SDA SRS2 Adcom 5400 - Hollow metal echo on certain songs

David P
David P Posts: 6
edited March 2014 in Vintage Speakers
I have early model SDA SRS2 and recently added a used Adcom 5400 for power. My receiver is Harman Kardon HK3490. The speakers sound fine when connected to HK. They usually sound fine when connected to the Adcom. One song in particular sounds horrible when using the Adcom, Gaslight Anthem We Did It When We Were Young. The speakers sound like they are in a large metal tube, a metalic ringing echo sound. The sound clears up when I unplug the interconnect cable. Makes me wonder if something is wrong with the Adcom. I don't want to push the power up until I know everything is OK. Anyone have a similar problem? Any suggestions?
Thanks,
Dave
Post edited by David P on
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Comments

  • F1nut
    F1nut Posts: 50,554
    edited February 2014
    Verify that the amp is common ground.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • F1nut
    F1nut Posts: 50,554
    edited February 2014
    I did a little digging, that amp is not common ground. Do not use it until you verify with Adcom that you can tie the negative outputs together. If you can be aware that it will affect the sound quality to a degree.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • ZLTFUL
    ZLTFUL Posts: 5,648
    edited February 2014
    You can strap the grounds on the Adcom GFA-5XXX. I have had to do so on my 5503 while I indent to do so on my 5500.

    That being said, I would go the Dreadnaught route myself.
    "Some people find it easier to be conceited rather than correct."

    "Unwad those panties and have a good time man. We're all here to help each other, no matter how it might appear." DSkip
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  • zingo
    zingo Posts: 11,258
    edited February 2014
    ZLTFUL wrote: »
    That being said, I would go the Dreadnaught route myself.

    Not possible on an early model SRS 2; blade-blade.
    Jake
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  • ZLTFUL
    ZLTFUL Posts: 5,648
    edited February 2014
    zingo wrote: »
    Not possible on an early model SRS 2; blade-blade.
    I knew that... I just overlooked the "early" part. :redface:
    "Some people find it easier to be conceited rather than correct."

    "Unwad those panties and have a good time man. We're all here to help each other, no matter how it might appear." DSkip
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  • David P
    David P Posts: 6
    edited March 2014
    Thank you to everyone for the replies.
    Adcom says this is common ground amp. I read 2 ohms between negative terminals with my Fluke digital meter.
    I may try tying the negative terminals together to see if there is any difference. What modifications would need to be made to the early model SRS2 to make them the same as the later model units compatible with the AI-1 interconnect cable.

    "David,
    The GFA-5400 is common ground. You should consider having the amp evaluated by a service tech to see if it is performing at factory specs. You may need to consider a higher power amp.
    Jim
    Jim Donnelly
    J&B Distribution llc
    PO Box 54096
    Phoenix, AZ 85078
    PH:480-607-2277
    FX:623-505-9523
    EM: jdonnelly@adcom-usa.com"
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  • F1nut
    F1nut Posts: 50,554
    edited March 2014
    Yet, the issue you describe is one of the possible results when trying to run SDA's with a non-common ground amp.
    What modifications would need to be made to the early model SRS2 to make them the same as the later model units compatible with the AI-1 interconnect cable.

    Can't be done.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • F1nut
    F1nut Posts: 50,554
    edited March 2014
    Here, read this thread. http://www.polkaudio.com/forums/showthread.php?57569-Adcom-GFA-5400

    It appears to have a secondary winding resulting in a floating ground, so no go with your SDA's.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • FTGV
    FTGV Posts: 3,649
    edited March 2014
    If configured like the 5800,5802 it's highly probable there is some resistance isolating the grounds of each channel from the other.Jumpering the negative terminals would then be necessary to make it SDA friendly.
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  • Schurkey
    Schurkey Posts: 2,101
    edited March 2014
    David P wrote: »
    Adcom says this is common ground amp. I read 2 ohms between negative terminals with my Fluke digital meter.
    One suspicion: What scale was your meter set to? I thought I remembered that other Adcom 5xxx series amps had two HUNDRED ohms between the channels, based on a pair of 100 ohm resistors.
    David P wrote: »
    I may try tying the negative terminals together to see if there is any difference.
    Good plan.
    David P wrote: »
    What modifications would need to be made to the early model SRS2 to make them the same as the later model units compatible with the AI-1 interconnect cable.
    F1nut wrote: »
    Can't be done.
    Possible, not practical.

