Please note that the manual for the USB board contains detailed schematics of direct i2s connection of the board right to various DAC chips including PCM-56.
You can download a manual with detailed explanations here.
The designer of the board advices to use software upsamling filter for this purpose. A foobar resampler solves this problem easily.
It seems to me that this whole thread is based on some "guidelines" you have read from the internet. While not strictly nonsense these types of guidelines cannot be blindly followed.
As with RF signals the best connection for single ended I2S is using properly terminated coaxial cables e.g. with SMA or U-FL connectors. The 2-row pin header connector using flat ribbon cables also works in most cases. This is typically implemented so that the other pin row has ground pins which results having ground wires beside every signal wire in the ribbon cable to reduce noise pickup. These signal/ground wires are however not differential nor do you need all ground wires connected. If the I2S is single ended you only need to run one ground wire.
The "acceptable" length of the I2S connection also depends on other implementation details such as are drivers or buffers used.
IME daisy chaining works a lot better than passively split transmission lines into poorly controlled impedances. The latter may be one of the worst cases for causing jitter and timing problems. Daisy chaining the dac chips as I suggested with a series load resistor somewhere in the middle of the I2S signal lines will probably work best, with the least signal distortion. It will probably help make the resulting longer lines perform more reliably. Rise time will be slightly decreased, but often not a problem for dacs if not too excessive. IME, even some single dac chip designs will also sound better with the I2S signal lines slightly over damped. This has been known by some dac designers for a long time. I'm not saying its always better, its an experiment that can be performed if interested in tuning for optimum performance. In other words, the answer to your question is that I have experience and knowledge that you don't have. I can try to explain in simple terms and give some suggested advice. Up to you if you want to try it or not. If it were my dac or if you brought it to me to fix, I would probably check to see if mounting the USB board underneath the dac board was possible. I prefer to have the USB board and dac ground planes facing each other. The purpose of that is to reduce radiated EMI/RFI coupling between the USB board and the dac chips. If you had a scope I could tell you how to look for some evidence of that radiated noise. Either way, USB board on top or bottom of the dac board, I would try daisy chaining the I2S signals with a little resistive damping roughly in the middle of the lines somewhere or other. If that didn't work, I would probably have to design a I2S buffer board to send each dac chip its own isolated I2S signals. That's probably not really necessary here though.
EDIT: Also, I would get rid of the other non-twisted-I2S ground you added.
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I have already written above that according to my experiments the best sound is achieved when ground wires that go in parallel with four i2s wires are connected to the ground only from one side. Only because of this I had to use a separate ground wire between the USB board and the DAC board.
Okay. Please just make up your mind what it is you want, help to fix the dac more properly or else to leave it as it is. If you are happy now then why not leave it?
I am pretty happy about both of my DAC's now. The main reason for creating this thread is that I am surprised by the results of my experiments and I would like to share them with you. There's no need for any cure, I think, because the sound is to my liking. What more can I wish in this life?
So the only lesson to be learned from this thread is that even with highly questionable implementation and lack of understanding it is possible to get satisfactory results.
I would reply as follows: is it too difficult to connect a USB board to a DAC board? Is any special knowledge required for it? All one needs to know is contained in the manual and one needs to take into account the results of my experiments with i2s grounding.
The correct solution is to stop playing with a multitude of interconnected boards and to make / use a unitary project made on a single correctly designed board.
Such a solution eliminates the need for buffers from the start and minimizes until neutralization the benefits of a possible re-clocking because the signal is already clean.
Such a solution eliminates the need for buffers from the start and minimizes until neutralization the benefits of a possible re-clocking because the signal is already clean.
You know, of course I agree with you that this would be the best solution but the beauty of the I2soverUSB board is that it allows us to modify old DAC's or CD Players and convert them into USB DAC's very cheaply. A new project requires a lot of money but here one can save lots of money and achieve quite reasonable quality by attachning a USB board to almost any old DAC or CD Player.
Take a sheet of paper and draw a interconnection diagram so the guys here could really help you!
JP
JP
For this you must use a different interconnection interface. The I2S is not made for this type of interconnections.
For example (not the best) can be used a SP/DIF output from CD player and a DIR circuit near to DAC. All these components can be put inside of CD player if you want.
Disagree. It is possible to connect a USB board to a dac board quite effectively if done properly. A pic and partial explanation of a method that can perform very nearly as well as a carefully designed single board solution can be found at: ES9038Q2M Board ...Post#7342. However, there are some series damping resistors on the dac board that were not included in the post text.
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That is only a botch. It is working but remain a improvisation.
If this is how your digital boards look, then it's no wonder you're starting to hear differences between digital connection cables.
The cabling in the pic was to bring I2S into an AKM eval board. AKM's design for doing that was far worse than my implementation. No other option but to do something like that if I2S was going to be used with the AKM board.
Sound quality of the setup in the pic is very close to the same as that of a board I designed with direct plugin of the USB board followed immediately by reclocking with D-flip flops to sync the I2S signals with the dac master clock. The USB board was configured to use an external master clock, in this case the master clock on my board.
Sound quality of the setup in the pic is very close to the same as that of a board I designed with direct plugin of the USB board followed immediately by reclocking with D-flip flops to sync the I2S signals with the dac master clock. The USB board was configured to use an external master clock, in this case the master clock on my board.
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