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  1. #1

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    Default Adcom GFA-555 (original?)

    Just traded my CC-300 + klipsch sound dock for this amp in minty condition.

    Thoughts on this model? It's not the II, and I have no idea what the difference is.

    Speaking of which, I need to take that CC-300 off the for sale list
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  2. #2

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    My limited knowledge of the 555 is that it's a pretty good sounding (I can attest that it indeed is) amp for the $, and is rock solid dependability-wise (so far, so good). Judging from what they bring on Agon, ebay, and the FM here they seem to hold their value pretty well, and IIRC they're a tad more highly regarded than the II. I've only had mine for a few months but I'm quite pleased with it.
    2 channel rig: MMF 2.2 turntable, Adcom GFP-715, Adcom GFA-555, Adcom ACE-515, Carver M-1.0t, Denon 5900 CD/SACD, SDA-SRS 2.3s (Zardoss modded), AQ Diamondback & King Cobra IC's and AQ Type 4 speaker cables

    HT rig: Panny 50" G20 plasma, Directv DVR, Insignia BRD/DVD/SACD/DVD-A, Denon AVR-890, Fronts: Polk Monitor 70's, Rears: Deftech Mythos Gems, Center: Polk CS1, Sub: Polk PSW-505

  3. #3

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    +1, I have to agree raffi, seems like more folks who have had both models prefer the original design. Not that the II's are slackers, sometimes, old things are better.

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    Sounds good. I made a good deal then. He wanted my CC-300 (removed from flea market now) and another piece of equipment. Made out pretty well.
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  5. #5

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    The 555 is a solid amp. It is 2ohm stable stereo, and 4 ohm bridged
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
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    Ben knows his Adcoms better than I. I will add that I am also the owner of an original GFA-555...the gift that keeps on giving. Get yourself a good pre-amp and you'll be surprised just how clean this piece can sound.

    I've been rocking to mine for a couple of years now and am really only thinking of upgrading my pre to the GPA-750.

    And enjoy!

    cnh

  7. #7

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    I've got a Yamaha pre, NAD 114, and Rotel RC-972 to play with the amp, hehe.
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  8. #8

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    I have one. It is a solid amp!! for the $ cant beat it.

  9. #9

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    Hooked it up to my Rotel RC-972 pre, DV-59AVi source, and RTi70 speakers for a test and even the guy selling/trading it to me was impressed.
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  10. #10

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    Quote Originally Posted by ben62670 View Post
    The 555 is a solid amp. It is 2ohm stable stereo, and 4 ohm bridged
    and a Nelson Pass design which i don't think the 555 II is

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    Quote Originally Posted by pitdogg2 View Post
    and a Nelson Pass design which i don't think the 555 II is
    That's what I heard. What's the advantage to it?
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    Quote Originally Posted by nguyendot View Post
    Just traded my CC-300 + klipsch sound dock for this amp in minty condition.

    Thoughts on this model? It's not the II, and I have no idea what the difference is.

    Speaking of which, I need to take that CC-300 off the for sale list
    It's in the archive, I've posted it atleast 1/2 dozen times in the past 2 years. Do a search and you will find all the info and more about Adcom 555's.

    I am not posting it again, I thinks 6 times is enough.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  13. #13

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    Quote Originally Posted by pitdogg2 View Post
    and a Nelson Pass design which i don't think the 555 II is
    Not really. The 555II was just made more complicated by Adcom engineers.

    http://www.linearaudio.nl/interviews/np.pdf

    See pp 12 and 13. The original 555 is less complicated and I feel it sounds better overall although the differences are slight.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

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    Quote Originally Posted by heiney9 View Post
    It's in the archive, I've posted it atleast 1/2 dozen times in the past 2 years. Do a search and you will find all the info and more about Adcom 555's.

    I am not posting it again, I thinks 6 times is enough.

    H9
    Gotta keep you on your toes somehow. I actually read through it all last night, along with all the quotes. Good info.

    Do the 3 vs 2 output transistors make it any less stable?
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    Quote Originally Posted by nguyendot View Post
    Gotta keep you on your toes somehow. I actually read through it all last night, along with all the quotes. Good info.

    Do the 3 vs 2 output transistors make it any less stable?
    Ok, good glad it helped.

