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Is this attentuator build simple and effective???

Discussion in 'Amp Input - Normal or Bright' started by bob_66, Jan 2, 2019.

  1. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Can i ask if the design i was following is dodgy . I would like the bright switch but the impedance switch is just for using with a 4 ohm speaker isnt it???? If so i can probably do without it as my amp/speaker im wanting to use it with is 8 ohm.
     
  2. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Right i removed the impedance switch with the big resistor out of the circuit altogether decided dont need it. I removed the bright switch as well temporarily.

    With the l-pad in the position shown in the photo i get 7.9-8.0 ohms with probes between A and B.
    Same 7.9-8.0 ohms between C and D..

    I also get 7.9 - 8 ohms ohms between lug 1 and 3 on the L-Pad.

    With the bright switch replaced i get the same readings.

    When i turn the L-Pad the A-B reading on the input Jack goes up , likewise the Reading between C and D on the output jack goes down.

    Am i finally getting anywhere . :) Is this sorted now???

    The on/off isolation switch seems to work ok.
     

    Attached Files:

    Last edited: Jan 9, 2019
  3. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Anyone???? Does the above sound right , i dont want to try it if not??????
     
  4. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    Please connect a speaker to the output C and D and start measuring A and B again exactly like you did (different settings using the L-Pad).
    Our problem is we give you advice and you are doing different things.
    That makes sorting out things more difficult for us.
    But now it starts to clear up.
    No offense.

    All the best,
    Robin
     
  5. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Sorry but its not easy over the net.
    Ive attached the 12 speaker from my combo into the output as you requested and i get :
    a-b = 4 c-d=4
    l-pad turned about a third , a-b=18.2 c-d=3.3
    " " " " " 2/3, a-b=35.3 c-d= 2.0
    "" " " almost all way a-b=43.3 c-d=0.9
     
  6. johnnymg

    johnnymg Most Honored Senior Member Strat-Talk Supporter

    Sep 5, 2015
    Central Coast Ca
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  7. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    I am listening but the website i followed looked pretty straightforward and i like to try and find out whats wrong when i do something.
    Like you and fez keep saying i will probably end up going with the basic circuit but would like the bright caps as my combo is sounding on the dark side of tone already .
     
  8. johnnymg

    johnnymg Most Honored Senior Member Strat-Talk Supporter

    Sep 5, 2015
    Central Coast Ca
    Ok........... here ya go! You don't really need any switches for the bright cap.

    L-Pad.jpg
     
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  9. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany

    @bob_66
    Thank you.

    It seems you somehow separated the l-pad (which is a double pot) - you connected the input to one of them and the output to the other.
    You should get nearly 8 ohms on all readings/measurings as you know.
    You need the speaker load it is essential.
    Four solutions:
    1. wiring not correct.
    2. speaker not connected
    3. broken wire or bad solder joint
    4. broken L-Pad
    You have to check those things, sorry.
    And yes, it is not easy doing such things over the INet but we are still on a good way.

    All the best,
    Robin
     
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  10. Tone Guru

    Tone Guru Senior Stratmaster

    Dec 13, 2011
    Music City TN
    Verify the pinout of the LPad you are using.
    It may not match the "1", "2" and "3" markings in the drawing.

    In particular, I've seen circuits where the input connects to "3" and the output to "2".

    Also, I'd recommend using a separate direct ground wire from the input to the output jack sleeves.
    Without doing so the ground return path uses the metal box.
    It's not good design practice to use a metal chassis as a conductor.
    It should only be connected as a shield.
     
  11. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
  12. Robins

    Robins Dr. von Loudster Strat-Talk Supporter

    Dec 22, 2010
    Germany
    Double pot - two potentiometers. That is how an L-Pad works. A stereo L-Pad would be 4 pots alltogether.
    Two internal pots - if you higher the resistance on the first pot the other goes lower and vice versa.

    You did not reversed the lugs and it would not matter because we are talking about AC and not DC.
    By the way 3 is input and output is 2 but numbering is looking on front of the pot (as it faces you in the housing - looking on the dial/knob).
    As long as you didn´t change polarity on just one connection it doesn´t matter if you connect 1 to + or 3 to +.
    2 is the output (the wiper).

    BUT! 2 is not your output but your input. So the L-Pad looks for the load on the input jack and not the output jack....
    I am confused already xD


    All the best,
    Robin
     
  13. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Right went back to basics to try and see if its correct before adding anything else, as Fez keeps saying:mad:

    As in photo attached .
    Readings IN OHMS with L-Pad in X position: A-B=0.0 C-D=7.9 B-D=7.9 1-3=7.9

    In Y position: A-B=25.7 C-D=28.9 B-D=3.8 1-3=28.9

    In z position: A-B=43.2 C-D=43.6 B-D=1.0 1-3= 43.6
     

    Attached Files:

  14. Tone Guru

    Tone Guru Senior Stratmaster

    Dec 13, 2011
    Music City TN
    The wiper, terminal #2, should be used as the output.
    Double or triple check the documentation for your LPad.
    If you don't read German look below it for the English "input" and "output to speaker".

    Connect an 8 Ohm load to the output and measure again.
    As mentioned previously, the input connection should present a suitable load to the amp at all times.
    A tube amp output transformer will not tolerate the loads you have listed as values for "A-B".
     
  15. RJ Squirrel

    RJ Squirrel Strat-O-Master

    Age:
    64
    770
    Jan 28, 2018
    Frostbite Falls
    [​IMG]

    According to the above diagram, you have the input and output connections reversed. Tab 3 is the input from the transformer. Tab 2 is the output to the speaker. This pot has two 8 ohm resistive elements. From the readings that you are getting, it appears that they are audio tapered elements, with one of the elements being reverse taper. Swap the connections that you have for tabs 2 and 3. Then measure the resistance from points A to B and C to D. These should measure 8 ohms +- 10% no matter the setting of the wiper. Measuring points B to D does not provide any meaningful information as this is a measure of the resistive elements in series with one another.
     
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  16. RJ Squirrel

    RJ Squirrel Strat-O-Master

    Age:
    64
    770
    Jan 28, 2018
    Frostbite Falls
    In reading the documentation. It does not specify a resistance measurement for the L-Pad. The Pad may be a 25K or higher resistance pad that when in parallel connection with the speaker provides a constant 8 ohm load. Measure tabs 2 to 1 and 3 to 1 at both ends of the pot rotation. This will measure the resistance of each resistive element.
     
  17. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Thanks for the further input ,here is the diagram for the Monacor L-Pad but looking from the knob side .So reversed when looking from the inside of the enclosure.
     

    Attached Files:

  18. RJ Squirrel

    RJ Squirrel Strat-O-Master

    Age:
    64
    770
    Jan 28, 2018
    Frostbite Falls
    From the picture that you posted, you have the input from the amp going form the input jack to tab 2 (the middle tab) of the L-pad. The input jack should connect to tab 3 as represented in your picture. The output jack for the speaker should connect to tab 2.
     
  19. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    refering to post #56 the L-pad reads at 11 o clock 1-2=0.00 1-3=8.00

    at around 2 o clock its 1-2=43.5 1-3 = 43.5

    If i turn it any further than 2 o clock toward 12 o clock the meter just goes to 1. and doesnt read anything.
     
  20. bob_66

    bob_66 Strat-Talker

    Age:
    53
    115
    Sep 22, 2018
    England
    Im totally confused again. Is the L-pad faulty or something.