isd4003 arll that matterr
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  1. #1

    Default isd4003 arll that matterr

    I need to record voice in an ISD4003. Using the audio input with a condenser mic isn't sensitive enough. I added a 1 transistor preamp which works well but it now has a ticking noise. Filtercaps eveyrwhere don"t help. Any suggestions? Thank you.

  2. #2
    Join Date
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    Default Re: isd4003 arll that matterr

    A circuit schematic would be useful here.
    "If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte

  3. #3
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    Default Re: isd4003 arll that matterr

    I would suggest using an MAX8914 breakout board from Adafruit. Connect the microphone in single ended mode with a voltage divider and set maximum input voltage for ISD4003 for 32 Millivolts. Cap coupled of course.
    Dave Purola,
    N8NTA
    EN82fn

  4. #4

    Default Re: isd4003 arll that matterr

    Thanks guys. I am attempting to attach the schematic of what I'm doing (never did this before). Like I said, any attempt to record has a loud ticking in the back round. Shorting the 1K in the mic circuit has no effect. Disconnecting the mic has no effect, removing the 220uF has no effect. Adding disc caps in parallel to the 220uF has no effect. Reversing the ANA IN + and - has no effect. The only way to stop the ticking is to disconnect the circuit. Capacitively coupling the mic directly to the ANA IN pins works but you need to put the mic up to your lips and talk very loud. This will be a modification to an existing prototype circuit board to be mass produced. Any suggestions would be appreciated.

  5. #5

    Default Re: isd4003 arll that matterr

    That didn't work Trying to attach again PDF file.
    Attached Images Attached Images

  6. #6

    Default Re: isd4003 arll that matterr

    I forgot. There's a 10K to B+ on the collector of the transistor.

  7. #7
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    Default Re: isd4003 arll that matterr

    Not sure about 1K and 220uf there;
    Also, instead of 1M, 100K may be better. Or have a 1M pot to see where it performs better.
    "If the Earth were a single state, Istanbul would be its capital." Napoleon Bonaparte

  8. #8

    Default Re: isd4003 arll that matterr

    The transistor amplifier is not going to work. Bias points are wrong, currents are way too low, and a few other errors. If you don't know how to bias the transistor, Google is your friend. Here, for instance: https://backyardbrains.com/experiments/transistorDesign

  9. #9

    Default Re: isd4003 arll that matterr

    Charlie I'm running the circuit at 3V and getting about 1/2 that on the collector, class A. The amp does work. It increases the sensitivity and picks up a normal voice about 10 inches away from the mic. It's just the ticking in the back round that's holding me up. This happened to me using a different ISD chip a while back. The solution was a few .1uF discs to eliminate it. In this case nothing seems to work. BTW thanks for the link - very informative.
    Last edited by peterdeco1; - 15th March 2019 at 14:03.

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