ADCOM GFA 555 II - Any Thoughts?

[Lasareath]

Hello All,

I was thinking of buying a Pair of ADCOM GFA 555 II's and running them in Mono for my 1.2TL's

Does anybody have this setup already?

Does anybody have any thoughts or suggestions?

I heard that some Adcom's have some issue with their transformer leaking or something like that.

TIA,

Las

[DarqueKnight]

I have owned three GFA-555 Mk II's. I still have one powering my rig at work. I once hooked up a pair of bridged (and strapped) GFA-555 Mk II's to my 1.2TL's. I was not impressed with the sound.

I have never heard of the "transformer leakage" issue you mentioned. Sometimes the electrolytic capacitors will dry out with age (after 15 years or so). You can usually tell if your electrolytic caps are going bad because you will have problems with humming.

I do not recommend running the 1.2TL's with bridged GFA-555 Mk II's for the following reasons:

1. The distortion and sonic character of the amp changes in bridged mode. I would characterize it as a noticeable loss of detail and an additional "hardness" to the sound.

2. The GFA-555 Mk II is specified for use with 4 ohm or 8 ohm speakers in bridged mode. When you flip the switch to bridged mode, the amp only "sees" 1/2 of the speaker's actual impedance. For the 1.2TL, which is a 6 ohm speaker, the GFA-555 Mk II would see an effective load of 3 ohms in bridged mode. The Adcom GFA-565 mono amps would be a better choice.

The 1.2TL's manual and sales brochures state that it is "compatible with 8 ohm outputs". This means that the impedance is very stable over its operating range and has a load variation characteristic as good as or better than 8 ohm speakers.

[Lasareath]

Ok, Thanks DarqueKnight, I will keep an eye out for a pair of Adcom GFA-565's.

What are your Ultimate choice for amps for the 1.2's?

Thanks,

Las

[DarqueKnight]

Pass Labs x600.5 mono blocks...but these are balanced output amps, so they aren't strappable into a common ground configuration...which means I would have to use the dreaded AI-1 interface adapter.

Some people have reported audible diminished performance with the AI-1 in place and others have not. Polk says that the AI-1 was designed as a "workaround" and may diminish detail. "Workarounds" seldom provide optimal performance. I might have been one of the lucky ones who did not realize diminished performance with the AI-1. However, I did not want to take a chance on buying an expensive amplifier and finding that I did not like the sound with the AI-1.

My second choice amp is what I have now, Parasound JC1 mono blocks.

[Lasareath]

My second choice amp is what I have now, Parasound JC1 mono blocks.

There are 3 Parasound JC1's for sale right now on ebay. I was looking at them, they look really nice.

I guess you have two of them?

[DarqueKnight]

Parasound JC1 Mono Amplifiers - First Impressions (http://www.polkaudio.com/forums/showthread.php?t=42773)

[jdhdiggs]

Lasareath:

I have a pair 565 mono's packed and ready to be shipped if you are at all interested. If so, PM me.