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  1. #1
    GV#27
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    Default PASS B1 buffered pre amp.

    In case anyone is interested,Nelson Pass is making plans available for a DIY version of his new B1 buffered(no gain) JFET preamp.http://www.enjoythemusic.com/diy/070...eamplifier.htm

    This would be a nice little project for anyone that does not need any gain in their pre but don't like the loss of dynamics that accompany the puerly passive pre approach.
    It should be very simple and reasonably inexpensive to build.He will apparently offer the PC boards for sale soon but this can easily be built on some perf or vector boards.And as with other NP designs one can expect it to sound very good.Im currently using another one NP's DIY JFET designs but Im thinking of building this one just for the heck of it.

  2. #2

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    I'll have to look into this, thanks for the heads up.

  3. #3

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    I wonder how it compares to the bride of zen. Seems a strange design for pass as most of the Aleph amps have very low gain and need a medium-high gain pre to sound their best.

  4. #4
    GV#27
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    Quote Originally Posted by Gaara View Post
    I wonder how it compares to the bride of zen.
    The fact that it uses jfets as opposed to the MOSFET's used in the BOZ,it should have considerably lower noise and distortion.I have a BOZ and while it sounds good I much prefer the sound of my DIY jfet pre that Nelson outlined in his DIY op-amp article.
    Seems a strange design for pass as most of the Aleph amps have very low gain and need a medium-high gain pre to sound their best.
    Yeah his First Watt amps (F1-F5)are also a little on the low side as far as gain is concerned(ie.15.5db for the F5) but it will be highly system dependant as to the need of extra gain in the pre.

  5. #5

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    yep... made the B1 last night. nice sounding. fills in the upper end, made gainclone sound much smoother and more balanced. will try driving couple other amps with. should be useful protecting my weak sources an 'output opamp removed' modded sb3 and monica2 with no iv stage.

  6. #6
    GV#27
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    Quote Originally Posted by rawsonte View Post
    yep... made the B1 last night. nice sounding.
    Cool ,now its a must for you to post some pics:D,A couple of questions if I may.
    1.did you use a stepped attenuator or pot for the volume control?

    2.where did you sourced the jfets from?


    BTW welcome to the forum.

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    post quick pics of it later tonight... really easy to do on perf board. i used 12uf polyprop dayton's i had laying around on output. 4.7uf polypropolene axon (brand like NP uses on output) on the input.

    used basic linear power supply. transformer -> rectifier -> 1000uf||1000uf -> 1 ohm -> 1000uf||1000uf -> 1 ohm -> 15000uf like the B1 article ps there on.

    used a basic 50k ohmite pot i had laying around, maybe swap a panasonic one in there. eventually get around to ordering another batch of alps blue velvets. can't bring self to put big money into pot since i tinker and go through so many electronics.

    oh yeah... can get the jfets, sk170's, from mcm electronics or ampslab. been ordering most of my little jfets from ampslab recently.

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    Would this work well teamed with a Welborne ST-70? I have a Dynaco Pat 4 that I can gut out and use as a home for the PASS B1. It would be for a bedroom rig with a pair of fairly efficient Tannoys.

  9. #9
    GV#27
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    Quote Originally Posted by Face View Post
    Would this work well teamed with a Welborne ST-70? I have a Dynaco Pat 4 that I can gut out and use as a home for the PASS B1. It would be for a bedroom rig with a pair of fairly efficient Tannoys.
    Yeah ,assuming the source is a CD/DVD player with the standard 2volts of output and the Tannoys are atleast 90db ish efficient then it should work just fine.
    Last edited by GV#27; 07-11-2008 at 03:41 PM.

  10. #10
    GV#27
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    Quote Originally Posted by rawsonte View Post

    used basic linear power supply. transformer -> rectifier -> 1000uf||1000uf -> 1 ohm -> 1000uf||1000uf -> 1 ohm -> 15000uf like the B1 article ps there on.
    I have a little Talema toroid that I plan to use with an LM7818 regulator,then duplicate NP,s schematic.I ll see how much PASS wants for the PCB's ,if too pricey I'll use just some perf board.


    oh yeah... can get the jfets, sk170's, from mcm electronics or ampslab. been ordering most of my little jfets from ampslab recently.
    I don't know of any supplier in Canada so I ll check with Ampslab.

  11. #11

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    Quote Originally Posted by rawsonte View Post
    yep... made the B1 last night. nice sounding. fills in the upper end, made gainclone sound much smoother and more balanced. will try driving couple other amps with. should be useful protecting my weak sources an 'output opamp removed' modded sb3 and monica2 with no iv stage.
    Hi Tim. Monica II is pretty weak, I recall having to turn it up ~ 10db to match my other DACs, so thats what .2v output? Your SB3 sounds like what RWA used to do, they bypass the op-amp with a auricap, running the signal direct from the dac chip.

    P.S. Welcome to club polk, theres a fun thread on the Audio Zone gear somewhere on here, might want to check it out.

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