How to verify the KAB subsonic filter works?

Discussion in 'Audio Hardware' started by Strat-Mangler, Mar 20, 2017.

  1. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    Bought one from a seller on US Audio Mart and it arrived in great condition.

    Installed it by plugging the RCA wire from the output of my preamp into the Input connectors of the KAB and then the Output of the KAB into my amplifier.

    I still have woofer pumping. Tested on 3 LPs, all of them with a slight warp. Would it solely work on pancake-flat LPs or should I no longer have any pumping whatsoever? Occasionally, I have a loud THUMP out of nowhere.
     
  2. empirelvr

    empirelvr Forum Resident

    Location:
    Virginia, USA
    Ideally, you should have no pumping whatsoever. It makes me wonder if your issue is more related to the amplifier. Have you tried connecting a line level source and seeing if the woofers still pump playing back from there? That "thump" sure sounds wrong, too.
     
  3. Mr Bass

    Mr Bass Forum Resident

    Location:
    Mid Atlantic
    Can your bookshelf speakers even register a sound at the subsonic level? This must be a problem higher up the frequency range so I guess I agree with empirelvr.
     
  4. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    I have a sub which is why I got this thing as my sub would sometimes register a loud THUMP on some records and thought it'd be nice to eliminate that.

    So far, no change whatsoever.
     
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  5. empirelvr

    empirelvr Forum Resident

    Location:
    Virginia, USA
    A powered sub?
     
  6. Mr Bass

    Mr Bass Forum Resident

    Location:
    Mid Atlantic
    OK I was going to ask you if you had a sub. Subs can be rather problematic with vinyl and imperfections. My guess is that the frequency bump is occurring slightly above the range of the subsonic filter. Is it a powered sub with controls you can adjust?
     
  7. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    Yes sir!
     
  8. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    Yes, although the only controls which can be adjusted are the phase and volume.
     
  9. Mr Bass

    Mr Bass Forum Resident

    Location:
    Mid Atlantic
    Try adjusting phase and see if that helps.
     
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  10. empirelvr

    empirelvr Forum Resident

    Location:
    Virginia, USA
    What do you get when you play a CD or DVD audio? Still pumps or is it only when playing the phono?
     
  11. feinstei9415

    feinstei9415 Forum Resident

    Location:
    South Bend, IN
    I had subsonic thumping problems and did the following to eliminate it:

    1) My turntable was hanging on a wall-shelf. I removed it from the wall shelf and put it on a low table.
    2) I weighed the lower shelf of this table down with probably 30 lbs of bricks. This eliminated most (if not all) of the subsonic problems.
    3) I moved the speakers away from the walls.
    4) I bought a KAB filter. This firmed up the bass a little bit without adding any subsonic problems.

    The best thing that you can do to cheaply fix the problem is to try the "little table with bricks" solution.
     
  12. RandyHat

    RandyHat Member

    Location:
    Denton, Texas
    I have the KAB subsonic filter in my system and it works like a charm. It completely eliminated the woofer pumping and in so doing not only improved the bass but opened up the midrange. This a powered filter. Did you receive the walwart power supply and cord when you purchased it? If so, and if everything is connected up correctly I would suspect that the unit is faulty. The improvement was so obvious in my system it's hard for me to believe that if the unit is working correctly that you wouldn't notice it immediately.
     
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  13. chervokas

    chervokas Forum Resident

    The ideal way to deal with subsonic resonances from vinyl playback is mechanical -- if the problem is an arm/cart compliance mismatch, change carts; use an arm with some kind of fluid or other damping for subsonic resonances; etc. Sticking a filter in line is always going to mess, at the very least, with the phase and timing performance of the audio signal, and even if you filter the signal, the physical subsonic oscillation of the arm and cart are still going on and modulating with other frequencies and effecting the arm/cart's mechanical and tracking performance.

    That said, sounds like the filter you have is doing no subsonic filtering (unless the problem you're having is not coming from the table). I'd be concerned about this loud thump out of nowhere. Subsonic oscillation as a result of an undamped arm/cart resonance is more or less continual, it can build and feedback and just kind of oscillate out of control until things go crazy. But I dunno about one off loud thumps out of nowhere. Are you sure your cart's not bottoming out on these warped records? Are you only having problems with warped record or are you having continual woofer pumping? What tracking force are you using?
     
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  14. Combination

    Combination Forum Resident

    Location:
    New Orleans
    No, you should be feeling your woofer as "steady" - i.e., no pumping that isn't there with the music. I always checked it with my hand.

    I don't remember how mine is hooked up going from memory, but I believe I have the output of the KAB fed into a tape input - which amp input are you using?

    And of course, just make sure the sucker is plugged in. We've all been there.
     
  15. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    I'm using the amp in my profile, the Arcam AVR350 and am connecting the KAB into the same input I was connecting my turntable to, so the chain is essentially ; turntable > preamp > KAB > AUX input in amp.
     
  16. Combination

    Combination Forum Resident

    Location:
    New Orleans
    Maybe just try a tape input to see if it makes a difference. When I have a chance, I can double check the way I have mine hooked up.

    If you happen to have a processor switch/input on the amp, it can be hooked up that way as well.
     
  17. jupiterboy

    jupiterboy Forum Resident

    Location:
    Buffalo, NY
    Run the line out of your phono preamp into a laptop and use a VST plug-in from Vonexgo etc. to evaluate the output. I can see a little 10Hz bump that gets shaved off when the filter is active.
     
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  18. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    Please do. That'd be extremely helpful. :)

    I don't have RCA inputs in my PC so that's a no-go over here. :(
     
  19. Combination

    Combination Forum Resident

    Location:
    New Orleans
    It may be tomorrow, but it'll happen, no worries.
     
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  20. jupiterboy

    jupiterboy Forum Resident

    Location:
    Buffalo, NY
    I have one of those $25 USB interfaces with RCAs for just this sort of thing. I can monitor both channels in real time. It's been more useful than I would have thought for sorting things out and checking set ups.
     
  21. Combination

    Combination Forum Resident

    Location:
    New Orleans
    Finally had a chance to look - mine goes like this:


    Turntable output to phono preamp input

    Phono preamp output to KAB input

    KAB output to amp's tape input


    Worst case, I believe Kevin at KAB is pretty open to answering queries, if I remember correctly!
     
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  22. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    This was his reply.

    "What you have is fine. If you have a traditional tape monitor button you could use the tape loop and it be able to switch the filter in and out via the tape monitor button. But most gear made after 1980 does not have a tape monitor button."
     
  23. WntrMute2

    WntrMute2 Well-Known Member

    I had one and it worked perfectly. Contact KAB though. I was instructed to use the tape loop and not the output from the preamp IIRC. I don't remember the details though. It does need a wall wart for power. I didn't see your response to that question.
     
    Last edited: Mar 24, 2017
  24. Strat-Mangler

    Strat-Mangler Forum Resident Thread Starter

    Location:
    Toronto
    Yes, I got the wall wart and am using it.

    Please note the response from KAB about whether using a tape loop is needed.
     
  25. WntrMute2

    WntrMute2 Well-Known Member

    Sorry, I missed that. Mine worked so dramatically that you could just watch the woofers. Off, they flapped on almost every album warped or not, on - the woofers were next to motionless. I suspect something is wrong with the unit if you don't get results like that. What eliminated the pumping and therefore the need for the filter was a move from ported speakers to transmission line ones and about at the same time an upgrade in my stand from a floor mounted one, as described earlier, to a wall mounted shelf. My basement system never pumped as the stand is grounded into a concrete slab. VPI TNT turntables in both systems seem also particularly immune to problems.
     

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