The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    PAS 3; Z-mod Phono upgrade hum?

    Share

    Dingojazz

    Posts : 39
    Join date : 2010-09-03

    PAS 3; Z-mod Phono upgrade hum?

    Post by Dingojazz on Mon Jan 17, 2011 4:14 pm

    I now have the Z-mod phono board installed in my PAS 3, which also has the VTA dyna-clone linestage and PS modules, as well as I/O jack upgrade.

    The Z-mod phono is sounds better than the VTA dyna-clone phono board it replaced, but while the gain is about the same, there's significantly more hum (starting at the 12:00 volume position and increasing from there).

    I did install the small (47uf)'lytic caps on the board, anticipating correctly that I'd need the gain. Oh, and I also have updated the selector with one that resembles the white one on the site photo.

    Any help/ suggestions for hum reduction appreciated.

    Thanks,

    Kevin

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: PAS 3; Z-mod Phono upgrade hum?

    Post by tubes4hifi on Thu Jan 20, 2011 2:44 am

    Hi Kevin,
    I believe we took care of this via email earlier today, the filament circuit on the upgraded phono board (PC6) was designed to work with the upgraded line stage (PC5) which you didn't get,
    so the key is to ground the "floating" filament supply as was done on the original phono board.
    With the complete Zmod for the PAS3 that filament voltage is tied to a B+ voltage divider to "lift" it up around 40vdc which removes the noise floor.
    Roy www.tubes4hifi.com

      Current date/time is Fri Sep 30, 2016 7:44 am