[TangerineSDR] VLF 4-channel ADC

[David G. McGaw]

First:  The lowest performance part of the AKM series, the AK5534VN is 
actually better than the Cirrus part we were considering and Digi-Key 
SAYS they have 1900 of them.  We could stock up on enough to prototype 
and hope they get the fab back up quickly.  The eval board data sheet 
has their schematics and enough info that I could work up a BOM and I 
can help with a schematic and layout for a prototype.

Second:  TI/Burr Brown also has 4-channel parts giving a range of 
performance, with up to 123dB SNR (with Dynamic Range Enhancement 
enabled).  I also know them to like to work with students.  There are 3 
choices that I see:
PCM1840 - good dynamic range, good 192 kHz filter

PCM4204 - better dynamic range, sloppy 192kHz filter
TLV320ADC6140 - highly integrated front end, good dynamic range (113dB 
w/o DRE, 123 w/ DRE), good 192kHz and above filters.  One problem: it 
says it supports an input signal bandwidth up to 80 kHz (bottom of page 
30).  Perhaps this could be enhanced with an external input filter.

Note that Dynamic Range of audio converters is usually reported 
"A-weighted".  This is a somewhat bogus approximation of what the ear 
would hear.  We are actually interested in the "Unweighted" figure, but 
not all manufacturers report this.  It is usually about 3dB less than 
A-weighted.

David

On 10/27/20 8:12 PM, Jonathan wrote:
> I was able to get a response from an AKM sales rep, but it was not
> with good news. He told me the fab this ADC is made in caught fire
> last week and had a very negative impact on business. They can't sell
> me an evaluation board and won't procure gerbers/BOM because of it.
> See his email below:
>
> Hi Jonathon,
>
> As Peter mentioned, the AKM fab that produces this A/D converter
> caught fire last week.  We don’t know the impact yet to our business,
> but it’s not going to be good.  Providing you the board layout docs
> won’t help you if you can’t find any A/D’s to populate it.
>
> We are overwhelmed with customer issues that use our converters in
> production, please understand we can’t support your request.
>
> Thank you.
>
>
>
> Robert (Bob) Wayland
>
> AKM Semiconductor, Inc.
>
> Area Business Development Mgr
>
> 856.904.7878
>
> Digi-Key is depleted in stock until March of 2021. I couldn't find it
> anywhere else.
>
> I still feel this is a great direction to be going in and it's still
> early with their fab fire.
>
>
>
> On 10/27/20, David G. McGaw via TangerineSDR
> <tangerinesdr at lists.tapr.org> wrote:
>> Yes, that is correct.  These are high-end consumer and professional
>> audio components.
>>
>> By the way, SACD is not anything special.  It is just a bit stream from
>> a sigma-delta ADC modulator minus the FIR filter.  In fact, the original
>> SACD spec was based on the 1986 vintage Analog Devices AD1879 in a test
>> mode that outputs the 1-bit stream from its modulator.  This was never
>> intended to be used this way, so the SACD spec audio actually has a
>> tremendous amount of noise above 20kHz which was intended to be cut by
>> the digital filter.  It was created by Sony because their CD patent had
>> run out.  DVD-Audio was always the better format.
>>
>> David N1HAC
>>
>> On 10/26/20 11:40 PM, Jonathan wrote:
>>> David,
>>>
>>> Thank you for finding this! Scotty and I are looking at it now. It has
>>> really good performance!
>>>
>>> Nathaniel,
>>>
>>> I think this will be a suitable replacement. It looks like it is
>>> designed for recording high definition audio, like the kind of high
>>> definition audio in SACDs and similar formats.
>>>
>>> Jonathan
>>> KC3EEY
>>>
>>> On Mon, Oct 26, 2020 at 11:04 PM David G. McGaw via TangerineSDR
>>> <tangerinesdr at lists.tapr.org <mailto:tangerinesdr at lists.tapr.org>> wrote:
>>>
>>>      Here is an AKM 4-channel part that has extremely good THD+N and
>>>      dynamic
>>>
>>>      range and can do the full 192kHz bandwidth.  It can run up to 768kHz
>>>
>>>      sample rate with even greater bandwidth.  It also has DSD output that
>>>
>>>      would allow custom filters.
>>>
>>>
>>>
>>>      $13.02 from Digi-Key single part price!
>>>
>>>
>>>
>>>      https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.akm.com%2Fus%2Fen%2Fproducts%2Faudio%2Faudio-adc%2Fak5574en%2F&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C462a278ea4b74c4c628f08d87ad62a65%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637394407535698554%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=9v7H%2BiBiPIGzvot1CazuZ6d4brsnnyn0aBvazUpoyJ4%3D&reserved=0
>>>
>>> <https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.akm.com%2Fus%2Fen%2Fproducts%2Faudio%2Faudio-adc%2Fak5574en%2F&data=04%7C01%7Cdavid.g.mcgaw%40dartmouth.edu%7C462a278ea4b74c4c628f08d87ad62a65%7C995b093648d640e5a31ebf689ec9446f%7C0%7C0%7C637394407535698554%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=9v7H%2BiBiPIGzvot1CazuZ6d4brsnnyn0aBvazUpoyJ4%3D&reserved=0>
>>>
>>>
>>>
>>>      73,
>>>
>>>
>>>
>>>      David N1HAC
>>>
>>>
>>>
>>>      --
>>>
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>>>
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>>>
>>