How to use/set oscilloscope to track down weird overtones in plexi build

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, May 20, 2020.

  1. itsGiusto

    itsGiusto Tele-Meister

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    Oh yeah, that's a great point! It's possible I did not turn the system volume up enough.

    BTW, which signal generator app do you use?
     
    Last edited: May 22, 2020
  2. itsGiusto

    itsGiusto Tele-Meister

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    Is it safe to probe the amp with the oscilloscope after the power tube stage, pre OT? What about after OT pre speaker? Don't know if the extremely high volts or current would cause an issue, or the fact that (I think) the power tubes' plates are not referenced to ground.
     
    Last edited: May 22, 2020
  3. elpico

    elpico Tele-Holic

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    Um don't laugh... but I've just been playing color bars for a decade now



    Always available whether someone hands me a PC, Mac, Linux, Android, iPhone, tv clicker, xbox, iPad, whatever. No installation required.

    That's a function of the cables you have around not the signal generator. You can easily put alligator or flea clips on the other end of any cable you plug into your phone. Because it's a floating battery powered device there's no possibility of ground loops or power noise either.


    Edit: oh I think this is where you're supposed to repeat the mantra about high voltages etc. Please don't clip your phone to spots without knowing you can clip your phone to that spot.
     
    Last edited: May 23, 2020
  4. BobSmith

    BobSmith Tele-Meister

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    Is it possible the Weber mass (which places a coil in series with your external speaker) makes a reflected wave? The oscilloscope would detect this. A signal generator may also help find it if you can sweep the frequencies. (May only be there on certain frequencies). You could you see what happens on bypass (maybe when you neighbor is mowing the lawn).
     
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  5. itsGiusto

    itsGiusto Tele-Meister

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    Cool, that's a good idea, and I will look into it further, try to find a time to crank it, maybe.
    The reason I am skeptical it has is to do with the attenuator, however, is that I have probed the circuit to listen to the audio, and I think I still hear the overtones in the post-phase inverter section of the amp. Though it is hard to tell, because I have to have a load connected to the amp, and even though I turn down the normal speaker volume all the way using the attenuator while probing, the normal speaker still makes some sound, even at minimum attenuator setting. So it's possible I'm hearing the noise coming from the normal speaker output, not the probe-amp output.
    Weber makes the claim on their website that it is safe to unplug the normal speaker and run the Mass as a dummy load, but I'm always afraid of damaging something if I do that.
     
  6. BobSmith

    BobSmith Tele-Meister

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    Its safe. A small amount of signal is passed thru, that’s normal. It’s no more dangerous than placing a dummy resistor load (of proper power handling capacity) at the end. Just make sure you are on Max attenuation.
     
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  7. SoK66

    SoK66 Tele-Afflicted

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  8. itsGiusto

    itsGiusto Tele-Meister

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    That is what I did, I made one of those devices years ago, and I've been using it to test my amps. But this particular problem of mine has proved ruthless, and impossible to track down using only that.
     
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