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My new boo-teek preamp

Discussion in 'Amps and Cabs [BG]' started by fdeck, Nov 16, 2009.


  1. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    :D

    ebpre.

    This is the circuit that I have been fiddling with for a while. Everything is from my spare parts bin. I will post a schematic soon. It's my attempt to find out how a DIY bass amp would sound with a simplistic discrete design. So far the feature set is:

    Input gain stage
    Active bass / treble control
    Active semi-parametric midrange
    Master volume
    Final gain stage

    If you count carefully, there are nine transistors.

    Yeah, yeah, how's it sound? So far I have only played with it at moderate volume in my workshop to confirm that the controls function.
     
  2. UncleFluffy

    UncleFluffy

    Mar 8, 2009
    California
    Head Tinkerer, The Flufflab
    Nice. Like the build style - I'm normally more of a stripboard man for prototyping, but that's incredibly neatly executed.
     
  3. Interceptor

    Interceptor Supporting Member

    Mar 29, 2005
    Madison, WI
    I'm a kind of old RF guy - love the dead bug construction. It looks just like something out of one of the old ARRL Handbooks. Beautiful!

    Simple circuits are the hardest to optimize. I'll bet a Capitol beer Francis has a good one here!

    I'd love to give this a whirl.

    Jim
     
  4. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Post yer clips! :bassist:

    Very cool build Francis...that's about as far away as possible conceptually from my newest build that I'm currently finishing up. I love all the different takes we see on DIY stuff here on TB. :cool:
     
  5. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Thumbs up!
     
  6. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Close that lid or you'll never be able to sell it for $3000 ;)

    I like the look of it, F...I'm all for having as few parts as possible. Except for tubes...those are necessary.

    :bag:
     
  7. Christian Waiau

    Christian Waiau

    Jun 16, 2005
    las vegas/maui, nevada/hawaii
    Endorsing Artist: Spector, Aguilar, Darkglass
    if he added a couple tubes... he could still sell it for $3k! ...tubes dont even need to be part of the circuit.. :bag:
     
  8. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    i like too. once you get it all sorted, all it would take is a a little dab of silicone here and there to make it roadworthy and vibration-proof for some of those 'floating' components. nice work!
     
  9. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    that is PTPTPTPTP if i ever saw one... nice nice.
     
  10. chicago_mike

    chicago_mike

    Oct 9, 2007
    Chicago - LA - Rome
    Endorsing Artist : Genz Benz
    what type of trannies? J201's? Oh, and, get rid of that green meanie:bag:
     
  11. Jim C

    Jim C Spector#496:More curves than Sophia + better sound

    Nov 29, 2008
    The creativity on this board never ceases to amze me.
    Beauty; here's to hoping the tone is exactly what you like.
     
  12. oerk

    oerk

    Oct 16, 2009
    Bavaria
    That's certainly a nice take on point-to-point.

    I'm looking for a simple preamp like that myself, can't wait to see the schematic!
     
  13. Subscribed...
     
  14. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Hey fdeck,

    Great schtuff! Let's see some projected EQ center and Q specs, input, S/N and noise and so on.
     
  15. Morfman6

    Morfman6 Supporting Member

    May 7, 2005
    Northern Virgina
    so cool! subscribed!
     
  16. PSPookie

    PSPookie

    Aug 13, 2006
    Marietta, Ga
    Very tidy indeed.

    I'd love to see/hear graphs and clips.

    Nice work :)
     
  17. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Thanks for the many kind and encouraging words!

    Here's the schematic:

    http://personalpages.tds.net/~fdeck/bass/ebpresche.jpg

    I should offer some caveats. First, I didn't use exactly these component values, because I had to use what was in my parts bin. Second, there's a problem, because a circuit like this will suffer from tolerance variations in the parameters of the JFETs. Typical fixes include selecting parts, adding bias adjustments, or putting up with it. I chose the latter, in order to get the circuit built.

    I am on the fence about the bass / treble control, since a passive James circuit would also work there. The active circuit should provide better noise performance.

    Next steps include:

    1. Document the design
    2. Testing, after I coax Windows 7 to run my testing software
    3. Record some clips with my crummy bass
    4. More careful parts selection
    5. Lay out a printed circuit board
    6. Share the results

    Critique is welcome!
     
  18. svtb15

    svtb15 Commercial User

    Mar 22, 2004
    Austin,TX - McKinney,TX - NY,NY, - Nashville,TN
    I play it all. Whatever works for the gig
    NICE!
     
  19. UncleFluffy

    UncleFluffy

    Mar 8, 2009
    California
    Head Tinkerer, The Flufflab
    In the Baxendall circuit, are J5/J6 there to provide a virtual earth?
     
  20. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    I thought it was Baxandall - Peter James Baxandall, Her Majesty's Secret Audio Service ; }

    That'll help when you are googling ; }