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Dynaco PAS-3 tube preamp mods and parts

  • original circuit replacements

  • Z-mod upgrades

  • PAS3-AIKIDO upgrade

  • Tone Control Line Amp upgrade

  • regulated power supply upgrade

  • PAS3 upgrade catalog

  • VTA-Z preamp


    original circuit replacement PCBs

    Dynaco PAS3 preamp rebuild

    for those on a budget but wanting an updated/upgraded PAS3, we offer high-quality original circuit replacement PCBs with better than original parts.


    PC6 phono amplifier and PC5 line amplifier . . . . . . . . . . . . . . new power supply board

    click here to see our PAS3 upgrade catalog


    VTA PAS3-Z modification

    Vacuum Tube Audio Zmod upgrades for the PAS3

    Finally, a set of hi-end modifications for the Dynaco PAS3 preamp. We haven't seen anything new in the past dozen years or so,
    and the only real alternatives are the Curcio kit for $662 and the VanAlstine kit for $449, now VacuumTubeAudio at www.tubes4hfi.com
    offers an easy plug-in 3 piece circuit upgrade for the PAS3 that is identical to it's highly reviewed SP6 preamp kit.
    This is for customers that want to KEEP their PAS3 chassis rather than building an all new preamp in a newer chassis.

    Our Vacuum Tube Audio upgrade circuits for the PAS3 replace the 50 year old circuit designs with modern high performance high fidelity drop-in replacements.
    Our Zmod-PC6 phono preamp uses a 12AX7 gain stage followed by a highly accurate passive EQ, followed by another 12AX7 gain stage, for a total gain of 45 db.
    This has higher accuracy and uses no negative feedback, for much improved sound quality and frequency accuracy, with no flabby bass and a clear natural hi-end.

    The Zmod-PC5 line stage uses a pair of 12AU7 in a cascode SRPP gain stage with excellent linearity and low output impedance.
    This is a pure hi-end design with no tone controls and no negative feedback for perfect reproduction of the original source.
    For those who want to maintain a tone-control design, see below for our Zmod-TCLA circuit as an alternative.

    The Zmod-PS power supply makes use of the original 12X4 tube rectifier for soft-start, replacing the old "quad cap" with 266uF of B+ power supply capacitance
    (compared to the original 80uF) with more reserve power for bass and complex music reproduction, and a lower power supply impedance.
    The filament supply is also improved with 6600uF of capacitance for lower noise and more reserve power (compared to original 4000uF).

    Printed Circuit Boards are mil-spec FR4 double-sided with plated-thru holes. Easy installation, with full documentation included.
    An assembly manual, schematic, layout diagrams, parts list, and installation instructions are included, along with online tech support.

    We also have available every part that is used in a PAS3 preamp, most are higher quality than the original types.
    See our parts listing of volume, balance, selector switch, slides switches, LED power indicator, and our very high quality RCA jacks for input-output.

    click here to see our PAS3 upgrade catalog


    PAS3-AIKIDO modification/upgrade

    This new board is the ultimate line amplifier for the PAS3, it takes our hi-end SP12 preamp circuit and sizes it to fit into the PAS3 chassis. The AIKIDO circuit consists of 4 - 12AU7 (or equivilent) tubes with voltage gain and noise-reduction cathode follower output. This circuit design has been optimized to be used with the standard PAS power supply, or even better, with our new regulated power supply. This board delivers the sonic goods. It offers low distortion, low output impedance, a great PSRR figure, and feedback- free amplification. The secret to its superb performance- despite not using global feedback- lies in its internal symmetry,which balances imperfections with imperfections. As a result, the circuit works at least a magnitude better than the equivalent SRPP or grounded-cathode amplifier. This is the ultimate preamp, now in your PAS3 !!


    Zmod TCLA (tone control line amplifier) modification/upgrade

    Finally, a hi-end modification for the Dynaco PAS3 preamp that INCLUDES TONE CONTROLS !!

    This modern circuit uses four 12AX7 tubes in an active Baxandall design for the extra required gain and tone control processing.
    New accurate linear tone controls are included that allow +/-12db of boost/cut for bass and treble frequencies.
    Easy installation takes about 1 hour. Full documentation included with the kit includes assembly manual, schematic, layout diagrams,
    parts list, and installation instructions.

    .

    our new regulated power supply for the PAS preamp

    This new regulated power supply is simpler and less expensive than our previous version.
    This includes two new power transformers (one for B+ and one for filaments) and fits right where the old transformer and power supply were.
    It will require drilling two small holes. Simple installation. Fantastic performance, our ultimate power supply for the PAS preamp.


    click here to see our PAS3 upgrade catalog


    NEW input-output RCA jack panel

    Our 2nd most popular upgrade (after the power supply) is this high quality RCA jack panel.
    The old cheap quality RCA jacks that are crowded together too closely are replaced with a PCB with wider spacing and gold-plated RCA jacks.
    This has 7 pairs of jacks rather than the original 9 pair (most of those were never used anyway!).

    . .


    replace this mess . . . . . . . . . . . . . . . . . . . . with this . . .


    Our new selector switch replaces the old fragile original with a modern 2P6T rotary switch, a nice match to the new RCA jack panel.
    This will eliminate the "rats-nest" of wiring on the original.

    click here to see our PAS3 upgrade catalog


    PAS preamp photo collections (we've worked on several hundred of these, browse to see some photos):

    page one

    page two

    page three


    VTA-Z preamp

    Gone are the limitations of a small size chassis and a terribly underpowered power supply.
    This alternative is less expensive than building a new reproduction PAS3, and it sounds twice as good!!

    The VTA-Z preamp kit is an alternative to the 50 year old Dynaco PAS3 preamp, offered in a new, modern chassis with a contemporary design, and more space inside.
    New power transformers have much higher current capability of the originals. The high voltage B+ power supply has 4X as much current capability.
    KITS include ALL parts to build a complete preamp, including the tubes - chassis, transformer, circuit boards, volume, balance, source selector,
    power switch and LED indicator, front panel knobs, rear panel RCA jacks, AC cord, rubber feet, EVERYTHING for completion !
    This preamp also includes higher a quality blue ALPs volume control. Delivery time is 2-3 weeks - priced starting at $550 !!

    Also available with the TCLA option for those that prefer to have tone controls, this is a modern hi-end design with super accurate tone controls.

    Add our Zmod-PC6 phono preamp for only $80 additional. Uses a 12AX7 gain stage followed by a highly accurate passive EQ,
    followed by another 12AX7 gain stage, for a total gain of 45 db.
    This has higher accuracy and uses no negative feedback, for much improved sound quality and frequency accuracy,
    with no flabby bass and a clear natural hi-end.

    Printed Circuit Boards are mil-spec FR4 double-sided with plated-thru holes. Easy installation, with full documentation included.
    An assembly manual, schematic, layout diagrams, parts list, and installation instructions are included, along with online tech support.


    complete VTA-Z preamp kit $550 plus $30 shipping in USA, includes all parts and tubes

    Also available with the TCLA option for those that prefer to have tone controls
    VTA-Z-TCLA preamp kit $650 plus $30 shipping in USA includes all parts and tubes

    PH-6 phono

    this is a 2 tube (12AX7) phono only PCB used in the VTA-Z and VTA-Z-TCLA preamps
    basic PCB kit with parts and tubes for $80

    PH6 PHONO PCB with parts kit ADD $80



    PAS3 upgrade catalog


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     tubes 4 hifi
     "the path of least resistance is through a vacuum"