GFA-555 & GFA555ll

hydrostream

Is there a big difference between the 2 amps would i be able to
use a 555 and a 555ll in bridged mode to power a set of RTi12s?
thanks

heiney9

Do a search I already wrote a very lengthly post on the subject.

The short answer is no big difference. Yes, you could run them mono but it's not nec. as they are powerhouses in stereo mode and you tend to lose some audio quality running a stereo amp in mono config.

Either one will give you all you need and more in stereo mode unless you are a DJ or something trying to fill a very large room at deafening levels.

george daniel

+1 on that,,Having owned two 555's,,I prefered to run them in stereo. Good luck,,enjoy and have fun.:)

hydrostream

I have a onkyo 805 with 2 RTI8 CSi3 center with 2 T20s for
surrounds and PSW10 sub.
I had a GFA-545 running the RTi8s and got it dialed in pretty
good.
Then i picked up a GFA-555ll and now thats running the 8s but
it seems like just a small improvement. I was thinking it would
be like nite and day but its not. Do you think maybe i should have
it checked out as far as the overall performance?
Is it possible that its not up to snuff?
jerry

george daniel

I would not expect a "nite and day" difference between the two,as they are both pretty solid performers,, the bass with the 555 should be a litter better and somewhat more pronounced and controlled with a little better headroom.If you went with 565 mono's,,well that would be a different story,,the 545 is a solid little performer,,with my favorite being the smaller 535,,,now thats a sleeper.;)

hydrostream

Do you think the 555 will power a set of RTi12s my local tweeter
has a pair that i feel is a good price.
It seems like all my upgrades are just coming up short.
jerry

engtaz

Nelson Pass, I believe said that they did some minor improvements. Not much but one of the hind site things where "we should have done it this way"

engtaz

ben62670

hydrostream wrote: »

Do you think the 555 will power a set of RTi12s my local tweeter
has a pair that i feel is a good price.
It seems like all my upgrades are just coming up short.
jerry

The question should be is there any normal home speakers that the 555 can't power?
The answer would be no.

hydrostream

Ok great looks like i have to tell the wife were going to tweeter
i may have to give her some extra loving.
thanks

heiney9

hydrostream wrote: »

I have a onkyo 805 with 2 RTI8 CSi3 center with 2 T20s for
surrounds and PSW10 sub.
I had a GFA-545 running the RTi8s and got it dialed in pretty
good.
Then i picked up a GFA-555ll and now thats running the 8s but
it seems like just a small improvement. I was thinking it would
be like nite and day but its not. Do you think maybe i should have
it checked out as far as the overall performance?
Is it possible that its not up to snuff?
jerry

I actually slightly prefer the 545. I think it has a little bit more finesse than the 555, but you can't go wrong with either and moving from the 545 to 555 was a lateral move and then not much if any improvement.

I'm sure the 555 is fine not much difference between the 2 amps if you are only running RTi 8's. You might notice a difference if you were running a really hard speaker to drive. Otherwise they are very similar.

heiney9

engtaz wrote: »

Nelson Pass, I believe said that they did some minor improvements. Not much but one of the hind site things where "we should have done it this way"

engtaz

I'm curious where you heard this and what you are referring to? I've read a lot from Nelson Pass an spoken to him (via e-mail) he is very aloof and cryptic when speaking about Adcom products and the exact role he played in designing the amps. He had a general dislike of their in house engineers messing with the prototypes he was hired to design (especially the series II amps). So the last part of your sentence makes no sense.

He stated they made the series II amps much more complicated than they needed to be. He had very little if any extra input into the series II amps. They were still very similar to the original series as an overall design of his.

H9

P.s. Not to mention you post is barely in English . Take your time typing so I can understand it.

engtaz

It was in one of the forums that he post to. I can't remember where the post is. Yes I agree he is cryptic in his answers. This is going off of memory (that's scary). They only changed a few things, nothing major. Most changes were due to the "I should have done it this way, type of thinking".

engtaz

heiney9

engtaz wrote: »

It was in one of the forums that he post to. I can't remember where the post is. Yes I agree he is cryptic in his answers. This is going off of memory (that's scary). They only changed a few things, nothing major. Most changes were due to the "I should have done it this way, type of thinking".

engtaz

I see. Thanks for a little more explanation. Personally, I still prefer the series (I) amps if we are talking about the 535;545;555. The 5800 is a nice unit and if I wasn't hell bent on getting a Pass Labs Aleph, I'd seriously consider a 5802.

555 II has larger cooling capacity; slightly larger transformer; nicer Teflon coated input terminals; they are capacitor coupled rather than direct coupled (IMO, less desirable); they also use a Darlington output configuration which allowed them to boast it could drive a 2 ohm load without cutting out; also had a higher class A bias.

IMO, and NP seemed to indicate this too, they added things to make the design more complicated when to older design was just fine. I'm a big advocate of K.I.S.S. and the addition of coupling caps and the Darlington output config. just seemed to muck things up.

The series II amps are still excellent, don't think they aren't. Many reviewers felt the series II sounded even better (take that FWIW) I just prefer the sound and simplicity of the original series.

H9

lakesailor

I once new a guy who worked at Adcom. Basically Heiney’s comments are spot on. The fellow I knew from Adcom told me that they wanted to make the GFA 555 more stable at lower impendence loads in order to cater to the then very popular planar speaker market.

Keep in mind at one point Stereophile magazine did a subscriber survey and discovered that planar speakers (e.g Maggies & other ESL’s) were very popular amongst subscribers.

Adcom was very successful with the GFA 555 Mark 2 and the amp went on to receive rave reviews and even out scored the original GFA 555 review in Stereophile magazine. As Heiney points out, the Mk.2 did become a less reliable unit (long term) compard to the original 555; mostly because the coupling caps can require replacement and of course the original 555 did not use them.

I have owned both and personally prefer the Mark 2. The Mark 2 version did have upgraded connectors and later models (like mine) also offered a removeable power cord; a nice touch. For some; the fact that you could get the Mark 2 in white was also considered a good thing.

Either way GFA 555 or the GFA 555 Mark 2, both are amazing amps for the money and can pretty much drive anything. If you have Planar speakers or anything else low impedance likely the Mark 2 might be a better bet.

As for Nelson pass the only comment I have heard was that Adcom would continue to “improve” his products until they ended up having to many parts and becoming to expensive to build and they would re-hire him to start the process all over again on a new component.

Best of Luck.