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A Stretch

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

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  1. Audioguru

    Audioguru

    2,832
    634
    Sep 24, 2016
    You bought a pot that is labelled POT LIN. Lin means linear. It can be used but it will be difficult to adjust since a volume control is usually a LOGarithmic one.
     
  2. SparkyCal

    SparkyCal

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    6
    Mar 11, 2020
    Timely because I decided to rebuild from scratch, so I will get a proper one. Will look on amazon. I hope I find the right one this time.
     
  3. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    Hi folks.

    I have changed my approach somewhat, partly because it is starting to get expensive screwing up and then having to buy more parts ;-)

    I have started the circuit over from scratch. For those who are willing to continue to guide me, I thought I would post my step by step process in the hopes that you might check my progress before I get too far.

    To make it easy, please refer to this schematic, which is the one I am working from:

    https://www.electronicspoint.com/forums/threads/a-stretch.293212/

    Here is what I have done so far. I would appreciate it if you could check the work. Hopefully, looking at the schematic, and reading the steps should make it easy to visualize what I have done by referring to the schematic.

    1. Soldered R3 (10K resistor) on PCB.
    2. Connected one end of that resistor to C23 ( 470 nF Capacitor) . I used a film capacitor. The package it came in had the following label on it - CAP FILM RDL 0.47 UF 250V 15SL
    3. Connected R41 (1M resistor ) to one leg of the C23 ( 470 nF Capacitor). R41. Will run to the power part of this circuit, but for now, I left the other end for a later step.
    4. Soldered an 8 pin socket to the board, to house the Op Amp. The data sheet I am using for the TL081 op amp is here:
    https://www.st.com/resource/en/datasheet/tl081.pdf

    5. One leg of C23 ( 470 nF Capacitor) has been connected to Pin 3 of the Op Amp socket (non-inverting input)

    6. Placed C31 (100pF film capacitor on the PCB)

    7. One leg of the C31 (100pF film capacitor) has been connected to Pin 2 of the op amp socket. (inverting input)

    8. The other leg of the C31 (100pF film capacitor) has been connected to Pin 6 of the op amp socket. (output)

    Thank-you!!!

    P.S. Yes, it's me. Just decided to upload an avatar.
     
    Last edited: Jul 1, 2020
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Following such a verbal description is difficult.
    Here's how I proceed when breadboarding:
    1. When you breadboard a circuit, make sure to have a hardcopy of the schematic on paper ready. And colored markers..
    2. With every connection you make, mark this one connection on the hardcopy (e.g. using a colored pencil). You may also want to number the connections sequentially, just in case. This latter step is not required.
    3. Once you think you are finished having made all connections, the hardcopy shall show no unmarked connection. If it does, you forgot to make this one.
    4. If during making connections you come across a connection that is already marked on the hardcopy, you have made an error. Check whether the supposedly existing connection is truly present. If so, the connection you are currently working on is wrong. If the marked connection is not present in the circuit, you obviously goofed when making the first mark. You then have to trace back your work (here's where the numbering during step 1 comes in handy) and identify the error.
    This is what this wouldlook like:
    upload_2020-7-1_12-41-19.png
    So far, so good.


    I also usually start by making the Vcc and GND connections. Why? Because these have the most connections going to different components. It is (my personal opinion) easier to make these connections while the breadboard is not yet a mess of other wires.
     
    Martaine2005 likes this.
  5. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Thank you. I use the method you described, in that I have a highlighter that I colour all the connections I make with. The issue for me is not whether I have made a connection or left one out; it’s whether I have correctly interpreted how things connect to each other. That’s why I am telling like a step by step story, so that someone can easily say- hold on, you connected that wrongly.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    In that case you need to be more specific. For example:
    and
    Which ones? As I marked in the schematic hopefully the same one...
     
  7. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    Hi Harald. Thanks for the feedback. I have edited my specification below, adding more detail in terms of which legs of the connectors I am using. Hopefully, that will provide sufficient clarity.

    1. Soldered R3 (10K resistor) on PCB.
    2. Connected right side of that resistor to C23 ( 470 nF Capacitor) . I used a film capacitor. The package it came in had the following label on it - CAP FILM RDL 0.47 UF 250V 15SL
    3. Connected left leg R41 (1M resistor ) to right leg of the C23 ( 470 nF Capacitor). R41. Will run to the power part of this circuit, but for now, I left the other end (right leg) for a later step.
    4. Soldered an 8 pin socket to the board, to house the Op Amp. The data sheet I am using for the TL081 op amp is here:
    https://www.st.com/resource/en/datasheet/tl081.pdf

    5. Right leg of C23 ( 470 nF Capacitor) has been connected to Pin 3 of the Op Amp socket (non-inverting input)

    6. Placed C31 (100pF film capacitor on the PCB)

    7. Left leg of the C31 (100pF film capacitor) has been connected to Pin 2 of the op amp socket. (inverting input)

    8. Right leg of the C31 (100pF film capacitor) has been connected to Pin 6 of the op amp socket. (output)
     
  8. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    My next step will be to connect the 1n4148 diodes
     
  9. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    Here is my updated steps:

