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    VTA driver board pot settings

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    petes

    Posts : 1
    Join date : 2016-06-27

    VTA driver board pot settings

    Post by petes on Sun Apr 01, 2018 1:21 pm

    Just got a vintage ST70 with the VTA driver board installed.
    there are two potentiometers on the bottom of the VTA driver board.
    What are they for, and how should they be adjusted?
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    Bob Latino
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    Posts : 2634
    Join date : 2008-11-26
    Location : Massachusetts

    Re: VTA driver board pot settings

    Post by Bob Latino on Sun Apr 01, 2018 8:51 pm

    petes wrote:Just got a vintage ST70 with the VTA driver board installed.
    there are two potentiometers on the bottom of the VTA driver board.
    What are they for, and how should they be adjusted?

    Those two pots are 10K AC balance controls. They are placed on the bottom of the amp so you WON'T be able to adjust them once the amp is built. When you build the amps from a kit you are instructed to to set them at their mid-position. What you do is make sure that the resistance from the center pin to each outer pin on that 10K pot is about 5K. Then you install the two pots. The newer VTA driver boards from about April of 2012 to the present do not have these 10K pots. We now have an LM334 IC that has a local feedback circuit which gives a constant current source in the tail of the phase splitter part of the circuit (CCS).

    Just leave those two 10K pots as they are.

    Bob

      Current date/time is Thu Apr 26, 2018 2:48 pm