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  1. #1

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    Default Common Ground Amps

    I have an NAD2200, which I was told on this forum isn't common ground. So, I built an AI-1. The NAD is solid, but I'd like to go back to the plain cable. You loose something with the transformer.

    From what I can tell, wheather an amp is common ground or not is never published. Does anyone know if the other NAD amps 2600, 2700, 2400, c270, etc.. are common ground? I'm worried it might be a design feature of NAD in all their amps.

    Are 99.9% of the amps out there common ground? Or is non-common ground fairly common. (no pun intended)
    Jolida Tube
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    A large majority are common ground. I even have a "dual mono" that is common ground. Usually I check with the manufacturer if I have any doubts.

    Onething to think about is brigdeabilty. Normally if you can bridge it, it's common ground.

    FWIW, I know the NAD 2700 is, I have one.
    I smell ass, burning ass, glowing cherry red spanked ass.

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    Most two channel amps are common ground. From what I've seen, those that are not common ground often have a statement on the back of the amp or in the user manual saying something like "This is a balanced amplifier, do not connect to ground" which is usually there to alert people to potential problems with speaker switching devices rather than SDA's. This doesn't apply to all amplifiers though, so the first thing to do as said above is to check with the manufacturer's customer service line, and once you get an amp (even despite being told it is common ground) check the speaker terminals for continuity yourself with a meter to be sure it's working as designed. It's simple to do and potentially saves blowing something up.
    1. JM Labs Electra 920.1 and CC30; MB Quart Vera Sub; Pioneer SC-57; Squeezebox Touch; Panasonic BDT-500 Blu-Ray; Samsung 52" LCD; FIOS; PS Audio Power Plant Premier; MIT S3 cables
    2. Polk SDA-SRS 2.3TL; Sonic Frontiers Line 3 SE; Classe Model 25; Marantz SA8004; Acoustech PH1P; Squeezebox Touch; Music Hall MMF7; PS Audio P1000; MIT S2 cables
    3. Polk SDA 2A; Parasound Halo JC-2 and A21; Musical Fidelity X-DAC; Squeezebox Touch; PS Audio 4.7; MIT S1 cables

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    If you bridge two NAD 2200 mono they are not common ground. A single NAD 2200 in stereo mode, the grounds to the speakers are common. Take a VOM and measure (with the power off, unplugged would be better, with the speakers disconnected) from the ground of the right channel post to the left ground of the left channel post, you will find the reading is zero ohms.

  5. #5

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    Why not buy my 2200 PE and bi-amp your Polks...
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    Quote Originally Posted by hearingimpared
    A single NAD 2200 in stereo mode, the grounds to the speakers are common. Take a VOM and measure (with the power off, unplugged would be better, with the speakers disconnected) from the ground of the right channel post to the left ground of the left channel post, you will find the reading is zero ohms.
    This is incorrect. The grounds are not common on this model, The ground of one channel is common with the hot of the other channel. It has something to do with making use of both halves of the power supply.

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    I could be wrong here. I used 2200 on SRSs in the late 80s. I don't remember having any problems with them used as a single amp in stereo mode. I ran into problems when I used two bridged mono, one for the left and one for the right channels.

    I read through NADs literature on the 2200 and don't see anything about non-common ground on a single stereo amp.

    Here is the pdf of the 2200 manual.

    The only thing I see about a difference in signal is the section entitled, "Inverted Channel for Powerful Bass." I think the best thing to do is to call NAD and check with them.

    If I am wrong I apologize for the misinformation.

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    Quote Originally Posted by amulford
    A large majority are common ground. I even have a "dual mono" that is common ground. Usually I check with the manufacturer if I have any doubts.

    Onething to think about is brigdeabilty. Normally if you can bridge it, it's common ground.

    FWIW, I know the NAD 2700 is, I have one.
    Thats not always true. If it has a bridge switch it is most likely common ground. If it is the style(like a car amp) where you hook the the speaker up to the left pos and the right neg (or vice versa) the it more than likely is not. In this style of amp the left pos would be the hot, and the right neg would be hot also, but inverted.
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    Which is why I say to check with the people who made it if you have any question...
    I smell ass, burning ass, glowing cherry red spanked ass.

    RT1

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    Talking

    Quote Originally Posted by amulford
    Which is why I say to check with the people who made it if you have any question...

    exactly
    Speakers:SDA2a, sub:Atlantic Technologies 172 PBM
    Pre:B&K PRO-10MC(2ch)
    Amps:Parasound HCA 1000a
    SourcesOppo DV-970HD, Xbox360, Kenwood KT-5300
    Cables:Philips/RCA/Monster

    Life's short, Listen to SDA's
    Life is short live Sui Juris
    Where did SOPA go?

