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Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

ES9038Q2M Board
ES9038Q2M Board
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Old 10th January 2019, 09:06 PM   #3611
Markw4 is offline Markw4  United States
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Today working on design layout for a DS90LV018A one-channel differential line receiver to single-ended LVCMOS output to drive the clock input on one of the AK4137 boards. The receiver will be mounted on a small Surfboard attached to the underside of the AK board, and it will get power from the 3.3v LDO on top that previously provided power to the 22.5MHz (or 25MHz recently tested) clock that has been removed. u.fl connectors will be attached to the receiver Surfboard for inputs and output. u.fl to SMA adapter cables will bring differential clock output signals from the clock divider board to the receiver. Clock input to divider board will come from a copy of the dac chip MCLK signal routed out through a GPIO pin. Lots of work to test an idea that may or may not work, but what else can one do? Too many things unspecified in AK and Q2M data sheets to know exactly what they need to work in a ultra-low jitter compatible configuration. Pictures will be posted later as construction progresses enough to show something.
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Old 12th January 2019, 06:33 PM   #3612
Markw4 is offline Markw4  United States
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A little ongoing progress preparing for some testing in the near future. A pic is attached below showing the LVDS to LVCMOS adapter board. In the background, and unfortunately rather out of focus, is the clock divider chip evaluation board. The adapter board has .002uf, .1uf ceramics, and 10uf tantalum polymer decoupling caps in the back right corner. Need to see if I can get a .01uf ceramic in there somehow too. On the left are two u.fl connectors and some SMD 50 ohm SMD resistors for the LVDS differential inputs. Two 50 ohm resistors are in series to terminate the LVDS signals with 100 ohms. On the right is the single LVCMOS compatible output and its u.fl. connector.

Just have to keep doing a bit each day so this keeps moving along. Sure would be nice if it works, but we'll just have to see if I get lucky or not.
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File Type: jpg AKDiv3.jpg (778.8 KB, 232 views)
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Old 13th January 2019, 03:04 PM   #3613
Bret burrill is online now Bret burrill  United States
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Looking at buying one of these and learning to modify it. Can someone answer a couple questions about it? What is the voltage output on the rca's and can it be modified? I see a white connector on the board, one diagram labels it iis. Is this used to interface with other boards? Can I design ways for this to interface with other input devices by attaching a board to it? If this is not the right thread to ask basic questions then I apologize. Thank you.

Oh yeah, is it a bad idea to buy one off ebay? Do some manufacturers use inferior components?

Last edited by Bret burrill; 13th January 2019 at 03:07 PM. Reason: Ebay question
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Old 13th January 2019, 04:21 PM   #3614
Markw4 is offline Markw4  United States
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Hi Bret,
You are definitely in the right place to ask those kind of questions. The RCA output voltage is the same as the voltage on the 1/8" stereo jack, which is about 2V RMS, also known as line level. It should be about enough to drive most power amps.

The IIS input, aka I2S, is one of three inputs on the dac board. That input is most commonly used for USB input, either directly from a little USB to I2S converter board, or with an intervening AK4137 sample rate converter board.

The best dac boards for modding are this brand (with or without the optional display): ES9038 ES9038Q2M DAC Decoder board Support IIS DSD 384KHz Coaxial Optical DOP | eBay

ES9038 ES9038Q2M DAC Decoder board Support IIS DSD 384KHz Coaxial Optical DOP For hifi amplifier audio Rectifier power supply -in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

Most USB to I2S boards are either XMOS or Amanero (original or clone) types:
2018 XU208 XMOS USB U8 Audio Asynchronous Card DSD II2S PCM Amanero | eBay

AK4137 boards come in two varieties:
AK4137 I2S/DSD Sample Rate Conversion Board Supports PCM/DSD Interconversion DOP | eBay
HIFI AK4137 DAC SRC flagship high-end audio 786K 32Bit DSD256 DSD IIS conversion | eBay
...with the more expensive ones including SPDIF and TOSLINK inputs. The low cost version is I2S input only.


