40106 oscillator circuit into LM386 amp

Discussion in 'General Electronics Chat' started by Jonathan Shirley, Apr 9, 2015.

  1. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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    So i got a simple 40106 oscillator set up, which is pin 14 to 9v, pin 7 to GND, 0.1 uf decoupling cap between 14 & 7, pin 1 to ground through a 0.1 uf cap, 100k resistor between pin 1 and 2 and finally, and a 10k resistor from the pin 2 output (similar to the screenshot below)

    The pin 2 output of the 40106 is then going through a B10k potentiometer (variating the output amount) into the input of an LM386 (9v powered) amplifier circuit which is modelled on these two Youtube videos from the same dude:






    The LM386 circuits works great IMO (outputting into an 8ohm speaker). However, when i adjust the B10k potentiometer to change the volume, the pitch that the 40106 is producing changes also. Is there a way I can isolate the two to prevent this. Any help would be hugely appreciated. :)

    P.s I am a total amateur.
     
    Last edited: Apr 9, 2015
  2. Jonathan Shirley

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    Apr 9, 2015
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  3. DickCappels

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    Aug 21, 2008
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    Can't hear the pitch changing but it sounds to me like the harmonic content is changing. That may suggest that your signal into the audio amplifier is too large at the start.

    How is the volume control connected to the output of the Schmitt trigger?
     
  4. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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    the volume control is connected to pin 2 of the schmitt trigger (one of its outputs) and there is a 10k resistor between. Basically one side of the Pot is connected to LM386 input and the other side is connected to the Schmitt trigger output.
     
  5. DickCappels

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    Aug 21, 2008
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    Is there a DC blocking capacitor between the pot and the input of the LM386?
     
  6. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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    oh sorry, i should have said. There is a 100nf cap between the pot and the input of the LM 386.
     
  7. DickCappels

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    Aug 21, 2008
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    Good!
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Sounds like you're loading the oscillator. Use one of the other inverters as a buffer between the oscillator and the amp.

    A schematic would be helpful as it's unclear how you're using the potentiometer to attenuate the signal.
     
    Last edited: Apr 9, 2015
  9. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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  10. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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    Sorry about that, i have just uploaded a hand drawn schematic
     
  11. dl324

    Distinguished Member

    Mar 30, 2015
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    Hi Johathan,

    You're loading the output of the oscillator. Insert one of the extra inverters between the oscillator output and the pot.
     
  12. Jonathan Shirley

    Thread Starter New Member

    Apr 9, 2015
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    Il get to it now, Dennis. is this buffering it? see attached image
     
  13. dl324

    Distinguished Member

    Mar 30, 2015
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    Hi Jonathan,
    It's simpler than that. Just feed the oscillator through one of the unused inverters, then to the pot.
     
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