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  • palmerr's Avatar
    Today, 02:21 AM
    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 PCB, just mount them...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    Today, 12:26 AM
    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 same SPI channel. ...
    6 replies | 109 view(s)
  • palmerr's Avatar
    Today, 12:06 AM
    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 initialisation, so...
    24 replies | 8097 view(s)
  • palmerr's Avatar
    06-01-2020, 02:04 AM
    As for ground plane design, the basic tenets of mixed signal ground plane design are well-covered in this app note from Analog Devices. https://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html
    6 replies | 85 view(s)
  • palmerr's Avatar
    06-01-2020, 01:59 AM
    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 low-pass filtering...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-30-2020, 01:46 AM
    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 ESP32 digital power...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-28-2020, 01:20 AM
    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 T3's and T4's due to...
    11 replies | 181 view(s)
  • palmerr's Avatar
    05-26-2020, 12:52 AM
    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 nicely. ADAT input is...
    12 replies | 1563 view(s)
  • palmerr's Avatar
    05-26-2020, 12:38 AM
    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 the CS42448 is best...
    46 replies | 2696 view(s)
  • palmerr's Avatar
    05-20-2020, 11:43 PM
    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 provide that option when...
    44 replies | 1612 view(s)
  • palmerr's Avatar
    05-20-2020, 06:45 AM
    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 that you can see might...
    44 replies | 1612 view(s)
  • palmerr's Avatar
    05-17-2020, 06:37 AM
    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 boost modules in hand...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-17-2020, 05:57 AM
    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!
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-17-2020, 05:54 AM
    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 are not fully tested...
    44 replies | 1612 view(s)
  • palmerr's Avatar
    05-16-2020, 02:29 AM
    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 finalise things this week -...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-15-2020, 07:46 AM
    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 THAT chip really...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-11-2020, 03:36 AM
    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 (US) taper and see...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-09-2020, 06:05 AM
    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 the simulation: ...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-08-2020, 07:34 AM
    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 (such as close-miked...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-08-2020, 03:50 AM
    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 - red = clipping
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-08-2020, 03:36 AM
    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 to board dimensions,...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-08-2020, 12:16 AM
    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 touching a discipline...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-07-2020, 07:34 AM
    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 good trade-off for the...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-07-2020, 12:56 AM
    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 daisy chains from one...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-07-2020, 12:54 AM
    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 daisy chains from one...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-06-2020, 11:11 PM
    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 on the headphone...
    14 replies | 248 view(s)
  • palmerr's Avatar
    05-06-2020, 11:03 PM
    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 reference point, so...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-06-2020, 07:27 AM
    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 the red rectangles. ...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-06-2020, 05:50 AM
    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 out of something...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-06-2020, 03:57 AM
    @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, is as high as any...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-05-2020, 04:47 AM
    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 supplies, particularly...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-05-2020, 12:40 AM
    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 it to mic level again...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-04-2020, 05:57 AM
    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 = 50dB, may need to add...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-04-2020, 03:15 AM
    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 available in SOIC packages...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-04-2020, 12:49 AM
    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) @ 20dB gain is top...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-03-2020, 07:56 AM
    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 you can control the...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-03-2020, 05:01 AM
    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 line inputs. ...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-02-2020, 02:13 AM
    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 requiring more GPIOs to...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-01-2020, 08:11 AM
    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 when turning on/off...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    05-01-2020, 12:47 AM
    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', information. 1. The...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    04-30-2020, 07:37 AM
    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 equipment. For pro...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    04-29-2020, 08:19 AM
    Yes, it is nearly as straightforward as that. However: - Input caps on the audio shield need to be rated at 48V. - HV supply needs to be relatively well filtered. - Paul's Audio shields are not set up for...
    65 replies | 1255 view(s)
  • palmerr's Avatar
    04-27-2020, 12:25 AM
    OK, A change of plan isn't a bad thing if you hit a brick wall! With that error, which pops up every now and then. Usually, it's a badly written call to the constructor, but your call to AudioInputAnalog ...
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-19-2020, 11:17 PM
    Not surprising you get a negative output with the + input biased to 3.3 * 2.88/12.88 V and the - input coming from a ground-referenced source! Try this: - bias the + input to half the rail voltage. - add an...
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-19-2020, 02:35 AM
    OK, I'm not sure which "output" you're referring to. If it's from the Teensy DAC , then you'll need to offset the value output, so quiet (sample == 0) is equal to half the maximum output value, AND put a series...
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-18-2020, 12:56 PM
    yes, but they're not required for this application. Audio opamps are used for very low noise (hiss) / low distortion, neither of which match your description of static/ crackling. those are most often associated...
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-17-2020, 03:16 AM
    I already have Teensy Library Ethernet Audio working (without AVB). https://github.com/palmerr23/EtherAudio This version (V1) carries stereo pairs of audio, plus a general protocol for messaging between hosts. ...
    36 replies | 1031 view(s)
  • palmerr's Avatar
    04-16-2020, 11:46 PM
    Jay, Sorry to come in late to this discussion. An excellent design - and I like the "lean and mean" concept. When I was working on the new CS42448 board, I had several helpful suggestions for what should be...
    36 replies | 1031 view(s)
  • palmerr's Avatar
    04-14-2020, 12:46 AM
    Good to hear that the basics are working well, and you're now tweaking! I'm surprised that the tweets are triggering the bass channel. You should have nearly two decades of frequency between them (i.e. nearly 20 dB...
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-11-2020, 12:08 AM
    Yes, that's right. DC and CS (SS) for the display and any other device are separate, MOSI, MISO and SCK are shared. What can sometimes trip up code is that some drivers are not respectful of shared SPI (that's...
    4 replies | 244 view(s)
  • palmerr's Avatar
    04-10-2020, 11:56 PM
    Yes, the sample-width settings are for how the signals are transmitted, rather than the native sampling accuracy. Paul has set the transmission mode to TDM (24 bits in a 32 bit frame), and the extra 8 low-order bits...
    2 replies | 212 view(s)
  • palmerr's Avatar
    04-08-2020, 11:26 PM
    You are definitely not trying to do too much. I have an audio card running on a T3.2 with a busy SPI Ethernet card, and the average CPU load is < 50%. On a T3.5/6 this is much lower. Your pin selections look OK,...
    4 replies | 244 view(s)
  • palmerr's Avatar
    04-07-2020, 01:22 AM
    Yes, that's the general understanding of single supply mode in op amps. :-)
    39 replies | 1523 view(s)
  • palmerr's Avatar
    04-06-2020, 11:57 PM
    It's the same pins as for the 2 channel Audio Board. TDM uses the same pins as I2S, but in a different way. SPI is also remapped. Here's a screen capture from my updated CS42448 board, of the T3/4 jumpers section...
    3 replies | 316 view(s)
  • palmerr's Avatar
    04-06-2020, 11:47 PM
    The root cause is that T4.x clocks generate exact 44.1kHz and T3.x only approximate it as gfvalvo has noted. Even if his suggestion works, you will only space the dropped / extra packets out further. I had the same...
    4 replies | 327 view(s)
  • palmerr's Avatar
    04-06-2020, 11:37 PM
    A 741 will need +/- supplies of > 5v to deliver anything like the voltages required. They don't drive inputs anywhere near the rail voltages. Try an LM358 series OpAmp, which works well in single supply mode at low...
    39 replies | 1523 view(s)
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