New to me SDA-2a Amplification?

mwc951
mwc951 Posts: 12
edited October 2013 in Vintage Speakers
Yesterday I scored a pair of SDA-2a's for sale on CL.
Fantastic deal after a bit of low balling, the grills have some stains, but overall nice condition, 7/10.
I think they are "A"s...Two horizontal blade connections on the SDA cable?
They sounded great during the audition powered with the owner's Sansui G5500.
Can't wait to get these plugged into my main system.

Should I power them with:

Adcom GFA-5800

OR

Conrad Johnson MV-75A1

I've researched and found they love power...more is better.
I've been addicted to tubes & Klipsch for several years now.
Not certain the CJ is a common ground amp, or the Adcom for that matter.
Post edited by mwc951 on
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Comments

  • drumminman
    drumminman Posts: 3,396
    edited October 2013
    You already know the prime requirement: common ground. If you have a multi meter you can check by placing one probe on one negative speaker output terminal and the other probe on the other one. Set to the lowest resistance setting and the reading should be "0" or very close to it.

    For additional safety check with the manufacturers.

    If both are common ground try both and see which you like better.
    "Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills/jantzen inductors, Gimpod's boards, Lg Solen SDA inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips, interior of cabinets sealed with Loctite Power Grab, AI-1 interface with 1000VA A-L transformer
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  • pitdogg2
    pitdogg2 Posts: 25,442
    edited October 2013
    Adcom 5800 is not common ground.....correct me if I'm wrong but see many vintage post about it being non-common ground.
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  • Schurkey
    Schurkey Posts: 2,101
    edited October 2013
    Reasonably sure the mosfet line of Adcom amps is NOT common-ground. The 5500 is not common-ground, as confirmed by Adcom customer service in Thailand.
    http://www.polkaudio.com/forums/showthread.php?152275-SDA-compliant-amps-recievers&p=1961158&viewfull=1#post1961158

    I am NOT sure if it can be made common-ground by adding a short jumper wire between the negative terminals of the two channels, as I did with my Aragon 8008BB.
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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    Thanks very much for the assistance!
    Appears I have not searched enough!
    Adcom is not common ground.
    If I believe what I read, might not be as simple as an output ground jumper.
    Trying to determine if the Conrad Johnson tube amp is common ground.
    Although my TAD-60 is common ground. So possibly use it by default.
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  • westmassguy
    westmassguy Posts: 6,850
    edited October 2013
    Welcome to Club Polk. I have a pair of 2As as well, that have been completely upgraded, so if you need help or advice. This is the place to be.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
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  • NJPOLKER
    NJPOLKER Posts: 3,474
    edited October 2013
    Call Adcom

    As I recall I bought a Adcom 5500 and it is not common ground but a jumper worked fine.

    Call Adcom

    The C. S. department is familiar with the need for common ground for Polks, at least the guy I spoke with so CALL THEM LOL

    My first pair of SDA's were 2a's and I loved them and still have them tucked away. Upgrade the tweeters to rdo-194's and go from there. For about a hundred bucks you can't go wrong.
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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    Adcom tells me the GFA-5800 IS A common ground amp.

    I will attempt to verify with a volt meter tonite.
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  • Schurkey
    Schurkey Posts: 2,101
    edited October 2013
    mwc951 wrote: »
    Adcom tells me the GFA-5800 IS A common ground amp.

    I will attempt to verify with a volt meter tonite.
    Truthfully, I'd expect it to be common-ground. Doesn't hurt to verify, because I don't trust the CS department in Thailand.
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  • agfrost
    agfrost Posts: 2,428
    edited October 2013
    FYI there are some blade-blade 2B's out there, so you might as well check. If you pull a mid driver, that'd help: The 2A's had two MW6510 drivers whilst the 2B's have a 6503 and a 6511.
    Jay
    SDA 2BTL * Musical Fidelity A5cr amp * Oppo BDP-93 * Modded Adcom GDA-600 DAC * Rythmik F8 (x2)
    Micro Seiki DQ-50 * Hagerman Cornet 2 Phono * A hodgepodge of cabling * Belkin PF60
    Preamp rotation: Krell KSL (SCompRacer recapped) * Manley Shrimp * PS Audio 5.0
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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    So I verified the 5800 is common ground, both with a meter and through Adcom CS.
    Hooked it up to the SDA's this weekend.
    Poof...cooked 'em.

