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Back to the Breadboard

Discussion in 'General Electronics Discussion' started by SparkyCal, Jun 13, 2021.

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  1. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    AG, Bertus and Halrald, and anyone else....

    I need to really drill down to see if my distortion pedal woes are due to using faulty op amps. Thus, I need to go back to basic breadboarding, so that I don't drive myself and others nuts.

    Can you tell me if this will work:

    I have two variable power supplies (bear this in mind)

    I don't want to build a voltage divider circuit just yet. So, I was thinking of using one of the variable power supplies to supply 1/2 the voltage (ie: 4.5 volts) at pin 3. That would eleimnaiunte the need to build a voltage divider for now. The only reason I want to skip building it, is because I want the emphasis to be on finding out if the op amp is faulty, and not having to build the voltage divider, eliminates an error I could make at that step (although, I'm confident I could build it, I really don't want to breadboard it, as breadboards introduce noise etc- so I though, why not just provide the 4.5 volyts through my second supply)

    Then I will use the other power supply to feed the circuit its 9volts that the battery ordinarily would have.

    My goal is to simply get the op amp driving the sound (although I know it will be loud), just to see if it is the IC chip that is faulty or not.

    I suppose AG, I should place a 220K resistor between Pins the - In and the Out of the op amp? I am going to use a single op amp, to eliminate having to buffer the second op amp on a dual.

    As mentioned, I want to really focus on getting the sound out of the op amp. If the op amp is faulty, I can be chasing my tail. So best I think to breadboard and see.

    Thoughts?
     
  2. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    An opamp will not work if you short its sounds input at pin 3 with a power supply.
    Why Use a 4.5V power supply when a voltage divider is simply two identical value resistors in series and a filter capacitor to ground? The 4.5V is fed to pin 3 with a 1Meg resistor and the audio is capacitor-coupled to pin 3.
    The 1 Meg resistor passes the +4.5V to pin 3 and prevents the voltage divider from shorting the input signal.
    An opamp in a linear amplifier circuit will not work without the AC and DC negative feedback provided by a resistor or piece of wire from its output to its - input.
     
  3. VenomBallistics

    VenomBallistics

    167
    38
    Aug 30, 2018
    yeah ... that's kinda sketchy ... your 9V and 4.5V will be in business for themselves.
    the divider is the cheapest ... a center tapped, bridge rectified 9V transformer would be great, giving you +4.5/0/-4.5.
    You can just tie your output to - input for a unity gain input buffer. This is commonly done
     
  4. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    This is a "pedal" circuit. While playing the guitar he pushes the pedal (stomp box) with his foot to activate it.
    Most pedals are used near the guitar and are powered from a single 9V battery.
     
  5. VenomBallistics

    VenomBallistics

    167
    38
    Aug 30, 2018
    why yes ... but for now it seems the objective is diagnostic in nature. unity into unity in a +/0/- supply would pass of fail the component just as well as the 9/4.5/0 of the divider supply.
     
  6. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    ok. I took your advice and but the voltage divider. So, now I have a voltage divider feeder the 4558D op amp (decided to stick to dual amp for now).

    The pins are properly mapped and I have disabled the second op amp by connecting pins 6 and 7 together and running Pin 5 to that place that AG previously told me to (to the voltage divider).

    I also ran a 220K resistor between pins 2 and 1 (- In and Out )

    From the op amp, it runs to the 1uF capacior (C3), and then out. (Ikeptmit simple)
    I am getting nice and clear sound with no biuzzing.

    My Pin readings in Volts are as follows:

    Pin 1. 4.51
    Pin 2. 4.5
    Pin 3. 4.1
    Pin 4. 0
    Pin 5 4.4
    Pin 6. 4.4
    Pin 7. 4.4
    Pin 8. 8.99

    I think we can also conclude the the 4558D op amps I am using are good.

    I have also attached a pic of my breadboarding. Actually, you will notice a small regular board which is the voltage divider which feeds the circuit.

    Based on the fact that I am getting a good sound without any buzzing, and that the Pin readings seem normal, I think we have succeeded. If this seems right to you, I will move on to build the rest via the breadboard. Next will be the installation of the pots.


    After we get that going properly, I will do the diodes and the 500K gain pot.
     

