Princeton reverb volume/reverb issue

Discussion in 'Amp Tech Center' started by JonFirstCoast, Sep 2, 2020.

  1. JonFirstCoast

    JonFirstCoast TDPRI Member

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    Hello everyone and thanks in advance for any help you can provide.
    I recently finished a Princeton reverb build that someone else started but they were unable to finish. I've got the amp done for the most part but it has an issue where the reverb knob is acting almost as a master volume as well as a reverb control. It does this with or without a reverb tank hooked up. I have checked for bad grounds as well as grounds that shouldn't be there.I have checked coupling caps around that part of the circuit and I have tried multiple tubes etc... Voltages all seem to be pretty much in line with what they should be (allbeit a touch low). If anyone has any suggestions I'm all ears.
     
  2. Jon Snell

    Jon Snell Tele-Holic

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    Check your reverb ground points.
    Which version?
    Schematic?
    Photo?
     
  3. JonFirstCoast

    JonFirstCoast TDPRI Member

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    The amp was originally a Weber (6a14) kit with some additional parts sourced elsewhere by the original builder. It is an AA1164 with a few basic changes (grid stoppers and screen grids on the output tubes etc.) The Reverb jacks all have Chassis ground. I know the build isn't pretty as I just took what was dropped off to me and tried to get it working but here are some pictures;

    IMG_9802.jpg IMG_9803.jpg IMG_9804.jpg IMG_9806.jpg IMG_9807.jpg IMG_9809.jpg IMG_9810.jpg IMG_9811.jpg
     
  4. D'tar

    D'tar Friend of Leo's

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    try turning the reverb pot to zero and ohm from V3p7 to ground.... Whatcha got?

    I'm guessin about 470 ohms:)
     
    Last edited: Sep 3, 2020
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  5. D'tar

    D'tar Friend of Leo's

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    this looks to be yellow-violet-black-black... not yellow-violet-black-orange.

    upload_2020-9-3_9-48-52.png

    Edited for five band instead of four band color code.
     
    Last edited: Sep 3, 2020
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  6. D'tar

    D'tar Friend of Leo's

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    reorder your magnitude;)
     
  7. zook

    zook Friend of Leo's

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    Check your circuit against the schematic from input to speaker out. Something is wired wrong. Also check the values of your resistors and capacitors the same way.
     
  8. D'tar

    D'tar Friend of Leo's

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    Welcome to the Forum by the way!
     
  9. EmWeAh

    EmWeAh Tele-Meister

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    @D'tar strikes again ;)

    @JonFirstCoast while this might not be your main problem, make sure to go over some of the solder joints on the board and definitely touch up the ground bus bar on the pots. Some of the connections look pretty much like they might be cold joints.
     
    Last edited: Sep 3, 2020
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  10. D'tar

    D'tar Friend of Leo's

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    Ha! If you're having half as much fun at this stuff as I am...... Then I'm still having twice as much fun as you!
     
  11. D'tar

    D'tar Friend of Leo's

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    decided for more fun....

    This one looks suspicious as well. Should be 47r NFB tail resistor. Yo will need to lift one end of it to get a proper reading.

    upload_2020-9-3_13-9-5.png

    I suggest printing out a layout and schematic and go through with a highlighter and a multimeter to verify every single component value and connection. once confirmed highlight it on your documents.
     
  12. JonFirstCoast

    JonFirstCoast TDPRI Member

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    Im at work and but if thats the mixing resistor I t measures at 3.3m
     
  13. D'tar

    D'tar Friend of Leo's

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    upload_2020-9-3_14-11-5.png
     
  14. D'tar

    D'tar Friend of Leo's

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    upload_2020-9-3_14-11-48.png
     
  15. JonFirstCoast

    JonFirstCoast TDPRI Member

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    You were absolutely correct and that was the issue. It was definitely a 470 not a 470k. Good eyes. Thank you everyone for your help and hopefully one day i can help someone else out.
     
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  16. D'tar

    D'tar Friend of Leo's

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    Sweet! Did you confirm that NFB resistor value? Yellow viloet black gold? The gold almost appears grey is why I ask.

    Enjoy your Princeton!! Wonderful Amp
     
    Last edited: Sep 3, 2020
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  17. King Fan

    King Fan Poster Extraordinaire

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    Wow. You posted the pics at 0620 (is that my time?) and @D'tar posted the 470K note at 0746? Apparently he has a laser implant in his left cornea to read resistor codes in real time, and an electrode implanted in his visual cortex that superimposes the original layout (or schematic, if needed) on top of photographs we post.

    D'tar, my friend, what kind of coffee you drinking??? Nice one....
     
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  18. JonFirstCoast

    JonFirstCoast TDPRI Member

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    Yes it was correct. The amp sounds great but its not mine. I was helping out a friend. Although i do have an aa1164 that i built for myself a while back and i love it. Thanks again for your help... now i can move onto the next project.
     
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  19. D'tar

    D'tar Friend of Leo's

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    HOT..... HOT coffee!:)

    LOL... No super powers but I do have a pornographic memory.... Hey... Wait.... Wrong forum....

    It's all here in the first paragraph,

    Take it to the schematic,

    upload_2020-9-4_9-4-3.png

    Photos just confirm the suspicion.

    Maybe we could lose the 470k all together and rewire with a 500kl pot like so,

    upload_2020-9-4_9-11-52.png
     
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