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Thread: MAD - Modular Audio Devices

  1. #1
    Senior Member MickMad's Avatar
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    MAD - Modular Audio Devices

    Hey there,

    I'm working on this project full time since 5 months now: https://hackaday.io/project/20982-ma...-audio-devices

    It's a set of modules aimed towards hifi audio applications with the Teensy 3.x

    The CORE module sports an AK4558EN from AKM and a ultra-low noise LDO for the analog power, stereo input and output on 2.54mm headers that also provide power to small external amplification modules (cleaned by an LC filter on the USB/ext. 5V power supply), and a Teensy pins breakout on one side on 1.27mm pitch headers. The breakout headers might go away in the next revision to leave place for external RAM chips like on the Teensy Audio Shield, but I was planning on using that breakout for future modules. The 2.54mm headers can be connected either to small breakouts that I designed for 1/4" TRS jacks and for 1/8" jacks for simple applications, or to external analog interfaces. The CORE module also provides solderable jumpers to easily configure the board to use either I2S channel available on the Teensy, so that you can stack two boards together and have 4 ins 4 outs.

    The IN module sports two THAT Corp 1246 differential line receivers with per-channel volume control, +4dBu or -10dBV reference level switch, and external preamp modules inputs selectable with a pushbutton; the OUT module sports a stereo volume control with impedance-balanced ouptuts, auxiliar output for connection with external power amp modules, and a separate headphone output jack selectable with a switch and powered by a ultra-low distortion TPA6120A2 amplifier.

    There's also a HI-Z module to be used as an external preamp module for the IN one, that as you can imagine, adapts the signal of an instrument like a guitar to an acceptable signal for the line receivers; this module has its own gain pot and its own mono jack.

    Finally, I also developed a small split rail power supply using TI's DC-DC converters and audio-grade LDOs (we're talking of uVs of ripple on the supplies, not mV) to power everything up. The PSU module can be powered by USB, 5V DC on a standar barrel jack connector, or through a terminal block to connect for example a battery pack.

    You can read more details on the hackaday.io page.

    Now, you might ask, "what's the reason of this post if everything is already on that other page"?

    Well, I have the intention of crowdfunding this project and I'd like to know how much people is really interested in such boards. In particular, I'm planning on making a campaing for the CORE module in the next month/months, and I would like to receive some feedback about its functionalities, its pros, its cons, etc. from you guys, you that make the Teensy community thrive. I've been using the Teensy since 2013, my first biggest achievement was getting USB Audio to work and now that's part of the Teensy core library, I already worked with the AK4558 codec and that's already natively supported by the Teensy too; this year with my last job I achieved ultrasound sampling at 700KHz through the amazing Teensy SPI and DMA capabilities, and I'm planning on using that same SPI/DMA duo with a custom serial interface to control a LOT of buttons, LEDs, knobs/sensors etc. to make HUGE control interfaces; I'm planning on making 192 KHz/24 bit audio on the Teensy a stable thing, not just a hack, and I'd love to make ASIO (instead of USB audio) a thing too. I really want to give something back to this community and this is my way of doing it.

    I made this post because I want to share the vision I have with you; this is only the beginning of a series of modules that I'm working on to make any kind of audio application powered by Teensy as easy as possible to build and program; the time will come for MIDI IO, Ethernet support with PoE, then some more like a pro level mic interface, fully differential outputs (not impedance balanced, but real, actively driven balanced outs), a more powerful power supply with transformer to be able to use vacuum tubes for preamps, or to make power output amplifiers for passive speakers... I'd like to go as far as I can.

    I need time and support to make my vision come true; if I'll get no support, I'll have to go back to work full-time for someone else, bringing someone else's ideas to life, and if that happens, I will not have the time anymore to work on my ideas... you get the point.

    I'm waiting for your comments

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Good examples could go a long way towards demonstrating the real-world value.

    The same could probably also be said of the audio library....

  3. #3
    Senior Member MickMad's Avatar
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    I know, but good examples (read: more boards) also require money that, being fully autofinanced (by unemployment money), I don't really have.

    First thing that comes to my mind is open source usb audio interface, something that simply does not exist on the market, then there's a plethora of synths demos here that could well benefit from the hi performance of the codec and of the interfaces; just add some keys and knobs and that's it.

    I was waiting to have a barebones port expander ready, but I suppose that for the sake of examples I can easily use a breadboard with 16 buttons, some knobs, and make a simple mono acid bassline sequencer on the Teensy. Then, another example program could use the same buttons and knobs to show the USB MIDI function as well.

  4. #4
    Senior Member PaulStoffregen's Avatar
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    If you have a camcorder or recent model smart phone, you could shoot some videos showing what it can do.

    You'll need to put together a video to have any chance at crowdfunding, so might as well get started with shooting video...

  5. #5
    Senior Member MickMad's Avatar
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    So, I finally got all my prototypes working and I started making some content to showcase the CORE module as well as the others; here's the first video I put on YouTube.

    https://www.youtube.com/watch?v=HKmbYeUzcwQ

    You can see more action of the same sketch running in the youtube words, with less talking and no modules other than the CORE and the Teensy 3.2 on Facebook:

    https://www.facebook.com/modularaudi...2009146145005/

    I'll post more content soon

  6. #6
    Senior Member MickMad's Avatar
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    In this latest video you can see all the prototypes I've been working on, including the IN HI-Z module, an instrument preamplifier.


  7. #7
    Very nice. Can you further explain your HI-Z module: What it is doing and maybe post a schematic.

  8. #8
    Senior Member MickMad's Avatar
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    Quote Originally Posted by daperl View Post
    Very nice. Can you further explain your HI-Z module: What it is doing and maybe post a schematic.
    The HI-Z module is, as the name suggests, an high impedance preamplifier with gain control; its output is connected to the IN module frontend, which is a switched differential line receiver done with an INA137 (switched because you can either use an onboard jack or an external preamp such as the HI-Z, through a pin header); the IN module also provides full analog volume control for two channels.

    You can find more information about the whole project in the link I posted in the first post; same thing for the schematic, everything is on the Hackaday project page. For your convenience, here's the link for the HI-Z schematic: https://cdn.hackaday.io/files/271981.../in%20hi-z.pdf

    Bear in mind that this is a prototype: I noticed that the gain gets way too high and it overloads the amplifier after half rotation of the gain setting pot; also, since the IN module has a differential line receiver I thought that it would have been better to have a differential output on the HI-Z module, but it turns out that the line receiver does not like the way I did it that much (maybe because of the overloading caused by the gain setting) so the next revision of the HI-Z will have a simple single ended output.

  9. #9
    Thank you. Keep up the excellent work and looking forward to your next update.

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