    THE ADCOM GFA-5800 IS NOT A COMMON GROUND AMP!!!
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  • F1nut
    F1nut Posts: 50,557
    edited October 2013
    How did you check the amp with the meter? What did the meter show? What got cooked?
    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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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    Unplugged the amp. Checked negative outputs for continuity. Showed open.
    Awful "horn" noise and immediately shut down the amp.
    Smoke rolled from the cones of the mid bass drivers.
    I was so disappointed I didn't mess this them anymore.
    I'll try the SDA's with a tube amp later this week.
    I'm thinking the idiot proof Klipsch & tube combo is a better bet for me!


    .
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  • TennMan
    TennMan Posts: 1,266
    edited October 2013
    I hate to hear that your speakers got damaged.
    mwc951 wrote: »
    Unplugged the amp. Checked negative outputs for continuity. Showed open
    Your test proved that the amp was NOT common ground. I wish you had posted that here before you hooked the amp up to the speakers.
    • SDA 2BTL · Sonicaps · Mills resistors · RDO-198s · New gaskets · H-nuts · Erse inductors · BH5 · Dynamat
    • Crossover upgrades by westmassguy
    • Marantz 1504 AVR (front speaker pre-outs to Adcom 555)
    • Adcom GFA-555 amp · Upgrades & speaker protection added by OldmanSRS
    • Pioneer DV-610AV DVD/CD player
    • SDA CRS+ · Hidden away in the closet
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  • F1nut
    F1nut Posts: 50,557
    edited October 2013
    Checked negative outputs for continuity. Showed open.

    That means there is no 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: 50,557
    edited October 2013
    Oops, sorry TennMan I didn't read your post before I posted mine.
    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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  • TennMan
    TennMan Posts: 1,266
    edited October 2013
    No problem F1. It's good to know you agree.
    • SDA 2BTL · Sonicaps · Mills resistors · RDO-198s · New gaskets · H-nuts · Erse inductors · BH5 · Dynamat
    • Crossover upgrades by westmassguy
    • Marantz 1504 AVR (front speaker pre-outs to Adcom 555)
    • Adcom GFA-555 amp · Upgrades & speaker protection added by OldmanSRS
    • Pioneer DV-610AV DVD/CD player
    • SDA CRS+ · Hidden away in the closet
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  • eeagle
    eeagle Posts: 226
    edited October 2013
    Not sure if an AI-1 cable is still available from Polk; it was meant to resolve the common ground issue w/a transformer if I recall.

    DarqueNight post #13 in this old 2005 thread may be of some interest regarding this topic:

    http://www.polkaudio.com/forums/showthread.php?26816-SDA-SRS-s-and-the-Adcom-5802...&highlight=+'s,%201.2TL's,%20SDA%201C's,%20CRS%20negative%20speaker%20terminals

    My Adcom 5802 has always provided my SDA's with that tube like MOSFET sound I love.
    SDA SRS 1.2
    Adcom GFA-5802
    Adcom GFP-750
    Sony DVP-NS999ES
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  • F1nut
    F1nut Posts: 50,557
    edited October 2013
    You cannot use the AI-1 with blade/blade SDA's such as the OP'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 October 2013
    Mwc did you strap the negative terminals together?I looked up the schematic for the 5800 and while it does not use a bridged/ balanced output stage it is non common ground.This due to the fact that there are a pair of 100 ohm resistors isolating each channels ground from the other.Adding a wire jumper between negative terminals effectively jumpers the resistors making it common ground thus SDA friendly.
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  • zingo
    zingo Posts: 11,258
    edited October 2013
    mwc951 wrote: »
    Awful "horn" noise and immediately shut down the amp.
    Smoke rolled from the cones of the mid bass drivers.

    Terrible!
    Jake
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  • leftwinger57
    leftwinger57 Posts: 2,917
    edited October 2013
    What is the design change that made this particular Adcom not so friendly to SDAs?I like many here I have a gfa555 and find it works great both as my booster to my AVR originally then went w/ a seperate pre to have an effective 2-chl system and pushes the 2Bs w/ an ease that will not allow me to go higher than my 10 pos on my pre for fear of blowing out the things.I think 555s are from the 80s and 5800s are a generation newer being from the early 90s.Again to be brutally honest when I brought home the 2Bs I had no idea these speakers were specifically tied to a common ground amp, dumb luck on my account I just plugged and played.Just did notice that there are resistors in the way or seperatintg the 2 channels and that's what could fry these great speakers ,2 resistors? Is this also w/o thermal or any other protection mode the Adcom might have.
    2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #400HD Speaker set-

