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    Your "a little bit of stiff wiring" should be OK....

    Your "a little bit of stiff wiring" should be OK. An inch or two is a reasonable limit for unshielded wire.

    The mic cable can be yards long without affecting quality, when shielded cable is used.
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    Yes, one set of pullups for each I2C bus. The...

    Yes, one set of pullups for each I2C bus.

    The best value depends on the I2C frequency, rail voltage and the bus capacitance (related to the wire length).

    As a rule of thumb for 400kHz...
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    As I2C is an open drain bus, it will float up to...

    As I2C is an open drain bus, it will float up to whichever supply the pullup resistors are attached to.

    As Paul provides pullups on the Audio Board, attached to the 3.3V rail, you should be OK.
    ...
  4. A compressor would be a worthy addition to the...

    A compressor would be a worthy addition to the audio library.

    I have working code for a soft/hard limiting compressor if you would like a place to start. The existing project uses a gain cell to...
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    Hi Nevin, A quick read of the BOM looks OK,...

    Hi Nevin,

    A quick read of the BOM looks OK, but here's one directly derived from the schematic for comparison. (It's from the standard BOM ULP in Eagle). 20548

    The diode types are outlined on...
  6. Yes, you can do that, but better to get the...

    Yes, you can do that, but better to get the volume levels right in code - to maximise the number of bits available, and therefore noise and distortion.

    The Headphone output also has a maximum gain...
  7. Yep, it needs to be completed well within a 2.9...

    Yep, it needs to be completed well within a 2.9 mS window (44.1KHz / 128 samples) and leave plenty of time for other processing.

    https://www.pjrc.com/teensy/td_libs_AudioProcessorUsage.html
    ...
  8. Not really enough free pins on most Teensy...

    Not really enough free pins on most Teensy projects for even an 8-bit parallel interface!

    The only 3.5" SPI/SPI TFT boards I could find were designed for the RPi - and this library works OK with...
  9. Good to hear that you got it going.

    Good to hear that you got it going.
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    I'd be inclined to do the output connections...

    I'd be inclined to do the output connections separately, as on a single board layout, you are constrained to "in one line" layouts and the board would get quite long.

    There's really no need for a...
  11. Hi, Unfortunately the Ethernet code, and...

    Hi,

    Unfortunately the Ethernet code, and particularly the WIZ routines, are not re-entrant and particularly do not fare well if any (software or hardware) interrupt-driven code tries to use the...
  12. Hi, My two ILI9486 libraries are modifications...

    Hi,

    My two ILI9486 libraries are modifications of the Adafruit ILI9341 code - one generic and one based on the ILI9341_t3 Teensy-optimised code. From memory, the only changes I made were in the...
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    As for ground plane design, the basic tenets of...

    As for ground plane design, the basic tenets of mixed signal ground plane design are well-covered in this app note from Analog Devices.
    ...
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    Sure, any audio op-amp could be used. Here is a...

    Sure, any audio op-amp could be used. Here is a common configuration. It's relatively simple in concept, but needs a reasonable number of components to ensure the circuit is stable and add some...
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    Hi Nevin, Doing well thanks. Your design...

    Hi Nevin,

    Doing well thanks.

    Your design is pretty stable for now, (files on my github) and I'll make any changes required if the spec evolves further.

    I'm currently distracted with an...
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    The simplest solution may be to move to the T4.1...

    The simplest solution may be to move to the T4.1 (or any T4), which has accurate 44.1kHz sampling rates.

    I got caught with dropped frames in the Ethernet library when transferring samples between...
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    The CoolAudio chips are definitely the way to go....

    The CoolAudio chips are definitely the way to go.

    I believe the ADAT timing issues have been resolved on the T4 - which has an exact 44100 clock frequency. So ADAT output will probably sync...
  18. Just to add to the layout discussion, small...

    Just to add to the layout discussion, small component spacing is a pain for home builders but also fabricators.

    Keeping the analog and digital ground planes separate, and joining them up under...
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    Thanks for the heads up. I'm keeping to things...

    Thanks for the heads up.

    I'm keeping to things that are in the core of the Teensyduino library at the moment, but will watch the FNTE/Native Ethernet developments with interest and definitely...
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    In what way? The core of the 4.1 is identical to...

    In what way? The core of the 4.1 is identical to the 4.0, so the basic code should be OK.

    If you wish to use the extra SPI pins - SPI remapping is already in place.

    Are there other features...
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    The +/- 12V boost module works OK down to 3.2V...

    The +/- 12V boost module works OK down to 3.2V with a 100Ma load on one leg.

    At 3.0 V input the output is down to 7.5V, which is still adequate for our needs.

    I don't have one of the phantom...
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    There's no real reason why it won't work, but the...

    There's no real reason why it won't work, but the current draw from 3.3v would be nearly twice that from 5V.

    I'll try the PSU modules out on the lower supply voltage and see!
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    Try the files in my development repo ...

    Try the files in my development repo

    https://github.com/palmerr23/audio

    They have some updates that make them behave better with certain other modules (SGTL5000 and CS2448 specifically), but...
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    Sleeping on it provided the answer: - Go back...

    Sleeping on it provided the answer:

    - Go back to a simple switched gain arrangement for the THAT chip 20/40dB.

    - The pot controls the gain (0-20dB) of the final stage.

    Let's try and...
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    Good to hear that your T4.1 is on the way! ...

    Good to hear that your T4.1 is on the way!

    I've been trying to sort out the gain issue that mhelin identified in my spare moments this week.

    So far I haven't found an elegant solution, as the...
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    The unity DC gain idea is a good one on the op...

    The unity DC gain idea is a good one on the op amp.

