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Thread: Rebuilding my old analog console

  1. #261
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    Lasermaster1977 and Brian - yes and yes

    Lasermaster 1977 - I was thinking along the same lines. Feeding the AM sweeped signal into another AD633 and AM modulating that signal, Brian - I did the the 2 oscillators as you described and did get the modulation working at a basic level. More experiments required.

    Thanks you,

  2. #262
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    Quote Originally Posted by Kevint View Post
    Lasermaster1977 and Brian - yes and yes

    Lasermaster 1977 - I was thinking along the same lines. Feeding the AM sweeped signal into another AD633 and AM modulating that signal, Brian - I did the the 2 oscillators as you described and did get the modulation working at a basic level. More experiments required.

    Thanks you,
    By jove I think you've got it! "More experiments required". That's all there is to it!
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  3. #263
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    Been busy with family and church.

    Started hardwiring stuff together. It is going to take a while to put all this stuff together, so my posts maybe infrequent. I am sill interested in adding rotation and other effects but that will come later. My goal now is to just get a stable working console with what I have. Everyone on this thread has been great and has made this project a reality for me - with sincerity, thank you.

    Just playing around I got this image and thought it was interesting.
    Attached Files Attached Files

  4. #264
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    Glad to hear the AD633 rotation circuit is working. That is a fun and exciting circuit, not previously available, to my knowledge. Thank you laserist. You should get an award for your drawing. Kevint: Did you get the continuous turn sin cos pot supplying the rotation signal? I haven't tried using the sin cos signals from a quadrature oscillator as the rotation inputs yet, though I could patch it in cyc.java and generate a simulation, or drop lines of code into the belas.


    When you get the ramp working, you'll have circles, spirals, ramps, rotation, and AM. That's a big place to explore. Do you have a favorite op amp circuit for what I've heard called a summing amplifier?

  5. #265
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    I'm using TL07X for my op amps in most cases

    I have a general electronics question. I see zero gain op amp circuits use 1K, 10K and 100K values for the input and feedback resistors. Are all of these functionally the same? or is one configuration better for the type of analog signals used in laser light show consoles?
    Attached Thumbnails Attached Thumbnails Resistors.GIF  


  6. #266
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    [QUOTE=Kevint;365384]I'm using TL07X for my op amps in most cases

    This was posted in error. See last post.
    Last edited by lasermaster1977; 10-30-2024 at 19:30.
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  7. #267
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    Quote Originally Posted by Kevint View Post
    I'm using TL07X for my op amps in most cases

    I have a general electronics question. I see zero gain op amp circuits use 1K, 10K and 100K values for the input and feedback resistors. Are all of these functionally the same? or is one configuration better for the type of analog signals used in laser light show consoles?
    Actually, these are not zero gain circuits, they all have gains of 1. The 10K version would be my pick.
    Hi Kevin, the examples you show are for inverting summing amplifiers which sum the voltages appear on each op amp input resistors. The value of these input resistors set the input impedance for each input and also determines the input signal current for a given input resistor. The ratio of an input resistor Rin(n) to the op amp feedback resistor Rf, (Rf/Rin) determines the closed loop gain of the summing amp for each Rin(n) input signal. The op amp inverting and non-inverting inputs can be thought of as virtual grounds, so the current flowing through any given input resistor can be calculated using Ohm's Law I=E/Rin(n). That said, the lower the op amp's input resistor the higher the input current and visa-versa.

    1K input resistors are typically out of the norm. Acceptable input resistor values for general purpose op amps should be kept higher than 4.7 to 5K. Also, the higher the input resistor values the higher the resulting input-offset voltages will occur at the inputs and be multiplied on the op amp outputs. So, 5 - 10K is a good input resistance value for many common op amp families
    e.g. 741, 747, 748, 348, 4136, TL07x, TL08x, etc.

