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    High gain or low gain version of ST-70 board, guidance needed.

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    viridian


    Posts : 14
    Join date : 2010-02-19

    High gain or low gain version of ST-70 board, guidance needed. Empty High gain or low gain version of ST-70 board, guidance needed.

    Post by viridian Tue Apr 27, 2010 10:17 pm

    So, I have my ST-70 board and have the caps in hand. I will be upgrading a vintage ST-70. Does anyone have any thoughts or guidance on the sound quality of the low gain version of the board, versus the high gain version? I do use a preamp, and have horn speakers, which tilts me to the low gain version, but I am more interested in hearing about ultimate sound quality than system gain architecture, at least for the moment, and it's time to start ordering resistors! Tube availablility is not an issue, I have plenty of NOS 12AT7, 6201, 12AU7, 12BH7, etc. Thanking any and all in advance for your gracious guidance. Marty Kohn.
    Bob Latino
    Bob Latino
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    Posts : 3114
    Join date : 2008-11-26
    Location : Massachusetts

    High gain or low gain version of ST-70 board, guidance needed. Empty Re: High gain or low gain version of ST-70 board, guidance needed.

    Post by Bob Latino Wed Apr 28, 2010 10:12 am

    viridian wrote:So, I have my ST-70 board and have the caps in hand. I will be upgrading a vintage ST-70. Does anyone have any thoughts or guidance on the sound quality of the low gain version of the board, versus the high gain version? I do use a preamp, and have horn speakers, which tilts me to the low gain version, but I am more interested in hearing about ultimate sound quality than system gain architecture, at least for the moment, and it's time to start ordering resistors! Tube availablility is not an issue, I have plenty of NOS 12AT7, 6201, 12AU7, 12BH7, etc. Thanking any and all in advance for your gracious guidance. Marty Kohn.

    Hi Marty,

    I have listened to both boards and IMHO there is no real audible difference between the standard gain VTA driver board which uses 12AT7 tubes and the lower gain version which uses 12AU7 or 12BH7 tubes. In your situation, with very efficient horn speakers, you may be better served with the lower gain version.

    Bob
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    viridian


    Posts : 14
    Join date : 2010-02-19

    High gain or low gain version of ST-70 board, guidance needed. Empty Re: High gain or low gain version of ST-70 board, guidance needed.

    Post by viridian Wed Apr 28, 2010 11:24 am

    Bob, thanks so much for the guidance. That settles it, low gain it is, which also gives me the option of 12AU7 or 12BH7. But that decision leads to another funky question.

    Can a 12AU7 be used in the central, input position while using 12BH7s as the drivers, and other than drawing very slightly less current than three of the 12BH7s, will there be any other sonic advantages of this setup? I suppose I should just get building and answer my own question though.
    Bob Latino
    Bob Latino
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    Posts : 3114
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    High gain or low gain version of ST-70 board, guidance needed. Empty Re: High gain or low gain version of ST-70 board, guidance needed.

    Post by Bob Latino Wed Apr 28, 2010 4:13 pm

    viridian wrote:Bob, thanks so much for the guidance. That settles it, low gain it is, which also gives me the option of 12AU7 or 12BH7. But that decision leads to another funky question.

    Can a 12AU7 be used in the central, input position while using 12BH7s as the drivers, and other than drawing very slightly less current than three of the 12BH7s, will there be any other sonic advantages of this setup? I suppose I should just get building and answer my own question though.

    Marty,

    You can use either a 12BH7 or a 12AU7 in any of the three positions. The center tube is the initial voltage amplifier for both channels and this tube affects the sound quality (IMHO) more than the two side tubes. The two side tubes, which are the phase splitter/phase inverter tubes for their individual stereo channel, should both be the same (either 12AU7 or 12BH7).

    What I would do is try it both ways and let your ears decide which way sounds best to you ..

    Bob
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    viridian


    Posts : 14
    Join date : 2010-02-19

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    Post by viridian Wed Apr 28, 2010 4:43 pm

    Bob, thanks again for taking the time to educate me. I am really looking forward to the project.
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    viridian


    Posts : 14
    Join date : 2010-02-19

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    Post by viridian Sun May 02, 2010 1:01 pm

    Bob, you are already costing me money, and I haven't even built the thing yet! I couldn't pass on some GE black plate 5814 tubes yesterday. I will give those a try as well as all of the others and post back with my subjective take on things.

    Best,
    Marty

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