Adjusting VVR Maximum Setting

Discussion in 'Shock Brother's DIY Amps' started by Bitsleftover, Oct 11, 2019 at 6:19 AM.

  1. Bitsleftover

    Bitsleftover Tele-Meister

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    Hi
    Ive installed a Tube-Town Vo-Co VVR board to a 5watt single ended amp.
    I’d like to permanently reduce the Maximum setting so that with the 1meg pot on 10, it is always knocking the voltage down by about a third or so. This equates to about halfway (5/10) on the dial.
    Ive found info on adjusting the lower limit. But not the upper.
    The reason I want to do this is because I control my VVR and Master Volume on a shared 1meg duel pot.
    I find the amp sounds best with the VVR on 5 and the MV on 10 then reduce the output [​IMG]volume by winding them back at the same rate.
    I really would appreciate some direction.
    Thanks in advance.
    Here’s a picture of the VoCo circuit-


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  2. Wally

    Wally Telefied Ad Free Member

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    I suppose you could measure that VVR pot at/the setting you like and sub in a resistor of that value.
     
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  3. Bitsleftover

    Bitsleftover Tele-Meister

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    Thanks Wally.
    I still need it adjustable. Kinda from half to zero.


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  4. Bitsleftover

    Bitsleftover Tele-Meister

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    I’ve tried putting a 470k resistor between the wiper and B-
    No change.
    I tried putting a 470k resistor between the wiper and B+
    No change.
    I tried putting 1 meg across B+ B-
    No change.
    I tried putting a 1 meg resistor across R4
    No Change.


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  5. jonrpick

    jonrpick Friend of Leo's

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    Seems to me you'd want the resistor between one end of the pot's WAFER (not wiper) and B- or B+.

    The wafer is the part the wiper makes contact with (the outer two connections, not the middle one).

    An example: Since the pot is 1M, putting a 1M resistor at one end would effectively make it a 2M pot, which at max would be in the middle position.

    Edit: Yeah, that's right. The pot is simply an adjustable voltage divider. The resistance values don't matter as much as the ratio between the upper and lower values in a typical divider (made with two individual resistors). So whether you had a 1M pot or 5M pot, it would function the same. And since you're only adjusting voltage, not signal, I would *think* that things like input/output impedance would be less critical. Anyone can feel free to correct me if I'm wrong.

    I say put a 1M resistor between the wafer (outer lug) of the pot and B+...
     
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  6. FenderLover

    FenderLover Friend of Leo's

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    I'm with Jonrpick. You will not see R4 in other VVR schematics, so it is probably only there to modify the taper of the pot. Remove R4, or move it to the top of the pot to B+ for a lower max setting, and/or add resistance from bottom of pot to B- for minimum setting other than zero.
     
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  7. Bitsleftover

    Bitsleftover Tele-Meister

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    Brilliant advice! Thank you both so much for taking the time to answer.
    I’m away working at the moment but I’ll try that out as soon as I get home on Wednesday.


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