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Thread: Adcom GFA 5800

  1. #1

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    Cool Adcom GFA 5800

    Hey guys, I just scored an adcom GFA 5800 and was just about to hook it up to the sda 2.3 when I remembered to check for continuity between the negative speaker terminals... got 200ohms.

    The amp is not common ground.

    Anyways, I have read conflicting accounts. I have one questions.


    Can I simply run a speaker cable from the left amp negative to the right amp negative (strapping?) to make the amp common ground to use with the SDAs?

    I am dying to hook it up and start listening.

    Thanks everyone,
    I have read the other post about this but it seems some people say yes and others say different.

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    I had the 5503 with my 2.3s and that is what I did - I strapped the negatives together and did not have any issues.
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    Not sure about this myself BUT read last post on this thread http://www.polkaudio.com/forums/show...ble-to-get-one...

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    Thanks for the replies,

    I emailed the tech and we will see what they say.

    I read somewhere that someone fried their sda by hooking it up to this amp, but that was without strapping.

    I did the common ground test but got 200ohms resistance between the negative terminals - most other amps I've tested read a slight resistance (1 ohm etc) but there is continuity. To me this would go against what the tech said from that other thread.

    Thanks for helping me through this... I can't wait

    Mike

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    +1 too risky. Good luck & nice amp BTW

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    20 ohms between the negative terminals on my Aragon amplifier made my SDA1Bs sound terrible. Another member here had the same amp, the same 20 ohm resistance, and it shut down when powering his SRS 3.1TLs. 200 ohms would be even worse. The amp IS NOT common-ground for the purposes of compatibility with SDA speakers.

    Yup, you're going to need a jumper wire (or an AI-1 or aftermarket equivalent) between the negative terminals.

    I told Jim Donnelly of J&B Distribution llc (Adcom distributors for USA) about this when another poster had issues with his Adcom GFA-5400. Jim sent me the schematic for the 5400. Perhaps he'll send you the schematic for the 5800.

    jdonnelly@adcom-usa.com

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    Smile Schematic

    I found the schematic,

    Apparently someone else strapped the 5800 and it worked out ok with SDAs. I'm starting to gain confidence, just don't want to toast the speakers.

    Thanks again for all of the help.



    AdcomGFA5800.pdf

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    My Adcom 5802 has the neg terminals strapped and plays my SDA SRS's without a problem. Before strapping the resistance was 200ohms, after strapping .3 ohms. Below is some information I saved from a post by DK- in quotes.

    "My email to Adcom on 11/12/2000:
    Subject: Adcom GFA-5802 with Polk Audio SDA-1B speakers
    "Is the GFA-5802 a "common ground" amplifier? My speaker specifications state that only common ground amplifiers must be used. I just purchased a GFA-5802. The sound from the speakers seemed "echoey" and out of phase. When I removed the interconnecting phase array cable from between the speakers, the sound was normal. I was previously using an Adcom GFA-555 amp and never experienced this problem. Any ideas on what is causing this?"

    Adcom's response on 11/14/2000:
    "There are 2 options for you to do. You can get a cable from Polk for those speakers, the AI-1 cable. This connects the 2 speakers and deals with the common ground problem. The other option is to take a piece of speaker wire and run it between the 2 negative terminals of the amplifier that you are using. This will not hurt the amp at all so dont worry about that. This a problem that has been common with the 5800, 5802, and 5500, all our newer amps and those model speakers.
    Thanks and good listening Adcom" "

    In my case the AI-1 cable was not an option but strapping worked fine. According to Adcom's reply, it is ok to strap the 5800 too.

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    Quote Originally Posted by MAD View Post
    I found the schematic,

    Apparently someone else strapped the 5800 and it worked out ok with SDAs. I'm starting to gain confidence, just don't want to toast the speakers.

    Thanks again for all of the help.



    Attachment 98491
    There is 200 ohms(2x100R) isolating the grounds of each channel from the other(and chassis ground).Strapping will effectively short these making the amp common ground and SDA friendly without defeating the chassis safety ground.It does not have a bridged/balanced output stage so go ahead and strap away.
    Last edited by FTGV; 06-09-2014 at 04:28 PM.

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    Mad,whenI called Adcom ages ago before I knew for sure that my gfa555 was common ground the techs were so young they were not sure of my vintage and couldn't give me a definative answer. Luckily it was and I as found out many here use 555s. Becareful when you call Adcom, and if the guys here say strapping works on your 5800 then they are not going to let you blow your speakers or damage the amp. If you ask DK he also knows a bunch about later Adcom models but it does seem strapping will work.
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    Default Thanks everyone...

    Giving it a shot tonight...going to strap the negative terminals of the amp.
    Thanks for all of the support, can's wait to hear the SDAs with a powerful mosfet amp, so excited to compare.

    Thanks again,

    Mike

  12. #12

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    Cool all good....

    Thanks again, a quick update, all seems good with the strapping.

    Now it's time to assess the amp.

    Mike

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    Enjoy.

  14. #14

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    A quick update.

    In comparison with the kenwood 700m.
    The adcom works well and seems to have some sparkly highs bordering on grainy especially with the sl2000 tweeters.
    It also has deeper bass, but I seem to enjoy the naturalness of the kenwood especially for voice/guitar.
    I think I will need to give the adcom more of a chance to warm up as it could have been sitting unused for years.

    The wire jumper worked well and is without issue.

    Thanks again.

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