Mini microphone amplifier

Discussion in 'The Projects Forum' started by sstbrg, May 11, 2011.

  1. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
    54
    0
    Hi, I'm in the process of making a mini portable microphone amplifier on a single layer PCB.
    I'd like your opinion about my work so far.
    My goal is a small PCB with the circuit powered by a single 3.7V LiOn rechargeable battery.
    My greatest fear is noise and interference. I did a test run using wire-wrap and a 9V battery, and it turned out to be OK.
    However I fear the results once it's on the PCB... any recommendations (component placement, track widths etc)?
    It's the first board I'm making all by myself :eek:
    Thanks :)

    Circuit

    Amplifier datasheet
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,127
    3,049
    Consider building your board inside an Altoids tin or similar metal box. Use shielded cable for the mic leads, and for the amplified signal. You can't avoid the effects of EM interference on the mic element itself, but shielding as much as you can helps a lot.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The IC is an inverting power amplifier. Its input impedance and voltage gain are too low to be the preamp for an electret mic unless you scream very close to the mic.

    Usually a non-inverting opamp is used that has a high input impedance so it doesn't load down the fairly high output impedance of an electret mic.
     
  4. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
    54
    0
    Thanks for the replies!
    Audioguru, do you have any suggestions for another IC (preferably from TI due to their awesome free samples program)?
    Also, is it possible to add something to the electret microphone to solve this problem and still use the TPA152 ? Maybe a FET or something?
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Did you select the little power amplifier because it will drive low impedance earphones?

    Sorry, I don't know of any low voltage little power amplifier iCs that are samples from TI.

    Try the little TPA152 to see how well or how poorly it works.
     
  6. sstbrg

    Thread Starter Active Member

    Nov 29, 2008
    54
    0
    Yeah, I selected it because I thought it will be good to drive earphones.
    I did run a test and it seems to be OK at x250 amplification (friend speaks in far corner of the room very quietly - can be heard well enough in the earphones), as long as it's powered by a battery (other power sources induced noise!).
    Since in my case I want a battery powered amplifier, this thingy has a chance.

    I'll try to make the PCB in the next couple of days... any recommendations regarding the PCB, by the way (component placement, track width etc etc)?
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Keep the input traces on the pcb away from the output traces.
     
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