Adcom GFA 5500

strokin
strokin Posts: 63
in Vintage Speakers
Can anyone tell me if this amp is a common ground amp? Should I run a strap between negatives anyway? Its 200 watts in 8 ohm, 325 in 4 ohm. Where would it be at 6 ohm?
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  • boston1450
    boston1450 Posts: 7,638
    Answer ✓
    Not 100% positive. But i think i read somewhere it is NOT common ground. There were 3 listed that i recall & i think this is one of them. I will try to dig for info. There are ways you can check if any amp is. Others may chime in
    ..
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  • Malbec
    Malbec Posts: 553
    Answer ✓
    I own a 5500. It is not common ground. You can strap the negative terminals together and power SDA's with no problem.
    A dreadnaught isolation transformer would be a better option.
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  • Schurkey
    Schurkey Posts: 2,101
    Answer ✓
    strokin wrote: »
    If my amp is putting out 200 watts per channel in 8ohms, and 325 per channel at 4ohms, does the wattage change with 6ohm speakers? and if so,how much?
    Somewhere in between 200 and 325. Quick answer would be 262.5.

    Point is, instead of thinking about watts, you should be thinking about voltage and amperage--and while the amperage is increasing into the lower impedances, the voltage isn't keeping up. If the amplifier could maintain voltage while doubling the amperage into the 4-ohm load, it'd be rated for 400 watts instead of 325.



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Answers

  • boston1450
    boston1450 Posts: 7,638
    http://forum.polkaudio.com/discussion/comment/1783540
    ..
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  • strokin
    strokin Posts: 63
    Malbec wrote: »
    I own a 5500. It is not common ground. You can strap the negative terminals together and power SDA's with no problem.
    A dreadnaught isolation transformer would be a better option.
    thanks Malbec,
    Its nice to feel 100% about this.
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  • voltz
    voltz Posts: 5,384
    I have a Adcom 5503 and it is common ground also.
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
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  • Schurkey
    Schurkey Posts: 2,101
    voltz wrote: »
    I have a Adcom 5503 and it is common ground also.
    Or not.
    voltz wrote: »
    holy smoke I made a horrible mistake on the Adcom 5503...just check it and it is not common ground, I swore when I check them all for my CRS's I check it too along with my other 3 amps, I could not have metered it and just thought I did...
    I Apologize for telling you wrong :(

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  • strokin
    strokin Posts: 63
    I used my Adcom5500 on my sda1c's for about 2 months before I found out that it was not a common ground amp. Does not sound any different now that I have strapped it, did I hurt anything?
    second question: Does anyone know where my ohms would fall with a 6 ohm speaker on my amp...Malbec?
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  • voltz
    voltz Posts: 5,384
    edited February 2015
    THe Adcom is not common ground ..I swore I check all my amps...soME how I must not have tested my adcom 5503 as I just did the other day AND NO IT IS NOT A common ground amp... And I was SERIOUSLY WRONG. wrong...:( HORRIBLE MISTAKE ON MY PART
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
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  • Schurkey
    Schurkey Posts: 2,101
    strokin wrote: »
    I used my Adcom5500 on my sda1c's for about 2 months before I found out that it was not a common ground amp. Does not sound any different now that I have strapped it, did I hurt anything?
    Maybe. My Aragon amp had 20 ohms resistance between the channels, and it made my 1Bs unlistenable. Inserting the jumper between the negative terminals made a HUGE difference. I don't understand why you don't hear a difference with your system.

    I had an Adcom schematic downloaded, but I must have deleted it. I'm thinking the Adcom uses a pair of 100 ohm resistors where Aragon used a pair of 10 ohm resistors, where my amp had 20 ohms between the channels, I think the Adcom has 200 ohms.
    strokin wrote: »
    Does anyone know where my ohms would fall with a 6 ohm speaker on my amp...Malbec?
    I don't understand your question.

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  • strokin
    strokin Posts: 63
    Shurkey, I'm not really understanding my own question myself, lol. Let me ask it like this, If my amp is putting out 200 watts per channel in 8ohms, and 325 per channel at 4ohms, does the wattage change with 6ohm speakers? and if so,how much?

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  • strokin
    strokin Posts: 63
    Thanks for clearing that up.
    I'm a little new at this.
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