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Thread: audio over USB v. optical

  1. #261
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    FYI for everone:

    Hi,

    we will make something like this we'll have the EB02 and also an amplifier but unfurtunally I don't know exactly when they will be ready but as soon as they are you will see them on the website

    Joel

    ----- Original Message -----
    From: Jan Bennett
    To: [email protected]
    Sent: Saturday, February 17, 2007 9:44 AM
    Subject: Multi Output USB Dac


    Is it possible to build a multi output DAC (say 4 pairs of RCA outs) with higher output voltages? (around 4v)

    I'm very interested in something like this as it currently doesn't exist.

    Please let me know,

    Jan
    Jan Bennett
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  2. #262
    Newbie HIPPOhifi's Avatar
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    Hello All,

    I am amazed at how much interest this thread has got in such a short period of time.

    I would like to introduce myself, I am the owner and designer for HIPPOhifi. We recently launched a USB DAC "The Bloat", that essentially achieves what you are after except for the option of multiple outputs. I was referred to this thread by a very recent owner, Felix509.

    The reason I mention this is not soo much as to try to sell you an USB DAC but to help you on your journey into the DAC world. Whether that is to create a custom design or review another design I would be more than happy to help. I have read a number of the posts and want to reply to nearly all but that just isn't feasible. So feel free to fire some questions. I will start replying to a few now.

    PS. I also have a CarPC, my turn to return the favor after nearly downloading all the Road Runner skins.

    cheers,
    Brent

  3. #263
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    #1 question.

    What would it take to get a multiple output dac?

    Quite simply, a single set of outputs is nearly pointless in car audio unless you're going from it to a processor or just a single amp.

    #2 question.

    I notice that the Bloat has options on the OpAmps, is that something that's done when it's ordered, or is it possible to swap those out yourself?
    Jan Bennett
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  4. #264
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    Quote Originally Posted by RedGTiVR6 View Post
    #1 question.

    What would it take to get a multiple output dac?

    Quite simply, a single set of outputs is nearly pointless in car audio unless you're going from it to a processor or just a single amp.
    I completely understand and it would take a considerable amount of time to redesign. There would be two options:

    (a) tapping into the digital out of the USB receiver and using multiple DACS, more expensive option.

    (b) using a number of op amps in parallel after the I/V stage. A somewhat cheaper option.

    The other considerations is the power supply, obviously adding more opamp/DACs will draw more current and some kind of redesign in that area would be required. And of course, can't forgot a new case design.

    I am not out ruling this but just say a quick fix is not possible...

    Quote Originally Posted by RedGTiVR6 View Post
    #2 question.

    I notice that the Bloat has options on the OpAmps, is that something that's done when it's ordered, or is it possible to swap those out yourself?
    Due to the size of The Bloat, ie credit card size, I had no choice but to use SOIC devices. You can change these without to much difficulty, but they would require a soldering iron.

  5. #265
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    Quote Originally Posted by Felix509 View Post
    As Far as I know, the PCM2707 is stereo(2 channel)
    Yes the PCM2707 is 2 channel.

    Quote Originally Posted by Felix509 View Post
    Supposedly the 24 bit Burr Brown PCM1794 chips are the hottest DAC chips right now.
    Yes they do sound very detailed and clean when used in the recommended configuation.

    Quote Originally Posted by durwood View Post
    Cool. Now the question is that can one of your USB to IS2 chips commmunicate to mutliple dac chips? I think turbocad is right, we might be building a soundcard if we need a processor to go between the USB/I2S chip and the DAC chips. Hopefully we don;t need a processor since we only need routing, not processing. Processing is a link in the change of audio that is not needed since the computer CPU is going to do the processing. I think we need to contact an expert on USB DAC design to see if it's possible to route signals with any USB to I2S Chips. I'll look into this a little myself but I am a total newbie on DAC design.
    I was considering this last night when Felix asked me this over email. After reviewing the I2S specification (http://www.nxp.com/acrobat_download/various/I2SBUS.pdf), I beleive this is possible if you use the USB receiver as the master. I will add this to my "to test" list with the Bloat, 1 receiver and 2 DACs...


    Quote Originally Posted by Road_Dog View Post
    There are chips that can do volume control using I2C commands. That could possibly lead to the computer adjusting the volume via USB. Let me rummage through my bookmarks.
    Most USB receivers can be controlled by the Wave volume slider. I have a guide on my web site, in the downloads section that is very basic.


    Quote Originally Posted by JasonWW View Post
    Speaking of Kmixer, does anyone know if it is still the big nasty in the new Vista or is the sound quality improved?
    As felix said, eventhough it looks more complicated it isn't really that bad, from a SQ perspective I am impressed. If you have concerns take a look at ASIO4All (http://www.asio4all.com/).

    Quote Originally Posted by RedGTiVR6 View Post
    what I have been told, is that if at all possible, volume control should always be done in analoge.
    True, essentially to reduce the volume you drop bits of resolution. That being said I have heard price-comparable 16bit DACs completely blast away 24bit DACs.

    More replies to follow soon.

  6. #266
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    "Most USB receivers can be controlled by the Wave volume slider. I have a guide on my web site, in the downloads section that is very basic."

    wouldn't that also cause drop in resolution at lower volume?

    also, as far as vista is concerned, yes it is better than xp kmixer, much better even, but it is still not bit perfect...

    for a real good handle on vista audio check this monster thread.... I'm still only half way through it, but this is "from the horses mouth"

  7. #267
    Car Audio Moderator durwood's Avatar
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    Welcome HippoHifi!

    I was looking at your products after Felix linked to it. I hope you can help us, since your product is exactly what we want, except it's missing to multichannel part.

    (b) using a number of op amps in parallel after the I/V stage. A somewhat cheaper option.
    ALthough this is an option, would any type of computer software recognize this as multiple outputs, or is that just going to add on outputs like a y-splitter would do?

    The other considerations is the power supply, obviously adding more opamp/DACs will draw more current and some kind of redesign in that area would be required. And of course, can't forgot a new case design.
    We were thinking it would need to have additional power from 12V to help power the opamps. USB bus power would not be enough to drive to opamps.

  8. #268
    Constant Bitrate Felix509's Avatar
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    Welcome aboard Brent!! It will be great to have some Technical Insight from you!

    In regards to the Multiple outputs, it is equally important to have the same amount of inputs so as to do the processing in the computer..

    Correct me if wrong, but we would need a seperate USB to I2S receiver chip for each stereo pair.(highs, mids, midbass, sub) Would (4) of the PCM2707s show up in windows as 4 seperate devices?? Maybe you could test that out???

    In all reality, 4 of 'the Bloat' mounted on one board(or 4 seperate stereo boards in one case) would almost be the answer...

    I am sure their would then be clock issues with the DACs being totally independent from each other. From talking with Doede from the DDDAC1543 fame, I was understanding we could sync all of the receiver chips and all 4 DAC chips to the same High precision clock????? Does that sound right??

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  9. #269
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    By inputs, are you referring to the USB to I2S chip inputs?

    Or are you talking about actual input ports on the DAC?
    Jan Bennett
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  10. #270
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    Apps like console only allow the use of one sound card for input/output, so all 8 channels would need to show up under the same device, not separate ones for things to work.

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