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Thread: Various I2S chips output levels, questions, and opinion on options

  1. #1
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    Various I2S chips output levels, questions, and opinion on options

    Hi everyone, thanks you for taking a look at this.

    I've been trying to work out an ideal output stage for my project since my last post about using the A14 DAC on the 3.2 and I've shifted directions a bit after running into loads of issues there with the analog circuits from that approach.

    I've since moved on to a few options and I've got a few questions about them individually and generally. I feel like maybe one of the issues that I'm having is that I'm basically trying to run noise out of the teensy and audio tool. Making a sort of complex white noise machine and I feel like that noise is making things behave less consistently, but I'm also just not confident.

    1. PJRC audio adaptor / shield

    This is working great, the STGL5000, is working well. But my understanding is that because of the way that chip works, I'll need to have 2 jacks, one for headphones and one for line out due to the VGND on the headphones. Ideally I'd like to just have one jack out that can drive headphones and can double as a line out someone could use on a set of powered computer speakers if desired. Is that impossible or improbable to accomplish? I could use the line out and go to an external headphone amp circuit which I think will be the next thing I try to get around the VGND issue.

    2. CS4344

    I purchased a cheap CS4344 widget and got it working but it's really quiet and has a lot of distortion in my application (filtered noise), I'm not sure what's going on here, but I think it might have something to do with the filter. I was attracted to this chip for it's low part count and easy solderability. I don't think this will be an option unless I've done something wrong here...

    On a teensy 3.2 I connected as follows
    MCLK >11
    LRCLK > 23
    SCLK > 9
    SDIN > 22


    3. PCM5102

    I purchased a cheap PCM5102 widget and got it working and it's great, I'd say equal to the audio shield, if not somewhat louder. My main questions with this is that I put headphones in the jack just to see and it seemed to work out fine with some Koss portapros (60 ohms). But something tells me from what I've read about everything else that this is maybe a bad idea / the wrong thing to do?

    On a teensy 3.2 I connected as follows
    SCK > 11
    LCK > 23
    BCK > 9
    DIN > 22

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  2. #2
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    I could use the line out and go to an external headphone amp circuit which I think will be the next thing I try to get around the VGND issue.
    I tried this, and it works with a LM4808, but its pretty quiet compared to the audio shield. I might have the impedance off or something?

  3. #3
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    Ideally I'd like to just have one jack out that can drive headphones and can double as a line out someone could use on a set of powered computer speakers if desired. Is that impossible or improbable to accomplish?
    Someone on another forum suggested to me that a headphone driver can easily drive a line input, but a line output can not necessarily drive a headphone. I'm pretty sure that the difference between a headphone output and a line output will be it's "power". I guess that means VRMS, but I'm sure impedance plays a role here. I can say from experience that my line output will drive my headphones. Am I breaking something in the long run? I don't know. I'm not super familiar with the virtual ground situation of the STGL5000.

    The PCM5102 is a greater quality DAC. It's a line-level output, but if it runs your headphones fine I would think this would be a nice choice. If you find that running your headphones you aren't getting enough power, than you know what the issue is (not enough power).

    There are drivers for the WM8731. I'm pretty sure it's that chip (or something similar) that is in some iPods. Clearly you can use the iPod as a headphone driver or a line driver - so this chip would be quite nice for your needs. Since it has a driver for the Teensy Audio Library it would be easy to implement. Looks like there are a few inexpensive development modules using this chip out there.

    TLDR; A headphone driver can drive a line-input, a line-output driver can't necessarily drive a headphone properly. Hopefully I didn't over simplify this, excuse me if I have.

  4. #4
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    Quote Originally Posted by JayShoe View Post
    Someone on another forum suggested to me that a headphone driver can easily drive a line input, but a line output can not necessarily drive a headphone. I'm pretty sure that the difference between a headphone output and a line output will be it's "power". I guess that means VRMS, but I'm sure impedance plays a role here. I can say from experience that my line output will drive my headphones. Am I breaking something in the long run? I don't know. I'm not super familiar with the virtual ground situation of the STGL5000.
    the line vs HP was my understanding as well. I'm just hoping not to end up with something that will not break in the long term

    Quote Originally Posted by JayShoe View Post
    The PCM5102 is a greater quality DAC. It's a line-level output, but if it runs your headphones fine I would think this would be a nice choice. If you find that running your headphones you aren't getting enough power, than you know what the issue is (not enough power).
    Good to know, this could be a workable option then!

    Quote Originally Posted by JayShoe View Post
    There are drivers for the WM8731. I'm pretty sure it's that chip (or something similar) that is in some iPods. Clearly you can use the iPod as a headphone driver or a line driver - so this chip would be quite nice for your needs. Since it has a driver for the Teensy Audio Library it would be easy to implement. Looks like there are a few inexpensive development modules using this chip out there.
    The wm8731 looks interesting, does that mean with the wm8731 chip the headphones are not using a VGND? I see on the datasheet that it has pins for DGND, AGND, and HPGND. I'm not really sure how to decipher the difference between these.
    https://statics.cirrus.com/pubs/proD...M8731_v4.9.pdf pg.60 for typical application

    Quote Originally Posted by JayShoe View Post
    TLDR; A headphone driver can drive a line-input, a line-output driver can't necessarily drive a headphone properly. Hopefully I didn't over simplify this, excuse me if I have.
    Not over simplified I appreciate the straightforward answer!

    This is really why I'm trying to figure out the best way to get that functionality together so in my project I can safely have one jack that can drive HP and can be used as a line out in case someone wants to connect to headphones / external gear / mixer / computer speakers / etc. I feel like this is a pretty typical scenario on consumer electronics, but maybe I've just been mistaken all these years!

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