Need some help with a project

Discussion in 'The Projects Forum' started by oldblindguy, Apr 8, 2016.

  1. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    I am trying to change the capacitors so that I can hear human voices. Right now all I can hear is traffic and planes and little wind. Occasionally I can hear a bird but not much else. The admin at the forum for my kit said to experiment with increasing the value of c11 and c12 it would reduce the frequency range. So I guess males can hear from85-180hz and woman 165-255 but I would also like to hear nature and other things too. c11 and c12 are 100pF (100, 101) I am not much of a schematics reading kind of guy but I can soldier like crazy. I amazed my self how clean and simple this little kit really was and it turned out working perfect the first time. When I started it the first time I pointed it at my home theater and I had to get right at the speakers to hear them clearly. I have this device connected to a parabolic dish with 2 mics and I have a converter that shows me where to get the focal point from. I have all shielded wire and there is no weird noises so all the placement and soldering went well. But its the way it was designed and it just needs a little tune up to make it what I want. Thank you for any assistance that you can give.
     
  2. Dyslexicbloke

    Active Member

    Sep 4, 2010
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    That is two basic single rail based audio amplifiers, one for each mike and subsiquently ear.
    If the amps are C 11 is in the feedback circuit whic controlles the gain of the amp allong with the several other bits.

    To understand what is going on you would need ti read up on OpAmps and audio amplifiers but to be honest with rest equipment ypu will struggle to fault find pr get any real help that is targetted.

    You can certainly play with values but hre and threr but you risk damaging individual componants ifcyou just do it blindly.

    However.....
    Given that you appear to be hearing relativly quiet sounds I suspect the amp is good and the dish/mike allignment is off, physically.
    try pointing it at a known sound source and then fiddling with the focal point a bit.

    To do what you want well you would be better with a noise cancling system.
    basically you have two amps but they are arranged so thet the outputs are inverted relati t each other.

    one mike in at the dish focal point and one at its center, on the parabola. local sounds from a source that will focus reack both mikes but are muck louder at the focul point the low volume negative sound adds to the high volume focuseed sound and you get a slightly quieter focussed sound. unfocuswed sounds are the same at both mikes so add to nothing, well almost, so although you just sacrificed a little of what yoh want yoy also got rid of everything ypu dont want.
    with another amp and a few resistors yoh could modify what you have to work like that but I woukd sorxt out this one first if I were you.

    do you have an old PC with a sound card? Look up PC Soundcard oscilloscope, easy to do if you can soldr small stuff and will probably help a great deal with your project along with a cheap multimeter.
    I an assuming you are interested in kearning this stuff.

    Al
     
  3. BR-549

    Well-Known Member

    Sep 22, 2013
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    Describe the noise or sounds that is covering up the human voices.

    Us older folks usually lose the high side of hearing, not the low.
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    If I read the schematic correctly it uses a NE5532 for the amplifier. That IC can only output within 2 volts of each power supply voltage. It looks like it uses 3 batteries - so 4.5 volts. This only leaves .5 volts for sound. It has a gain of 50, which for a mic is not a lot. So the first thing I would do is use a 9 volt battery. Be careful to get + & - the same as the battery pack.
    Then you can make R1 & R2 lower - say 15 or 20 ohms.
    Much louder.:eek:
     
  5. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    Ronv I can hear everything else at about 1/4 volume,the unit works very good except that it was designed to hear things above the human spectrum so I am told. I asked the support admin from where I bought it and he was the one that told me to experiment with the values of the capacitors (c11 & c12) he said that would reduce the frequency. Now I know for a fact that you people are a whole lot smarter than I am. So what your telling me is that the volume is too low and that is why I cant hear people. the first person to respond said that the alignment of the mic could be off. I have tried lots of positions and then I found a program that does the equation for positioning and it seems to work. You say r1 and r2 those are 10k resisters, Correct?? I am such a dumba** when it comes to electronic stuff but I dont give up and usually I smoke the unit but sometimes I do what I set out to do and thats quite fullfilling. ok I have 2 of them so I will change a few things and and let you nice know what happened. Thanx for all your help
     
  6. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    So Al are you telling me that I should try to preposition the mics at 2 different spots? thats sounds like it could work .I dont have these mics attached to the unit itself I ran then on a shielded wire so I could move them to different positions. And I put the kit inside a aluminum bow and attached it to the back of the dish. I bhave a real good multi meter and I only have my core 17 4500 desktop. I am sure that that thing could handle anything I throw at it.
     
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
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    The capacitors only keep it from oscillating they don't really do anything for the frequency response.
    If only high frequencies are what you hear the problem may be the size of the dish.
    https://en.wikipedia.org/wiki/Parabolic_microphone

    I's still soup it up. :rolleyes:

    Edit:
    We can turn down the high frequencies if the dish is the problem.
     
