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    OK, it ain't tubes or Dynaco - it's a s/s Hafler DH-101 preamplifier

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    deepee99

    Posts : 2019
    Join date : 2012-05-23
    Location : Wallace, Idaho

    OK, it ain't tubes or Dynaco - it's a s/s Hafler DH-101 preamplifier

    Post by deepee99 on Thu Sep 27, 2018 3:33 pm

    Just acquired a Hafler DH-101 preamplifier - functional and very clean cosmetically. (I built one decades ago and still have fond memories of it.)
    I'd like to a full restoration of this new baby. I have a PC-4 cap upgrade kit that's a few years old but never installed/used. I assume the unused caps are still good, but perhaps not?
    I've seen a variety of options, all the way from turning it into a tube preamp using 6922s:
    http://www.musicaldesign.com/paspro1a.html
    which seems like maybe overkill,
    to Musical Designs' http://www.musicaldesign.com/MC_Haf_premod.html
    down to the PC-4 kit.
    Have also ordered a set of gold-plated RCA input jacks to replace those crappy aluminum ones
    The PC-4 kit doesn't contain anything for the power supply, but assume newer and beefier caps wouldn't hurt.
    Any suggestions would be much appreciated.
    This will be driving a Hafler XL-280 amp in my "auxiliary" system.
    Tnx
    dave
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    Peter W.

    Posts : 933
    Join date : 2016-08-07
    Location : Melrose Park, PA

    Re: OK, it ain't tubes or Dynaco - it's a s/s Hafler DH-101 preamplifier

    Post by Peter W. on Fri Sep 28, 2018 8:25 am

    a) A few years on caps is fine, and modern small-value (non-electrolytic) caps will last indefinitely.
    b) New jacks are good.
    c) P/S caps - upping the voltage by perhaps 25 - 50% is good. Upping the capacitance by the same is good. If you go any higher in capacitance than 50%, be sure to bridge them with a small 0.10 uF film cap. Not a bad idea anyway. And do check B+ to make sure it has not climbed too high. Try not to go over 50% in voltage - *some* (but not all) electrolytic caps get 'lazy' when under-driven by too much. It very much depends on the internal chemistry. This tends to occur at higher voltages in any case. My rule-of-thumb is nothing less than 35V in my stuff - even if only a 10V cap initially. And, if you can, look for 105C electrolytics. Heat is the enemy of electronics.

    As to the rest of it - let it be for 50 hours or so before committing any modifications. These are surprisingly mellifluous preamps with a surprisingly good phono stage. You might be sufficiently content to let it be. And it is an excellent match to the 280.

      Current date/time is Thu Oct 18, 2018 5:28 pm