Home > DIY HiFi > FIFO-Clock Isolation Board

FIFO-Clock Isolation Board

October 19, 2012 Leave a comment Go to comments

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.



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 🙂


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]


  • ADP-150 (Digikey $1.10[link]) – Noise 9 uV RMS
  • TPS79333 (Digikey $0.86 [link]) – Noise 32 uV RMS

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.

  1. qusp
    October 19, 2012 at 14:32

    Hey mate, can you do me a favor, can you please test the resistor network from one ‘cell’ to another with your DMM? I soldered them in place and I get ~33ohms across each element with no direct short, but I dont have open circuit measuring from one ‘resistor’ to another, very high and increasing resistance and finite 16uf or so (from memory) capacitance.

    There are no other parts in parallel or my fingers, the soldering job seems fine and the datasheet for the part doesnt mention any connection between them, but since its all on the one substrate I wonder if thats causing it or i’ve used too much heat or solder, though you would think this would give me a direct short and would result in a different value for the resistor as there would be a cap and/or a short in parallel.

    the increasing resistance is consistent with measuring resistance of a cap

    • BlogGeanDo
      October 19, 2012 at 15:37

      Hey qusp, first I probably have to do some practicing or even get a new soldering iron/tip before attempting to solder these resistors. However, one can use small 1/8 W discrete resistors instead…

      • qusp
        October 19, 2012 at 16:50

        dont make the mistake of thinking that a very fine tip should be used on parts this size. a 1-1.5mm chisel is perfect, heat the pad, flow solder onto the junction, clean up with flux and wick. its actually pretty easy to use a larger tip like a 3mm chisel and solder all the pins at once, then clean up with wick.

        as for the part, I think it has to be correct, all measure the same and theres no shorts, guess i’ll ask Ian.

  2. qusp
    October 19, 2012 at 14:33

    they are the only things soldered to the board at this stage, so nothing to interfere and all parts measure the same

  3. October 19, 2012 at 18:48

    hehe, what an interesting thing, right now I also resolving some issues regarding isolation but in my RF design. I have some problems with USB powered digital+analog part where I need to return back audio signal to integrated sound card. Those two ports due large current consumption from USB power (culprit for this is Si570) have about 20mV voltage drop on USB cable (I lower down to 5mV with some quality USB cable, 40mΩ GND end-to-end) and makes me hum in audio signal! Now I locking for solution and asking myself where to make cut, does on USB, does on I2C or on clock signal? I try with different method to isolate clock with transformer but that did’t makes me good results. I need to transfer up to 160MHz clock. Probably I will make cut on I2C bus due lower component cost. Other issue I have is also similar to yours, I need isolated DC-DC modules if I wand to keep power from USB. What a mess …

  4. September 17, 2016 at 08:35

    Today, while I was at work, my sister stole my iPad and tested to see if it can survive a 30 foot drop, just so she can be a youtube sensation. My iPad is now destroyed and she has 83 views. I know this is totally off topic but I had to share it with someone!

  5. September 25, 2016 at 16:45

    Very well written post. It will be useful to anyone who usess it, including me. Keep doing what you are doing – looking forward to more posts.

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