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Old 6th July 2019, 05:49 PM   #1
ishizeno is offline ishizeno
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Join Date: Mar 2015
Default 8 AK5578EN + 8 AK4499EQ ADC/DAC Boards

WARNING: This thread had a tortuous start during the initial four weeks. Therefore, new readers are invited to start from this recap post, which should save them a lot of frustration. Curious readers can then go back to the earlier posts in order to get a sense of how we got there in the first place... I hope you enjoy the ride!

###

I am currently working on a modular audio interface with the following specs:

- Dedicated ADC board powered by 1 XMOS XUF232-1024-FB374 (isolated)
- Dedicated DAC board powered by 1 XMOS XUF232-1024-FB374 (isolated)
- 8 balanced mono inputs (XLR or mini XLR, TBD)
- 8 balanced mono outputs (XLR or mini XLR, TBD)
- 8 AK5578EN 32-bit, 768kHz, 130dB ADC chips in mono mode
- 8 AK4499EQ 32-bit, 768kHz, 140dB DAC chips in mono mode
- 192 OPA1612 Op Amps for input channels
- 64 OPA1612 Op Amps for ouput channels
- TOSLINK S/PDIF + ADAT Input
- TOSLINK S/PDIF + ADAT Output
- 5-pin LEMO Jack Clock Input
- 5-pin LEMO Jack Clock Output
- CC-BY-SA-3.0 Open Source License (Hardware + Software)

I am making good progress, but I have a few questions:

# Op Amp Selection
- Is the OPA1612 the best option?
- Would the OPA2156 CMOS be a better alternative?
- Should I give the mysterious RT6862D/RT6863 of the Khadas Tone Board a shot?

# Input Buffers Design
I am designing the DAC board following AKM's reference design, which is making things pretty straightforward. Unfortunately, the ADC reference design is using the obsolete NJM5534. Where could I find a reference design for an ADC input buffer using the OPA1612 or any pin-compatible Op Amp?

# Connectors
For many applications, the small footprint of the mini XLR connector is really attractive. Unfortunately, it is more expensive, less reliable, and less versatile (male versions cannot be found in certain for factors). Therefore, I am inclined to mount the input and output connectors on separate boards. When doing so, how should I design the connection between these connector panel boards and the ADC and DAC boards?

# Shielding
Should I shield the ADC and DAC chips? If so, which other passive components should be covered by the shields?

Just for kicks, these interfaces will be connected to a Xilinx XCZU15EG-2FFVC900I FPGA with 3,528 DSP slices for low-latency/low-jitter sound processing, using an Enclustra ME-XU7-15EG-2I-D12E System-on-Module mounted on an Enclustra Mercury+ PE1-300 base board. And for the user interface, I will use a Khadas Edge mounted on a Khadas Captain. All this goodness will be released under CC-BY-SA-3.0 as well.

Last edited by ishizeno; 19th August 2019 at 12:45 PM.
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Old 6th July 2019, 07:07 PM   #2
Markw4 is offline Markw4  United States
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Location: California
Quote:
Originally Posted by ishizeno View Post
...The DAC board will use 8 OPA1612 op amps per mono channel (64 op amps in total), following the ...
That looks like the wrong reference design for use with AK4499. It's different from the earlier AK44xx chips in multiple ways, current out instead of voltage out is a big difference, as one example.

Last edited by Markw4; 6th July 2019 at 07:09 PM.
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Old 6th July 2019, 07:14 PM   #3
ishizeno is offline ishizeno
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Quote:
Originally Posted by Markw4 View Post
That looks like the wrong reference design for use with AK4499. It's different from the earlier AK44xx chips in multiple ways, current out instead of voltage out is a big difference, as one example.
I am using the reference design provided on Figure 83. External I-V Conversion Circuit Example (Mono mode), page 110 of the 019001308-E-00 document provided by AKM upon registration for the AK4499EQ.
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Old 6th July 2019, 07:22 PM   #4
Markw4 is offline Markw4  United States
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Location: California
The document I have for AK4499 Rev. 0 Evaluation Board is akd4499-b0-01e. That shows the Reference Voltage power supplies (similar to Jung regulators) and other necessary things that are also different for AK4499. I/V conversion is only one of multiple issues.
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Old 6th July 2019, 07:28 PM   #5
ishizeno is offline ishizeno
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Ouch! I did not know about this evaluation board. Any idea where I can find more information about it? At the very least, which Op Amp(s) are they using for it? And do they provide more information about mono mode?
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Old 6th July 2019, 07:33 PM   #6
chris719 is offline chris719  United States
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Location: Connecticut
I don't understand why would you use a $2000+ dollar Zynq. The whole point of a Zynq is to have full ARM CPUs integrated (Cortex A53 in this case), and I don't see how you are using that? You're also adding another ARM SBC on top of it just to drive a front panel, which the Zynq is already overkill for?

