FIFO-Clock Isolation Board
Just received Ian’s FIFO to Clock isolation board. Photos of front and back:
The purpose of the isolation board is to obtain that “last drop” of performance from the FIFO re-clocking board. By isolating the FIFO board from the clock board, using separate GND and PS lines, all possible noise coming from the source can be stopped and completely isolated prior to the clock board.
In addition, having the isolators positioned between FIFO and clock, the added jitter by the isolators do not propagate downstream to the DAC because the signals are to be re-clocked by the clock board. This is the best scenario possible for using an isolator for I2S signals. In other implementations, the isolator is positioned immediately before the DAC’s I2S input lines. In such configuration, the added jitter by the isolator goes straight to the DAC.
BUILDING AND PARTS CONSIDERATIONS
The BOM, schematic diagram and build instruction document is in post 1087 [link]
The resistor pack for the board is miniscule. I’ll probably have to get a new soldering iron and do some practicing with scrap boards. And also watch this video: http://www.youtube.com/watch?v=3NN7UGWYmBY
It actually looks very doable in the magnified photo. The issue is steady hands and good eyesight and a lot of flux 🙂
CHOICE OF ISOLATORS
You can use the following isolators:
- IL260E (Digikey: $10.08 [link]). The IL260 is the same as IL715 (used in many other designs) but with 5 channels instead of 4 channels
- SI8650BC-B-IS1 (Digikey: $3.39 [link]). These go on the back of the board.
Spec-wise, the IL has better (added) jitter numbers but since this isolator goes before the clock board, it does not matter, so I’ll likely buy the SI parts. More on isolators here: [link]
CHOICE OF LDO REGULATORS (SOT-23-5 package)
There are regulators with even less noise, but not in SOT-23-5 packages and much harder to solder.
These photos are from from diyaudio post 1105 [link] and show component location.
Connecting FIFO board to isolator and isolator to CLOCK board. Notice that there are no additional power lines as the power is carried by the existing cables.
The isolator board powered via the 10P FFC/FPC cables by the FIFO board and clock board from both side. So, no any power connector is needed for the isolator board. You just need powering the FIFO board and clock board with different power supply which could be isolated from each other.