    Bdrm- Nikko 6065 receiver- JBL -G-200s--Pioneer 305 headphones--Sony CE375-5 disc
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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    When I say "open"...I mean the needle on my old school meter went to "0".
    I ASSumed this is what supposed to happen to show continuity.
    I get the same result when I checked my CJ MV-75a1, which powered the SDA's for one day.
    I'm located one hour south of Pittsburgh...anyone interested in these I'll make you a great deal!
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  • leftwinger57
    leftwinger57 Posts: 2,917
    edited October 2013
    I just took out my old digi to be sure .I used a known valued resistor on the lowest scale and it read it correctly @3.9 ohm. Open leads w/o touching 1. closed leads o.oo I think you saw a dead short.
    2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #400HD Speaker set-

    Bdrm- Nikko 6065 receiver- JBL -G-200s--Pioneer 305 headphones--Sony CE375-5 disc
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  • pitdogg2
    pitdogg2 Posts: 25,442
    edited October 2013
    mwc951 wrote: »
    So I verified the 5800 is common ground, both with a meter and through Adcom CS.
    Hooked it up to the SDA's this weekend.
    Poof...cooked 'em.

    THE ADCOM GFA-5800 IS NOT A COMMON GROUND AMP!!!

    Funny how that was brought up in post 3 yet ignored......
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  • mwc951
    mwc951 Posts: 12
    edited October 2013
    Yes, pitdogg...you were right...I was wrong.
    Following another senior member's advice, I called Adcom CS to verify, they told me the opposite.
    I checked with a meter and thought all is well.

    So now I either fix the damage or turn the cabinets into firewood.
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  • FTGV
    FTGV Posts: 3,649
    edited October 2013
    mwc951 wrote: »
    Yes, pitdogg...you were right...I was wrong.
    Following another senior member's advice, I called Adcom CS to verify, they told me the opposite.
    I checked with a meter and thought all is well.

    So now I either fix the damage or turn the cabinets into firewood.
    Again since the output stage is not a bridged /balanced configuration simply adding a wire jumper across the two negative terminals would make it common ground.Not doing so may result in some nasty sounds as you experienced and possibly result in the failure of the two 100R resistors.The fact that smoke appeared out of your mid bass drivers indicates a possible output FET failure resulting in high level DC reaching the drivers.
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  • FTGV
    FTGV Posts: 3,649
    edited October 2013
    leftwinger57 wrote: »
    What is the design change that made this particular Adcom not so friendly to SDAs?
    Although from the same designer the 5800 is a completely different animal vs the earlier 555 era Adcoms.I believe they were atempting to go upmarket so started with a clean sheet of paper.It is a more elaborate design with separate power supplies for voltage gain and output stages,MOSFET instead of Bipolar output devices etc.As I mention above they should be fine with SDA's with negative terminals jumpered.
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  • Schurkey
    Schurkey Posts: 2,101
    edited October 2013
    Schurkey wrote: »
    Reasonably sure the mosfet line of Adcom amps is NOT common-ground. The 5500 is not common-ground, as confirmed by Adcom customer service in Thailand.
    http://www.polkaudio.com/forums/showthread.php?152275-SDA-compliant-amps-recievers&p=1961158&viewfull=1#post1961158
    NJPOLKER wrote: »
    Call Adcom

    As I recall I bought a Adcom 5500 and it is not common ground but a jumper worked fine.

    Call Adcom

    The C. S. department is familiar with the need for common ground for Polks, at least the guy I spoke with so CALL THEM LOL
    FTGV wrote: »
    Mwc did you strap the negative terminals together?I looked up the schematic for the 5800 and while it does not use a bridged/ balanced output stage it is non common ground. This due to the fact that there are a pair of 100 ohm resistors isolating each channels ground from the other.Adding a wire jumper between negative terminals effectively jumpers the resistors making it common ground thus SDA friendly.
    Schurkey wrote: »
    I am NOT sure if it can be made common-ground by adding a short jumper wire between the negative terminals of the two channels, as I did with my Aragon 8008BB.
    The Aragon had a mere 20 ohms of resistance between the two channels, and the sound quality genuinely sucked until I stuffed the jumper-cable into the negative terminals. Didn't blow anything up, though.

    DO NOT try to jumper any amplifier that has one inverted channel (some Carver products come to mind) or that uses a "bridged" or "balanced" design.
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  • zingo
    zingo Posts: 11,258
    edited October 2013
    mwc951 wrote: »
    I'll try the SDA's with a tube amp later this week.

    I would not try a different amp until you take apart the speakers and check each driver and crossover for damage.
    Jake
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