Amanero Isolatior: built-in isolator without adapter?

 

The XMOS-cored USB to I2S has a lots of implementation, since its design is widely open, we have seen so many variations that includes built-in Galvanic isolator. 

That means many USB XMOS converter cards can directly output isolated I2S signals, for example, WaveIO provides both isolated and non-isolated output.

Another beloved USB-I2S solution is Amanero Combo384; unlike XMOS, Amanero is provided as OEM solution, people get fully assembled PCBs from Amanero. Barely no varied version is on the market. 

So, there is no Amanero Isolated USB to IIS officially. We have to make it on our own.

Luckily, some HiFi guys have the same idea. Below is the application note of Combo384, the manufacturer published a schematic that provides isolation.  

The Isolation solution suggested by the manufacturer:

The Isolation solution designed by a Japanese engineer.

Here we can see the key pinout of combo384, which has a standard 20-pin I/O. The I2S signal are located at pin 1, 3, 5, 7. These are the 4 pins that we focus and have to be isolated.

About the Isolator IC.

Isolator IC inevitably increases, or say, adds jitter to the signal chain. It provides isolation but also jitter that we don't want most. So, this is kind of dilemma, we need isolation but not additive jitter, as jitter is the enemy that hifi guys tries their best to eliminate. 

Now, what we can do is to choose the best isolator with lowest additive jitter. IL715 seems to be a good one. 

Many DIY projects or application notes suggest TI's ISO and ADI's ADuM series solution. 

However, looking at the datasheet, TI's ISO series has about 4~8 times jitter higher than IL715! 

I found a open sourced IL715 USB Isolator.  You can download it here. 

However, what we need is a isolator that are at the last stage of I2S output of Amanero or XMOS. 

I saw some DIYers has already make this idea real. The I2S output was "filtered" by isolator, then there is final output to downstream devices or DAC.

I want to make it more delicate. That means the isolator is integrated on the board, and the 20-pin I/O provides signals isolated already. In this way, no isolator adapter is needed; this makes Amanero Combo 384 directly pin-to-pin compatible with official version, no change is needed!

Let's start the work.