Amplifier circuit with 555 ic

Discussion in 'The Projects Forum' started by Copey84, Aug 11, 2016.

  1. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Hi all, need some help with a amplifier circuit that I have built on breadboard but can't seem to get working.
    Confident all connections and components are ok, so beginning to think maybe there's a problem with wiring diagram.
    I've included the diagram hoping someone could check over it and confirm that it will actually work.
    Appreciate any replys, thanks.
    555 as amplifier circuit.gif
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Can't read the component values. Can you post a slightly bigger/clearer pic?
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The schematic is too small to read in detail. Also, this isn't an IQ test - what is it you are trying to achieve, and how do you think the circuit is supposed to work?

    Hint - why is pin 7 not connected?

    ak
     
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    555 as amplifier circuit-h.gif
     
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  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Your circuit wont work, a 555 is an osc/timer, not an audio amp.
     
  6. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Thanks for doing that ak resolution on mine is bad, can already see two errors I have made.
    Had circuit running on 5 v instead of 9, only had a 680ohm resistor instead of 680k.
    Wanted to learn about amplifiers so pulled circuit from internet, got a few others working ok just had problems with this one.
    Had thought pin 7 might be an issue, do all pins on a 555 timer ic need connecting?
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Contrary to opinion, this circuit will work (after correction) as an audio amplifier, just not a very good one. But, the tone of you response makes me think that you think this is a "normal" approach. It is not. This is one approach to what is called a Class D audio amplifier, basically a pulse-width modulation (PWM) switching power supply with an output that varies at audio frequencies rather than make a constant DC voltage. There are many other, and mostly better ways to do this if your intent is to experiment with class-D audio. If you just want a simple little amplifier, look for circuits based on the LM386. There are tons.

    For a pulse-width modulation (PWM) circuit, pin 7 usually is tied to pin 6, as in the PWM circuit on the 555 datasheet.

    ak
     
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  8. BR-549

    Well-Known Member

    Sep 22, 2013
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    "
    555 AMPLIFIER
    The 555 can be used as an amplifier. It operates very similar to pulse-width modulation. The component values cause the 555 to oscillate at approx 66kHz and the speaker does not respond to this high frequency. Instead it responds to the average CD value of the modulated output and demonstrates the concept of pulse-width modulation. The chip gets very hot and is only for brief demonstrations.

    "
     
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  9. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Thanks ak didn't think it was most conventional way to amplify, still not working.
    Replaced 680 ohm resistor with 680k and powered of 9v battery, speaker crackles but nothing else.
    Will read up on 555 timers again, even with link to pin 6 and 7 no audio at speaker.
     
  10. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Thanks for reply BR-549 still can't get it to work though.
    No plans to use it in any project, no now there are better ways to amplify circuits.
    Have used a condenser mic, is that ok for this circuit ? The speaker is 8ohm 0.5w
     
  11. BR-549

    Well-Known Member

    Sep 22, 2013
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  12. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Got the amplifier working correctly although the speaker still crackles a bit when talking into mic.
    Does the speaker crackle because of the PWM signal, or is it something else?
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
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    It might be because the PWM is getting interrupted. Like being over driven.

    Try speaking softly into the microphone.
     
  14. OBW0549

    Well-Known Member

    Mar 2, 2015
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    If the circuit you're trying to make is this one, the top of 10 kΩ resistor R5 should be connected to pin 3 of the 555, not to the positive supply rail.
     
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  15. Copey84

    Thread Starter Member

    Jul 27, 2015
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    No I have used similar circuit to the one you found fault in, did try building that circuit but didn't work now I know why. The circuit I used is in first post, ak posted a better quality pic of it.
    Tried speaking softly into mic still same problem, alot of crackle and hiss, maybe it's becaus its not a very good amplifier. What else would cause crackle and hissing in audio? it's present even when not speaking into mic.
     
  16. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    OBW is correct. The Garage site copied the circuit incorrectly.

    ak
     
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  17. BR-549

    Well-Known Member

    Sep 22, 2013
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    Then try connecting pin 7 to pin 3, and see if noise goes down.

    Have you got a scope?
     
  18. Copey84

    Thread Starter Member

    Jul 27, 2015
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    Have used the circuit from engineers garage with a link from pin 7 to pin 6, wasnt until I increased voltage to 12v that audio could be heard although there was alot of noise in the circuit.
    If I connect 10k resistor to pin 3 as pointed out by OBW will the enginners garage circuit still work, even though the capacitors are not the same size.
    By having the 10k resistor connected to positive rail and not connected to pin 3, would this create noise in circuit.
    Also how could noise go down with connection of pins 7and3?
     
  19. hp1729

    Well-Known Member

    Nov 23, 2015
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    Would a resistor between the collector of the transistor and +V help? I don't remember the 555 having a pullup on that input.
     
  20. BR-549

    Well-Known Member

    Sep 22, 2013
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    There is a difference between circuit noise and circuit distortion.

    There is no use worrying about noise til we see what kind a linearity we can get with your setup first.

    We need to see if the input to pin 5 is driving the frequency change out of the linear range.

    Do you have a scope? I have not seen a 555 configured that way. I am wary.
     
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