    An op amp's overall linear frequency response when used in a negative feedback, inverting op amp configuration is determined by the op amp's open-loop gain curve and the ration of Rf/Rin. For a given value of Rin, the maximum linear frequency response occurs when the loop gain = 1 or 10K/10K. As Rf increases, in value in order to for the closed-loop op amp circuit to further amplify the input signal, the frequency response is reduced the greater the input signal is amplified.

    The output resistors and Rf/Rin resistor values have no direct bearing on each other. The mentioned op amp families can easily drive 2-4 milliamps (in some cases a bit more) into a resistive load. Your op amp's output voltage swing will determine the best load resistor value depending on how much load current you want to drive into a resistive load

    All this said, it is best to learn how to look at the open-loop gain graph and determine the frequency response-to-gain bandwidth. I'll try to post an example of this soon.

    This YT video covers the this open-loop vs closed-loop frequency response range in easy to understand language.
    https://www.youtube.com/watch?v=FSHB9K_1fw8

    I hope this is helpful.
    Last edited by lasermaster1977; 10-30-2024 at 19:38.
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  8. #268
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    Quote Originally Posted by Kevint View Post
    I'm using TL07X for my op amps in most cases

    I have a general electronics question. I see zero gain op amp circuits use 1K, 10K and 100K values for the input and feedback resistors. Are all of these functionally the same? or is one configuration better for the type of analog signals used in laser light show consoles?
    Short answer:

    Functionally, all 3 circuits are the same because the gain follows the ratio of the feedback resistor over the source, but low resistor values like 1K draw much more current and that's just wasteful. Many op-amps are limited to a max current of about 20mA so it's important not to load them too hard. Values in the 10-100K range should be just fine.

    Dean

  9. #269
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    Lasermaster1977 - great video and very informative. Thanks for clarifying - not zero gain but gain of 1 - 1K/1K or 10K/10K, ... So, from what you guys are saying. I=V/R so at 1K this would be 15V/1000 (15V is the output voltage from the 4423's) = .015A (15ma) and at 15V/10000 = .0015A (1.5mA). Since this a going to be a summing amp, 10K ohm resistors would allow for more signals to be summed together without overloading the op amp. Looking at the TL07X data sheet. it says the input signal current is max 10ma. Hypothetically, if 6ea 15V inputs were summed together the total current would be 9mA which would be <10ma spec on the TL07X. Hope I got this right.

  10. #270
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    Quote Originally Posted by Kevint View Post
    Lasermaster1977 - great video and very informative. Thanks for clarifying - not zero gain but gain of 1 - 1K/1K or 10K/10K, ... So, from what you guys are saying. I=V/R so at 1K this would be 15V/1000 (15V is the output voltage from the 4423's) = .015A (15ma) and at 15V/10000 = .0015A (1.5mA). Since this a going to be a summing amp, 10K ohm resistors would allow for more signals to be summed together without overloading the op amp. Looking at the TL07X data sheet. it says the input signal current is max 10ma. Hypothetically, if 6ea 15V inputs were summed together the total current would be 9mA which would be <10ma spec on the TL07X. Hope I got this right.
    Happy to help a tiny bit.

    Not only do you need to know what I=V/R is, but that also dissipated Power in Watts=I x E or (V/R) x E, so with 1K resistors with a 15v drop across it means the resistor must have at least a 1/4 Watt rating.

    It is wise to not operate devices so close to their maximum ratings. 10K would be a far better choice for these inverting input resistor(s) and output load resistor(s).

    Now, you do not provide much qualified information about the true nature of your 15V inputs. Is this a peak-to-peak bipolar value, a peak value? What are the supply voltages for operating the op amp? +15 and -15V? If so, the supply voltages set the absolute limits for how large a voltage swing the output can have.

    Take the worst case were the op amp has a gain of 1 (also known as unity gain) and all 6 inputs are instantaneously at +15v. The sum of 6 x 15v = 90v, a value that far exceeds the op amps supply voltage range. Now I'm pretty sure that isn't what you are planning but it is food for thought.
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