Adcom GFA 555 II

Don't do it! The GFA555 is already putting over 200 watts into each speaker! Bridging will make each amp "see" a constant load of 2 ohms or less! NO GOOD!  Distortion will double, as will current. Too much stress (heat) on the output stage transistors! Stick with ONE amp! If you desire louder SPL's get a more efficient pair of speakers (hint: JBL 100's).

Thank you very much  roberjerman1 for your advice I do have a few more set's of speakers that are more efficient to utilize for louder spl, but i'm kinda really liking the Maggie sound so maybe i'll step up to a larger model although i do like the set up as it is but got excited when i ran across a great offer on a 2nd GFA 555ii and decided to question the purchase as i am pretty new at this and have never ran any of my amplifiers bridged.

Agree with roberjerman, any bridged amp should not be used with a speaker having an impedance of less than 8 ohms.

daywalker702,

As I understand it, the Adcom 555 II amps were designed by Nelson Pass and are stable down to 1 ohm. However, even Nelson Pass has stated on DIY Audio that the Adcom 555 was not a great bridged amp.

https://www.diyaudio.com/forums/solid-state/53551-gfa-555-upgrade-substitutions.html?perpage=35&...

I also understand that Magnepans in general present a relatively benign and stable impedance load to amps of about 4 ohms without big peaks or dips.
Based on my experience driving my older 4 ohm Magnepan 2.7QR speakers with a stereo Adcom 555 MKII (200w @8 ohms and 400w @4 ohms) amp, I’d suggest a better solution would be a powerful class D amp.
I’ve used 3 class D amps on my Magnepans with all of them outperforming the Adcom 555 MKII. I initially used a ClassD Audio SDS-440-CS stereo amp (440 w/ch at 4 ohms), then an Emerald Physics EP100.2SE stereo amp ( 150 w/ch at 4 ohms) and currently a pair of D-Sonic M3-600-M monos (1,200 w at 4 ohms).
All 3 of these amps provided better bass response, a lower noise floor, a more detailed but still smoother mid-range/treble response and much improved dynamics than the Adcom.MKII in my system.  All 3 were also capable of very high volume levels in my spkrs without clipping or distortion (at levels far beyond my normal listening level during testing).
I’m fairly certain you’d notice similar performance improvements with a good class D amp driving your Magnepan MG-12QR speakers.
I have no associations with any class D companies; I’m just a big fan.
Tim

Huge Thanks  noble100  wow i didn't even think about checking out class D amplifiers, that opens up so many more options and the prices aren't too bad on the ones you listed above. I will be checking the local shops to see if they carry any class D amps at all just to get an idea of the characteristics and performance of them, if not i'll check with a few guys that i have dealt with here in Vegas to see if they have a class D in their collection that i can check out. Also can you please advise on why you moved on from the ClassD Audio SDS-440-CS and the pros and cons that you experienced with it.