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Svt 3 strange low end cone movement

Discussion in 'Amps and Cabs [BG]' started by Chris_315, Apr 27, 2010.


  1. Chris_315

    Chris_315

    Apr 27, 2010
    I have an svt 3 pro into an EV 15"+8" TL (8ohm) its a little quiet but I knew that before I bought it. It seems a little muddy in the low end but since this is my 3rd second hand EV box (2 owned before this amp) I thought It was just the cabinet. I plugged the amp into another speaker and it still has this strange behaviour.
    I was always told that if you can see the cone move then there is wasted power there. normally low freq cone movement is a blur, like 40 cycles per second. what I mean is when playing with 'gusto' (4 string G&l bass) I can see the cone moving, like its changing from its centered position (like its at 3hz) and it moves 3/8"
    maybe this cone over excursion is causing the muddy sound?
    could a bias issue be causing this?
    it also does this 'excursion' when changing the tube/SS bias knob (but warns of this in the manual)
    I have the amp set on full tube, even if i cant hear the difference. I have the low end shelving to boost too.
    I cant afford to waste power on non musical freqs and since there is no compressor or crossover on the amp I cant filter them out.
    What do people think?
    Regards
    Chris
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You've been paying attention to the wrong sources. If you're really concerned you can add an external 40Hz high-pass filter, but I wouldn't worry about it. Bass amps have high-pass filtering built in to prevent excess power and excursion in the sub-sonic frequencies. If you have graphic EQ pull down the sliders below 40 to accomplish the same thing.
     
  3. craig.p

    craig.p

    Sep 28, 2008
    New Hampshire
    No offense to Mr. F, but...

    Yes, subsonic cone motion IS ABSOLUTELY a waste of power, and you SHOULD be worried about it, not only in terms of getting maximum AUDIBLE power from your amp but also in terms of driver longevity. Back in the late '70s I used to build battery-powered 18dB/octave high-pass filters into Bud boxes and take them around to the larger clubs. It was a long time ago but I seem to recall using either TL072 or NE5532 op amps. I'd look for systems where the low-end drivers were doing the hoparound (similar to your situation), tell the sound man what I had with me, get him to agree to plug it into his effects loop, and watch him go all bug-eyed at the increase in dynamics and decrease in mud. $SOLD!$. (Tuition for tech school, and money for Rotosounds.)

    If you're seeing cone hop, the presence or absence of high-pass filtering in your amp is moot. As Bill says, you can do your part to minimize it. Keep in mind the additive nature of your amp's tone controls. You have three circuits available on that amp to create the very problem you describe. Injudicious/over-aggressive tone shaping at the bottom end will overcome any amp's tendencies to behave as a high-pass filter, unless the slope is cliff-like, OR the tone shaping is done in the digital domain and there's enough intelligence in the code to allow frequencies below, say, 20-25 Hz simply to be discarded.
     
  4. This becomes more of a problem for those of us who have piezo equipped basses in their collections. With my pre/power setup I can watch the cones move as I simply push gently down on the strings. Solution was a 36dB/8ve high pass filter in line from my pre to power amp.

    Paul
     
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    The SVT 3PRO has zero feedback in the power amp, but it DOES have a 'servo" that is supposed to keep the output DC voltage at zero..... it is really pretty slow, way below audio....

    if that servo is causing trouble, or if certain (not horribly expensive) problems occur in the power amp circuitry, that kind of DC offset shift can occur.

    AND..... IF THE POWER AMP DRIVER TUBES ARE FLAKY, THAT CAN HAPPEN ALSO........ you might try swapping tubes.
     
  6. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    I know exactly what you are talking about
    I have the same B15M cabinet and did have a SVT 3 Pro
    I never used extreme EQ and did not have abnormal speaker excursion issues, so as mentioned by Jerrold, there sounds like something is amiss

    OTOH, I have an SWR SM400 that has no extreme low frequency protection; in fact, I think Steve Rabe was out to make a reference amp that produced anything you put into it; even with the bass knob turned down, paramtric EQ flat, the 30 hz slider pulled down 15dB, if you moved a string gently toward the pickup, the driver would dance with any Fender style bass
     
  7. Chris_315

    Chris_315

    Apr 27, 2010
    ok all interesting points there and I will look into it more, it seems more user error than an amp fault.
    So I'll; adjust my low semi parametic shelving eq,
    depress the deep switch,
    notch out lows with the graphic eq,
    dont push on the strings
    and install low cut (I only have 6db octave one)
    I wonder if there will be any bass left? lol
    but seriously thanks all, I was dreading spending money as these are all free!
    chris
     
  8. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    well they say the best things in life are free.

    but it's a load of crap. the best things in life are really really expensive.

    :D
     
  9. Chris_315

    Chris_315

    Apr 27, 2010
    'the best SINS in life are really really expensive'
    I'll take your work on that jimmy!
     
  10. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Chris,
    Try it flat with with the low switch off; if you have a passive bass and the problem still exists, I would think the amp needs servicing
    I had one for over 15 years and didn't have this problem (although did have issues with solder traces)
     
  11. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The only major adjustment you should need to make is to pull the 33Hz slider down, 3/4 of the way should do it. If you need to add boost at 50Hz with the Ultra Low switch you may need to pull the 33Hz slider down more to compensate. The same applies to the bass control. I wouldn't run the bass knob higher than at 2 o'clock, if you want a fatter sound you're better off boosting the 80Hz slider, which will have little effect on the sub-sonics.
     
  12. Chris_315

    Chris_315

    Apr 27, 2010
    so with the eq flat and low off the problem goes away but so does the bass!
    thats the problem with the 'scooped' tone I like, I needed that bass to make an impact. I only boosted the bass so much in the first place to drown out those dreaded mids.
    I moved back the pickups away from the strings to get some more headroom in the preamp, and moving the string toward the passive pickups wasnt causing the problem. its my liberal eq settings
    changing the power amp bias to 'SS' causes less subsonics, it seems the 'tubes' are a bit more 'flabby'.
    So now I am trying to get my scoop back safely, but now I hear an overwhelming 'resonant' tone from the speaker, it sounds like an octaver (but always around 150hz). this 15TL box doesnt have wadding in it, and Im not sure it only happens when the speaker is hot.
    I really miss the 8x10 (it was only a peavey) but it seemed to love the scoop, do I need to go back to 10's?
     
  13. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Now try my suggestion. There's absolutely no reason to run the EQ flat, if that was the case Ampeg would have saved you a lot of $ by leaving it out. And there's no reason to kill the bass entirely, only kill it where you don't need it, at 33Hz.
     
  14. Chris_315

    Chris_315

    Apr 27, 2010
    so yes Bill i didnt say but i did notch the 33hz and that is the answer. Thanks
    my gripe was now I hear this 'coloured' sound by this 'resonance' from my speaker now the rumble has gone. it was there before but it wasnt the dominant 'sound'
    So i will try removing the grill, stuffing a towel or pillow in the box, try block the ports
    you know you put one fire out and...
     

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