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A Stretch

Discussion in 'General Electronics Discussion' started by SparkyCal, Jun 23, 2020.

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  1. duke37

    duke37

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    767
    Jan 9, 2011
    And connect the +ve side of C3 to the op amp output.
     
    bertus likes this.
  2. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    I have incorperated the comments on the polarity of the capacitors in the schematic:

    Overdrive pedal with tone-control comment.png

    Bertus
     
  3. SparkyCal

    SparkyCal

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    Mar 11, 2020
    The schematic calls for a 500K potentiometer. I only have 100K ones. Any thoughts?
     
  4. bertus

    bertus Moderator

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    Nov 8, 2019
    Hello,

    With 100K the gain will be lower.
    If you must use the 100K, lower the value of R46 to 220 Ohms to get about the same gain.

    Bertus
     
  5. duke37

    duke37

    5,361
    767
    Jan 9, 2011
    The 500k pot is used as a variable resistance and the higher the resistance, the higher the gain If you replace with 100k then the maximum gain will be reduced by a factor of 5 but this may be enough, depending on the input signal level.
     
  6. SparkyCal

    SparkyCal

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    Mar 11, 2020
    You folks are fantastic.
     
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    Usually a 470nF capacitor (0.47uF) is a non-polarized film type (marked 474). All 470uF capacitors are 1000 times the value and are polarized electrolytic type. Use a film type of capacitor.
     
  8. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Hi..I decided to go to the electronics store and buy the right pots. I will report back
     
  9. SparkyCal

    SparkyCal

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    Mar 11, 2020
    I bought the stuff I need and now I am creating the breadboard again.

    With reference to the schematic, I have connected R3, C23, OA1 (TL082), C31, D2, and D1

    My next step is to connect the 500K Potentiometer, which is located right underneath D1.

    I have the following questions:

    a) The pot I bought has the three pins on its face, and then it has two pins at the bottom of it. (see attached pictures)

    Are the two pins on the bottom the switch? The pot clicks off when I turn it all the way to the left, and then clicks on when I turn it to the right. So I assume there is a built in switch and I assume the bottom two pins relate to the switch? Correct?

    Also, is the switch part optional. If i don't connect those two pins, will it work regardless?

    b) If we think of the three pins on the face of the pot, as Left Centre and Rihght, how do i connect them , in accordance with the schematic?

    Does the left one go to Ground,
    the middle to Pin 2 of the Op Amp
    and the Right to Pin 1 of the Op Amp?

    I have attached pictures of the pot I am referring to.

    btw- I am trying to switch out the capacitors from polarized to regular ceramic ones.


    Thank-you
     

    Attached Files:

  10. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Hi folks...Bertus- thanks for finding that page in which this schematic is further explained. Didn;t know the page existed and it is very helpful.

    In addition to the question I have re: how to hook up the potentiometer (see above). I have a capacitor question.

    The schematic calls for a 220nF capacitor (C28). I searched my stuff and I do not have a ceramic capacitor of that value. According to my research, the capacitor must have the number 224 on it, in order for it to be a 220nf capacitor.

    I don't have one of those, but I did find ceramic capacitors with the number 221 and 222 on them. Curiously, I found a number of capacitors labelled 221, but one is about 1/4 diameter, and the other is tiny - maybe 1/16th of an inch diameter. But they are both labelled 221.

    I guess I am asking wether the 221 or the 222 can be substituted for the 224?

    Thanks!!!
     
  11. bertus

    bertus Moderator

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    Nov 8, 2019
  12. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Great resource. I've book marked it. If I don't have a ceramic capacitor that comes close, i may have to use the polarized one, because I believe i have those of that value.
     
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    Ceramic capacitors are not used for audio, they are used in high frequency radio circuits and power supplies.
    220nF is usually a non-polarized film capacitor. Here is what they look like:
     

    Attached Files:

  14. SparkyCal

    SparkyCal

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    Mar 11, 2020
    I only have ceramic and the polarized ones that look like a tin canister. Can i use them?
     
  15. Audioguru

    Audioguru

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    Sep 24, 2016
    Instead of me looking for these simple things, you should look for them in Google Images.
     

    Attached Files:

  16. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Sorry..I may have mis-asked my question. i wasn;t expecting anyone tio look these up. i was just asking. In this schematic I am building, if it calls for a non polorized film capacitor, and all I have in my stuff are ceramic or the the other kind that are polorized and look like cannisters, can they be interchanged? I know you said that ceramic capacitors are not used for audio, they are used in high frequency radio circuits and power supplies; but in this application, can they be used?
     
  17. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Update:

    Well I predicted I would need your collective help. Here is where I am at:

    - I built the entire circuit on a breadboard (see picture).

    - It does not work

    - I was extremely careful with the following the schematic, but that is not to say I have not made errors. I plan to carefully look at the breadboard connections when I get some solid time to do so.

    In the interim, here are some things that I came up with that may have caused problems:

    1. As you can see , I used different kinds of capacitors, depending on what I had available. So, you will see that i have used ceramic capacitors and polarized electrolytic capacitors. I wonder if this is causing the issue. If it is, I am happy to go buy the right capacitors, but I am trying to figure out what they are. AudioGuru advised that ceramic capacitors should not be used for this purpose. Should I be buying non polarized film capacitors for every capacitor value called for in this schematic?

    2. I am not using the same op amp that he used in his schematic. But in his video, he was swapping out op amps on the fly. He said that having dual op amp ICs, enabled him to pop out one op amp and change it for another, on the fly, for comparison purposes, So the Op Amp I am using, is this one: https://www.amazon.ca/gp/product/B06XK6VW8X/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

    I downloaded the data sheet and was careful to ensure I was using the right pin mappings.

    But can this be causing a problem; the fact that I am using this particular op amp?

    I can't think of anything else that could have gone wrong.

    Thanks for hanging in with me. I am learning and sometimes the best way for me to learn is trial and error.

    P.S. I am also learning a lesson about breadboarding. I recognize it as a valuable tool, but I think that when you get into so many components and connections, it gets hairy trying to make all the components connect properly.

    I am tempted to switch to a virtual breadboard (using Everycircuit).
     

    Attached Files:

    Last edited: Jun 27, 2020
  18. Audioguru

    Audioguru

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    Sep 24, 2016
    Ceramic capacitors have a wide range of tolerance, produce audio distortion and act like a microphone to knocks.
    Film capacitors do not have these problems.

    The TL082 dual opamp should not be used, a TL081 single opamp is all you need and if you use a socket for it then you can easily replace the opamp with a different one.

    The dual opamp you found is a very old one that is completely different to the TL081 single high input impedance opamp. It will work but differently.

    The solderless breadboard is a nightmare of wires all over the place and I cannot see which connects to what.
    I always solder things neatly on a stripboard where each strip is planned and cut to length. Then the strips and a few short jumper wires become a pcb.
     
  19. SparkyCal

    SparkyCal

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    Mar 11, 2020
    AudioGuru- thank-you. I am going to the electronics store to get parts today, and your post was very timely. As an aside, I bought 100 of those dual op amps on Amazon. So, I hope I can find a use for them some day ;-(
     
  20. SparkyCal

    SparkyCal

    216
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    Mar 11, 2020
    I noticed in the schematic, that he has three capacitors that have marked polarity. these capacitors are C30, C27 and C3. Does that mean that those particular capacitors are electrolytic ones, or are those still film capacitors that come polarized?
     
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