I am currently working on a USB DAC project as a part of a headphone amplifier. My idea is to use the AK4493 as my DAC and the Amanero Combo384 as my USB to I2S interface for the DAC.
I am afraid to have some kind of ground-loop or noise introduced from my PC which is why i am considering a galvanic isolation somewhere between the PC and my DAC chip.
Amanero recommend the use of an ISO7640 4ch 150MHz isolator. But their solution does not let the masterclock pass through the isolator.
Would it be a solution to change the chip form a 4ch to a 5ch to let the masterclock pass through, or will the isolator introduce more problems than it solves when used for the about 22MHz masterclock?
Or should I drop the isolation and go for an entirely different way to minimize noise and ground-loops originating form the PC side of the USB interface?
I am afraid to have some kind of ground-loop or noise introduced from my PC which is why i am considering a galvanic isolation somewhere between the PC and my DAC chip.
Amanero recommend the use of an ISO7640 4ch 150MHz isolator. But their solution does not let the masterclock pass through the isolator.
Would it be a solution to change the chip form a 4ch to a 5ch to let the masterclock pass through, or will the isolator introduce more problems than it solves when used for the about 22MHz masterclock?
Or should I drop the isolation and go for an entirely different way to minimize noise and ground-loops originating form the PC side of the USB interface?
Why don't you just get a proper usb/i2s adapter which not only isolates but also reclocks all the signals at output? Using isolation without reclocking is not so great.
Because the combo384 is the only one that show up when I search for it on Google and at the same time want the capability to run 380khz/32bit.
But I am open to suggestions if there is better plug n play options out there.
But I am open to suggestions if there is better plug n play options out there.
Isolation/reclocking boards for the Amanero Combo384 are available from TwistedPear Audio, or AckoLabs
Cronus Reclocking
AckoDAC - MISC
In both cases you can power the "dirty" side with the same 5V supply that you currently use to power your Amanero.
The "clean" side requires a separate (and preferably good quality) 5V supply. I like this regulator -
Single Rail TPS7A4700 Ultra Low Noise</br>Power Supply
Cronus Reclocking
AckoDAC - MISC
In both cases you can power the "dirty" side with the same 5V supply that you currently use to power your Amanero.
The "clean" side requires a separate (and preferably good quality) 5V supply. I like this regulator -
Single Rail TPS7A4700 Ultra Low Noise</br>Power Supply
380kHz is tough requirement 😀
I use the JLSound board and have a slight preference for the v2. Apart from isolation and reclocking it also outputs a huge variety of output formats which makes it compatible with many non i2s dacs without any additional logic.
I2SoverUSB - I2S over USB Audio
It seems like the AckoDAC card is pretty similar to my suggested solution, except that it has the reclocking feature added. The isolation itself seems to be a 200MHz version of the chip I have already looked at.
When that is said then for 189$ I should be able to make a reclock circuit cheaper.
The I2SolverUSB seems to be a newer version of the Combo384. The board seems similar and the features is the same except for the added support for 768kHz. But the issue is the same for that board regarding isolation.
When that is said then for 189$ I should be able to make a reclock circuit cheaper.
The I2SolverUSB seems to be a newer version of the Combo384. The board seems similar and the features is the same except for the added support for 768kHz. But the issue is the same for that board regarding isolation.
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Ahh sorry didn't see it had the isolator build in. All other features looks the same as the combo384 board.
The thing is that I already have the Combo384 so if anyone can suggest a reclock circuit then I should be alright.
The thing is that I already have the Combo384 so if anyone can suggest a reclock circuit then I should be alright.
Ah, that's different 🙂
The reclock circuitry is a serious project by itself. Unfortunately with the board you have reclocking the MCK is impossible - you need higher frequency oscillators.
The reclock circuitry is a serious project by itself. Unfortunately with the board you have reclocking the MCK is impossible - you need higher frequency oscillators.
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Ahh okay. I think I will just have to get the I2SoverUSB then. The digital part was not intended to be the main part of this build. Thank you for your help
One thing i am still not sure of, is if this isolation is even needed. I see a lot of high end DAC configurations where the USB input is not isolated at all.
How common is the issue with noise being transmittet from the USB input making it all the way to the analog outputs of a dac?
The entire reason for my fear of noise form the source originates form my old headphone project where i got a ton of 100hz noise from my phone if i plugged in the charging cable whole the amplifier was grounded.
How common is the issue with noise being transmittet from the USB input making it all the way to the analog outputs of a dac?
The entire reason for my fear of noise form the source originates form my old headphone project where i got a ton of 100hz noise from my phone if i plugged in the charging cable whole the amplifier was grounded.
Why don't you simply try it? I think isolation is entirely optional and even slightly detrimental to sound quality if there is no reclocking on the clean side. The noise in question depends on the particular pc but is usually not something directly audible as it is above the audibility range.
Or alternatively forget the reclocking and use an isolator for the i2s signals snd the MCK. Serious manufacturers have done this in the past.
That was also my inital idea, to just get a 6ch isolator and move everything over with one chip, but i dont know if that wound introduce too much jitter for my master clock to be any good.
You will get some additional jitter.
The ideal way is to have the clock on the DAC side and send it to the USB part through an isolator.
If your USB interrface has a clean clock, you might get an OK solution by using a transformer for the MCLK and isolators for the other signals. With most DAC's only the MCLK is critical in terms of jitter.
The ideal way is to have the clock on the DAC side and send it to the USB part through an isolator.
If your USB interrface has a clean clock, you might get an OK solution by using a transformer for the MCLK and isolators for the other signals. With most DAC's only the MCLK is critical in terms of jitter.
I have considered the transformer solution too, but wouldnt that result in a phasshift/time delay between the MCLK and the other i2s signals? or does that not matter for an application like this?
A transformer for MCK? Never heard of this idea. What would happen to the square wave? Would it not be worse than jitter?
