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Thread: CS42448 board update for T4 pinouts and improved performance

  1. #26
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by neurofun View Post
    Just for the sake of correctness.
    Your statement is only valid for T3.x.
    On the T4.0 the audio lib runs @ 44100Hz.
    ... and it supports any other frequency. 48kHz should work, with minimal jitter, but I have not tested it.
    48kHz is interesting, so if there are any problems I'm willing to help to solve that.
    Last edited by Frank B; 01-10-2020 at 01:02 AM.

  2. #27
    Quote Originally Posted by palmerr View Post
    Thanks Mhelin for the commentary,
    One part of the circuit I'm not yet happy with is the 5V power changeover from VUSB to external. I've simply left it that you shouldn't plug both in a the same time. Not very elegant. I originally included a jumper, as it merely duplicated the "don't plug both in together" instruction. The only other solution I can think of would be a power management chip, but this would be better on the Teensy board than a daughter board.
    What if you just required that the board is powered only using USB, a phone charger for an instance when it's not connected to PC, or connect the +5V socket to VUSB pins (on teensy) directly, they are directly connected anyway. Teensy 4.0 VIN is +5V. You could of course use a small 5V relay which disconnects VIN supply when VUSB is connected.

  3. #28
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    Neat idea - I hadn't thought of using Teensy's USB as ext pwr - simplifies that things a bit, and we're unlikely to get anywhere near the 1A limit (or even 500mA) of a phone charger.

    As for the relay (or FET) - it's at least another 5 components. I've culled a lot of nice features to keep complexity and board size down, so probably not, this time around.

  4. #29
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    Watching with interest.

    Any thoughts of solderable bow-tie jumper arrangement to allow use on T3x?

  5. #30
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    Thanks for the bow tie suggestion - it's saved some real estate and allowed "normal" operation OOB on the inputs and outputs.

    While, I'm not trying for T3 / T4 compatibility on this iteration (first prototype), maybe later. There's plenty of real estate under the Teensy to allow for this, if needed. I've taken the view that Paul's version works with T3s, and that the sample rate differences between T3 & T4 make synchronizing digital connections between T3/T4s a pain (dropped or extra packets), that everyone will move fairly quickly to T4's, particularly if Paul does some T4.x's with extra pins someday (I'm personally not a fan of the Teensy's underside pads).

    Here's the current state of the schematic and board layout.

    @mhelin - I've decided to keep the AUX_ADC header, as I think some one who wants 6 inputs is more likely to want 8 than some of the other features I've had to forgo. As for a long MCLK degrading over distance - good point - I was thinking of a direct plug daughter card, rather than a ribbon cable, to keep signal line short.

    I've kept the I2C, as some of the preamp designs I have in mind have digital pots for gain control.

    I've combined all the ext power inputs into a single header. Possibly a pain with Ext 5v/USB powering and +/-V as well. I've kept a separate EXT_5V header just in case.

    Board size is 109 x 90 - so within the Eurorack limits.

    I'm getting to the point where I'm thinking about price points - as I suspect many more people would adopt a board populated with the basic components (everything except the LM358, shrouded I/O, ext power and I2C headers?) I can't see that I can get anywhere near the cost of Paul's SGTL5000 board - particularly with a small run.

    $A40 BOM ($10 of this is the 3.5mm sockets)
    $A17 - board, assembly and shipping, run of 20.

    That brings the cost to $A56 (or $A46 without 3.5mm sockets), before overheads, postage etc. So the retail price would be around $A60 without sockets, and $A70 with. What do you think?
    Attached Files Attached Files
    Last edited by palmerr; 01-11-2020 at 05:11 AM.

  6. #31
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    I felt bad about saying the jumpers for T3 / T4 could be a later addition.

    Updated schematics and layout attached, with T3/4 jumpers included.

    Please check my pinouts for both T3 & T4.
    Attached Files Attached Files

  7. #32
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    Hey thanks for running with the idea. I'm not up to speed with all the details of which pin goes where yet. Been mulling over building a Teensy synth incorporating some tricks I used in a self-build in the late '70s. Starting the audio design tool tutorial in the near future after installing some holes.

  8. #33
    Quote Originally Posted by palmerr View Post
    I felt bad about saying the jumpers for T3 / T4 could be a later addition.

    Updated schematics and layout attached, with T3/4 jumpers included.

    Please check my pinouts for both T3 & T4.
    BLCK is still connected to wrong pin D22 it should go to D21.

  9. #34
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    Many thanks. BCLK fixed now.

    Will republish in a few days after others have had a chance to comment.

    Hope to send of the boards for a prototype (board only) run for completion before Lunar New Year takes my Chinese PCB house offline for a couple of weeks.

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