Adcom 555 vs 5500 for subs?

Discussion in 'Archived Threads 2001-2004' started by Shade Watson, Jul 19, 2001.

  1. Shade Watson

    Shade Watson Stunt Coordinator

    Jan 24, 2001
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    Hi all,
    I am about to buy a used Adcom amp to power my two EBS Shivas. I have found that I can get the GFA-5500 for about the same price as the popular GFA-555.
    Does anyone have an opinion on which would be better. The 5500 is rated at 350W @ 4ohms x2 vs while the 555 is rated at 325W.
    Adcom's site has poor stats for the 555. However, when I compare the 555mkII to the 5500, the 555mkII looks better to my untrained eye. It has lower THD and moor headroom at 4ohms. The 5500 uses mosfet technology and weighs 9 pounds more.
    Even if the mosfet design is better, it wouldn't help with a sub application right? The 5500 is the current replacement for the 555 series. I would hope that the newest version is better, but we all know that a redesign is sometimes just to lower cost and not necessarily for better performance.
    Any thoughts on this are welcome, and remember, I'm asking about the 555 vs 5500. I don't have a deal for the 555mkII.
  2. Wayne A. Pflughaupt


    Aug 5, 1999
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    Katy, TX
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    Were we separated at birth or something? I have an Adcom GFA-555II powering my Shiva subs. I’ve been using it for several years now (even though the Shivas are only the most recent driver I’ve used in my subs).
    To answer your questions: The difference between 325 and 350 watts is not enough to make an audible difference, no matter what kind of speakers you’re talking about, subs or mains.
    Lower THD will not be audible in a sub. Any driver exhibits multiple times the distortion specs of electronics.
    MOSFET topology might make an audible difference in main speakers, for good or bad, but that may or may not make a difference in subs. Typically what matters in subs is brute force (read power) and dampening factor. If a MOSFET amp exhibits dampening characteristics that improve sub performance, that might make an audible difference in a sub. However, dampening characteristics often make only a subtle difference. Perhaps someone else who knows a lot about the whys and wherefores of the various amplifier designs can comment further.
    Of the things you mentioned for our consideration, I feel the headroom at 4-ohms specs are probably the most important, as it will make the difference in extra “umph” at high output levels.
    Perhaps this will help you determine the right amp for your needs. My Shivas are a sealed-design, connected for a 4-ohm load to my Adcom, which means each speaker gets 325 watts maximum from the amp. My listening area encompasses 6200 cubic feet. Generally the Shivas hold up even with the amp’s clip lights hitting, but occasionally the Shivas will bottom out. I have EQ’d the Shivas for flat response (the Adcom would probably never clip it I hadn’t done that).
    So, if your Shiva alignment is more efficient than a sealed design, and/or your listening area is smaller, either Adcom amp will work fine. If not, you may need a more power than this Adcom can deliver.
    Hope this helps.
    Wayne A. Pflughaupt

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