Has the dealer gone mad?

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giroux
giroux Posts: 3
in Vintage Speakers
I find it hard to believe the dealer would sell me an amp that wasn't compatible with my SDAs. That said, he sold me an NAD 2400 back in the late 80s. At that time I just assumed he new what he was selling me. Along with my Carver CT- 7 and Vector Research EQ, it sounded fantastic! Then, one day, no audio. Since then, everything has been sitting in the basement for 3 decades, unused. Just recently I hooked everything up, minus the EQ and experienced BIG distortion. Swapped out preamps, and same result. Could it be the 2400 is not common ground? NAD support told me, just the other day that the 2400 does not use a common ground. So, I'm confused.
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  • lawdogg
    lawdogg Posts: 470
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    Grounds are connected in that amp.

    qrzfk77sqq8l.png

    That said, they go through a 0.1uF cap to the amp's circuit ground, but I dunno if that matters for SDAs.
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • daddyjt
    daddyjt Posts: 3,263
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    giroux wrote: »
    I find it hard to believe the dealer would sell me an amp that wasn't compatible with my SDAs. That said, he sold me an NAD 2400 back in the late 80s. At that time I just assumed he new what he was selling me. Along with my Carver CT- 7 and Vector Research EQ, it sounded fantastic! Then, one day, no audio. Since then, everything has been sitting in the basement for 3 decades, unused. Just recently I hooked everything up, minus the EQ and experienced BIG distortion. Swapped out preamps, and same result. Could it be the 2400 is not common ground? NAD support told me, just the other day that the 2400 does not use a common ground. So, I'm confused.

    Your amplifier is almost FORTY YEARS OLD! It is perfectly compatible with your speakers, however it needs a refresh. Electrolytic capacitors only last 25-30 years…
    “Human beings are born with different capacities. If they are free, they are not equal. And if they are equal, they are not free.”
    ― Aleksandr Solzhenitsyn
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  • Unknown
    Unknown
    edited June 2025
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    This content has been removed.
  • lawdogg
    lawdogg Posts: 470
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    Too late to edit - I obviously meant "speaker grounds" aka negative terminals are connected!

    Good to know SDAs need speaker negative terminals connected to each other AND to circuit ground!
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
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  • Unknown
    Unknown
    edited June 2025
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    This content has been removed.
  • F1nut
    F1nut Posts: 52,406
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    daddyjt wrote: »
    giroux wrote: »
    I find it hard to believe the dealer would sell me an amp that wasn't compatible with my SDAs. That said, he sold me an NAD 2400 back in the late 80s. At that time I just assumed he new what he was selling me. Along with my Carver CT- 7 and Vector Research EQ, it sounded fantastic! Then, one day, no audio. Since then, everything has been sitting in the basement for 3 decades, unused. Just recently I hooked everything up, minus the EQ and experienced BIG distortion. Swapped out preamps, and same result. Could it be the 2400 is not common ground? NAD support told me, just the other day that the 2400 does not use a common ground. So, I'm confused.

    Your amplifier is almost FORTY YEARS OLD! It is perfectly compatible with your speakers, however it needs a refresh. Electrolytic capacitors only last 25-30 years…

    THIS!!!
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  • daddyjt
    daddyjt Posts: 3,263
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    pitdogg2 wrote: »
    daddyjt wrote: »
    It is perfectly compatible with your speakers.
    Are you sure that cap would not effect the common ground architecture?
    Maybe I'm thinking a resistor?
    Gosh I'm getting old I vaguely remember something between the negatives would affect the common ground.

    Yes - it’s the negative speaker terminals that must share a ground plane for an amplifier to be common ground. For example, a Carver 1.0t is a common ground IF it is a “non-inverting” model (speaker terminals that are red/black/black/red). HOWEVER, the “inverting” model (red/black/red/black) is NOT common ground amplifier, as one channel is inverted - meaning one negative speaker terminal and one POSITIVE terminal share a ground plane. The havoc comes in when the interconnect cable is used, which couples the negative speaker terminals. This is a serious issue when amplifier channels do not share a ground plane.
    “Human beings are born with different capacities. If they are free, they are not equal. And if they are equal, they are not free.”
    ― Aleksandr Solzhenitsyn
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  • giroux
    giroux Posts: 3
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    Using a multimeter set to "Ohms" and putting both leads on the negative speaker terminals, it reads Zero ohms. Oh, I'm speaking of the NAD 2400. NAD support told me the 2400 does not use a common ground config. So apparently they are wrong.
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  • giroux
    giroux Posts: 3
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    Is it possible my SDA's crossover networks have gone bad over the years?
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  • VR3
    VR3 Posts: 29,749
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    Yes
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • invalid
    invalid Posts: 1,559
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    giroux wrote: »
    Using a multimeter set to "Ohms" and putting both leads on the negative speaker terminals, it reads Zero ohms. Oh, I'm speaking of the NAD 2400. NAD support told me the 2400 does not use a common ground config. So apparently they are wrong.

    You would be surprised at how many manufacturers get this wrong.
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