The BOM cost for this will be astronomical. As you currently have it specified, at least $1000 in op-amps, $2000 for FPGA board, $400 if not more for the AK4499s alone based on AK4497 pricing.
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Old 6th July 2019, 07:40 PM   #7
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by ishizeno View Post
Any idea where I can find more information about it?
You would have to talk to the AKM wholesale distributor for your sales region. Depends on whatever they might be willing and or able to do for you. The rev 0 board is a pre-release version.
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Old 6th July 2019, 07:43 PM   #8
ishizeno is offline ishizeno
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Join Date: Mar 2015
Quote:
Originally Posted by chris719 View Post
I don't understand why would you use a $2000+ dollar Zynq. The whole point of a Zynq is to have full ARM CPUs integrated (Cortex A53 in this case), and I don't see how you are using that? You're also adding another ARM SBC on top of it just to drive a front panel, which the Zynq is already overkill for?

The BOM cost for this will be astronomical. As you currently have it specified, at least $1000 in op-amps, $2000 for FPGA board, $400 if not more for the AK4499s alone based on AK4497 pricing.
The BoM is just shy of $4,000, including quite a bit of USB glue between the different components. The big FPGA is there for sound synthesis and sound effects. I am trying to bring the analog components of Eurorack synthesizer modules into the digital domain, while bringing the sound effects of DAWs on silicon, considering latency as enemy #1. All the while, I am trying to make modular synthesizers and control surfaces a lot more modular, using USB 3.0 as primary fabric for a LEGO-like system.

The ARM SBC is added to the mix because it is cheap (less than 10% of the total BoM), while providing many useful interfaces, especially with respect to displays and cameras. I do not want to build all this from the ZYNQ SoM, and I certainly do not want to build my own ZYNQ base board... If you were to take 8 of these systems, you'd get something that is 5 times less expensive than any comparable setup, but with 10 to 50x more DSP power...
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Old 6th July 2019, 07:46 PM   #9
ishizeno is offline ishizeno
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Join Date: Mar 2015
Quote:
Originally Posted by Markw4 View Post
You would have to talk to the AKM wholesale distributor for your sales region. Depends on whatever they might be willing and or able to do for you. The rev 0 board is a pre-release version.
Thank you for this. I will get in touch with them right away! Fingers crossed...
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Old 6th July 2019, 08:27 PM   #10
ishizeno is offline ishizeno
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Join Date: Mar 2015
Quote:
Originally Posted by chris719 View Post
I don't understand why would you use a $2000+ dollar Zynq. The whole point of a Zynq is to have full ARM CPUs integrated (Cortex A53 in this case), and I don't see how you are using that? You're also adding another ARM SBC on top of it just to drive a front panel, which the Zynq is already overkill for?

The BOM cost for this will be astronomical. As you currently have it specified, at least $1000 in op-amps, $2000 for FPGA board, $400 if not more for the AK4499s alone based on AK4497 pricing.
Also, you can cut the BoM in half by using a cheaper SoM. For example, the SoM with ZYNQ 7030 is only $150. Also, the current $4K BoM includes a $169 Samsung PM851 1TB attached to the SoM and a $490 Samsung SSD 970 EVO 2TB attached to the SBC. Remove these and the BoM goes below $1,500, which is quite affordable for an 8+8 ADC/DAC interface with mono chips on both ends.
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