    I've been batting around which taper would be better. THAT suggests reverse audio (log) tapers for the pots, as you note, so I'll start with C...
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    Yes, I got a fairly good outcome with a dual...

    Yes, I got a fairly good outcome with a dual ganged A taper pot. The Bourns PTD90 series pots are the same width as the original, so no change needed to the board outline.

    Here's the curves from...
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    We already have separate phantom power for each...

    We already have separate phantom power for each channel, with switches S1 & S2.

    The discussion @Mhelin and I have been having is about overload on the microphone preamps with very loud inputs...
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    BTW, with the multi-coloured LEDs, Focusrite uses...

    BTW, with the multi-coloured LEDs, Focusrite uses them for general gain adjustment:

    - off = very low signal
    - green = signal > -24dB(FS) - i.e. level is OK if this is coming on with the signal ...
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    Nevin, We could achieve the desired result...

    Nevin,

    We could achieve the desired result with a switch / pot - Bourns PTM90 series, for instance. The switch would provide 20dB less gain on the mic circuit These are 9mm wide, so no difference...
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    I eat my words! (and will re-think the front end...

    I eat my words! (and will re-think the front end of the design to avoid potential front-end overload).

    Thanks for being persistent in correcting my rookie error - one of the side effects of not...
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    Nevin, I'm thinking of using the WS2812 idea...

    Nevin,

    I'm thinking of using the WS2812 idea on the 8 channel board, as it saves 7 GPIOs. Going with normal LEDS on this project makes good sense, as one GPIO (particularly on a T4.1) is not a...
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    I'm thinking of using the WS2812 idea on the 8...

    I'm thinking of using the WS2812 idea on the 8 channel board, as it saves 7 GPIOs.

    Your call about including it on this one, it's a simple change - 5v is nearby and the control signal simply...
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    I'm thinking of using the WS2812 idea on the 8...

    I'm thinking of using the WS2812 idea on the 8 channel board, as it saves 7 GPIOs.

    Your call about including it on this one, it's a simple change - 5v is nearby and the control signal simply...
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    Answering your question about 1.5V between HP L/R...

    Answering your question about 1.5V between HP L/R outputs and ground.

    Yes, you should see ~1.5v between them and the power supply ground, but 0V between the outputs and the local (virtual) ground...
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    Nevin, These are rotary encoders, rather than...

    Nevin,

    These are rotary encoders, rather than pots - so no use for analog volume controls, unless we change the design to include digital pots as well. Second issue is that rotary encoders have no...
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    Here's a draft PCB layout. This version doesn't...

    Here's a draft PCB layout. This version doesn't have tricolor Overload LEDs, as you haven't had a chance to confirm that item yet.

    The two power supplies are mounted underneath, as indicated by...
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    I don't know of any small illuminated push button...

    I don't know of any small illuminated push button switches that are not momentary contact.

    I'm sure they're available. One trick that you can use is to make a sleeve to go around the pushbutton...
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    @Mhelin Good points: I usually design mic...

    @Mhelin

    Good points:

    I usually design mic preamps for a transfer factor of around 20 mv/Pa, which, using the useful table you have referenced, is 4dBu (or -56dBm) @130dB SPL. (Which, IMHO,...
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    Oops! Sorry Nevin, I didn't look closely...

    Oops! Sorry Nevin,

    I didn't look closely enough at the author, as this thread has just been us until now.

    Mhelin's comments were useful in challenging the design. I should have used +/- 12V...
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    Nevin, 1. The mic pre on the SGTL 5000 is...

    Nevin,

    1. The mic pre on the SGTL 5000 is MONO. It will have significantly worse noise and distortion performance than the THAT chip and it is VERY BAD practice to have a preamp and then reduce...
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    Here's another idea for the circuit. THAT1512...

    Here's another idea for the circuit.

    THAT1512 for the mic preamp (fixed gain). +/-5V supplies.

    LM833 final preamp (inst) volume control for both Mic/Inst input.

    Max mic gain is 30 + 20dB =...
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    OK, Most of the components will be reasonable in...

    OK, Most of the components will be reasonable in size (0805 or bigger) so straightforward enough to hand solder - it's the ICs with 0.5mm lead spagin that get really tricky! The THAT chips are...
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    If we were going for a 24 bit design and had...

    If we were going for a 24 bit design and had +/-12V supplies readily available the THAT1512 chip is an excellent match. I'm very familiar with it. Its EIN (equivalent input noise) of 4.6 nV/root(Hz)...
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    Happy to include clipping LEDs - software...

    Happy to include clipping LEDs - software controlled.

    Here's a first cut at the schematic.

    1. I went back to "real" rather than virtual volume controls - it's a lot easier to avoid clipping if...
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    Yes, I agree that option 2 makes more sense. I...

    Yes, I agree that option 2 makes more sense.

    I re-read the SGTL5000 spec, and I got the number of mic inputs wrong - as the block diagram is somewhat misleading. There is ONE mic input, and two...
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    Good catch on the XL6009 modules! I'll substitute...

    Good catch on the XL6009 modules! I'll substitute them into the design.

    The rotary encoder/switch idea is a good one, though a little prone to accidentally turning on/off phantom power, and...
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    Zeners can be yet another noise source! Yes,...

    Zeners can be yet another noise source!

    Yes, you can (and generally should) turn on the SGTL's gain ramping function to reduce popping.

    I was referring to the large transients that can occur...
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    Nevin, This is the design I created for my...

    Nevin,

    This is the design I created for my CS42448 board update. The specs you are proposing will need some changes.

    Here's the schematic of the example board for your, and others',...
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    Nevin, This all looks fine. With the...

    Nevin,

    This all looks fine.


    With the balanced output, it's relatively simple technically and can be accomplished with a single op amp package. However, it's an unusual requirement for non-pro...
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