problem with clipping

Discussion in 'The Projects Forum' started by gee_emm, Apr 12, 2008.

  1. gee_emm

    Thread Starter Active Member

    Jan 16, 2008
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    I built an electret mic amp, that I was originally going to hook up to an LM3915 to "display" room sounds. But, just by listening with headphones, it clips. It works fairly well with low sounds, but anything louder than a whisper, I have this problem. Any suggestions would be very much appreciated. Thanks in advance for any help.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Can you provide the component values?

    hgmjr
     
  3. gee_emm

    Thread Starter Active Member

    Jan 16, 2008
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  4. Audioguru

    New Member

    Dec 20, 2007
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    Sure it clips. It is "an amplified ear" and uses a supply of only 1.5V, its AGC cuts off the first transistor and its output transistor puts DC through the headphones.
    http://www.redcircuits.com/Page38.htm
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    My Sound Level Indicator project has plenty of headroom in its electret mic and its preamp. It has a peak detector to drive the LM3915 so the peaks are held long enough to be seen. The AGC extends the sensitivive/loud range 20dB so the total range is 50dB. It detects a pin dropping on the floor of the next room (I must hold my breath) and it shows all loud music.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    So, Audioguru - what's your "fix" for this circuit?

    After all, audio IS your forte', right?

    Seems like you've seen this circuit before - you must've already come up with a better one, or - perhaps not?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You know, it's really unsporting of you to take the bait before I post it.

    ;)
     
  8. gee_emm

    Thread Starter Active Member

    Jan 16, 2008
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    Thanks for the replies. Ive seen your Sound Level Indicator, Audioguru. Which is exactly what I want to build, and tried to build but, unfortunately I had no luck with it. I think I found it on aaroncake, or something like that. So I was trying other alternatives.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    So, what did you change from Audioguru's parts list?

    If you built it by his specifications, using the same components, it should have a very decent chance of working.

    Of course, there IS the off chance that you got a bad part or two.

    But I'm sure he'd love to know if you tried to change anything, or if you merely got some bad parts?

    When dealing with linear circuits, no two parts are precisely the same.

    He's the expert - he's right here, and he might actually give you some suggestions on fixing it.

    Of course, if you substituted components other than spec'd, that's your most likely problem area.
     
  10. gee_emm

    Thread Starter Active Member

    Jan 16, 2008
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    Perhaps I will re-buid Audiogurus circuit again, and list the changes Ive made (if any), and see what happens. Then post my results and questions/problems I find. Thanks again everyone for your time.
     
  11. gee_emm

    Thread Starter Active Member

    Jan 16, 2008
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    ok, so Ive re-built this circuit, using, first a 5218a op-amp, (still had problems), then using an ne5532 op-amp, same problems with all leds being on, even in complete silence and with the mic removed. Then went back to the 5218. So, just messing around with it,being frustrated :p,.. I put the op amps first output (c4) to the signal input of LM3915. Also pin 6 (Rhi) to pin 7 (REFout), of the 3915. Still did the same thing, but then I removed Q1, and it worked pretty well.?.?. Dont know why, but it seems to be doing what I want it to do now,.. anyone think it will be ok like this, or will I eventually fry something?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    My Sound Level Indicator has worked fine for over 2 years. It worked perfectly the first time it was turned on. A few people have built it and said theirs also worked fine.
    The MC33172 dual opamp is hard to find today so other people substituted an LM358 which worked pretty well except at high audio frequencies.

    The "Amplified Ear" project is for deaf people who cannot hear its horrible distortion.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    The MC33172 isn't THAT hard to find. Mouser has thousands of them in stock.
    http://www.mouser.com/Search/Refine...&OriginalKeyword=MC33172&Ntk=Mouser_Wildcards

    Digikey has over 10,000 of them:
    http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&keywords=MC33172&x=20&y=12

    Electronic Goldmine has them as well:
    http://www.goldmine-elec-products.com/prodinfo.asp?number=A10006

    Allied has 121 left @$0.28/each (best price I've seen so far)
    http://www.alliedelec.com/Search/SearchResults.asp?N=0&Ntk=Primary&Ntt=MC33172&sid=48029E806DFCE17F

    Audioguru, one thing on your schematic could be misinterpreted; namely where to connect the collectors of Q1 & Q3. There is only a "+" indicated, rather than +5 or +9.
     
  14. Audioguru

    New Member

    Dec 20, 2007
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    The MC33172 and the LM358 have outputs that go down to 0V. Other opamps like the NE5532 need a negative supply for their outputs to go low enough so that many or all LEDs do not light in my circuit.

    I haven't looked for the MC33172 for a while. Now everybody has them in stock.
     
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