I have a question for you. If that thing truly isolates one side (the PC side) from the other side (the dac side), then how does the dac side of the isolators get power? The only power is the +5v coming from the computer.
To cut to the chase, they need power for both sides, so what do they do? They use a little SMPS that transformer or capacitor isolates the grounds on both sides. So, yeah, they can isolate the grounds. But what about EMI/RFI noise from the SMPS? Now that's going to get into your dac. It won't sound like a hum probably. Maybe more like a veil over the sound. If your system is crappy enough, then maybe you won't notice any veiling that may be taking place. Or maybe you will hear some garbage from the SMPS. Either way its not good.
EDIT: please take a look at the attached. Search for terms like 'veiled' or 'grainy'
Thank you for this stuff, Mark! It seems really interesting, I'll thoroughly read it!
Warm regards,
Gaetano.
Warm regards,
Gaetano.
AFAIK USB requires the GND line for highspeed detection https://microchipdeveloper.com/usb:high-speed-detect, it's using the data lines also for signalling via voltage against the GND line.
If you're worried about jitter, you can send the clock signal through an ethernet transformer instead of the isolator. Rip one off of an old LAN card and it's a free solution.
ETH trafo is possible, but it is much better to place the oscillator close to the DAC and send it through I2S isolation to clock the source.
In this case, for most DACs isolator's jitter has no effect.
(since they are sensitive to master clock jitter only, for others - is possible to use flip-flop to re-clock the signals, using master clock at the DAC side)
But of course, this is for DIY. For not-DIY USB isolator may be used.
For example, I have my own ADC for the measurements, with I2S isolation. But when I bought IVX's Cosmos ADC, I had problems with some measurements (due to a ground loop), which were solved with High Speed USB Isolator
Alex.
In this case, for most DACs isolator's jitter has no effect.
(since they are sensitive to master clock jitter only, for others - is possible to use flip-flop to re-clock the signals, using master clock at the DAC side)
But of course, this is for DIY. For not-DIY USB isolator may be used.
For example, I have my own ADC for the measurements, with I2S isolation. But when I bought IVX's Cosmos ADC, I had problems with some measurements (due to a ground loop), which were solved with High Speed USB Isolator
Alex.
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