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AP-16+ schematic — Parallax Forums

AP-16+ schematic

richaj45richaj45 Posts: 179
edited 2014-01-31 12:56 in Propeller 1
Hello:

The schematic for the AP-16+ board is not in the user guild and i don't see it on it's web page.

Any one know were i could get the schematic? I don't like buying stuff without a schematic.

Thanks
rich

Comments

  • JonnyMacJonnyMac Posts: 9,107
    edited 2014-01-30 22:21
    The AP-16+ schematic is not available at this time (it's not an open-source product).

    I designed it (with my partner, John Barrowman, at EFX-TEK), so I can sort out any questions you have that go above-and-beyond the basic documentation. We have full support section for it on the EFX-TEK forums.
  • richaj45richaj45 Posts: 179
    edited 2014-01-31 06:20
    So what is the design of the audio output driver?
    Is it Class-D?
    How much filtering is there?
    Does use a single chip amplifier like a LM3886?
    What would be the THD+N at 1W,5W,10W,20W output powers?
    But is your clock source to keep the 44.1KHz output rate stable?
    Can you do 48KHz audio samples?

    Just want to know about the audio circuit quality.

    Regards,
    Rich
  • JonnyMacJonnyMac Posts: 9,107
    edited 2014-01-31 08:59
    The present design uses a class AB amplifier (we have a Class D design in the works)
    Filtering? (probably pertains to Class D question)
    Each channel uses one TDA7240A (rated for 20W with 18V power supply and 4-ohm load)
    See TDA7240A docs for THD specs
    We use a 6.25MHz crystal with 16x PLL for system clock of 100MHz
    The present software limits to 44.1kHz, but I have tested an update that will play 48kHz files

    On the sample rate issue: The design uses an RC DAC with a roll-off of about 17kHz so there is no advantage using 48kHz files. In fact, they just create problems because of the serial access of the SD card; the larger the sample rate, the bigger the file, and some SD cards have trouble keeping up. We recommend re-sampling files to 32kHz; this minimizes the file size without affecting the apparent fidelity of the file.

    Please keep in mind that the AP-16+ is a low-cost, consumer/industrial-grade product. If you're looking for high-fidelity, 48kHz playback it will cost you far more than $130.
  • richaj45richaj45 Posts: 179
    edited 2014-01-31 12:51
    Thanks for the info.

    That cover what i wanted to know.

    cheers,
    rich
  • JonnyMacJonnyMac Posts: 9,107
    edited 2014-01-31 12:56
    You're welcome, Rich. Feel free to give me a call on the EFX-TEK support number if you ever need more information.
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