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Part Replacement in Circuit

Discussion in 'General Electronics Discussion' started by SparkyCal, Aug 20, 2020.

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  1. SparkyCal

    SparkyCal

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    Mar 11, 2020
    I am trying to build this circuit and gathering all the parts:
    .
    The schematic for it is at 6:50 of the video.

    It is a Theramin- which is a musical gadget of sorts. It makes zany noises when your hand moves toward it.

    To see Lez Zeppelin use, one, see 6:15 of this videohttps://www.youtube.com/watch?v=JoTyCwRkm3I

    In any event, in the video, the builder of the circuit uses a TIS58 JFET transistor (which has long been discontinued). He says he used this type, because it is what he had lying around. I don't know if that means that you could use any transistor. I looked at the data sheet and searched for equivilants, but i don't seem to have any of the equivalents listed. But I do have a whole slew of transitors, as depicted in the attached picture.

    Is there anything in this army of transistors that you think I could use, in place of the
    TIS58 JFET transistor.

    He does say that most any JFET would work for this circuit. Is there a JFET im my pic that is a safer pick?

    Thank-you
     

    Attached Files:

  2. bertus

    bertus Moderator

    2,029
    763
    Nov 8, 2019
    Hello,

    That is half a theremin.
    It only controls the pitch and not the volume.
    A real theremin controls both.

    A theremin is not a real beginners subject.
    It contains several oscilators that must be adjusted for good results.

    This page has links to several theremin schematics:
    http://www.thereminworld.com/schematics

    And this page has some recordings of the theremin being played:
    https://www.thereminvox.com/

    Bertus
     
  3. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Thanks Bertus. I will certainly check them out. The only reason I leaned toward this one, was that he has a detailed video putting it together on a breadboard. He says that Thermanins that have volume controls, get very complex. That is why I stayed away from othe rones. But if I can find a schematic in the link you provided that doesn't look too intimidating, I'd rather built it properly with the volume.

    Thanks Bertus!
     
  4. PETERDECO

    PETERDECO

    178
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    Dec 19, 2019
    Just in case you go back to the original circuit, substitutes for the TIS58 come up as BF256A, 2N5485 and 2SK107.
     
  5. Audioguru

    Audioguru

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    732
    Sep 24, 2016
    I am amazed that the circuit works when it was built on a solderless breadboard with messy long wires and their stray capacitance all over the place.
    His soldered circuit needed two long wires rolled up inside to add come capacitance and the antenna length was critical.
     
  6. SparkyCal

    SparkyCal

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    Mar 11, 2020
    What do you think should be the appropriate antenna length?

    As I explained to Bertus, I am leaning towards this circuit because it has a detailed video explaining the breadboarding, but also explaining the math. I thought it would be a good first attempt, with a view toward learning and then going for a real theremin that includes volume.
     
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    I did not hear in the video about the radio frequency it uses and I did not calculate it because of all the stray capacitance. The video mentions that it picks up radio stations. The antenna length depends on the radio frequency and amount of stray capacitance.
     
  8. SparkyCal

    SparkyCal

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    30
    Mar 11, 2020
    Another question. In this video, he uses a particular transistor and references it’s drain and source. I am going to use BC537 transistors, but those commonly are referred to by collector, base and emitter. Why is the terminology different and do you think I can use the Bc537
     
  9. SparkyCal

    SparkyCal

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    Mar 11, 2020
    I researched it and learned that they are not interchangeable because one uses voltage and other, current. So I ordered soMe jfets. I hope I don’t already have some in that smattering of transistors that I posted.
     
  10. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Bought these.
    Leyal 10PCS MPF102 JFET AMP N-CH RF SS TO92 New
     
  11. Audioguru

    Audioguru

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    732
    Sep 24, 2016
    Digikey says that the MPF102 is obsolete and is not made anymore. They have a 10:1 range of current so you need luck to find some that will work in that circuit. I hope that whoever made the ones you bought used the standard pin-out:
     

    Attached Files:

  12. SparkyCal

    SparkyCal

    831
    30
    Mar 11, 2020
    I need to swap the pin mapping
     
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