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Building a preamp help

Discussion in 'Amps and Cabs [BG]' started by funky_bass_guy, Apr 24, 2005.

  1. Hey guys,
    For a bit of fun and to get a different sound from my SWR I have started building my own preamp. So far I have just got a basic clean boost circuit that takes the bass level up to line level. I am using an Alice Soundtech Matchamp, and extrememly low noise op-amp. This sounds pretty good going into my poweramp and the tone is as you would expect, unaltered.

    I would like to put some tone controls on it now but am not too sure how to go about this. Info like frequency centres would be very useful! I want to get a punchy modern tone to compliment by custom graphite necked 5 string.

    Any ideas?

    Thanks in advance
    Chris :hyper:
  2. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    What are you asking? Freqs for an EQ, circuits for FX? If I were building a preamp I'd incorporate a class A tube somewhere; you can make a nice almost 3d, yet still hi-fi preamp like the ones for Trace amps. A reverb tank and possibly some chorus would be awesome.
  3. Schematics, circuit diagrams, eq circuits anything really! I dont want to incorportate a valve due to the voltages and dangers.
  4. dood


    Dec 9, 2004
    sitting down,facingforward..UK
    Endorsements: Shuker Guitars, Dingwall Designer Guitars, D'Addario, Planet Waves, Barefaced Bass
    hi Chris, remind me tomorrow and I'll dig out some bits n bobs that may help.. if I can find them.

    Pm me at BW.

  5. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    Well if you ever need any help with a tube send me a PM as I have a ton of info in a PDF you can get. It really shouldn't be too hard to integrate a tube though, and as long as you take the necessary precautions it should be ok.
  6. [SD]


    Feb 24, 2004

    i would be interested in those PDF files. I'm curious about valve circuits and low voltage and high voltage driven valves...stuff like that
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Walt Jung has written a lot of books of audio circuitry. You could find some cool ideas to fool around with in them.

    For ideas on bass/mid/treble tone control circuitry, do a Web search on "baxandall tone control".
  8. Funkengrooven

    Funkengrooven Turn it down? You gotta be nuts!!

    also check out Walter Harley's stuff...
    He is a grerat resource and very easy to talk to.
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Cool circuit. I disagree with his assertions about "phase inversions" and op amp distortions. But I like the use of JFETs; biased the right way and with appropriate amounts of gain and negative feedback, you can get a nice, slightly nonlinear transfer function that is pleasantly tube-like.
  10. Passinwind

    Passinwind I Know Nothing Supporting Member

    Also check out Don Lancaster's books, especially the Active Filter Cookbook.

    This guy has schematics for an instrument preamp, and circuit boards for many of his projects: http://sound.westhost.com/; I'll be finishing up a project using some of his boards any month now. :cool:

    I made a very good sounding preamp simply by taking the Fender tone stack and sandwiching it between two opamp gain stages. I scaled the impedances down a bit, FWIW. I like the Baxandall stack a lot too though, but I used tubes for that one instead of going solid state.

    If you haven't been there already, go to Ampage on www.firebottle.com and poke around the forums, links, and reference sections. It's a great DIY resource.
  11. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
  12. Try this for tone circuits

    or this

    and maybe this

    The first one has a bunch of stuff for g****r players, but much of it would work. Lots of it is for effects. I haven't visited any of these for a while so forgive me if I'm all messed up.

    +1000 for Don Lancaster's book. It pretty much has all the theory you need without being over your head (or at least mine, being pretty low to start with ;) ) Try Partsexpress.com and audioxpress.com for other possible books on the topic.
  13. Passinwind

    Passinwind I Know Nothing Supporting Member

    I've been able to find both the Jung and Lancaster books at my local library, although we had to order them in from another branch. I used to hang in engineering libraries at a few colleges I lived near as well.

    Another decent source for design reference is application sheets from semiconductor manufacturers. I haven't done an online search in a few years, but I expect that stuff is still there if one looks hard enough.
  14. Thanks for all your replies guys :)

    Mr Wind I dont suppose you have a schematic for that preamp do you? What sort of sound do you get out of it? All these seem to be old-school sound style, I am looking for a more modern sound for some nice slapping and popping with funky fingering!

    Thanks again
  15. Passinwind

    Passinwind I Know Nothing Supporting Member

    I did have a schematic Chris, but it's long gone. IIRC, it's just two noninverting opamp gain stages, with 180 ohms on the negative leg to ground through maybe a 25uF cap, and around 10K in the feedback loop. Then, stick the Fender tone stack in the middle; you're done, pretty much. Peavey used something like this on some of their older solid state amps. Since the Fender stack scoops mids no matter what, it's pretty happening for slapping IMO, but if you want something really spanky, consider a hi-fi stack like Baxandall or the other one linked above, and add a band or two of parametric or semiparametric EQ to the mix. The one in Craig Anderton's book, Electronic Projects For Musicians is a reasonable place to start.

    What sort of sound do you get out of it?

    Mutant, fretless wind passing, mostly. :bassist: I don't play fretted bass at all, so I'm not sure how helpful these clips will be:

    This shorter one is live, miked slide fuzz bass, and dubbed "regular" bass direct to the soundcard, both through the Fender style preamp:


    This longer one is just straight-up miked live bass, recorded in stereo with the drums at the same time. The guitar-object noises are a dubbed guitar on this one, unlike the first clip. :cool:


    I'll try to get a recording of the ESP preamp up soon. It's just sitting on my bench, waiting to go into the rack case.
  16. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Looks interesting. Depending on the leakage current through C18, IC2a (tuner out) might give you some troubles, If I were to build it I would put a large resistor from the noninverting in (+) to ground.
  17. Thanks Wind, listening to them now.