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Attenuator makes my Littlemark.... louder?

Discussion in 'Amps [BG]' started by Pbassred, Oct 26, 2013.


  1. Pbassred

    Pbassred

    Joined:
    Feb 21, 2004
    Location:
    Hatfield, Herts, UK
    Here's one for the tech heads.
    My amp is too loud for rehearsals (yeah, i know), in that it is working with the master vol at around 1 which makes control too sensitive. So I decided to make an attenuator to insert in the send/return loop. Less signal to work with means less to amplify.
    I made a T-pad with 2x 5K resistors in line and a 22k pot to ground between them. Essentially a voltage divider.
    The result:- with the the pot set to minimum (i.e. dumping everything to ground), NO CHANGE! but with the pot set to max resistance (almost no dumping) it got slightly louder.

    How can resistors make it louder? Any clues? :confused:
     
  2. Codger

    Codger Supporting Member

    Joined:
    Apr 13, 2008
    Sort of makes sense. The default jumper places the effects loop in parallel rather than in series. Grounding the return (pot to minimum) disables essentially the effects input. When you minimize the resistance it puts it in parallel with some other resistance from the normal input. If you connect send to return with no resistance in between it looks like it should get louder so with some resistance (44k) in there, possible. One would have to go through the numbers to know how much.

    LM2 Schem
     
  3. B-string

    B-string Gold Supporting Member

    Joined:
    Nov 21, 2008
    Location:
    Lake Havasu City, Az USA
    Have you re-jumpered the effects loop for series (stock is parallel)? If it is still in parallel you are only changing the loading of the preamp.
     
  4. Pbassred

    Pbassred

    Joined:
    Feb 21, 2004
    Location:
    Hatfield, Herts, UK
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