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DIY High Speed (480Mbps) USB Isolator for audio using ISOUSB211

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drksy:
Hey guys,

I had been suffering with common mode noise and ground loops in my home studio set up for as long as I remember. Whenever I moved a window on the PC for example, I would hear this faint buzzing noise in my studio monitors. Tried PCIe interfaces, USB, different outlets for speakers, mains filter, nothing seemed to help. It seemed I had to find a way to isolate the analog audio ground from my PC's power supply ground somehow, while maintaining the audio fidelity of my sound card. A transformer in the analog signal path wasn't an option because of increased distortion. So I decided it's best to isolate the USB interface to the PC.

Long story short, after trying different USB isolators on eBay based on ADUM3160, none of them seemed to work. My USB audio interface (MOTU M4) refused to startup if the USB port was not capable of running at 480Mbps. Looking at the market, there aren't many buy options with a reasonable price to get high speed USB isolation. But after a googling this a few months ago, I came across an ASIC from Texas called ISOUSB211. This hasn't even been released yet as of today and is still in preview, but could be ordered directly from TI. There is of course a EVAL board for it for about 50 bucks which is a very good price, but I decided I could even beat that price by designing a 4 layer PCB since PCB's are so cheap these days, and I had all the passives and linear regulators, etc. Also I wanted a dedicated, low noise, linear power supply on the peripheral side.

So I did, and I wanted to share my design here. I designed the circuit in EasyEDA and manufactured it with JLCPCB. After assembling it, I've run it for about two months now, and it really works amazingly. All ground noise has been totally removed from my set up. Please note that I'm not an EE by trade, I only do this as more or less a hobby. So if you find things that are odd or can be improved, please feel free to let me know. Here are my design files so far:







What it looks like after building it:



To protect my audio interface from the power supply misbehaving, I added a voltage supervisor and protection IC (LTC4361). It cuts off power in case of over-voltage, under-voltage, and over-current in the matter of nanoseconds.

The PCB was manufactured with JLCPCB's 7628 stackup to get controlled impedance on the high speed traces. These were calculated to be 90 Ohm differential impedance using JLCPCB's calculator (https://cart.jlcpcb.com/impedanceCalculation). So if you want to order this PCB, make sure to use this exact stackup, called JLC7628.

Since I'm by no means a pro hardware designer, I have shared this here for the community to perhaps improve it or use it in other ways as you see fit. The design json files are attached at the end of this post. You can drag these to any EasyEDA projects. Comments, suggestions, welcome.

baconsteak:
Nice Job! Did you by chance measure the round trip latency with and without on your M4? I'm wondering if this setup would be good for use with a guitar.

moffy:
Thanks for sharing. Could be very usefull. :D

trobbins:
Very useful also for people who use their soundcard for audio circuit assessment using software like RE, where isolating as many items from mains powered equipment is a bonus.

jonpaul:
no need for this.

Use TOS-link optical digital audio, complet isolation.

format SPDIF.

Most high quality external DAC, ADC use TOS-link, SPDIF or AES EBU

Jon

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