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Building an ULTRA sensitive PC MIC

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Peter_wadley, Apr 10, 2007.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Maybe your electret mic is a 3-wires one instead of a 2-wires one.
    Maybe your electret mic is connected upside-down. Its metal case and the pin connected to it is supposed to connect to 0V.

    I don't know which circuit you made. My mic preamp circuit that I attach here again has a voltage gain of 101 which is fairly sensitive. My instructions say to inrease the value of R3 for more gain.

    Here is what another member said about my mic preamp circuit:
    "I tried the setup with out your mods - thanks guru - and the results were astonishing to say the least.
    I stood back about 20 feet and spoke with a normal voice. The sound recorder picked it up as if i was standing right next to it..
    With your modifications the circuit is more then I had expected! Unbelievable.
    By the way, if it isnt too much to ask, what is the gain set at with the 100K resistor?"
     

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  2. mneary

    mneary New Member

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    The red and white microphone wires should not be connected to the same place.

    Leave the red wire where it is, and connect the white wire together with the shield (screen) to ground (common, 0V).

    The resistor which gives power to the microphone is wrong. It it 150k (brown, green, yellow, gold), but it should be 10k (brown, black, orange, gold). 4.7k (yellow, violet, red, gold) would also work.
     
    Last edited: May 23, 2010
  3. anjana.larka

    anjana.larka New Member

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    Thanks for ur feedback audioguru, here it is ...

    My mic is of two pins NOT 3.
    yea it is metal case is connected to 0v with shield.
    : ( it is the same circuit about which another member said and you quoted. ( i just added a 9v regulator IC because i have to run it from 12V car battery.
    by the way, it could be too much as ask about the gain set at 100K as im not sooooooo good in electronics, if some tell me how to check gain then i can.... :)

    thanks guru
     
    Last edited: May 23, 2010
  4. dave

    Dave New Member

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  5. anjana.larka

    anjana.larka New Member

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    thnx friend,

    mneary :
    i will change that wire.
    wao.. you pointed out correctly i didn't checked that resistor its very much may be it is causing problem as it is not picking voice. I will change once i got back home (i am at work) and let you know.

    audioguru : my mistake : ( sorry !
    in the evening i will first do as mneary pointed and hope circuit will work as u designed : )

    sorry i have not learned much so i dont know about the deep working of components like formulas you use to calculate things, i just make circuit what i require as per you electronics gurus' schematics, but i would like to get this knowledge so some day i could design circuits : )

    further please let me know i have to keep mic far from the computer (around 5 meters) so which wire could be run long the mic one or the output (that is going to the computer mic jack) please let me know.

    thanks audioguru and mnery, i will let u know after required changes.
     
  6. anjana.larka

    anjana.larka New Member

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    Thanks friends for your time and help, i have changed that resistor with 10K and it just start working.
    As for mic i used only two wires (white wire NOT grounded with shield) beacuse of this image attached; fig1. (1:signal, 2:5v, 3:Ground)

    when i connected preamp output to mic jack pin1 and pin2 both tied together it was producing lot of noise, how ever i connected preamp output as shield to pin 3, and signal (redwire) to pin 2 and that bomardment noise vanished (i dont know why ; i am attaching image fig1 which i got from a website, according to them pin 2 is 5v; pin1 is signal)

    simple mic is working ok in this config fig2.
    any way i hook it with only two wires shield and ring at mic jack and got low noice (only humming and speaker feedback is there)

    Now the fun part,

    The circuit is picking up the voices very good like fan, scratching over mic wire or table it is very sensitive when the wire or circuit board is moved but my voice i am speaking at 3 foots is not upto the satisfaction. It is relatively better when I speek under one foot distance with normal voice.

    Actually i am using a voice recongnition software to send computer commands but due to this issue and may be little humming/noise, software feel diffculty in recongnizing my commands some times it is not listening at all.

    It seems that this circuit is very very good for public address system but not so good with computer microphone (i checked computer mic volume 100% with mic boost with out it results are even worst)

    any way i have completed it with input/output 3.5mm stereo jacks and power LED now looking for small plastic box to fit it into.

    please give me suggestions to cope with the sound quality issue so i can put this circuit on board :)

    should i decrease the value of resistor feeding power to mic as mneary suggested, and yes i will sure try to increase the value of R3 as audioguru told.

    waiting for your reply ... thanx in advance...
     

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  7. EternityForest

    EternityForest Member

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    if you're circut doesn't meet your needs Memorex makes a great 10-20$ headset mic that they might still sell at target. if not there are lots of cheap(<100) headset mics out there. what i would suugest is either get one, build one(infrared should be pretty easy) or use a blue microphones snowflake. it is a condenser mic with built in USB for 40$.


    A not on DSP:
    using software enhancements will improve the audio A LOT. VSTHost(link included) is easy to use and does not require installation(and is free)
    i would recommend a band pass filter or equalizer that boosts from 150 to 4.5khz to get rid of non-voice audio, followed by a compressor to even out loudness differences. hermann seib makes an exellent free audio effects program: VSTHost
    this program does realtime audio effects and can record the "output"(you can run it with the speakers off)
    using VST(virtual studio technology) plugins. these are a standard way to have dsp effect for musicians. i would recommend the GVST plugins
    GVST
    i would use gband followed by gcomp. set the compression ratio on gcomp to 1:2 to 1:15 or so and set the filter on gband to min 150hz and max 4.5khz. experiment till it sounds good
     
    Last edited: May 24, 2010
  8. transistor495

    transistor495 Member Forum Supporter

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    Picking up of scratching over table,mic,wires doesn't measure the sensitivity of mic. All will pick those. If you're using 100% volume with 'mic boost' on computer, then it is not even sensitive anywhere near standard level.
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    That is a 3-wires electret mic. My circuit is designed for a 2-wires electret mic and needs modifications to work with your 3-wires mic.

