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DIY bass preamp design

Discussion in 'Amps, Mics & Pickups [DB]' started by fdeck, Oct 1, 2005.


  1. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    www.execpc.com/~fdeck/bass

    Here it is, the design information for my BBBB -- Bare Bones Bass Blender. It is a complete solid-state bass preamp, more or less inspired by the Raven Labs Professional Master Blender.

    The dirty secret of DIY design is that you make up a "reason" for doing it, after it is already done. For the DIY'er, GAS takes the form of building new gadgets. My reasons were twofold. First, I found myself sitting down at the computer to unwind, every night after putting the kids to bed. Designing a preamp seemed like more fun than surfing the web.

    Second, I have an irrational compulsion to understand exactly how my gear works, and I learn by doing.

    At present, I have no intention to commercialize this design. If enough people are interested, I would be happy to order a small collection of bare printed circuit boards.

    More than anything else, I welcome all comments and criticism.
     
  2. Passinwind

    Passinwind I Know Nothing Supporting Member

    Thanks, and nice work. I'd be down for a couple of PC boards, might as well add to my ridiculous backlog of unfinished projects. :cool:
    I like the fact that yours is optimized for battery power, which is something I normally don't use for my DIY stuff. You included a lot of useful features for such a compact unit.

    I'll try to follow your example and post a couple of my bass oriented projects as I finish them up. Documentation has never been my strong suit though. It's more fun to build the widgets, eh?
     
  3. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004

    Hey, nice work! :) Baxandall controls, huh? As I recall, they effect sliding turnover points. Gosh, that's a memory that's 30+ years old. Now, if I can only remember what I had for dinner last night...
     
  4. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    That's a good point. Thanks DRURB.

    To elaborate a bit further, the Baxandall tone control circuit has two chief claims to fame: Independence between the treble and bass controls, and a definite "flat" setting. Of additional interest to a DIY'er is that it uses a tolerable number of parts. Compared to passive tone stacks, the Baxandall doesn't impose an insertion loss, making it easier to manage the dynamic range of the overall circuit.

    But the Baxandall circuit sets the corner frequencies with RC filters, and the effective "R" values depend on the knob settings, resulting in corners that shift when you turn the knobs.

    I can't think of a work-around to the shifting corners without additional op amps. Do you know if there is a trick?
     
  5. nsagan01

    nsagan01

    Nov 10, 2007
    mpls
    Does anyone have any suggestions as to how I would go about wiring up the DTar Volume and tone module to a piezofilm p/u and kemo m040 preamp?
     
  6. Francis, You amazed me with the compactness and usefulness of the HPF. If you construct a couple of these let me know. I'd gladly take the first one and try it out.
     
  7. Thanks for clarifying that, Fdeck.:confused::eyebrow:
     
  8. I can't see the circuit on the link. can you post it again?
     
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    The circuit is still there, but is now one among several links. The BBBB schematic diagram is under one link, just for show and tell, and then the documentation is under the other link.

    Note in edit: I have found that the BBBB circuit really has a whopping amount of gain, perhaps more than needed for many bass pickups, so it is worth reading the section in the documentation on choosing lower overall gain settings.
     
  10. dbassnut

    dbassnut

    Apr 1, 2008
    Malaysia
    Hi Francis,
    Thanks for the schematics. I build your quick & dirty preamp & it works really well. A little too well. :). One of the wires to the output actually behaved like an antenna & was sensitive enough to pick up noise if I sat the preamp on my bass amp when the preamp was plugged in but the bass wasn't. However, if I completed the circuit by plugging my double bass pick up in, the noise disappeared. I shielded the wire by wrapping it with copper foil & grounding it & this seems to help. I'm changing the case to a metal one later to see if this helps more. Once again, thanks for schematic.
     
  11. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Thanks for the kind words! Using a metal case should help. It might even be possible to shield the inside of a plastic case with foil, or self adhesive foil tape.

    There are a couple other ways that you can deal with the noise. First is to use a "switching" type of jack on the input, and use it to ground the input when nothing is plugged in. The other is to put something like a 100 - 200 pF capacitor in parallel with the input. This won't affect the response of the circuit very much, since a typical pickup already has around 10 nF of capacitance.

    What type of JFET did you use? It would be helpful for others to know what parts are easily available in your country.
     
  12. dbassnut

    dbassnut

    Apr 1, 2008
    Malaysia
    Hi Francis,
    I used the 2N5486 as per your recommendation. I wired everything to a breadboard & mounted the JFET on a 3 pin jack so I still have the option of swapping out the 2N5486 later. I work for a PCB design house so getting parts is not a problem.
    Thanks,
    Adrian
     
  13. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    Endorsing Artist: Black Diamond & SuperSensitive strings
    Is it possible to add a volume control to the original version? I'd like to get mine closer to unity gain.
     
  14. dbassnut

    dbassnut

    Apr 1, 2008
    Malaysia
    Hi FDeck,
    The preamp is great.
    I've been using the preamp I built using your schematic & advice for about 3 months now & have noticed the following when using it with my NXT.

    1. a little hum when the volume knob is set midway. None when volume is maxed out or set to zero. It's probably a grounding issue on the amp though but without the preamp there is no noise. I think that the preamp is amplifying the hum when the pot is set midway (equal resistance from the wiper to the end of the pot).

    2. Tone. - the NXT has a pizz/arco switch. Without the preamp, there is a big difference in tone when pizz( plucking the strings in arco mode gives a very boomy sound with quick delay, pizz mode - not much boom but longer decay) but using the preamp, both tones get warmed up so much that it's difficult to tell the difference when you pluck the strings that you can actually adjust the tone by changing your attack on the strings without having to switch.

    All in all, I'm very happy with the preamp & will probably build another to tweak around with.
     
  15. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    What resistance of pot did you use for the volume control?
     
  16. dbassnut

    dbassnut

    Apr 1, 2008
    Malaysia
    Hi FDeck, It's a stock pot. :). As the NXT is similar to WAV, it should be a 1Mohm. I've attached the schematic for your perusal.

    Regards,
    Dbassnut
     

    Attached Files:

  17. SEO services

    SEO services Banned

    Jan 8, 2011
    us
    @fdeck, Good work.[​IMG]
     
  18. Thanks a lot for this design Fdeck, I've just "successfully" made the phantom powered preamp and it complements my realist pickup well. I did notice a small buzz on the top end of the spectrum. I can get rid of it if I low pass the signal at around 8kHz but I was wondering if you had any suggestion regarding noise/buzz/hum?
     
  19. jadamita

    jadamita

    Aug 14, 2013
    Is there any chance you still have the schematic for this?
    thanks