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weird electronics mods?

Discussion in 'Hardware, Setup & Repair [BG]' started by steamboat, Jun 24, 2001.

  1. After I install a J pickup on my Peavey.. (see the mystery Dimarzio thread in pickups) I think I'm going to tinker with my electronics.

    My inspiration for this is the fact that Jack Bruce had a diode added to his EB-3 in order to try to replicate the sound he got out of cranked Marshall guitar cabs.. and this product from Stew-Mac:


    I can't find out anywhere what sort of diode was installed in Jack's bass (or how well it worked for that matter), and information on the Black Ice is pretty scarce too. A few people seemed to like it, others thought it was horrible. My guess is that regardless of how well it works on guitar, it's not worth spending 30 bucks on it for a bass application.

    I intend to do this mainly for a bit of fun.. if I actually get a useable sound then so be it. I have a bunch of diodes from this old electronics kit, so I guess I'll try those out. For my initial tinkering I would install the diode in place of my tone pot's capacitor (this is the method used for the Black Ice). If I found something useable I would set up another pot so I could still have a tone knob.

    I'll do all of my initial testing at low volumes through my little Crate.. that way if I end up producing any horrible speaker ripping noises it would matter so much. :)

    Anyone ever tried anything along these lines or have any idea what exactly was done to Jack Bruce's bass?
  2. I've thought about this. You may want to use a 1N914, which I think is a Germanium diode, instead of a standard silicon diode. The Germanium has a lower turn on voltage, like 0.2V or so. The silicon has a turn on voltage of 0.7V, and I don't think your bass puts out much above 0.2V. I'd put 2 diodes in parallel from bass signal output to the wiper of a 500K pot then the other end of the pot to ground, with the diodes pointing in opposite directions. That would make a symmetrical clipper circuit. Just the little bit I've thought about it.

  3. notduane


    Nov 24, 2000
    Dagnabbit t~nut! Ya' beat me to it :D .

    BTW...emailed Kendrick and got a reply from G. Weber
    hisself! All-tube Kendrick bass combo? :eek:;) .

    I found out about as much as you..."Dan Armstrong
    put a diode in Jack Bruce's bass to replicate the
    'bumblebee' sound." What it probably did was offer
    a clipping or fuzz due to the low turn-on voltage of
    a diode. This idea was adopted in early fuzzes (see
    2nd stage, below). I think it's official name is "integrator".
    MikeyD can probably tell ya' a lot more about this...
    bein' fresh outta' E.E. school :).

  4. That's a clipper circuit. An integrator would have a capacitor in place of the pair of diodes.(EE grad 5 years ago :D)

    D1 and D2 are in the feedback loop of the op-amp, and if they turn on at .2V, then the output is clipped at +/- .2V, which would be the pos and neg peak of an RMS sine wave of about 130 mv (.13V).

    You can figure out opamp circuits using the ideal case assumptions, infinite gain, infinite input impedance. If these were true, both the positive and negative inputs are 0V all the time (0V AC, not DC, in this case they are 1/2 9V=4.5V). They aren't true ever, but close enough for government work.:D

    Note on the circuit above, there is no adjustment of the amount of fuzz, just the output level. I'd put a 1M pot in for that 470K resistor to allow adjustment of the drive voltage. And if that didn't work, I'd try something else, per usual.

  5. notduane


    Nov 24, 2000
    Yeesh. What can I say? I been writin' software for
    the last 11 years :p .
  6. Thanks guys.. I'll give the two diodes in parallel a shot.
  7. Brendan

    Brendan Supporting Member

    Jun 18, 2000
    Austin, TX
    You know Throbbin...you lost me there on the Tech stuff...sheesh...you people make me feel so inadequate about what little knowledge I have...

    Oh...and from your signature there, I take it you to have been un-stuck in time as well? (Vonnegut)
  8. Err, just one quick point guys. The 1N914 is a silicon diode: silicon diffused to be precise.

    Rockin John
  9. Oops, I was just going on memory on that 1N914. I think Radio Shack has a little pack of tiny Germanium signal diodes, but I don't remember the numbers.

  10. Yeh.

    Err, OA47: OA91, AA119; OA200; etc.

    Some of the silicon Schottky diodes have a lower forward volt drop if the Germanium stuff's not around. Try: BAT41; BAT42 @ 0.4 Volts or BAT49 @ 0.42 Volts.

  11. pkr2


    Apr 28, 2000
    coastal N.C.
    Just for the sake of conversation, how do D1 and D2 work as an integrater circuit? I was of the opinion that an integrater ckt was usually an R/C circuit. I don't see them being any more or less than a clipping ckt.

    Of course I stand to be corrected if I'm out in left field here.

    By the way, for bread board purposes, the E to B junction of a transistor with the C left open works just fine as a diode.

  12. notduane


    Nov 24, 2000
    It ain't an integrator - it's a clipper, as t~nut pointed out earlier.
    You wanna' borrow my dunce cap? :p (J/K! :) )
  13. pkr2


    Apr 28, 2000
    coastal N.C.
    Yep! :)


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