Problem with LM386 audio amplifier and 40106 oscillator

Discussion in 'The Projects Forum' started by torgosaves, Dec 12, 2011.

  1. torgosaves

    Thread Starter New Member

    Dec 12, 2011
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    Hello. First time posting here.

    About a year ago I built a similar circuit. Essentially this 40106 circuit:
    http://fluxmonkey.com/electronoize/40106Oscillator.htm

    And this 386 circuit:
    http://fluxmonkey.com/electronoize/386amplifier.htm

    And I had it working and the 3 tones from the 40106 oscillators were mixing well and the amplifier sounded fine.

    Well now I've rebuilt the circuit (again on a breadboard), hoping to get it to work again 1.) the 40106 oscillators will not mix properly - only one tone will work at a time (perhaps they are feeding back into each other). I tried another 40106 chip, but I have the same problem. All the separate schmitt trigger oscillators create a tone, but they will not mix.

    2.) The LM386 amplifier will work for about a 1 1/2 minutes or so and than the sound fizzles out. Then if turn it off and let it sit, then turn it back on after a few minutes, it works again for about 1 1/2 minutes, then the sound fizzles out again.

    I tried buying another lm386, but it does the same thing. I've also tried connecting a Piezo contact mic - Again, the sound works for about 1 1/2 to 2 minutes and fizzles out. I've tried other configurations too.

    I've been using the book Handmade Electronic Music (2nd edition) by Nicolas Collins also, which has the same kinds of designs, only slightly different when it comes to the lm386.

    Is there anything to be done about these problems with the lm386 and the 40106?

    Is there another amplifier I can build that runs on a 9 volt battery?

    Thanks
     
  2. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    How are you trying to mix the oscillators? You don't show any connection between the oscillators and the amplifier.
     
  3. torgosaves

    Thread Starter New Member

    Dec 12, 2011
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  4. Audioguru

    New Member

    Dec 20, 2007
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    The CD40106 IC that makes the oscillators needs to have its own 100uF capacitor from +9V to 0V if it has its own battery and/or if the wires on the breadboard are too long.

    Note that there is no -9V, it is actually 0V that is sometimes called ground.

    The LM386 amplifier will oscillate at a radio frequency and get hot then it might fizzle out until it cools if your breadboard wiring is messy and/or if some parts are missing.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    You are probably using resistors for the output mixing that are less than 4k Ohms in resistance. That would load the outputs to the point where the inverters would no longer be able to oscillate.

    The link you posted shows 100k Ohm resistors being used for the mixing resistors. What value are you using for your mixing resistors?
    What is the color of the 3rd band?
     
  6. torgosaves

    Thread Starter New Member

    Dec 12, 2011
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    They are definitely 100k ohm resistors, brown-black-yellow.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    The oscillator circuit severely overdrives the poor little LM386 power amplifier.
    When the signals are all in phase then they add and the signal to the input of the LM386 is far more than the maximum allowed signal level (±0.4V) Which might stop the LM386 from working during those moments and might even damage it.

    Try connecting a 2.2k resistor to ground at the input of the LM386 to form an attenuator.
     
  8. sheldons

    Active Member

    Oct 26, 2011
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    also show us how you have built your lm386 amp just in case of any mistakes......heres a data sheet for that ic
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    You need a 0.1uf (100nF) capacitor between pins 14 and 7 on the 40106. The leads need to be as short as possible. With this type of breadboard, I generally "stretch" the cap right across the top of the IC.
    What values are you using for the timing resistors?
     
  10. torgosaves

    Thread Starter New Member

    Dec 12, 2011
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    This is the design I'm using:
    [​IMG]
    Though I should say I was using a 10k ohm potentiometer since I didn't have a 5k ohm. I wonder if that may have something to do with it?

    For the 40106 oscillators, I'm using 100k ohm potentiometers.
     
  11. torgosaves

    Thread Starter New Member

    Dec 12, 2011
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    Aw heck! I feel pretty dumb. I just checked the voltage on my 9v battery, and it's reading under 7v! Last time I checked it (which doesn't seem like too long ago) it was reading around 9v... so apparently it was drained somehow, or I drained it on some project and didn't realize. I need to get a better power source. I can't afford a lot of batteries.

    I tried connecting 2 drained 9v batteries that added up to around 15v and then used a voltage divider to bring it down (not sure how good of an idea that is for permanent use...) and the amplifier seemed to worked okay (thought it seemed staticky(sp?)).

    So, I better get some more batteries - Maybe a dc adapter and a 9v regulator.

    Thank you everyone for your help!
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Avoid using 9V batteries in just about ANY project. They only have 300-350mAh of storage.

    A AA Battery has between 2000mAh and 3000mAh for comparison. Get a 4 AA adapter and use 6V for your projects instead.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    As T.O.G. says, 9v "transistor" batteries are a poor choice for use in hobbyist circuits due to the very limited mAh rating. They are the most expensive way to power a project; even though you can frequently find such 9v batteries at a "dollar store" at two for $1 USD.

    Almost every household has one or more "wall wart" type plug supplies for an appliance that they are not using. If you don't have one, your next-door neighbor has a couple. If they don't, you can pick up some "wall wart" supplies from a thrift store for next to nothing.

    Try to look for regulated supplies. If they are regulated, they will say that they are regulated. If they are not regulated, you would need to regulate the output, which will add expense to the project.
     
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