Hello,
I purchased a PCM1794 DAC from Aliexpress, and when using their bundled LHY AUDIO Coax-to-i2s converter board, it sounds wonderful
However, I'd like to feed it i2s directly via hdmi cable from my DDC/Reclocker - but when I try feeding it i2s directly, I get mostly static. The static goes away when I grab and hold the i2s lines, so I know they are hooked up correctly.
I've been doing some reading of posts that have been posted over the years, it seems like some people say it's transmission line effect, and some people say it's due to reflections
I have two questions:
1. why does it work perfectly when I use the i2s output of the LHY AUDIO board? (the wires are the same length)
2. can I just solder in some 10 or 35 ohm resistors on the destination end (DAC side) of the wires? (I know that everyone says to put the resistors on the SOURCE side, but in my case the source is a DDC/Reclocker that sends out i2s over HDMI so I cannot do that)
Also I've read that people say you should alternate ground wires in-between your i2s lines, but how can I do that in this case, since the inputs are jumpers on the DAC board?
Thanks for any help you can provide,
-- Mike
I purchased a PCM1794 DAC from Aliexpress, and when using their bundled LHY AUDIO Coax-to-i2s converter board, it sounds wonderful
However, I'd like to feed it i2s directly via hdmi cable from my DDC/Reclocker - but when I try feeding it i2s directly, I get mostly static. The static goes away when I grab and hold the i2s lines, so I know they are hooked up correctly.
I've been doing some reading of posts that have been posted over the years, it seems like some people say it's transmission line effect, and some people say it's due to reflections
I have two questions:
1. why does it work perfectly when I use the i2s output of the LHY AUDIO board? (the wires are the same length)
2. can I just solder in some 10 or 35 ohm resistors on the destination end (DAC side) of the wires? (I know that everyone says to put the resistors on the SOURCE side, but in my case the source is a DDC/Reclocker that sends out i2s over HDMI so I cannot do that)
Also I've read that people say you should alternate ground wires in-between your i2s lines, but how can I do that in this case, since the inputs are jumpers on the DAC board?
Thanks for any help you can provide,
-- Mike
Are you sure there is no LVDS to CMOS converter missing? As far as I know, I2S signals are usually sent over HDMI cables as LVDS signals, while the DAC input probably expects 3.3 V CMOS levels.
one question - running it through that chip won't introduce any extra jitter will it? I'm trying to get the most pure clock signal into the DAC as possible
I don't believe so, but I'm not an expert. There are versions with an included isolator that would introduce jitter though.
There are quite a few different HDMI to I2S/IIS converters on Ali. That one I posted was just for example. Here are a few more...
https://www.aliexpress.us/item/3256803130141890.html?
https://www.aliexpress.us/item/3256801428433502.html?
https://www.aliexpress.us/item/3256802736707158.html?
There are quite a few different HDMI to I2S/IIS converters on Ali. That one I posted was just for example. Here are a few more...
https://www.aliexpress.us/item/3256803130141890.html?
https://www.aliexpress.us/item/3256801428433502.html?
https://www.aliexpress.us/item/3256802736707158.html?
All those seem to use DS90LV48. Datasheet of that chip does not specify jitter but it refers to an older jitter measurement document (https://www.ti.com/lit/an/snla166/snla166.pdf). According to that document jitter can be as high as 1ns. But it is likely that newer chips such as DS90LV48 have lower jitter.
This is good? As far as I remember, even ancient spdif receivers like CS8412 have a jitter of 0.2 ns, and the not so ancient DIR9001 has 0.05 ns.
Alex.
I think we need to take a step back here. I was ignorant to what a "DDS/Reclocker" is and ran with Marcel's comment about LVDS.
Now I see what a DDS is, I think OP is just using an HDMI cable to carry I2S signals, not recover I2S from an HDMI LVDS output? Possibly with another simple HDMI breakout board at the other end? I think he should elaborate.
EDIT: I guess there are DDCs with HDMI LVDS outputs, like the Denafrips Iris. So what is the whole point of a fancy reclocker if converting from LVDS to CMOS level will just introduce more jitter?
Now I see what a DDS is, I think OP is just using an HDMI cable to carry I2S signals, not recover I2S from an HDMI LVDS output? Possibly with another simple HDMI breakout board at the other end? I think he should elaborate.
EDIT: I guess there are DDCs with HDMI LVDS outputs, like the Denafrips Iris. So what is the whole point of a fancy reclocker if converting from LVDS to CMOS level will just introduce more jitter?
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Maybe something like MC100EPT21 is better to use than DS90LV48? It's rated at 5ps typical and 10ps max jitter. I can't find any boards than use them. They seem like a fairly simple part to implement though.
A couple more similar ICs...
Renesas 830S21I-01
TI SN65LVELT23
Still, every HDMI to I2S board I can find uses DS90LV048A. I don't know if it's due to price or what. It's significantly cheaper than the other devices, which you need 2-4pcs depending on the part.
I found a TI video on how to measure jitter. They give some examples of jitter from the DS90LV048A in different applications. One example is for audio at 100Mbps with a 10m cable length, which results in an unacceptable 540ps jitter.
Renesas 830S21I-01
TI SN65LVELT23
Still, every HDMI to I2S board I can find uses DS90LV048A. I don't know if it's due to price or what. It's significantly cheaper than the other devices, which you need 2-4pcs depending on the part.
I found a TI video on how to measure jitter. They give some examples of jitter from the DS90LV048A in different applications. One example is for audio at 100Mbps with a 10m cable length, which results in an unacceptable 540ps jitter.
So what is the whole point of a fancy reclocker if converting from LVDS to CMOS level will just introduce more jitter?
that is exactly what I am wondering now that I realize a CMOS chip is required to convert the signal!
The problem is the "easy" options available to you are no good, unless you want to re-reclock with an SRC4192 before the DAC.
I'm really surprised no one makes boards with those other chips I mentioned, since they have way better jitter specs than the DS90LV048A.
I'm really surprised no one makes boards with those other chips I mentioned, since they have way better jitter specs than the DS90LV048A.
I was planning on getting one of those Ian Canada boards, but there are so many to choose from that it looks like it will take quite a bit of research to figure it all out
I'm hoping that if I get one of those, I can do straight i2s without needing an LVDS chip
I'm hoping that if I get one of those, I can do straight i2s without needing an LVDS chip
If this was my project, I might be tempted to buy one of these boards...
https://www.aliexpress.us/item/3256801855872027.html?
Then remove the DS90LV048A and bodge in a pair of SN65EPT23.
https://www.aliexpress.us/item/3256801855872027.html?
Then remove the DS90LV048A and bodge in a pair of SN65EPT23.
The X-SPDIF 3 only has LVDS out for I2S so you cannot avoid a LVDS chip without modifying the box.
https://www.audiophonics.fr/en/inte...ipi-receiver-hdmi-to-i2s-dsd-dop-p-13981.html