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Maximizing volume on ISD1700

Discussion in 'General Electronics Chat' started by mik3ca, Sep 3, 2017.

  1. mik3ca

    mik3ca Member

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    Is there a way I can maximize sound volume with the ISD1700 so that I can hear it at least 1 meter away in a room through a 4.5W 8 ohm speaker?

    I asked because then I tried using an LM386 with it, I was told that I'd get worse results when I hooked the LM386 to the analog output pin.

    So I wondered at first if the analog in section could be improved on. I know it says 0.1uF capacitor but I used 0.047uF because thats what I can get an abundance of dirt cheap and because its more compact and filters out hum better. The good news is I can still record and playback audio with the 0.047uF capacitor. This is what the datasheet says about the analog input:

    Now what really gets me is the AGC pin. They say use 4.7uF capacitor between AGC and ground. Here's the datasheet details:

    Since I'm recording sound directly from my laptop's earphone output, could I just directly ground this pin to get max gain and adjust the volume from the laptop until I get max volume without distortion, then all my problems be solved? or should I use a lower capacitor value?

    or am I thinking this all wrong?

    Here's a link to the datasheet:

    http://www.nuvoton.com/resource-files/EN_ISD1700_Datasheet_Rev-2.0.pdf
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    As was explained endlessly in your previous thread, power output is restricted by the supply voltage you're using - to add a more powerful amplifier you first need a higher supply voltage for it.
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The preamplifier and AGC are for the microphone input that you are not using.
    Aren't you using a 5V supply? Then the maximum output to an 8 ohm speaker connected to both speaker terminals is about 0.5W which is like a cheap clock radio.
    Maybe the headphones output of your laptop is too low. The input level should be 1V p-p.

    Does the volume control button work so that you can increase and decrease the volume? When the volume is increased to maximum output level then the sound will be distorted if the volume is increased higher. Does this happen?
     
  4. dave

    Dave New Member

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  5. mik3ca

    mik3ca Member

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    So I guess I wasted a capacitor then

    Well if a cheap clock radio is loud enough then I'd be happy. I guess I'll add a class-d amplifier powered by a higher voltage to the analog output.

    With the AGC capacitor in place I haven't heard distortion. I can change the volume of the laptop's earphone output.
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The datasheet says (and its block diagram shows) that the microphone preamp has AGC (not the aux input).
    You should be able to turn up the volume controls until the amplifier output clips like mad producing severe clipping distortion. Your laptop signal is too low for this chip.
     
  7. mik3ca

    mik3ca Member

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    Ok, so I need a larger input signal source to make distortion. Would the AGC stop distortion though? This part confuses me. Well at least if I get a teensy amount of distortion then I know I'm on the right track because then I can turn the volume down somewhat at the source to correct things.
     
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Why don't you understand that the microphone preamp has AGC but you do not have a microphone. The Aux input does not have AGC.
    AGC is "automatic gain control" so that when you scream into the microphone the AGC detects that the input signal is too high then it reduces the gain so that the output has no clipping distortion.
    If the input signal into the aux input is too high then the output to the speaker will have clipping distortion.

    The mic input can be attenuated but since its circuit is a differential and your laptop signal is not then it would be difficult without seeing its schematic of the circuit that is inside the IC.
     

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