  11. #11

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    I have a 2200PE; the amp is common ground.

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    I was pretty sure the 2200 and 2200 PE were both common ground when in stereo mode.

  13. #13

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    If it is a common ground. That is awsome, because I can go back to the plain sda cable.

    I have a question into the NAD support site on this. I'll post what they reply.
    Jolida Tube
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  14. #14

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    NAD email support isn't answering after 5 days. My audio repair guy didn't have the service manual handy when I called him to ask, but says he "thinks" it isn't a common ground. He
    confirmed that checking for continuity with an ohmmeter on the black speaker terminals would indicate common ground.

    The ohmmeter test shows them to be common. Is that fallible?

    What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?
    Jolida Tube
    Polk 11T, 7, 5, 5jr, 4
    Standard equip not worth bragging about.

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    Quote Originally Posted by riglehart
    What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?
    You don't want to go there ...

  16. #16
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    Quote Originally Posted by riglehart
    NAD email support isn't answering after 5 days. My audio repair guy didn't have the service manual handy when I called him to ask, but says he "thinks" it isn't a common ground. He
    confirmed that checking for continuity with an ohmmeter on the black speaker terminals would indicate common ground.

    The ohmmeter test shows them to be common. Is that fallible?

    What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?
    That test is sure fire. If you get zero ohms across the two speaker ground posts you have common ground. . . infallible!

  17. #17

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    For what its worth, I used an NAD 7600 receiver to power my SDA's with no problem. It uses the 2200A amp section. Not sure how much difference there is in the "A" vs. non "A," but I would think they are made in similar fashion.

    And, I did try a 2200 with an NAD pre for a short term listen. Wasn't for a long time, but nothing happened to my speakers.

  18. #18
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    I've used my nad 2200 pe in stereo mode with all my sdas speakers without a problem.
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    As long as there is no reading on the volt meter between thr two ground posts there is nothing to worry about.
    rocketman

  20. #20

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    Default common ground

    I went through this issue when I bought Lexicon 501 monoblock amplifiers. Everyone told me there were definitely not common ground. After a call to Bryston (they made this amp for lexicon, it is just a Bryston 7B with a different logo on it) they also told me they weren't common ground 'as far as they knew'. I paid mucho bucks for these and wasn't ready to just dump them on ebay in favor of common ground setup (I have Polk SDA SRS speakers). I strapped the grounds and they have been working fine for over a year with tons of use. Apparently they are common ground...or I'm just frying them over time...who knows. Sounds damn good though.
    Alex Cagann

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  21. #21

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    I'm going through this issue as we speak, as I have located a nice Krell KSA-100 amp for sale. I'm just thinking whethere this amp (a) has enough juice for my 1.2 TL's and (b) whether it indeed is a common ground amp.

    Anyone here have any opinions?

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    yeah.. email the manufacturer and they'll know 100% for sure if the amp you are looking to power you SDA's is common ground or not. I did.. and found out my Adcom is common ground.

  23. #23

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    I just read this thread and to add a little more confusion...

    A NAD 2200 showed up for cheap on craigslist last year. I downloaded the online manual and after reading the sections "inverted channels" and "commutating power supply" I used the NAD webpage form mail to ask if this model is a common ground amp suitable for vintage Polk Audio SDA speakers with the interconnect cable. Three days later the reply was NO it is not a common ground amp. I followed up with another question asking which other models of this time period are not common ground and never received a reply. You don't want to see the fireworks that a non-common ground amp can cause with these.
    Life gets more interesting the more we play.

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    Since you have the 2.3TL, worst comes to the worst, you don't get the SDA effect. There should be no damage to either the speakers or the amp even though the amp is not common ground. The pin-blade cable doesn't strap the grounds of the speaker posts, not like the blade-blade.

    -fredv-

  25. #25

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    Here's the verdict from NAD "support center". Email reply was...

    2200 = common ground
    2600 = common ground (I assume 2700 is, too, since I can't find any difference other than the THX logo)
    270 = common ground
    272 = common ground

    These are the only ones I asked about.
    Last edited by riglehart; 12-05-2006 at 06:04 PM.
    Jolida Tube
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  26. #26
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    Quote Originally Posted by riglehart
    Here's the verdict from NAD "support center". Email reply was...

    2200 = common ground
    2600 = common ground (I assume 2700 is, too, since I can't find any difference other than the THX logo)
    270 = common ground
    272 = common ground

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