AA764 Vibro Champ Tremolo Intensity reduces gain.

Discussion in 'Shock Brother's DIY Amps' started by Bitsleftover, Aug 8, 2019.

  1. Bitsleftover

    Bitsleftover Tele-Meister

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    I have installed an AA764 tremolo circuit into a 5F2A.
    When I turn up the intensity, the sound from the amp drops in volume and gain. Quite dramatically. Maybe 50%.
    Is this normal?

    [​IMG]


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  2. zoran

    zoran Tele-Meister

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    that is not the expected result - not sure what the cause is but im also curious what the issue and solution is! hopefully someone from the community will be able to shed some light!
     
  3. Ten Over

    Ten Over Tele-Holic

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    Yes. With the tremolo off, the intensity raises the voltage on the V1B cathode. This reduces the gain of V1B and rounds off the positive half of the V1B output signal. Some people like it.
     
  4. markos

    markos TDPRI Member

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    Sounds unusable to me. Wouldn't expect anything like that from a bias vary tremolo. Intensity pot loading down the signal? And the gain decreases as you increase the intensity, with the tremolo turned on?... Wow, I'm stumped. How is it when the tremolo is turned off? Does the intensity pot have any affect then? or does this only happen when the tremolo is turned on?
     
  5. Mexitele Blues

    Mexitele Blues Tele-Holic

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    How does the absence of the V2B cathode bypass cap in the 5F2a affect the trem circuit here, compared to the Vibro Champ?
     
  6. Bitsleftover

    Bitsleftover Tele-Meister

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    At the moment I leave the intensity set to a fairly moderate level before the volume really starts to drop off too much. (Like the EC vibrochamp) Then I added the V1B cathode bypass cap which more than compensates for the drop.
    I actually worked it all into a 2 way toggle switch and an on/off footswitch.
    Toggle up = No tremolo (totally out of the circuit. No V1B bypass cap
    Toggle down = Tremolo armed (controllable by footswitch) V1B bypass cap in circuit.
    That way I can have
    No Trem-No boost
    Boost-No Trem
    Trem And Boost
    I just have to accept that if I adjust the depth it will effect the gain level. So I don’t do it. I’m lucky that it’s at unity just about where I’d normally set it.




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  7. Ten Over

    Ten Over Tele-Holic

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    I'm still not clear on whether the gain and volume drops when the tremolo is armed and on, when the tremolo is armed with the footswitch disabling it, or both.
     
  8. Bitsleftover

    Bitsleftover Tele-Meister

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    Not played with it for a while. I’m working away at the moment.
    I’ll be home later this week and report back.
    IIRC though, the best way I can describe it is. -
    With depth/intensity on say 2, the wiggle goes from 10~8 (Volume)
    With depth on say 4, the wiggle goes from 8~5 (Volume)
    With depth on 6, the wiggle goes from 6~3
    (Rather than the volume wiggling from 10~8, 10~6, or 10~4 etc)
    With the footswitch off, the volume drops by the same amount just without wiggling. (If I remember correctly. That’s what I need to double check)
    With it set somewhere in the middle and the addition of the V1B cathode cap, the overall volume is brought back up to where it should be and there is enough depth to the wiggle to make it quite strong without being staccato. I actually love it. But I just never adjust it from there.
    I hope you catch my drift. It’s a hard one to put into words.


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  9. Bitsleftover

    Bitsleftover Tele-Meister

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    So I guess to correct my earlier description-
    1/ No Trem-No boost
    2/ No Trem - Boost (or cut) (level dependent on depth pot position)
    3/ Trem And Boost (or cut)(level dependent on depth pot position)



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