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spring/plate reverb

Discussion in 'General Electronics Discussion' started by CiaranM, Jul 9, 2012.

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  1. CiaranM

    CiaranM

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    May 19, 2012
    hello, I'm just wondering if anyone knows about spring or plate reverbs, and how to build them? I bought a few piezo transducers, will they be needed?
    EDIT
    I superglued a spring to a mini speaker and a piezo transducer, and I was able to hear the piezo's output when I connected it to my (mains-power) speakers. I tried to make an amplifier on breadboard for a small speaker so I connected the piezo output to base, 9V DC to collector, and emitter to speaker. The speaker just clicked on and off when I (dis)connected the battery. Why won't it amplify?
    P.S. does the circuit use one or two grounds? I'm not sure whether the speaker and piezo which are connected by a spring should be grounded together or separately.

    I also had an idea; if I connected the piezo's output to the speaker's input through a variable resistor, could I alter the length of the reverb?
     
    Last edited: Jul 10, 2012
  2. BobK

    BobK

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    Jan 5, 2010
    An audio amplifier is more complicated than that. Use an LM386 chip.

    Bob
     
  3. CiaranM

    CiaranM

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    May 19, 2012
    I configured a LM386L to be inverting with 9V DC, Rin at 1K8 and Rf at 5K6, but no sound comes out. Why? I've never used the chip before, so it isn't faulty.. oh and do you know of any transistor amp circuits? I don't want to have to use ICs all the time..
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    LMGTFY
     
  5. BobK

    BobK

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    Jan 5, 2010
    That is not how an LM386 is used. Did you look at the application circuits? You simply ground the - input and put the signal to the +. That will give you a gain of 20. A 10uF across pins 1 and 8 will up the gain to 200, which is probably more like what you want.

    Building an audio amp out of dicrete parts is silly except as an academic exercise.

    Bob
     
  6. CiaranM

    CiaranM

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    May 19, 2012
    ok, thanks! I watched a tutorial on op amps, I didn't know that circuits with op amps require three rails. I built an amplifying circuit but there's hum and noise present, is there a way to eradicate it? also, should Rf and Rin be set to high values or low values (e.g. 1M and 10K as opposed to 10K and 100)?
     
  7. BobK

    BobK

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    opamps are typically not capable of driving a speaker. Why not use an audio amp as I susggested way back?

    Bob
     
  8. Raven Luni

    Raven Luni

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    Oct 15, 2011
    I know about spring reverbs. I've got a reverb unit salvaged from a guitar amp that went caught fire - just a piece of metal with spring and coils attached. I've been meaning to make something out of it for ages (long list of unfinished projects).

    A spring reverb works by using a coil to magnetically drive the spring. The magnetic flux is picked up at the other end by another coil. You need decent power amplification at both ends. The reverb effect is caused by the physical jarring of the spring by the induced field and the resulting phase noise (the bounce back of the spring actually contributes signal feedback).

    The driving amp should be low voltage and high current (higher voltage = more impedence losses). The receiving amp should have as high an input impedence as possible (non-inverting / buffered if youre using op amps).
     
  9. CiaranM

    CiaranM

    74
    1
    May 19, 2012
    thanks for your help BobK. I just needed an op amp to boost a piezo signal a bit (the signal is then routed to speakers).
    Raven Luni - are you saying that a spring reverb requires an inductor? I just superglued one part of the spring to a miniature speaker, works fine. I hope!

    I know how to build an op amp circuit with two 9V batteries, is it possible to do it with one?
    Is it something to do with a voltage divider? I think the +9V goes to a top resistor, -9V goes to the bottom resistor, and the 'ground' reference is placed inbetween the two (equal value) resistors. Is that right?
    thanks for your help; I know I'm an amateur, but my college tutor never taught me this stuff.. damn it
     
  10. Raven Luni

    Raven Luni

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    Oct 15, 2011
    Op amps come in many different forms. Some work from a single rail others need 2. Some are better for current others for voltage etc. See THIS THREAD for a basic discussion on dual rail supplies. I've included a circuit there that works great for me.
     
  11. duke37

    duke37

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    Jan 9, 2011
    The signal is sent down the spring which gives a delay before it gets to the other end. The transducers on the delay lines I have seen are like little speakers i.e. electromagnetic devices. You will need to drive the spring with an appropriate amplifier and receive the voltage with an appropriate receiver.

    My concern with what you have is cocerns the piezo transducer which I would think only responds to very high frequencies.

    You can feed some signal back from the output to the input to get a multiple reverb but too much feedback and the thing will go wild.

    You can get op-amps which run on a single supply but you should read BobK posts.
     
  12. CiaranM

    CiaranM

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    May 19, 2012
    thanks! I have a few last questions..
    - does the capacitance between either power rail and ground have to be 220u? I've used 100u; will that suffice?
    - does a DC battery supply a positive and negative voltage, or a positive and neutral (0V) voltage?
    - should a preset resistor be used in a potential divider for a single battery circuit (because of tolerances making resistance values unequal)?
     
  13. Raven Luni

    Raven Luni

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    Oct 15, 2011
    Capacitance depends on the application and the loads involved - the bigger the load the bigger the capacitors

    A 2 terminal battery is always + and 0

    Toleranes arent the only thing that affects resistor dividers. Rememer that a load is seen as an addition resistance in parallel. This is especially problematic in audio applications since that resistance is constantly changing with frequency (impedance). This is why you should use some kind of active feedback to keep the midpoint stable.
     
  14. CiaranM

    CiaranM

    74
    1
    May 19, 2012
    I've just read your message duke37, the piezo works great, its output needs a bit of amplification though. I tried connecting a wire from the speaker input to the amplified version of the piezo's output, but nothing happened. bit annoying
     
  15. CiaranM

    CiaranM

    74
    1
    May 19, 2012
    thanks, I didn't that about capacitors. Hmm, why does a battery have + and - marked on it? I thought that a battery had +V and -V, so that the electrons move to the positive charge.
    OK I'll read up on active feedback..
     
  16. Raven Luni

    Raven Luni

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    Oct 15, 2011
    The subject youre looking for is virtual ground circuits. As for batteries, yes theyre + and - but from the point of view of the circuit, the - is the common ground point and therefore the zero reference. The potential difference is +9V (for a 9V battery), otherwise it would be a 3 terminal battery with +4.5V, 0V and -4.5V. You can make that easily enough from individual cells - the only disadvantage is different drain at each side leading to an uneven split.
     
  17. CiaranM

    CiaranM

    74
    1
    May 19, 2012
    I just made a potential divider, now I understand how the reference affects the displayed voltage.. good stuff. One thing though, surely a potential divider (with equal values) is wasting half of a batteries energy? and what about overheating the battery?
     
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