. While I love a good deal, I am always concerned until the "deal" actually arrives. In this case I am VERY happy. The amp needed just a small amount of cleaning to look good, and most importantly... it SOUNDS good.

I spent a few hours listening to it through my B&W DM 602 S3s where it performed very nicely, and it will most likely end up powering them full time as part of my Home Office system. I also spent a short time listening to it in a bi-amp configuration on my Infinity RS 9 Kappas. I let the 555 II handle the upper ranges, while my 5802 was dealing with the woofers. The 9 Kappas are at their best when bi-amped, but I have been listening to the B&Ws for a few weeks now making it tough to judge how this arrangement compares to when the 5802 was pushing the Kappas on its own. Some more controlled listening is definitely needed to draw any real conclusions, but my first impressions of the 555 II are positive.

On a side note, I seem to be suffering from some kind of Adcom addiction. Not only have I bought this 555 II, I also have another GFA-545 II power amplifier and a GTP-500 II preamp/tuner on the way. When they get here I will have...

GFA-5802 Power Amp
GFA-555 II Power Amp
2 x GFA-545 II Power Amp
GFP-555 Preamp
GTP-500 II Preamp/Tuner
GCD-750 CD Player
GCD-575 CD Player
GDA-600 DAC

8 months ago all I owned was the 5802. Please, please don't let my wife see this thread!!!

Rob

....and, congrats.

We knew straight away, when you joined, you´d fit right in.

Thanks for ridding along and becoming such an important part of ST Rob.

How´s that basement of yours coming alomg?

Jorge

outstanding, and congrats!

i would expect that bi-amping with allow the Kappa's to be more open and give you a bigger and more well defined soundstage.

I haven't done much in the basement over the last few months, but it is much further along than I have updated you all on. I started coaching some youth sports teams and it has really eaten into my free time, so things have been sloooow. The good news is that my brother-in-law is visiting the weekend of April 12 & 13, and he is great with trim and moldings so things should start picking up again. We have been watching movies in the room, for a little while now, but the concrete floor and unfinished walls don't make for the nicest experience. I am hoping that by early to mid-summer things will be much forther along.

I own and enjoy a GFA 555 II as well and use it with DQ10s. I also have a 500 II so I can understand your fondness for them.

cubdog

Cool, a 555 thread. I think I'll add to this one.

I just picked up a Adcom 555 Pro power amplifier. When I powered it up, I could not hear the relay so I popped the top for a look. The outputs were heating up nicely so I tried some speakers and it works fine. I couldn't find the relay or is this one of the very few modern amps that does not have a relay? Interestingly, it takes 20 seconds or more for the filters to discharge after power off and all that time, it is still playing. I thought the power switch was broken!

Anyways, the 555 Pro appears to differ from the GFA-555 in having banana plug inputs and balanced XLR inputs. It can still be bridged and there is a switch for balanced and unbalanced input operation. The gain controls on the front panel require a screwdriver to adjust which is annoying because I like to go CD direct sometimes. And, the faceplate has holes for rack mounting. Not a heap of differences but enough to make the 555 a ROADIE.

Wow! I had almost forgotten about the "pro" model. BTW, none of the Adcom amps have relays on the outputs. Product literature says this is to eliminate the contact points in the signal path and supposedly improve sound quality. Not sure how much it helps, but it does mean that the speaker outputs will continue to provide power to the speakers until the energy stored in the power supply caps and transformer is depleted.

On a related note, I won an auction on Saturday for an Adcom GFA-555 (yes... yet another piece of Adcom gear). My winning bid was $234.00, which I think was pretty good deal. It should be here by the end of the week. I am really curious to -*test*-('") it head-to-head against the GFA-555II, and try to hear if their were any significant differences.

Rob

Very cool! Too bad we are not close or we could compare all three 555's side by side. Here is a pic of my Pro. Note the handles and the four resettable fuses that are in addition to the main AC fuse on the rear panel.

That Pro version of the 555 really does look the part, even if spec wise they are similar.

With usage and age every relay contact points degrades. No relays, no contact degradation, better sound.

Should I trust an amplifier with no relay? Hmmm....

I was listening to my 555 today and I thought the set seemed down on power. It could be the Sanyo Plus C-55 preamp. I'm just not that familiar with the C-55 and how it works. I think the C-55 has a linear gain control which means the know has to be cranked for power.

I'll have to try another pre that I'm more familiar with.

Well, it all depends of the amp electronic design...not only Adcom adopts that design.
One potential disadvantage of not using an output relay is that switch on and off thumps from either the amplifier itself or the signal source used are not so easily avoided, although they can be minimised by suitable choice of smoothing capacitors.

Many years ago most transistor power amplifiers used output coupling capacitors, and then there was much less danger of speaker damage, e.g. if one of the power transistors became shorted.
They also reduce damping factor at bass frequencies, have a small series resistance and are generally thought to be a "bad thing", but present designs reduces these problems of a coupling capacitor by including it in the overall feedback loop.

One more thing, cheap relays models - that almost any audio gear has - are introducing an inacceptable level of distortions due to improper contacts materials and/or mechanics.
Care should be taken when selecting the output relays. A high current model with silver contacts is definitely recommended, that's whay i'd change mine.