DIY'ing an inexpensive modular 2 to 8 channel DSP plate amplifier.

Discussion in 'DIY Speakers and Subwoofers' started by Matt Grant, Dec 2, 2021.

  1. #1 Matt Grant, Dec 2, 2021
    Last edited: Dec 3, 2021
    This is another idea that I have been kicking around for a couple years but finally purchased parts for and started messing with over the summer. Though I've been sidetracked with some other projects and waiting for lots of different parts so I haven't messed with it beyond testing the basic functionality.

    This is based around the Sure/Dayton TPA3116 amplifier boards with DSP which use the very capable but otherwise underutilized Texas Instruments adau1701 DSP chip. Those boards natively support 2 channel input and 4 channel output, 2 channels through the onboard amp and two unbalanced line level outputs. Combined with the Sigma Studio software it's a very flexible and feature rich DSP.


    The ADAU1701 also has 8 channel digital input and outputs which can be mapped to the GPIO ports. Unfortunately 4 of those GPIO ports are used up by the onboard pots on the Sure/Dayton amp boards. However you can utilize two i2c output streams each with two channels on the free GPIOs. Then using some inexpensive I2C DAC's you can easily achieve 8 channel output.

    While the design certainly isn't going to have state of the art noise and distortion levels, the ability to have 8 separate channels of DSP and amplification certainly opens up interesting new DIY speaker design prospects that cannot be replicated with passive or even 2 channel active amplifiers. Of which I have plenty of ideas for, many involving multiple shaded woofers for added directivity control.

    The remaining GPIO's can also be used for various controls and or indicators (I turned one into a basic adjustable clip indicator with the right programing).

    With my intended use as an amplifier for a single audio channel I'm using only one of the unbalanced inputs. However I believe the second unbalanced input can be utilized with the right configuration in the DSP and a stereo pot to allow for quasi-balanced audio input which I am going to experiment with.

    So far I've designed and had a couple prototype plates made up for mounting everything, the small version can be used as a 2/4 channel or the larger one which can be configured as 6/8 channel. I'm using the Yuan-Jing-TPA3116 boards here and some inexpensive 24v 9a power supply boards. This should allow for 8x50w into 4 ohms on the 8 channel version. I was just test fitting the boards at this point:
    IMG_2749-sm.jpg IMG_2750-sm.jpg IMG_2753-sm.jpg

    Of course during the testing phase I had a rats nest of wires to verify if I could get 8 channel output working from the DSP Beyond all the pins for the two I2C data lines and clocks I found I needed a separate 3.3v source because the 3.3v on the amplifier board doesn't have the current needed to run the external I2C DAC's.

    So I designed a simple expansion board which allows the PCM5102A DAC's to be easily mounted and splits the remaining GPIO's and the onboard Analog audio I/O into easy to use individual terminals. It also has headers for mounting an MP1584EN 3.3v DC-DC down-converter so it can be powered off the 24v supply.


    Need to find or make shorter cables:

    Alternate version where I swapped the 2 pin Audio I/O for 3-pin JST-XH to match the TPA13116 amplifier boards so they can be connected with a single cable. I still need to solder all the other headers to this board.

    Like I said before progress on this project had stalled while I was working on other stuff like building the new speaker testing turntable and getting new measurements on a whole bunch of my designs while it was still warm out. Now that winter is approaching I should be finding more time to continue with this and all goes well you'll start seeing a bunch of interesting new budget friendly active DIY speaker designs.
    Concept Box.png
    m4bgringo, mga2009 and MDuyck1292 like this.
  2. Looking forward to this development!

    I've experimented a lot with ADAU1701 (3E audio design with balanced output) and I see great possibilities there!
    Also there are a ton of cheap good/very good class D amps

    The only problems I see is that the ADAU1701 ADC are quite bad, so using them with pre outs of any AVR or any other analog input means you will be quite limited in THD and dynamic range. I have some I2S ADC with a PCM1802 chipset (USD$5) that haven't tried yet, but at least on paper is much better than ADAU1701 ADC.

    Right now I opted to bypass the ADC and just use a USB to I2S for 8 channels to feed the ADAU1701 and then connect another ADAU1701 thru TDM8 for a total 12 channels (using 2 extra PCM5102 I2S DACs)

    Anyways... great work! And those "interface/breakout" PCB's look neat!

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