LARMAR MV question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by sheikyerbouti, Nov 3, 2019.

  1. Vanyu

    Vanyu Member

    Messages:
    707
    Joined:
    Oct 11, 2015
    I’ve been down the adjustable feedback route before, and I really didn’t think it helped a whole lot in a Marshall 1959 w/ PPIMV. Made it a lot less stable for sure. If it were me I’d move NFB to the 16 ohm tap and be done with it, maybe parallel another NFB resistor on the old one if it still weren’t enough. The old 27K/16ohm combination works decently with a PPIMV.
     
  2. sheikyerbouti

    sheikyerbouti Supporting Member

    Messages:
    469
    Joined:
    Oct 30, 2006
    Location:
    CT
    The reason I asked is the presence pot is pretty useless right now, and I was thinking of moving the MV from the back to that spot.

    I didn't know if I could just disconnect it, or...if the NFB being on the same tap as the one I use for the cab was an issue.
     
  3. Vanyu

    Vanyu Member

    Messages:
    707
    Joined:
    Oct 11, 2015
    There’s no issue per se, just saying that you’d likely get some use of your presence pot back with a 27K NFB resistor on the 16 ohm tap. That’ll let a lot more voltage through to the P.I, you’ll also find that you’ll hit a ‘sweet spot’ on the pot a little sooner too, where the ‘bee’ frequencies disappear and your presence pot works nicely.

    Since you mention removing feedback, that isn’t such a bad idea with a PPIMV, and that approach works quite well if you simply replace your presence control with a Vox-style cut control. Great way to tame the highs with a PPIMV, and no NFB keeps things consistent through the whole sweep of the MV. I’ve heard of a few builders implementing this with good results, I’ll have to give that one a rip when I have a chance...
     
    Last edited: Nov 27, 2019
    pdf64 likes this.
  4. sheikyerbouti

    sheikyerbouti Supporting Member

    Messages:
    469
    Joined:
    Oct 30, 2006
    Location:
    CT
    Thanks Vanyu!

    I'll tell you, I don't miss the presence control on this amp. I also removed the bright cap and there is still plenty of highs for me.
     

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