    Gut the cabinets. Buy the drivers and crossovers from SDA 1C or the later SRS 2 pin/blade speakers. Install later components in your cabinets, re-using your passive radiators.

    The second way is to re-wire the SDA circuitry to be like the later generation common-conductor cable. I did this with my 1Bs (same drivers and nearly identical crossover to your SRS 2 blade/blade) and although it works, sound quality suffers. I went back to the twin-conductor SDA interconnect cable. It's possible, but NOT DESIRABLE.
    "David,
    The GFA-5400 is common ground. You should consider having the amp evaluated by a service tech to see if it is performing at factory specs. You may need to consider a higher power amp.
    Jim
    Jim Donnelly
    J&B Distribution llc
    PO Box 54096
    Phoenix, AZ 85078
    PH:480-607-2277
    FX:623-505-9523
    EM: jdonnelly@adcom-usa.com"
    Defective amp is entirely possible. I'm not saying it's likely. Not enough power isn't the problem. I suspect that Adcom doesn't consider the fact that we need a ZERO OHM resistance between the channels; and they're thinking that only a couple of resistors are in the circuit--so it's "close enough" to common-ground (for everyone except SDA owners.)
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  • FTGV
    FTGV Posts: 3,649
    edited March 2014
    David,I found a schematic for the 5400.It shows it to have separate power supplies for each channel.As I suspected each channels ground is connected to chassis safety ground through separate thermistors( instead of resistors).The small amount of resistance in the thermistors is enough to avoid the potential of a ground loop issue and provides some isolation between the grounds of each channel. Strapping the negative terminals might fix your issue.
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  • David P
    David P Posts: 6
    edited March 2014
    Thanks guys, this is starting to make sense.
    My digital fluke meter autoranges. There are no ranges to manually select. It displays ohms, K-ohms, or M-ohms appropriately for the range that it is reading. That being said, digital ohm meters sometimes give flaky readings when measuring active components. I measured the terminals again and got 11 to 12 ohms between the negative terminals this time. So it is clear that the negative posts are not tied directly together internally. The 5400 may technically be common ground according to Adcom, but the negative terminal on each channel must be attached to the case via some active component probably to drain static or transformer leakage, or to meet some UL safety regulation. The factory connection between the negative terminals is tenuous at best and does not meet the requirements of the SDA's. I have asked Adcom if it is ok to jumper the negative terminals together. I will let you know what I find out and how things work out.
    Thanks again,
    Dave
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  • FTGV
    FTGV Posts: 3,649
    edited March 2014
    The negative speaker terminals are at ground potential,connected directly to their respective power supply grounds.It does not have a bridged/ balanced output stage so negative terminals can be strapped together.Doing so effectively bypasses the resistance of the thermistors connected between the two channels grounds(making them truly common) while still providing a connection to chassis or saftey ground.
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  • David P
    David P Posts: 6
    edited March 2014
    Excellent. Thanks again. I will try the jumper/strap this weekend. I am very optimistic. I did get a response from Adcom, but I don't think the tech understands the requirements of the SDA's.
    Dave

    The GFA-5400 is a common ground amplifier, they are already effectively tied together unless something has been damaged or changed in the amplifier.
    Jim
    Jim Donnelly
    J&B Distribution llc
    PO Box 54096
    Phoenix, AZ 85078
    PH:480-607-2277
    FX:623-505-9523
    EM: jdonnelly@adcom-usa.com
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  • Schurkey
    Schurkey Posts: 2,101
    edited March 2014
    David P wrote: »
    I did get a response from Adcom, but I don't think the tech understands the requirements of the SDA's.
    I took the liberty of sending an e-mail to Jim Donnelly at the address provided, explaining the unique nature of the SDA speakers, and how the thermistors/resistors don't constitute a proper common-ground when used with SDA speakers. I explained about the jumper wire. We'll see what, if anything, happens from there.

    I did forget to provide a link to this thread, which I now regret.
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  • David P
    David P Posts: 6
    edited March 2014
    Strapped/jumpered the negative terminals together on the Adcom. All is good! Everything works fine now. Thank you to everyone for your help.
    Dave
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  • FTGV
    FTGV Posts: 3,649
    edited March 2014
    Great to hear.Enjoy your SDA's.
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