EDIT: Most people seem to buy the above items through ebay and aliexpress.com. It can pay to shop around to find the lowest price. There are some cheaper dac boards that can be modified too, but connecting an external microcontroller to access the dac chip control registers is much easier with the recommended brand. If considering a lower priced dac board, please post a link here before ordering so we can verify if it is likely to be a good choice. There are some that look sort of similar, but really aren't similar enough. The lowest cost boards that can be used are some blue color ones that otherwise look pretty close to the ones I linked to. https://www.aliexpress.com/item/ES90...AbTest=ae803_5

Last edited by Markw4; 13th January 2019 at 04:36 PM.
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Old 13th January 2019, 04:54 PM   #3615
Bret burrill is online now Bret burrill  United States
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Quote:
Originally Posted by Markw4 View Post
Hi Bret,
The RCA output voltage is the same as the voltage on the 1/8" stereo jack, which is about 2V RMS, also known as line level. It should be about enough to drive most power amps.

The IIS input, aka I2S, is one of three inputs on the dac board. That input is most commonly used for USB input, either directly from a little USB to I2S converter board, or with an intervening AK4137 sample rate converter board.
Thanks for the reply.

USB was where I was going with this. Perfect.

Can you estimate how much cost the coaxial and optical inputs add to overall cost of this product? I won't use them. If the cost of these is negligible, I will just live with having them on there.

What controls the line level voltage? Can I change it, or is it controlled by the processor?
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Old 13th January 2019, 05:21 PM   #3616
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Bret burrill View Post
Can you estimate how much cost the coaxial and optical inputs add to overall cost of this product? I won't use them. If the cost of these is negligible, I will just live with having them on there.

What controls the line level voltage? Can I change it, or is it controlled by the processor?
The coaxial and optical inputs on the dac board come with all the boards that we might use for this project. The components could be removed from the board, if desired. Since there are no otherwise suitable boards to use as a starting point for this project, an incremental cost for the extra inputs is not available. (Hypothetically, it might be that the extra inputs could come in handy sometime for troubleshooting purposes. If, for example, no sound out of the dac board, one of the extra inputs could be used to inject a test signal. If the dac starts working in that case, it can help to narrow down where to go looking for the problem.)

Volume is controlled digitally inside the dac chip. There in an MCU (microcontroller) on the dac board with pins for connecting a potentiometer. The MCU reads a DC voltage on the pot and uses that information to program the dac chip registers. Alternatively, since we recommend to eventually control the dac chip from a different MCU anyway (Arduino or Raspberry Pi), that new MCU could also be used to program the dac chip output volume level.

Last edited by Markw4; 13th January 2019 at 05:27 PM.
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Old 13th January 2019, 05:39 PM   #3617
Bret burrill is online now Bret burrill  United States
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Great. This looks like a good starting project that I can learn from. I take your word that 2v is a sufficient line level, I still want to experiment with it.
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Old 13th January 2019, 05:50 PM   #3618
Markw4 is offline Markw4  United States
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Originally Posted by Bret burrill View Post
Great. This looks like a good starting project that I can learn from. I take your word that 2v is a sufficient line level, I still want to experiment with it.
2v RMS should probably be about right. There is about 3v peak to peak after the first I/V amplifier stages, good, yet still low enough to prevent some types of distortion from creeping in. I probably would not recommend messing with gain much in the existing output stage since those amplifiers are also negative feedback filters (mainly the differential summing amp), and changing one thing affects other things. But if you need more level, an add-on output buffer opamp for each channel would be fine.

Another option that can save some construction work and pick up a little extra free output level might be to use a Twisted Pear Trident AVCC voltage regulator. They make them slightly hot at 3.6v rather than the standard 3.3v for whatever reason, probably just for that little free output boost. I don't know how Trident sounds compared to the opamp circuit we normally use for AVCC, but I'm guessing both approaches are likely to sound about the same. One of these days I will have to try it myself to see.

Last edited by Markw4; 13th January 2019 at 05:56 PM.
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Old 13th January 2019, 06:02 PM   #3619
Markw4 is offline Markw4  United States
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I should probably also mention there a post back some pages with an attachment file containing links to lots of possible posts of interest in this very long thread: ES9038Q2M Board
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Old 13th January 2019, 06:16 PM   #3620
Bret burrill is online now Bret burrill  United States
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Quote:
Originally Posted by Markw4 View Post
I should probably also mention there a post back some pages with an attachment file containing links to lots of possible posts of interest in this very long thread: ES9038Q2M Board
Yes, I meant to ask if that existed. 300+ pages is a lot to sort through.

I have another question. I read that the processor consumes 500mW. The complete working board requires 15v and some use dual 15v inputs. Is there a particular function that requires so much power, or is it more or less the sum of all the components working together that adds up to such high power consumption?

Last edited by Bret burrill; 13th January 2019 at 06:39 PM. Reason: additional question
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