E53 Master Volume Issue

Discussion in 'Amp Tech Center' started by mkerlin, Feb 18, 2020.

  1. mkerlin

    mkerlin TDPRI Member

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    This is my third kit (Champ, HP Twin were my others), and I am having an issue I am completely stumped on. I installed a Pre Phase Inverter Master Volume and I hear output from both normal and bright channels with the master volume pot all the way down. Also the MV pot doest really work for the first 10 deg or so and then pops up all of a sudden. I attached a few images. Any helpful troubleshooting suggestions would be appreciated. IMG_1858.jpeg IMG_1859.jpeg IMG_1860.jpeg
     
    Last edited: Feb 18, 2020
  2. dogmeat

    dogmeat Tele-Afflicted

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    double check the pot's ohm value and the taper (or not). I don't know that build but it should probably have audio taper
     
  3. mkerlin

    mkerlin TDPRI Member

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    CTS 1 megohm audio taper
     
  4. separateness

    separateness TDPRI Member

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    I am not familiar with this amp but I take it you put a 1MΩ pot between the two 12ax7 triode stages and you put it in place of the 1MΩ fixed resistor? A drawing of your modification would be helpful.
     
  5. nathan5782

    nathan5782 TDPRI Member

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  6. OldPup

    OldPup Tele-Meister

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    Why is one leg of that resistor floating between the mojo dijon and the black capacitor in the second photo?

    Edit: it's also visible in the third photo
     
  7. mkerlin

    mkerlin TDPRI Member

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    I lifted just the one side instead of removing it till I was satisfied with the mod without thinking that it would make a difference?
     
  8. mkerlin

    mkerlin TDPRI Member

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    Mine is the same unless I made a mistake? I didn't use the same color plan. Black (middle photo) goes to 22nF on the pot side of the board.
    Screen Shot 2020-02-18 at 7.20.16 PM.png
     
  9. mkerlin

    mkerlin TDPRI Member

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    Yes Screen Shot 2020-02-18 at 7.20.16 PM.png
     
  10. nathan5782

    nathan5782 TDPRI Member

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    I couldn’t tell if the black went into the blue heat shrink with the other wires, and came out as the ground out of the red heat shrink. The resistor with the lifted leg is just the bypassed 1M. I’m assuming this was a functional amp before the master volume mod. I’m guessing maybe some wire is contacting somewhere, I’ll look at mine later it’s about the same except I used a separate coax shield wire for each lug 1 and two of the pot I think.
     
  11. Jon Snell

    Jon Snell Tele-Meister

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    If you connect the volume as shown, you will always have volume because your common goes to the bottom half of the phase splitter and doesn't shunt the signal, it will always produce sound.
    If you wire the pot as it should be with the ground going to ground not the hot end of the 56k as that is still signal, place a 22n capacitor between the wiper and pin 7 then fit a 1M resistor from pin 7 to ground. 5e3_Pre_PI_Master_Volume_Schematic.png
     
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  12. mkerlin

    mkerlin TDPRI Member

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    Thank you Mr. Snell. I am a novice/hobbyist so please bear with me. I want to understand your recommendation clearly before I start making changes. First your recommendation differs from the schematic you posted which is how I wired it? I marked up a diagram (which I am more comfortable working from) based on your description. Is this a correct representation? If not could attach a marked up schematic? Also I assume I reconnect the 1M resistor from the 56k that was removed? Thanks for your help.
     

    Attached Files:

  13. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Why do you need no signal with the MV turned full down?

    Some people do report a rather non-linear volume effect with this master volume. I believe variations in 12AX7 tubes accounts for some of this.
     
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  14. mkerlin

    mkerlin TDPRI Member

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    I don't. I was just confused by it as it is my first deluxe build and I thought maybe I had assembled something incorrectly. I tested the MV pot today and determined that the taper was very flat for the 1st 30% and I had another that was much more gradual so I switched them and it is much better.

    I did install the 3-way NFB mod and its great, but at about 50% on the MV (which is pretty loud) I'm getting feedback. Is this typical? - and thanks for the post.
     
  15. robrob

    robrob Poster Extraordinaire Ad Free Member

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    No, the feedback is not typical. I would try switching the output transformer primary wires.
     
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  16. mkerlin

    mkerlin TDPRI Member

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    That did the trick. Its an entirely different amp now. I had the same issue with the HP Twin I built but it was evident the second I turned it on. Thanks for the help.
     
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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Sweet, I'm glad you got it sorted out.
     
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