  8. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    So this admin guy at velleman told me the wrong thing. The dish is only 13 inches and I guess I probably should get a new bigger dish before I start chewing up that amp.hehnehehe. OK thank you so much I will get a different dish and let you know how it is. Thanx again
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
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    A bigger dish will help, but the high frequency stuff will always be louder than the low frequencies due to the dish. If your not happy with a larger one it is pretty easy to increase the gain like above and then lower the gain at the higher frequencies to compensate for the dish.
    Give this a read.
    http://www.montana.edu/rmaher/publications/maher_aac_0805.pdf
     
  10. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    I have that pdf on my computer I have read it many times. let me ask you a question Is human voice considered High Frequency or Low Frequency. And how hard is it to tune the gain like you say?
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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    It's a little hard to say about the human voice as it has a lot of frequencies. The base frequency is 250 Hz, but to hear consonants you need about 3000 Hz.
    If you have a piano you could check it that way. Low note about 30Hz, Highest note 4100 Hz.
    It is not difficult to change it. To make all sounds louder change the resistors I mentioned above. Changing the capacitor the guy told you about to about 0.005 Ufd. would match it up to your dish a little better. (lower the high frequency gain) I would try the piano or guitar trick first to see if you can hear a difference.
     
  12. oldblindguy

    Thread Starter New Member

    Apr 8, 2016
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    I don't understand about the musical instruments but I don't have any anyway. I did do a sound check and I could start hearing at about 60hz and went to about 3200 and then I couldn't hear anymore. That capacitor you talk about there is 2 right??? that's what c11&c12 are correct?
    I'm asking because I am not the sharpest knife in the drawer. 0.005 Ufd. I don't know what this number is - (I think its a resister # but I will get some) and that admin guy talked this is his exact words
    "Disconnect R1 & R2.
    Replace R7 & R8 with wire jumpers.
    If necessary, decrease value of R14 & R15 to reduce gain."
    and that's what he said to do for increased volume
     
  13. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    That's not what Velleman say:

    "Stereo audio amplifier boosts sound 50 times. Great for the-hearing impaired (e.g. when watching TV), as a gadget, science project, … With volume control and on/off switch."

    Obviously, if it were designed to "hear things above the human spectrum" it would be useless because no human would be able to hear them with or without this device.
     
  14. Dyslexicbloke

    Active Member

    Sep 4, 2010
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    The noise cancling thing isnt about any speciffic freequency its abput getting rid of what you dont need.
    I hadent considdered freeqiency dependent gain on the dish but it a good point.
    that migt make noise cancling harder to impliment but not impossible.

    Audio amps are not my thing but I suspect that amp, all be it simple, has a freequency dependent gain. I think this because the feedback loop has both resistive and capacitive elliments which wil give diferent gain at diferent freeqiencies.

    You could play with the feedback loop using this http://www.falstad.com/circuit/ its only simple but as such is very easy to use.

    If you took hearing aids as an example you would find that many use two mikes, front and rear, leaving almost nothing when sound is 6he same volume on both mikes. sound louder from the rear is supressed completly and only sounds louder from the front remain.

    This is of course a wildly oversimplified view, most use complex algorythms controlling digital amplifiers but the theory still holds.

    If you wanted to play with it you can sum audio signals using 600 Ohm line isolation transformers which are easy to get and cheap.
    Despite the obvious line mismatch these are used extensivly in comertial audio over UTP applications, even high end ones.

    in your case you would take the output of amp 1 and feed it to TX1 primary, forwards. TX2 is simmilarly fed by amp 2 but in reverse.
    You then take the output from both secondries in seriese.

    A1 -------) | (------- Out
    ) | (
    Gnd------) | (---
    ) | (
    A2 -------) | (------- Gnd

    Al
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Simulation of your amp circuit as built shows this frequency response :
    FreqResponse.PNG
    It's flat (+-3dB) from ~ 15Hz to ~12kHz, i.e. over the whole of the human voice spectrum, so tinkering with the caps is unlikely to be beneficial unless you also boost the overall gain as Ronv suggested.
    For a human voice frequency of, say, 500Hz the wavelength in air is about 2ft. A dish to focus that well would need to be several wavelengths in diameter, so very BIG!
     
    Last edited: Apr 9, 2016
  16. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The NE5532 is not intended to drive a 40 ohm load (32 for headphones plus 8.2 for series resistor and 1 more for 470uF coupling capacitor. It also goes into short-circuit protection mode when trying to output more than 30 mA. So, when it tries to amplify a signal that is more than a distant bird chirp, the op amp output will swing up and attempt to charge/discharge that 470 cap and go into protection mode.

    This circuit would benefit from an output amplifier that is capable of driving a pair of headphones. Also, the headspace us so small with a 4.5V supply that it is, as you've noticed, worthless - as are many kits from Vellman. As mentioned above, use a 9 volt battery or, better yet, a pair of 9 V batteries in series. Then, all bound connections can be connected to the node between the two batteries and the caps between inverting input on the op amps and ground can be eliminated. Additionally, the (-) power pin on each op amp connected to the negative of the lower battery (now Vdd).
     
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