Guest dogmeninreno Posted November 29, 2003 Report Share Posted November 29, 2003 I recently acquired a 2nd Adcom GFA555II Power amplifier and am considering using one on each AR9. Any opinions regarding vertical Bi-amping the 9's or bridging the amps will be appreciated. the 9's are used in a home theater situation and the GFA555II clips sometimes when using 100% dynamic range on the Adcom Dolby digital decoder. Thanks, Dale in Reno..... Link to comment Share on other sites More sharing options...
Guest dogmeninreno Posted November 29, 2003 Report Share Posted November 29, 2003 I believe the GFA555II is 325 watts per channel into 8 ohms and 800 watts into 8 ohms bridged. Dale Link to comment Share on other sites More sharing options...
ar_pro Posted November 29, 2003 Report Share Posted November 29, 2003 That's a great combination, Dale...I've used a pair of 555IIs both with & without LF equalization on our 9's with fine results. As I recall, I originally tried bridging the amplifiers, but had an increase in idle noise and a bit of a ground problem using Adcom's passive preamp. In the vertical biamp mode, those problems went away, and as a bonus, offered the possibility of dedicated LF equalization. That said, it sounds as if you home theater set-up might be a more demanding situation in terms of peak requirements...do the speakers sound compressed or do they distort at high levels? Link to comment Share on other sites More sharing options...
Guest dogmeninreno Posted November 29, 2003 Report Share Posted November 29, 2003 >That's a great combination, Dale...I've used a pair of 555IIs>both with & without LF equalization on our 9's with fine>results. As I recall, I originally tried bridging the>They only seem to clip (pop) at middle volumes with the dynamic range set on the Dolby decoder at 100% so the system is demanding somewhat of a burst of power. No distortion that I notice during normal passages at medimum power. You seem to feel the 9's and not really hear the bass response but it clearly could use more power? You know I just thought about the fact that the leads to the 9's are about 10 feet using 18 gauge wire. I think I will replace with 14ga copper and bi-amp as you suggest. Will I expect any problems with the GFA555II's?? What equalizar are you using for the lower end? Thanks, Dale in Reno..... Link to comment Share on other sites More sharing options...
Guest Bret Posted November 30, 2003 Report Share Posted November 30, 2003 Dale, The GFA-555MkII manual, page 6, bottom:"Although the GFA-555II can generate a substantially greater amount of power in the bridged mono mode than when it is in its normal stereo mode, it requires the use of loudspeakers the nominal impedance of which does not drop below 4 ohms."It goes on to say that they don't recommend bridged operation into speakers that drop "substantially" below 4 ohms, but they don't quantify "substantial." And it goes on to say what I said in an earler post that in bridged mode the load is "split" between the two amplifiers and: "a 4 ohm loudspeaker load will be seen by the amplifier as a 2 ohm load."And I've confirmed the amp is 200w/channel into 8 ohms, 325w/channel into 4 ohms, and 600 watts into 8 ohms when bridged.Bret Link to comment Share on other sites More sharing options...
ar_pro Posted November 30, 2003 Report Share Posted November 30, 2003 The 555IIs were completely stable in my experience, Dale...I never had a problem. I'm no longer using the Adcom amps, but the equalizer was an Audio Control "Octave", which provided 4 left & right channel adjustments in the AR-9's woofer region. They also manufactured an EQ that was called the "Richter Scale", or something like that...it was supposed to be used with subwoofers, but might also work with the 9s. Would it be possible to run your system to the same spl without the Adcom Dolby decoder? Could it be that the distortion is within the decoder at the 100% level, or that its output is overdriving your 555IIs? Link to comment Share on other sites More sharing options...
ninohernes Posted December 3, 2003 Report Share Posted December 3, 2003 I have an Adcom GFA-5400, the replacement for the 545II and I think the 5400 is much better. This also holds true for the GFA-5500, which is the replacement for the 555II. The main difference is that the power supplies have been made much larger, so distortion is much lower. They also use Mosfet transistors as opposed to the older bipolar ones. Mosfets are much warmer sounding, and they are more resiliant to heat, they can drive low impedances very well, better than the older ones. Link to comment Share on other sites More sharing options...
Guest dogmeninreno Posted December 3, 2003 Report Share Posted December 3, 2003 >I have an Adcom GFA-5400, the replacement for the 545II and I>think the 5400 is much better. This also holds true for the>GFA-5500, which is the replacement for the 555II. The main>difference is that the power supplies have been made much>larger, so distortion is much lower. They also use Mosfet>transistors as opposed to the older bipolar ones. Mosfets are>much warmer sounding, and they are more resiliant to heat,>they can drive low impedances very well, better than the older>ones.Thanks, Joe, I am running the 9's on 2 GFA555II's in vertical Bi-amp mode. I will check in to the GFA5500. What is the going price for the 5500? Thanks, Dale in Reno..... Link to comment Share on other sites More sharing options...
ninohernes Posted December 3, 2003 Report Share Posted December 3, 2003 Look here for some specs and to get a good Idea of prices. Go to a dealer though, it will cost less. http://www.audioadvisor.com/store/mfglisti...umbs=1&Filter=0 Link to comment Share on other sites More sharing options...
Guest jbangelfish Posted December 5, 2003 Report Share Posted December 5, 2003 There are several on Ebay and looks like $400 to $600 is enough for a used unit. I'm a big believer in used amps and components in general, huge savings over new and they last a long time. I don't need waranties with the cost savings considered. Get rid of that 18 guage speaker wire though, 12 guage off the spool speaker wire works well for me. You can spend a fortune on speaker wire and interconnects if you want but I can't believe that it can be that much better. Better maybe, but not hundreds or even thousands of dollars better. Just my 2c. Buy good stuff but you don't have to spend a fortune to get good results in my experience. Link to comment Share on other sites More sharing options...
Guest dogmeninreno Posted December 5, 2003 Report Share Posted December 5, 2003 >There are several on Ebay and looks like $400 to $600 is>enough for a used unit. I'm a big believer in used amps and>components in general, huge savings over new and they last a>long time. I don't need waranties with the cost savings>considered. Get rid of that 18 guage speaker wire though, 12>guage off the spool speaker wire works well for me. You can>spend a fortune on speaker wire and interconnects if you want>but I can't believe that it can be that much better. Better>maybe, but not hundreds or even thousands of dollars better.>Just my 2c. Buy good stuff but you don't have to spend a>fortune to get good results in my experience.I replaced the 18ga wire with good ol' home depot 14ga speaker wire at .20 per foot. Don't notice any difference but who cares, it has to be easier on the power amps? Dale Link to comment Share on other sites More sharing options...
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