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Old 19th January 2019, 04:57 PM   #3681
Markw4 is offline Markw4  United States
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Join Date: Jul 2016
Location: California
Don't think I mentioned it here, but I recently wrote some tips on how to listen (or how to learn to listen) for dac sound quality. In case there is any interest in the subject, it is post #48 in the following thread: Improving AK4490 THD(+N) figures
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Old 20th January 2019, 11:02 AM   #3682
eslei is offline eslei  New Zealand
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Quote:
Originally Posted by Markw4 View Post
Hi eslei,
Don't know where you got that idea, but it is not what ESS says you should use for Vref. If you would like to see for yourself, there is a schematic of an older (maybe ES9008) evaluation board schematic on the ESS downloads page. You can clearly see that Vref is taken as half of AVCC for each channel using a voltage divider as we do in our AVCC board schematic. In addition, I have the schematics for the latest ES9038PRO evaluation boards from ESS and it is still exactly the same thing.

However, I agree with you about connecting I2C on the newer 1.07 SMP CB boards in that installing J1 and J2 should stop I2C bus activity by the MCU, thus making it unnecessary to do any trace cutting or pin lifting. However, I have a 1.07 board like that here and installing J1 and J2 didn't stop it. That same board also didn't work with an optional display I got to try out with it. I assume I happened to get a board with the wrong version firmware installed. If so, it appears to be a very rare problem. Really helps to have some kind of a scope available to check such things. Also, I just kind of assumed that since Kay asked the question, he knew he didn't have one of the boards that can be stopped with J1,J2. Maybe I assumed too much?
hi, there,

as ess has the nda i don't use their information but something i can have from the internet.

if the vref is 1/2 avcc, the opamp output dc voltage wound around +1.5v not null, if that's the case? the smp cb q2m dac schematic is exactly like i record.

your 1.07 board is a coincidence, i have handled more than 20 smp cb q2m boards they all have on problem.

cheers
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Old 20th January 2019, 05:54 PM   #3683
Markw4 is offline Markw4  United States
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Hi eslei,
Right, we agree that my 1.07 board firmware issue is an oddity. It's the only one we know of like that so far.

On the issue of 1/2AVCC, there is effectively no output offset with the 3 dual opamp output stage design we use. If you are talking about the original voltage output circuit (which I think you probably are) then that would be different. When people ask me questions here about AVCC it is normally because they are modding a dac board and aren't using the voltage output stage any more. Also, the reason for using 1/2AVCC is not to set an output offset or to cancel one out, it is to minimize distortion when doing I/V conversion. Fortunately, the differential summing stage we use removes the DC offset of the I/V opamps. Another possible good thing about doing it that way is that since the I/V opamps have an offset, we can run their outputs Class A all the time by choosing the I/V feedback resistor for about a 3v p-p output swing.

Last edited by Markw4; 20th January 2019 at 06:06 PM.
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Old 20th January 2019, 07:01 PM   #3684
eslei is offline eslei  New Zealand
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@Markw4

thank you, i ll try that i/v in the future when i have time. at the moment, we just enjoy the on board output stage.


cheers
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Old 20th January 2019, 08:43 PM   #3685
redjr is offline redjr  United States
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Join Date: May 2011
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Quote:
Originally Posted by eslei View Post
@ Markw4

hi, there,

can you post a functional block diagram of your system, i wonder how the ak4137 works on your system.


cheers
I've been following along in this thread, but have yet to start this project. In response to your query eslei and my own planning, I drafted the following diagram. This only shows the 'primary' mods that I'm aware of, realizing Mark continues with other 'minor' mods as well. I hope it's accurate enough and I will defer to Mark to point out any mis-representations, or other significant mod I missed. (I hope I got the voltages correct.)

My particular version planned is to add a RaspPi and use I2S to the reclocker in lieu of the XMOS USB board and have the audio output switchable with PRE-out. How each of these is implemented is obviously up to the individual user following Mark's more detailed instructions throughout this thread.
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Old 20th January 2019, 09:38 PM   #3686
eslei is offline eslei  New Zealand
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@ redjr

mine is simpler, have been put up many units already.

cheers
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Old 21st January 2019, 02:18 AM   #3687
Markw4 is offline Markw4  United States
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redjr,
Your diagram looks pretty good. The only things I would probably add would be +5v power also going to the AK4137 board, and then three LT1763 3.3v regulators soldered onto the dac board ground plane down at the digital end for the clock, for dac chip VCCA, and for DVCC.

Maybe good to label the AK4137 as a Sample Rate Converter rather than a reclocker, too. It is a SRC and PCM<->DSD converter.

Last edited by Markw4; 21st January 2019 at 02:24 AM.
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Old 21st January 2019, 11:15 AM   #3688
bisesik is offline bisesik  Kazakhstan
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Hi Markw4!

As I saw you have the same AK4137 board as mine ( HIFI AK4137 DAC SRC flagship high-end audio 786K 32Bit DSD256 DSD IIS conversion | eBay )
I have a problem with indicating the stream from my USB-I2S (XMOS from DIYINHK) on the display. All other rca\opt\etc inputs are recognized OK and showed on the display: PCM\freq. I2S input works, DAC played normally. But how to force 4137 recognize stream from I2S input correctly? There is no F0-F3 outputs on my USB-I2S board, I connected LRCK\DATA\BCK only, but pulling up (to +3.3V) F0-F2 on the I2S input header according to the table not helps. Any idea? Thank you!

My USB-I2S is exactly the same: DIYINHK Isolated XMOS USB Interface | H i F i D U I N O
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Old 21st January 2019, 01:02 PM   #3689
Markw4 is offline Markw4  United States
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Hi bisesik,
You may need to correctly set the signal on the I2S pin header which may be called, 'DSDON,' or some other name close to that. If you are sending PCM then DSDON has to be low, IIRC.

Also, not sure if it needs the correct values for F0-F3. Could be those only matter for DSD input.

You might try reading the detailed instructions for the other, lower cost AK4137 board since it describes the signals it needs in more detail. AK4137 I2S/DSD Sample Rate Conversion Board Supports PCM/DSD Interconversion DOP | eBay
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Old 21st January 2019, 01:30 PM   #3690
terry22 is offline terry22
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Hiu Guys,
I just received my TP 3.3v regulators, and as I can't find no documentation, I have some questions:

-Do you know what are the 2 connectors on the left?

-Does the out & gnd on the bottom and the ones at the upper right can be used indifferently?

thank you.
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