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Thread: Piezoswitch activated momentary noise gate.... suggestions?

  1. #1
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    Piezoswitch activated momentary noise gate.... suggestions?

    hey guys...i've got a an idea that i'm nearly ready to apply. i want to put a piezo element on the batter head of my bass drum that will trigger gate to be "open" whenever the drum is hit. the gate is between a guitar and amplifier. the guitar sound will only pass through to the amp when the drum is hit.
    i need some help working on the logisitics...
    i'm starting here: Taint Paul Triggered Drum Light

    i have two thoughts... one is that i can use the circuit above to trigger an LED to interact w/ a photosensitive resistor. (the resistor being open when the LED is off. closed when the LED is on.) the photo-resistor will simply be in between an input and output jack.
    the other thought is to use a momentary relay switch in place of an LED. hitting the drum vibrates the piezo which sends the voltage to the relay to allow the input and output jacks to "see" each other.
    one of my concerns is the amount of decay allowed for each guitar note. i don't want it to be such a short burst to have a stuttering effect, i'd like each note to have a bit of breath and taper off rather than be cut off abruptly. (which makes me think the LED photo-resistor is the better choice.)
    if the piezo circuits output voltage went into a charging capacitor before the LED, the LED could fade out gradually which in turn could fade the volume of the guitar signal out w/ it.
    if anyone has some words of wisdom, please lay it on me! i'm looking to get this project up and running in the next few days. thanks!

  2. #2
    Senior Member Enzo's Avatar
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    I am sure we could engineer somethiing, but why not use a commercial gate? Some have a side chain input so that some other signal can control the gate. Gates are adjustable for release and other parameters. Now all you have to do is trigger it.

    Is your bass drum mic'd into the PA? Got an insert on the channel? Or an AUX send you can use for this? Just send the kick drum to the side chain jack of the gate. Voila.

    Buy Alesis 3630 Dual-Channel Compressor/Limiter with Gate | Compressors & Limiters | Musician's Friend


    A piezo sends out a pulse when hit. Plug your trigger into an amplifier and listen to it. I'd be willing to bet the3 raw piezo signal would be capable of triggering the side chain input of a gate.
    Education is what you're left with after you have forgotten what you have learned.

  3. #3
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    That's exactly what I was going to suggest. A great many noise gates have "external keying", such that the signal used to turn the gate on is a source other than the input signal itself.

    Here's an easy circuit, that provides both a control voltage for keying a gate, and a gate output, for initiating a fixed envelope generator: http://www.musicfromouterspace.com/a...gger_final.gif

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    thanks for the links and advice, guys. i think mark's link is more up my alley. i'd rather spend a couple of hours building something than $100 on a rack unit.
    mark, in the schem you linked me to, what would i attach to the trigger-out?

  5. #5
    Senior Member Enzo's Avatar
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    Build it or buy it, the point here is that a standard gate circuit with side chain does exactly what you propose.
    Education is what you're left with after you have forgotten what you have learned.

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    so...this afternoon i built this: http://www.vdrums.com/forum/attachme...5&d=1237221392

    i copied this circuit and put a photo-resistor directly in front of the LED.
    the photocell is simply in series w/ an in and out jack in a dark enclosure.
    the ONLY problem i'm having is that when the LED is off, there is still 20-30%
    signal strength coming into the amp through the photocell. i need a way that the signal
    is grounded when the LED is off. ideas?

  7. #7
    Supporting Member Jazz P Bass's Avatar
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    Why the phto resistor.
    How about an opto-coupler.

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    don't really know anything about optocouplers off hand. do you think that would provide a better solution for me? i just grabbed some Radio Shack parts and went to work.

    since my last post, i found this: Reversing a Photoresistor?

    i added a 120k res from my output jack to ground. this has lessened my leaky pass-through signal without noticeably affecting the intensity of the signal passed when i strike the drum. said test was done at bedroom levels, so i'll have to wait to see how it translates to playing volume.

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    my piezo element has gone finicky. what gives? it worked flawlessly @ practice until all of the sudden....it didn't work at all.
    i isolated all of the cables and they're good.
    i isolated all of the pedals in the chain and they're good.
    i isolated my piezo activated circuit and it's good.
    i isolated the piezo element and found that it only works SOMETIMES.

    how does one break a piezo element? (full disclosure: this is a radio shack piezo, if not all piezos are created equally...) do they simply wear out?

    better yet...how does one repair a piezo element?
    i can get another one easy enough, but what's to keep me from needing to get a new one every week?
    i need all of the help i can get...the gig where all of this comes together is in 5 days!
    need a reliable solution!

    also...if i go back to radio shack, they have larger piezo elements as well- what difference would a larger element make for my purposes? anything?
    Last edited by methodofcontrol; 06-26-2011 at 07:51 AM. Reason: added info

  10. #10
    Supporting Member Jazz P Bass's Avatar
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    The piezo element is a crystal.
    I do not see any repairing.
    Being that it is a crystal implies that it is fragile.

  11. #11
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    new piezo element and new way to attach to drum seems to be more gentle on element and i now carry a backup element as well. success!

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