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  1. #41
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    Re: Newbie question on dynamic mic circuit problems

    I did not and I won't be able to do so until January 3rd because of holidays. But I will (I don't have all this with me).

    When I use any element I measure its values first - for capacitors and resistors. Also, I test transistors (when its required for the circuit) with a tester.
    I wish I had an oscilloscope but they're freaking expensive!

    The bypass capacitor is C1. Oh, sorry, this is the schematic I used:

    Click image for larger version. 

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  2. #42
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    Re: Newbie question on dynamic mic circuit problems

    Hi,

    As already recommended I'd use a series resistor at the input.

    Now some thoughts ...
    You use a very high quality, low distortion Opamp...
    If you want to maintain signal quality I recommend to replace the tantal capacitors in the signal path with foil capacitors.
    Tantals and electrolytics, but also ceramics capacitors will add distortion.

    Instead of buying a scope you could use a PC's audio input. It usually has less noise and higher resolution than a scope.
    But it's frequency range usually can't go down to DC ... but you don't need this anyway.
    There also is PC software available for scope view as well as signal analysis like FFT.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



  3. #43
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    Re: Newbie question on dynamic mic circuit problems

    I was right. Since you used a polarized capacitor for C3 then its polarity is backwards without an electret mic maybe holding down the input voltage low enough.

    - - - Updated - - -

    In the inverting opamp circuit provided by Texas Instruments, the input resistance is produced by the output impedance (about 3.9k) of the electret mic parallel with R1.
    A "foil" capacitor is 100 years old. A more modern film capacitor is smaller and has metal vaporized onto the plastic film.



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  4. #44
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    Re: Newbie question on dynamic mic circuit problems

    While I can't change anything until Jan 3rd I was looking at the film capacitors..? Never heard of them.

    Are these ones good enough? https://mouser.com/ProductDetail/KEM...WyFpYM2tpaU%3D

    BTW, are we talking about C3, C5 and C6?



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    Re: Newbie question on dynamic mic circuit problems

    A ceramic capacitor is microphonic, it produces a sound when it is touched, bumped or vibrated. A film capacitor is used to properly and quietly couple audio signals.
    The Mouser film surface-mount capacitor will be fine. It might melt and be a short circuit if you overheat it while soldering.

    C3 is the only capacitor that has an unknown polarity when there is an electret mic connected to it. C3 also is the only capacitor in the circuit that is very sensitive to being bumped.



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  6. #46
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    Re: Newbie question on dynamic mic circuit problems

    Turns out I don't have some tools to make double sided PCB... and time. But I made a PCB in Circuit Maker, made all the bypass capacitors closer to the op apm and the traces should be shorter overall. Not sure about less loops though...

    Well, I'll keep trying when the tools delivered.



  7. #47
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    Re: Newbie question on dynamic mic circuit problems

    So I was learning to make double sided PCB's and I chose to work on the 2x transformers circuit. I learned some things about PCB design... and I made a "sparking circuit"! Well, at least I'm good at something as consistency is the key! :)




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