Common ground question

Phil Dawson
Phil Dawson Posts: 288
edited September 2008 in Vintage Speakers
After reading a current thread I am still confused. This is my set up. I have a pair of SDA SRSs in the front bi-amped with PSE mono blocks on the bottom and a PSE stereo amp on the top. In the rear I have 2.3tls bi-amped with a pair of PSE stereo amps. I don't seem to have any problems except that sometimes I develop a feedback problem that can be cured by moving the various inter-connects behind the B&K pre-pro. All of the amps are plugged onto a switching unit giving each amp it's own on/off power switch. The system sounds good except for the occasional feedback problem. What am I doing wrong? (besides the things my wife always brings up)?
Thanks, Phil
Post edited by Phil Dawson on
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  • awe-d-o-file
    awe-d-o-file Posts: 146
    edited September 2008
    A couple of questions> What does the feedback sound like? LF, midrange(1K)? Does it come through all speakers? Are you using SDA interconnects with either/both sets of speakers? You say that you can move interconnects to fix the problem temporarily. Which ones?


    ET

    System: MF Trivista SACD > Placette passive> CJ passive horizontal bi-amp> MF 2500A(LF) MF2100(HF) > 1.2TL's

    Other: Speltz silver Eichmann IC's & speaker wire, Econotweaks Detail Magnifiers, PS Audio P-300(source), R. Gray 600, Al Sekala's AC R/C filters, R. Gray HT PC's, Oyaide R-1's,WPC-Z , M-1, Herbie's & DIY Isolation
    Room: Qty 7 - 4' tall 18" diam. bass traps, Qty 4 - 4' X 2' X 4" panels. All DIY - man my wife is tolerant!
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  • Phil Dawson
    Phil Dawson Posts: 288
    edited September 2008
    The feedback sounds like a 1K tone. This happens mostly when the tuna is in use. I'm not sure which interconnects because of cable ties and the like. When I move them I get a short burst of feedback and then it goes away. It almost seems like I am releasing a built up charge and that doesn't make sense to me. The SDA interconnects are in place. The feed back comes out of all speakers taht are powered up although I think that this has only been a problem in 2 channel modes.
    thanks, Phil
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  • ben62670
    ben62670 Posts: 15,969
    edited September 2008
    Take a multi meter and read between the speaker terminal's grounds. There should be no resistance. Let us know.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • Phil Dawson
    Phil Dawson Posts: 288
    edited September 2008
    Do you mean on each individual speaker as in left and right or between the two terminals top and bottom? I will do that tonight - I won't be back online till AM.
    Thanks, Phil
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  • ben62670
    ben62670 Posts: 15,969
    edited September 2008
    On the amp between the speaker grounds(cables disconnected). It should be near 0 ohms if it is common ground;)
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben
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  • awe-d-o-file
    awe-d-o-file Posts: 146
    edited September 2008
    ben62670 wrote: »
    On the amp between the speaker grounds(cables disconnected). It should be near 0 ohms if it is common ground;)
    Ben

    He has monoblocks right? Needs to check continuity between each amps speaker ground. Has anyone ever used monoblocks w/SDA?


    ET

    System: MF Trivista SACD > Placette passive> CJ passive horizontal bi-amp> MF 2500A(LF) MF2100(HF) > 1.2TL's

    Other: Speltz silver Eichmann IC's & speaker wire, Econotweaks Detail Magnifiers, PS Audio P-300(source), R. Gray 600, Al Sekala's AC R/C filters, R. Gray HT PC's, Oyaide R-1's,WPC-Z , M-1, Herbie's & DIY Isolation
    Room: Qty 7 - 4' tall 18" diam. bass traps, Qty 4 - 4' X 2' X 4" panels. All DIY - man my wife is tolerant!
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  • heiney9
    heiney9 Posts: 25,204
    edited September 2008
    awe-d-o-file wrote: »
    Has anyone ever used monoblocks w/SDA?

    Yes, many people have. The prerequisite has always been to find out from the manufacturer IF the negative terminals can be tied together to form a common ground. Mono blocks by their nature do not have a common ground.

    You can NOT use bridged mono blocks. That is; a stereo amp that can be bridged to run as a single channel amp. I know of none that when bridged can be made common ground. Plus when you bridge an amp there are serious impedance issues you need to be aware of when running a more difficult load like SDA's or other 4 ohm or less speakers.

    H9

    P.s. Using the AI-1 cable supplied by Polk for the models that can use the AI-1 cable solves this problem. Many feel since it's a work around there might be a small decrease in sound quality. YMMV
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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