Finally, a project I can build. Portable audio player.

Discussion in 'The Projects Forum' started by Enigmatic Entity, May 6, 2009.

  1. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
    19
    0
    Hello everyone,

    I think I finally have a project I can build without having to study loads of electrical laws, etc.

    At the moment it is called 'Just another microcontroller inside (an?) enclosure'.

    I've made the circuit diagram, layout, etc. but I have a few questions:

    1.) Should I be using polar electrolytic caps or non-polar poly caps for the high pass filter (HPF)?

    2.) Are my values for the HPF correct (need 590Hz cutoff), and is it in the right place?

    3.) Do I really need a pre-amp? I thought if I swapped pin 8 for 7 and 5 for 6 on one of the amps, resonant frequencies may cancel out (not shown on diagram.)

    4.) Is there a simple way to stop the 'pop' sound when the switch is turned on?

    5.) Can I reduce the voltage + current to the pre-amp to the minimum values, eg. 2V when original is 5? (to save battery).

    6.) How to determine best batteries - Is 5*1.2V (1600mAh ea.) better than 1*7.2V 2000mAh?

    Sorry for all the questions, I really want to make this work without having to re-do things 20 times. See pics below for more 'explanation'. Any help would be very much appreciated,

    e.E.

    edit: the last picture now shows the pins 7-8 and 5-6 swapped.
     
    Last edited: May 6, 2009
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    What is the input level?
    Why are you cutting the bass frequencies below 590Hz?
    Why are the highpass filters such a low impedance?
    Why are the speakers tiny without any bass frequencies?

    The TDA2822M has a voltage gain of 98. If you use one as a preamp then the total gain is 9604 and the output will be full of hiss.
    If you swap the pins 7-8 and 5-6 inputs then the TDA2822 amplifiers will not work.
     
  3. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
    19
    0
    a.) The input level is around that of an mp3 player.

    Question b is answered by question d.

    Question d is answered by the topic title - it is a portable audio player, hence the 40mm speakers. Also, the HPF is supposed to be controllable, so I can have just the normal audio or the filtered audio. I'm not trying to build a super-bass hi-fi system...;)

    c.) I just used values I entered into a calculator for HPF's. Also, I did ask whether the values were allright or not. It seems to me that they aren't.

    I believe I do not need a pre-amp, according to the responses so far. :)
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    A "portable audio player" should sound normal, not just make little squeaking sounds from speakers that are too small. Maybe you are from a country where music is little squeaking sounds.

    The input should be an attenuator since the gain of the TDA2822M power amplifier is too high. Then parts from a high impedance passive Baxandall treble tone control circuit can feed the TDA2822M amplifier IC as your adjustable highpass filter.

    The headphones jack should be at the input, not at the output of the circuit.
     
  5. zero_coke

    Active Member

    Apr 22, 2009
    294
    1
    Maybe this isn't so simple after all lol. Seriously I thought this stuff was easy, but I'm hitting the books and gonna learn it one way or another. Good luck!
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Many years ago I made a "portable audio player" for the beach. Ghetto blasters were not invented yet.

    I used 3" satellite speakers that produced frequencies from 150Hz to 20kHz and used a 4" woofer that produced frequencies from 60Hz to 150Hz.

    I used three bridged amplifier ICs that produced 4.5W into each 8 ohm satellite speaker and produced 8W into the 4 ohm woofer. They were powered from six AA Ni-Cad rechargeable cells.

    It was simple.
     
  7. Enigmatic Entity

    Thread Starter Member

    Feb 16, 2009
    19
    0
    :( No. Though if you take into account all the music from the USA that infiltrates Australia, then yes.

    This is unique. Sometimes I want more power coming out of the headphone jack because I plug things into it that aren't headphones.

    This probing for help is proving to be difficult...
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Look at the datasheet for the TDA2822M amplifier. When it is a stereo amplifier with a 6V supply then its output per channel at clipping into an 8 ohm load is only 0.25W which is slightly more than nothing. Into a 32 ohm load the output power per channel at clipping is only 0.08W.
     
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