    Not sure what you are referring to with 3 vs 2 output transistors. Did you also read the Stereophile reviews over the years? There is an on-line article about the 555II and they go into detail about the differences. They felt the II sounded better when compared directly to the original.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  16. #16

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    Let me go read over it again, I swear they said the II model went to triple outputs.
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  17. #17

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    Quote Originally Posted by nguyendot View Post
    Let me go read over it again, I swear they said the II model went to triple outputs.
    You are thinking of the "Triple Darlington outputs" that's a type of circuit not used in the original 555. They both use Bi-Polar output devices, the "Darlington" is a configuration. The Darlington outputs were used to allow the amp to drive 1 and 2 ohm loads, IIRC.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  18. #18

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    Ah. Thanks for the clarification. I had no idea what it meant. Yeah I'm not powering any magnepans so no problem.... :)
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  19. #19

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    The 555II used dc servo's to adjust for slight variations of DC offset and that maybe also be the reason the "Darlington" output stage was used. The original 555 had a fixed output that didn't compensate for DC offset.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  20. #20

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    Quote Originally Posted by nguyendot View Post
    Ah. Thanks for the clarification. I had no idea what it meant. Yeah I'm not powering any magnepans so no problem.... :)
    Doesn't matter the 555 will power Maggies just fine. The torture test were the Apogee Scintilla speakers, the 555 had a few problems driving those (they reach down to 1/2 to 1 ohm) so the 555II with the Darlington output stage had much less issue driving those insane speakers.

    http://www.apogeespeakers.com/review...tereophile.htm

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  21. #21

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    Quote Originally Posted by heiney9 View Post
    Doesn't matter the 555 will power Maggies just fine. The torture test were the Apogee Scintilla speakers, the 555 had a few problems driving those (they reach down to 1/2 to 1 ohm) so the 555II with the Darlington output stage had much less issue driving those insane speakers.

    http://www.apogeespeakers.com/review...tereophile.htm

    H9

    Interesting read, however I doubt I'll come across a pair any time soon.
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  22. #22

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    I used to own one. It's definitely a solidly built workhorse and is a decent amp for the price. Replace the caps on it if it hasn't already been done and it should give you many more years of dependable service. I found the sound a little on the bright side for my tastes with the set-up I had then. YMMV.

  23. #23

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    The caps didn't fail on those. Only some of the 585's and the 565's. Fresh caps never would hurt though
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  24. #24

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    Methinks this amp will be paired with RT-55s tonight for the hell of it.
    Should be good with 200w/channel to Polks best non-LSi bookshelf....and bass to boot.
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    So I read that this amp has no output relays... is that why the amp still has sound after it is turned off until the capacitors are drained?
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  26. #26

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    Quote Originally Posted by nguyendot View Post
    So I read that this amp has no output relays... is that why the amp still has sound after it is turned off until the capacitors are drained?
    Yep, well designed amps don't need current limiters or any type of soft start, muting, or output relays. I'll add that this is true for SS amps, tube amps may need a soft start or muting.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

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    Quote Originally Posted by heiney9 View Post
    Yep, well designed amps don't need current limiters or any type of soft start, muting, or output relays. I'll add that this is true for SS amps, tube amps may need a soft start or muting.

    H9
    Actually many a "good" SS amp use mute relays and soft start circuits.Because of high in-rush currents involved with charging large amounts filter capacitance (and some toroidal type transformers) soft start are all most a necessity.Also if a mute relay is used to remove bias current at turn off it will be sonically benign.

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    Quote Originally Posted by FTGV View Post
    Actually many a "good" SS amp use mute relays and soft start circuits.Because of high in-rush currents involved with charging large amounts filter capacitance and some toroidal type transformers soft start are all most a necessity.Also if a mute relay is used to remove bias current at turn off it will be sonically benign.
    Ok, I guess I'll be more specific, inexpensive and poorly designed mute relays, soft starts and the like are more detrimental than good. I've read many higher end designers state they would prefer not to use such devices unless absolutely necessary and yes, they can be integrated to be transparent but you don't find that on your everyday mass market piece.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30; Eastern Electric Mini Max; Adcom GDA600; MIT S3/Z Pc; SDA 1C; Squeezebox; Tubes add soul!

  29. #29

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    Sounds good. noticed it when I turned it on and off earlier. Had to wait longer to unhook it.
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    Quote Originally Posted by nguyendot View Post
    Let me go read over it again, I swear they said the II model went to triple outputs.
    Yes the output stage is a triple darlington config,while having superior drive capability into lower impedances it is not considered to be the best approach for pure sound quality.

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