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Mesa Boogie D800+ limiter/ clip?

Discussion in 'Amps and Cabs [BG]' started by D.A.R.K., Aug 25, 2017.


  1. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Just picked up a D800+.
    Great sounding amp, but one issue I noticed- when the limiter light kicks in, it makes an audible clicking/ clipping noise through the speakers.
    Is this normal for this amp? no overdrive or distortion through the speakers.
    Just the limiter kicking in on really low notes. i don't mind a limiter doing it's job, but this does not sound correct.
    Anyone else have this type of noise when the limiter kicks in?
     
  2. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Aged Horse? Any insight into this?
     
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    What speakers are you using?

    I'm wondering if you are hearing the speaker actually being damaged from too much power.

    The limit LED indicates that you have entered the output tube emulation limiting circuit, and you have about 6dB of operating compliance until you can, if driven hard enough, enter hard clipping (which is not nearly as nice sounding). 6dB of limiting is quite a bit actually (it's a 4:1 increase in average power due to a reduction in overall peak dynamics). If this LED is on for more than 25% of the time, it's quite possible to deliver 4x the average power without realizing it, thus putting additional thermal load on your speaker.

    This circuit is very robust and reliable, I can't think of ever seeing a failure with it.
     
    D.A.R.K. likes this.
  4. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Thanks agedhorse,
    I was running into a 4 ohm 800 watt continuous 2x15, so over powering should't be an issue.
    Definitely opening up the amp to see what it could do, but reasonably with gain stage and eq. No distortion or over excursion, or over drive going on with the speakers. The tone is really nice. The light would come on for just a second, just blinking on the occasional low note. Every time it would also result in a clicking sound, almost like touching the string to a pickup pole. Which is not you typical sound for a limiter, more of a hard clip. Definitely a sound from the circuit. Running it with just the occasional blink, by the description, I would think the limiter even with a hard knee would just do it's intended job of reduction without such an extreme artifact.
    Seems the limiter indicator on the amp is actually something you never want to hit sonically,
    it is purely a safety net function that results in artifacts.
    Or, do other folks hit their limiter light on occasion without any sonic artifacts?
     
  5. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal
    I dunno.....when I set the gain such that the yellow light on my 800+ flashes on the lowest notes, even quite frequently ,
    I get nothing but subtle, musical OD through my cab.



     
    D.A.R.K. likes this.
  6. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Thanks lomo, that's what I thought should be happening. Curious, what cab are you using?
    I'm going to have to investigate further, try another cab perhaps, see if the results are the same...
     
  7. mmbongo

    mmbongo Dilly Dilly! Supporting Member

    Aug 5, 2009
    Carolinas
    What kind of cab? The 800 watts is just the thermal rating, and the D800 could very easily push a cab with only 2 drivers well beyond the mechanical limit which it really sounds like what you have done. One thing you could try is to turn the high pass filter way up and see if that eliminates the noise just so you'll know. Also don't turn the bass EQ up. If the noise goes away with the HPF up, you were hearing your speakers being pushed beyond what they are meant to do.
     
    Aqualung60 and D.A.R.K. like this.
  8. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Well, raising the high pass also results in less gain from the spectrum being reduced, so it backs it out of limiting when I did that. Turning the input up to get the blinking to happen resulted in the same artifact though. This was happening with all tone controls at noon (not sure what setting are closest to flat on this amp), master at 3pm, input on active pad with gain at 10am. J retro preamp on a 4 string jazz run flat. So no real big boosts.
    The cab was an old 2x15 loaded with a couple drivers rated at 400 continuous each- drivers were definitely not reacting foul, i've put a lot more power into them than this amp provides without issue in the past (replacing a preamp/ power amp setup with the boogie). So although i'm going to try this on a different cab to make sure that isn't the issue, to my ears and information thus far it seems to be a sonic artifact generated by the limiting circuit.
     
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This is not a limiting circuit artifact, I'm sure if this.

    Exactly what speakers are you using, and is this a DIY box?

    There is a fair amount of LF extension present in the Subway amp, easily enough to run into mechanical limits on some 215 cabinets.

    It's also possible that there is already some damage to one or both of your drivers.

    Try your amp with a couple of Subway 115's if you can, as I know these are rated to handle 400 watts RMS thermally as well as mechanically. Otherwise try another pro level speaker, but beware of speakers that claim higher power than what real world testing might suggest as you don't want to damage somebody else's cabinet.
     
    D.A.R.K. likes this.
  10. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Yes, will definitely try some different cabs. The one I was using isn't DIY, eminence speakers, work horse, should be able to handle it but without a beta test i'm not ruling it out, as advised.
    Hopefully further testing reveals cable or cab fault, not like I need to be so extreme with the amp at all, but it's good to know the boundaries.
    Thanks so much for your time, all, this definitely answers my query on what to expect from the limiting function. Thanks for the detailed description of the circuit as well, agedhorse!
     
  11. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal
    I'm using MUCH wimpier cabs than you-either a GB NX2-112 rated at 300 watts or a Genzler 10-2 array at 250. I can easily get this effect at any volume, as it's purely a function of input gain/front end.
     
    Last edited: Aug 26, 2017
    D.A.R.K. likes this.
  12. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    Good info- i'll try driving the front end into some limiting before adding any master volume and see what the results are. this would definitely tell me wether or not it's something in the circuit, a bad cable or malfunction, as opposed to over powering speaker cabinets.
     
  13. mmbongo

    mmbongo Dilly Dilly! Supporting Member

    Aug 5, 2009
    Carolinas
    Do you have tweeters in your cab?
     
  14. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    No, no tweeters, not a fan.
     
    Raulplaysbass likes this.
  15. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    lomo, were you referring to the O/D indicator next to the input section, or the limiter indicator above the master?
    The O/D I can wind up the into without issue, limiter only kicks in post master attenuation..
     
  16. lomo

    lomo passionate hack Supporting Member

    Apr 15, 2006
    Montreal
    O/D. Sorry for the confusion.
     
  17. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    No problem, that makes sense.
     
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Exactly WHICH Eminence speakers? What box? Were they manufactured together as a system or did you put these speakers into the cabinet?

    This is all very important information, because true power rating is not based on numbers provided by the marketing departments. I deal with this sort of thing pretty regularly. If there's a problem with the amp, we will go out of our way to get it resolved, but we can't do this if it's actually the speakers.
     
  19. Ewo

    Ewo a/k/a Steve Cooper Supporting Member

    Apr 2, 2008
    Huntington WV
    IANA tech, but I'm wondering if you were putting enough into the cab that the voice coils were hitting the back plates...
     
  20. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    One possibility, or the excursion is enough beyond Xmax that the bottom edge of the VC is touching the ID of the top plate or OD of the pole piece.
     

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