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M pulse mid control

Discussion in 'Amps and Cabs [BG]' started by theshadow2001, Oct 5, 2005.

  1. theshadow2001


    Jun 17, 2004
    Ok so on the manual on my m pulse it says the mid control is boost only but it also says that its a passive control. So this seems a bit confusing. I've always thought that passive controls can only be cut ie when it's up full the output is 0dB anything below that becomes minus X amount of dB's depending on how far its rolled back.

    Also passive to me also means no power supply and if I remmber correctly you need a power supply of some sort to boost by x amount of dB's above the input signal level

    I read somewhere else here on talkbass that a walkabout or m pulse owner confirmed with mesa that this control is boost only and is passive. So could someone please explain.
  2. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
    The mid control is not boost only. It's flat when it's all the way on. Therefor you can never boost it, that's what the parametric eq is for.
  3. KevinMG

    KevinMG Supporting Member

    Jan 17, 2005
    Princeton, NJ
    I was equally confused with my Walkabout. Magazine reviews referred to it as cut-only - flat when all the way up. The manual indicates it's a boost-only circuit - flat when all the way off. I called Mesa myself to get straight on this and they told me it was boost only - flat is completely off - as stated in the manual. Mesa says it's a wide band boost centered at around 600hz. They also said that all of their tone stacks are different, so the big block 750 has a slightly different mid tone stack. But I think the M-pulse and the Walkabout are the same.

    I'm not an electronics guru so I don't know exactly how it works, but if the manual says it's boost only and the company says it's boost only, I'd say that's confirmation enough. But it really doesn't matter, set it to your liking and call it a day. Mesa doesn't respond to email, so you'll need to call to get more technical deets. Please share if you find out more. Enjoy!
  4. KJung

    KJung Supporting Member

    Lot's of confusion about this on a few other threads. I'm certain the 'boost only' is a typo in the manual. The mid control is passive... which means it is 'flat' all the way up, and will cut. However, the Mesa's have a lot of 'mid character' in their design.... the mid sounded 'flat' to me at 12 o'clock... and actually seemed to behave more like a typical active cut and boost mid. So, eve though it is technically a cut only passive circuit... just start out at the 12 o'clock setting and slightly vary to taste.... it works great.
  5. theshadow2001


    Jun 17, 2004
    There certainly does seem to be a lot of confusion on this topic. Ive been thinking about this and one way I can see it being boost only yet still being passive is if the signal is run to the mid control via a band pass filter where by the output of the filter is the band width of the mid control then boosted by a certain amount then sent to the actual passive control. So when the mid is up full the boosted signal is let through unchanged and when it's completely rolled off the signal is attenuated to 0dB

    In other words passive is always cut only, but if the signal is boosted before going to a cut only control it would give the appearence of a boost only control.

    Now this is just a complete guess and im pretty much talking out of my a$$ but what do others think.

    I dont think that mesa would have a type-o in the manual especially if there customer service is confirming what the manual says, if what kevin said up there is true(and I've no reason not to believe him)
    I think that it's good idea to know how your eq works when your trying to get that sound but more over Im just curious on how this apparant contradiction can be true
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    What is in question here is what constitutes an active versus passive tone control. In theory an active control will boost and cut, with the 12:00 position usually being flat. A passive control will only cut, but that doesn't necessarily mean that the full on position is flat. Far from it, actually, because when you combine a passive tone control with a gain stage, as is the case in most tube amps, the full on position delivers plenty of boost, 20dB not being unusual. But it will never give any cut. The argument can be made that the combination of a passive tone control and a gain stage is actually an active tone control, but the accepted definition of an active tone control remains one that can both boost and cut, with zero insertion loss at the neutral position. A passive tone control can either boost or cut, but not both, and does require a separate gain stage to achieve the boost function.
  7. tombowlus

    tombowlus If it sounds good, it is good Gold Supporting Member

    Apr 3, 2003
    Fremont, Ohio
    Editor-in-Chief, Bass Gear Magazine
    Thanks, Bill. That was my guess of what the Walkabout is doing, just from the tonal changes I have observed when varying the Mid knob. FWIW, I tend to think that somewhere around 10 or 11 o'clock is closest to "flat" (with all other knobs being set equal), but bear in mind that the Walkabout is not really designed to be a flat sounding amp - and I think the same can be said for the entirety of the M-Pulse line.

  8. KJung

    KJung Supporting Member

    +1 What Bill says makes total sense... since that mid control does seem very similar in effect to an active circuit... with somewhere in the middle range being 'flat'.
  9. theshadow2001


    Jun 17, 2004
    Cheers bill that laid my queries to rest. I hope my fellow boogies who were confused on the matter find this useful as well