    Attached Files:

  7. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    This breadboard thing is working out really well. I just added the 270K resistor to C3 (1uF Capacitor) and then went to the Out jack. Still works! So, I am able to add one component at a time and ensure it still works. I think we're finally going to be able to see this through.
     
  8. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    Congratulations, the voltages are correct and now it works well.
    I am glad you did not attach a photo of the breadboard because the mess of wires all over the place on a breadboard makes me laugh for hours until it hurts.
     
  9. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    270k is 1000 times more than the correct 270 ohms.
     
  10. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    Sorry.. I used the 270R but typed 260K in error.

    Now that this thing is working, I am able to experiment and swap out components to see their effect. I swapped out the 470nF capacitor with your recommended 1nF.

    I found that using the 470nF gives the sound a darker feel. the 1nF gives the sound a brighter feel. Through experience as a sound engineer, I have learned never to tame a signal outright. It is better to allow a signal to breath and then shape it as need be by use of EQ etc.

    So, the better pick, is your recommended 1nF. It gives me more to work with.
     
  11. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    Well guys. The circuit is completely built and it works like a charm. I am surprised that the breadboard is not as noisy as I thought it would be. I cut down the legs of the components, so maybe that made a bit of a difference.

    Anyway- it works and I'm really thankful to all of you. @AG - thanks for putting up with me ;-)

    Here is a clip (pardon the sloppy playing. I was trying to balance my guitar while working the pots)

    https://drive.google.com/file/d/13-xwZXyHQQ_CYpGaZkTTKDBn4TdveI13/view?usp=sharing

    My next step will be to solder this properly on a board and maybe even try to put it in a box.
     
  12. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    I can’t stand the mess of wires either, but it was a good tool to figure out what was going wrong.
     
  13. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    It sounds good and I am surprised about the sustain at the end of your playing. I guess the compression caused by the diodes allow the high gain of the opamp to produce sustain.
     
  14. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    It actually sounds better than the clip. Because my phone was far away from the amp, it recorded it too low in volume, so I boosted the volume through software. Without doing that, it sounds a lot better.

    The sustain is not a function of the electronics. It's a function of playing style. I made it do that so that you can hear the distortion trail off. I could have hard muted my playing my using my palm over the strings, or I could have let it sustain less, and dampened it after a second. I purposefully let it ring out and actually began bending the strings of the chord to accentuate the effect.

    I'll record a proper clip once I have it built on a board
     
  15. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    Funny...I have built this on a regular board. I am getting all the proper readings, except for on Pin 1, which is my Out. I am getting no reading. I will have to have a careful look and compare it to my breadboarded version, but any ideas as to what to look for?,
     
  16. Audioguru

    Audioguru

    3,305
    703
    Sep 24, 2016
    Did you replace the 220k resistor between pin 1 and pin 2 with a gain pot?
    No reading on pin 1 means 0V? If pin 1 is 0V then pin 2 should also be 0V.
     
  17. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    Yes, I put the Gain pot in, and it was fine in the breadboarding version.

    Something is definitely wrong in the board version. Here are my readings:
    Pin 1. 1 .3
    Pin 2. 48.8
    Pin 3. 4.1
    Pin 4. 0
    Pin 5 4.5
    Pin 6. 4.5
    Pin 7. 4.5
    Pin 8. 9.02

    Definitely a problem with pins 1 and 2.

    Coming from these pins, I have the two diodes, followed by the 100 pF ceramic capacitor, followed by the 500K Gain pot, then the 1 K resistor and the 220nF capacitor running from pin 2 in series.

    If I can'r figure this out, I may have to unsolder and rewire that whole diodes section.
     
  18. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    AG. dont worry. Turns out, this was bad wiring. Ever flip a board over and get the pins reversed? lol..thats what happened.

    I'm fixing it toinight/.
     
  19. SparkyCal

    SparkyCal

    660
    17
    Mar 11, 2020
    Hey guys. It worked. I fixed my mistake and it works like a charm. Now, I am going to attempt to put it in a box, but I need to think about whether I should do a formal stomp box, or a prototype.

    What I mean, is that I have a steel professionally painted stomp box enclosure. I also have the stomp box push button stomp switches, as well. One option is to do it tha way.

    I also have black plastic boxes. They are cheaper and may be a good choice, until I get more comfortable. But I guess the first step is to learn how to wire up the stomp box switch. Going to look on google for instructions.
     
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