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    VTA driver board, high or low gain?

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    alexg

    Posts : 7
    Join date : 2012-02-24

    VTA driver board, high or low gain?

    Post by alexg on Sat Mar 03, 2012 2:44 pm

    I just acquired my first Dynaco ST70 a few days ago, it was restored by somebody, I bought it to be upgraded.

    Am using a Bottlehead Foreplay preamp and the ST70 will be driving an Opera Seconda.

    I am deciding which is appropriate driver for me, the 12at7 version or the 12au7/6sn7 low gain version?

    Thanks.

    Bob Latino
    Admin

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

    Re: VTA driver board, high or low gain?

    Post by Bob Latino on Sat Mar 03, 2012 5:53 pm

    Hi,

    The high or low gain choice is usually determined by the sensitivity of your speaker. Those speakers 93 dB and above should use the lower gain board and those speakers with a sensitivity lower than 93 dB should use the standard gain board. Your speakers are 89 dB and an independent test (link below) revealed them to have an even lower sensitivity than advertised. My recommendation (with the Opera Seconda speakers) is to use the standard gain 12AT7 version of the VTA driver board.

    Opera Seconda review

    Bob


    Last edited by Bob Latino on Mon Mar 05, 2012 9:40 am; edited 1 time in total

    alexg

    Posts : 7
    Join date : 2012-02-24

    Re: VTA driver board, high or low gain?

    Post by alexg on Mon Mar 05, 2012 3:02 am

    Thanks Bob.

    I noticed on the VTA board that it is using smaller bias pots, what kind are those and what is the power rating?

    On my ST70, the pots are big and I think rested for 2 or 3 watts.

    Bob Latino
    Admin

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

    Re: VTA driver board, high or low gain?

    Post by Bob Latino on Mon Mar 05, 2012 6:20 am

    The bias pots on the VTA board are 1/2 watt pots and their 1/2 watt rating is beyond what you really need. The large bulky pots that Dynaco used could probably handle more power, but a pot like that with a 2 or 3 watt rating was not really needed.

    Bob

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