    Of course the 3-wires mic will not work when you short its pins together. Pin1 is +5V, pin2 is the output that probably needs a coupling capacitor to feed the preamp and pin3 is the metal case and is ground for the shield of the cable and is 0V.

    Your attachment did not work. We don't know which way the pins on your mic should be connected. Try it both ways.

    It is connected wrongly for a 3-wires mic.

    An electret mic works very well when its pins are connected properly.

    There should not be any hum. Hum is caused when the pins on the mic and the shielded cable are not connected properly.

    Here is a 2-wires electret mic and a 3-wires electret mic with the ways they connect to a preamp circuit:
     

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  10. THESTOCKSGUY

    THESTOCKSGUY New Member

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    sensi-mic

    Enjoy this clip-on mic, and if you want sensitivity any set of TL082's will get you to be able to 'Hear Crickets Chew Grass'. Preview any preamp diagrams. If she doesn't want to wear an earpiece then have the audio turned onto a 'reader board for the deaf' scrolled across a 45"er.
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why use an ordinary TL082 dual opamp? it has the same max voltage gain as any other opamp but it has no input bias current since its inputs are Fets. The lack of input bias current does not make it very sensitive as a mic preamp.
    A TL081 is a single ordinary opamp. A TL071 is a TL081 that was selected for low noise and is used as a mic preamp.
     
  12. anjana.larka

    anjana.larka New Member

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    Thanks for reply.

    1. yes of course i am using two wires mic.

    2. friend i am using two pins mic with your circuit and have to feed output to computer mic jack that' it so i dont need to keep mic on my lips and of course it is not possible when i am driving my car, the only best place i can fit that mic is around 2 foots.

    3. the attachment was only to show you people that what i did with circuit and computer mic jack to connect (finally i connected wire 2 and shield of jack with circuit output and its ok)

    4. that mic in question u said connected wrongly was a zoltrix clip mic i purchased in my child hood :)
    i just break the case and pull out the elektric mic with its own wire and stereo jack)

    5. yes humming gone when i changed microphone with new one, and put all that kit in a plastic box with stereo jack and dc power jack out. I will post pic later. First i have to check it in my car ; )

    6. but there is slightly a noise like air or some thing like that ( i mean speaker is not quite when i am not speaking in mic, it should be quite enough so that my voice recognition software pick my commands clearly and of course i will enhance the capability of project)

    In last thank you for your time and help and nice circuit, any suggestion welcome to fine tune this circuit according to my needs)
     
  13. anjana.larka

    anjana.larka New Member

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    so... ? what to do now ?
     
  14. anjana.larka

    anjana.larka New Member

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    sorry i dont think i can use those dlls with my software
     
  15. transistor495

    transistor495 Member Forum Supporter

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    I didn't expect that question...:)

    The producer of this oscar circuit will answer what's going on wrong. However high quality snapshots from different angles will definetely help. Also post a clear view of the particular mic showing it's terminals. Where you bought it?
     
  16. SPR

    SPR New Member

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    Hello audioguru,
    Can I use 5V (or 12V) instead of 9V as PWR IN.
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You forgot to say which microphone and which opamp you have.
    My mic preamp uses an electret mic.
    It uses a TL071 low noise opamp that has a minimum supply of 7V so it might not work with only 5V.
    The circuit works fine with a 12V filtered supply.
     
  18. SPR

    SPR New Member

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    Hello Audioguru,
    Thnaks for your reply. I am using a normal condenser MIC and is planning to use TL071 to increase the sensitivity of the MIC. Its quite not comfortable to hold the MIC in front of the mouth for clear sound. I am planning to use the 12V ,from the spare available on the PC SMPS. Hope electret MIC is same as a Condensor MIC, available in the normal PC headphone/Mic assy.
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A condenser mic needs a 48V supply. An electret mic is similar to a condenser mic but it has the 48V built into its electret material inside and has a Jfet impedance converter. The Jfet needs to be powered with 0.5mA at a few volts. Most modern inexpensive audio devices use an electret mic.

    Most shops call both a condenser mic.

    The 12V from a pc is very noisy and will need good filtering to power your extremely sensitive mic preamp.
     
  20. JCWagener

    JCWagener New Member

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    would there by any benefit in terms of noise if this circuit is converted to dual supply with two 9V batteries?

    I am also considering using the OPA134 which was suggested to me by audioguru.

    also, will the use of potentiometers on the electret bias and opamp gain resistor influence the noise level? I am currently using metal film resistors and I suppose the potentiometers (multiturn high quality) will be more noisy?
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    It won't make any difference.

    I never used one because I don't use extremely high gain for a mic preamp.

    The circuit does not need a pot to adjust the bias on an electret mic.
    Use a gain pot if you want.

    You will find that background sounds will be much noisier than electronic noise from the circuit. You might hear some electronic noise if you turn off the mic.
     

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