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DIY reverb device

Discussion in 'Effects [BG]' started by MadScience, May 16, 2019.

  1. MadScience

    MadScience Supporting Member

    Apr 15, 2019
    Bass Land
    So I've been messing around a fair bit with magnets, pickup coils, and wacky wiring.

    I've come up with a crude reverb device that plays off of vibrations from the cab.

    This is very similar to the natural reverb you get when playing at very high volumes close to the speakers.

    The basis for this device is a pickup coil placed on top of the speaker cab with a separate magnet also on top of the cab but a certain distance away from the pickup coil.

    The vibration from the cab is transferred to pickup and the magnet nearby induces a current. You want the magnet rigidly fixed to the cabinet but just having it stuck on some piece of metal is good enough.

    You want to wire this pickup in parallel with your bass. Easiest way to do this is with a quarter inch instrument cable y connector.

    Now this is going create a gnarly feedback loop that's driven by the acoustical tuning of your cabinet.

    The effect can be moderate or extreme depending on how close you place the pick up to the magnet. It can be anything from a mild lightly sustaining reverb to a full-blown feedback loop that makes itself louder and louder and louder.

    You'd better have robust protection circuit of you try this and things get out of hand.

    There are a couple ways you can affect the behavior of this feedback loop. Obviously changing the distance between the pickup and the magnet will have a strong effect on the overall output. Additionally because the extra pickup coil load is wired in series with the bass any changes to your pickup configuration output resistance will skew the output balance between your bass and the feedback pickup so you can easily tweet the intensity of the effect with your volume pot or if you have coil splitting going on.

    When you get the hang of it, it is possible to create some pretty interesting and potentially useful affects.

    If you're one of those vintage purists out there, it doesn't get any more analog than this.

    Now please, share your thoughts, or simply tell me I'm insane.
    Last edited: May 17, 2019
  2. callofcthulhu


    Oct 16, 2012
    Can you make a demo?
  3. ProfFrink


    Jan 16, 2015
    Cool idea. Seems pretty much in line with the way some other effects started: spring reverbs, tape echos, talk boxes, rotary speakers etc.

    You can try using this on other instruments as well.

    I wonder if we could start an "effects laboratory kit" where all the effects would be mechanical or physical in nature (more than the usual electronical):
    • a phaser made from a sliding tube
    • an optical compressor made with a light bulb
    • a reverb made with a closed stone enclosure
    • a synth /octaver made with diodes you have to lay out on a breadboard
    • etc
    all not too practical, but fun to ry
  4. MadScience

    MadScience Supporting Member

    Apr 15, 2019
    Bass Land
    Thanks for the tip, I'm lightbulb maybe what I need to tame this so I can stop tripping my power supply accidentally.

    I'll also need to look into the phaser idea.
  5. ProfFrink


    Jan 16, 2015

    On second though - a light bulb is probably going to be too slow (although I don't really know all kinds) A LED maybe?
  6. MadScience

    MadScience Supporting Member

    Apr 15, 2019
    Bass Land
    I've seen incandescent light bulbs used for circuitcircuit protection devices when people are working on amps.

    It's wired in series so that if you short your amp the bulb takes all the current.

    I need to measure the resistance of a light bulb. Since the filament resistance changes with temperature it makes senseand you could wire it so that it becomes the current hog at high loads.

    But, is definitely not enough output for a pickup coil to cause this effect. I'd be surprised if it could induce a faint glow in the filament in a dark room.

    Nevertheless there's learning and experimentation to be done.

    here's a wiring diagram for the current limiting device I snagged Screenshot_20190517-210628.png from Uncle Doug on YouTube
  7. Primary

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