    1. Soldered R3 (10K resistor) on PCB.
    2. Connected right side of that resistor to C23 ( 470 nF Capacitor) . I used a film capacitor. The package it came in had the following label on it - CAP FILM RDL 0.47 UF 250V 15SL
    3. Connected left leg R41 (1M resistor ) to right leg of the C23 ( 470 nF Capacitor). R41. Will run to the power part of this circuit, but for now, I left the other end (right leg) for a later step.
    4. Soldered an 8 pin socket to the board, to house the Op Amp. The data sheet I am using for the TL081 op amp is here:
    https://www.st.com/resource/en/datasheet/tl081.pdf

    5. Right leg of C23 ( 470 nF Capacitor) has been connected to Pin 3 of the Op Amp socket (non-inverting input)

    6. Placed C31 (100pF film capacitor on the PCB)

    7. Left leg of the C31 (100pF film capacitor) has been connected to Pin 2 of the op amp socket. (inverting input)

    8. Right leg of the C31 (100pF film capacitor) has been connected to Pin 6 of the op amp socket. (output)

    9. Soldered D2 (1N4148) diode as follows: Left leg to left leg of C31 (100pF) Capacitor and right leg of D2 (1N4148) diode to the right leg of C31 (100pF) Capacitor. The little black stripe on the diode, is to the right.

    10. Soldered D1 (1N4148) diode as follows: Left leg to left leg of D2 (1N4148) diode and right leg of D1 (1N4148) diode to the right leg of D2 (1N4148) diode. The little black stripe on the diode, is to the left.

    11. I have ordered the correct 500K pot and it is expected to be here tomorrow, so i will continue then. In the interim, i would really appreciate it if the steps above can be reviewed so that i know i have not made any errors.

    Thank-you!!!!!!
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    At a first glance sounds good.
    But: I'm sorry I do not have the time to follow these steps in detail. If you use the image from post #64 and mark the connections as per your descriptions you should be able to complete the circuit by yourself. I couldn't do more than add these markings anyway.
     
  11. SparkyCal

    SparkyCal

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    Mar 11, 2020
    Hi: I will continue along, report my steps, if only for my own sake, and if I run into a specific issue, i will ask. Let's hope it works.

    By the way, I tried to come up with a way to make easy for people to follow. I thought that if the narrative is read, and one looks at the schematic, it would take no time for an experienced person to note if I am off track. But perhaps this method works for me, but not for others. I apologize, I honestly thought it would be the simple way. Anyway, maybe I can report any questions if I come across them instead.
     
  12. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    ok..I am pausing because I don't want to make a mistake:

    On a previous thread, Bertus was kind enough to post the polarities of the capacitors in this circuit. It is here:
    A Stretch

    The person who designed this circuit, wrote to me a few days ago and said I should use film capacitors, except for the power section.

    I am at the part where I am to solder C3, which is the 1uF capacitor. I have attached a pic of the circuit to make it easy (please ignore the hand drawn box...it was from a previous question I had) .

    Given that C3 is marked with polarity, am I to use an electrolytic capacitor here rather than a film?

    Thank-you
     

    Attached Files:

  13. Nanren888

    Nanren888

    247
    50
    Nov 8, 2015
    I think Bertus was just indicating the polarity in case you had polarised capacitors that cared about such things.
    C3 is in the signal path, so does not need to be electrolytic, if you have film at 1uF.
     
  14. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    Great. Thanks
     
  15. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    @Nanren888 , I indeed indicated that if the capacitors are polarized, where the + should be:

    sparcal_Overdrive pedal with tone-control comment2.png

    @SparkyCal , Did you read the comment on the picture?
    I have put a red marking around it now.

    Bertus
     
    hevans1944 likes this.
  16. SparkyCal

    SparkyCal

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    6
    Mar 11, 2020
    Yes. That is and was clear. But I wanted to know whether it had to be a polarized one. Seems it doesn’t.
     
  17. Audioguru

    Audioguru

    2,832
    634
    Sep 24, 2016
    Non-polarized film capacitors are used for coupling signals in low distortion audio circuits.
    But since you want distortion in this circuit then a polarized electrolytic capacitor connected backwards will make additional awesome distortion.
     
  18. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    ok...so I will connect it as shown in the original diagram...connected backwards. i hope you were not joking. Being. a newbie, I can't tell
     
  19. SparkyCal

    SparkyCal

    222
    6
    Mar 11, 2020
    AudioGuru- what i meant to say is that i don't know if you were being sarcastic or whether connecting a polarized electrolytic capacitor backwards, will really produce additional distortion. Can you clarify because, i am getting near the end of this circuit and don't want to blow up a capacitor .

    Thanks1
     
  20. bertus

    bertus Moderator

    689
    240
    Nov 8, 2019
    Hello,

    Just use the film capacitors that you have available.
    No need to buy more components.

    When an electrolitic capacitor is mounted the wrong way around, some kind of diode efect may happen.
    This can have bad effects on the capacitor when the power is a lot, but not in low power audio circuits.

    If you want to have more guitar effect circuits have a look at these pages :
    https://www.montagar.com/~patj/gindex.htm
    http://www.muzique.com/schem/index.html

    Bertus
     
    hevans1944 likes this.
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