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    HIgh Gain VTA Board Change Tubes for Lower Gain

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    myaddiction

    Posts : 15
    Join date : 2009-03-27

    HIgh Gain VTA Board Change Tubes for Lower Gain

    Post by myaddiction on Sat Jul 04, 2009 1:22 pm

    I purchased and installed the high gain version of the VTA board for my ST70. I did this because I am running a stacked pair of Large Advents. I am wanting to reduce the gain. Can I just swap tubes and install the 12AU7s?

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: HIgh Gain VTA Board Change Tubes for Lower Gain

    Post by Bob Latino on Sat Jul 04, 2009 8:20 pm

    To reduce gain on the VTA driver board what I would do is first try a 12AU7 tube (gain factor 20) in the center position in place of the normal 12AT7 (gain factor 60). The center 12AT7 is the initial voltage amplifier for BOTH channels and the use of a 12AU7 tube in that position will drop the gain noticeably and IMHO does not really change the character of the amp that much. You can also try using a 12AU7 tube in the two side phase splitter positions but that won't change the gain as much as the change in the center tube.

    If the gain is still too high for you then I would Email Roy on the tubes4hifi web site and have him send you the complete resistor set to change the board from the higher gain 12AT7 board to the lower gain 12AU7 board. You will have to change out about 12 resistors.

    Bob

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