Home > DIY HiFi, USB AUDIO > More Tweaks on Amanero USB Board

More Tweaks on Amanero USB Board

November 8, 2012 Leave a comment Go to comments

Still striving for unlock-free behavior, I implemented what Mr. Abraxalito recommended:

Be careful with ultra-fast CMOS logic – it does require extremely good decoupling. Inside CMOS devices the transistors crowbar the supplies (quite literally) every clock transition. I discovered this with 74AC chips many years ago – even there I was using a multilayer PCB. I suspect the Potato chips are considerably faster! Get the smallest package size you can solder, decouple with 0603s and use a ferrite bead on the positive supply to reduce the bounce on the GND. Even with these precautions you’ll get some jitter from the bounce on the positive supply. Good luck! [link]


After the mods:

Basically I added a ferrite to Vcc and a capacitor to GND. Effectively, including with the previous bypass capacitor, it is a CLC filter which is symmetric from either side of the supply line (meaning it should filter noise coming into the flip flop and noise coming out of the flip flop through the power line).  I also paired the bit clock line with a ground wire to provide some shielding. Pretty standard and common sense tweaks.

Unfortunately I messed my my clean and professional looking implementation :-). If I were to do it again, I would put those components under the board.

(Update 12/3/12)

Based on feedback from readers, I’ve replaced the “magic red cap” :-)) with a much smaller ceramic cap



Seems very positive: I did the first interval for the unlock test, from midnight to 8:00 AM and there were Zero unlocks. It “survived” the “morning hiccup” where at the start of the day, electrical activity would cause one or more unlocks… We will see what happens in the afternoon.

Unlocks before:

Unlocks after: (8 hrs play time)

after 20 hours, the results are really good. Have never gotten this kind of performance in the past: ZERO unlocks (except, of course for the warm up time).  Here is the plot showing the full 20 hours of play time. Well, there is really nothing to show 🙂

This turned out a very effective mod, even with much less than ideal components. If done correctly (proper PCB with ground plane, proper bypass, compact layout, etc), the results would be even better (and finally beyond my “measurements” – not really, I just use higher sample rate material). Anyone wants to develop a small PCB?

  1. qusp
    November 8, 2012 at 18:13

    I suspect this isnt quite what he had in mind when he recommended soldering the ‘smallest package you can solder’ =D

    • BlogGeanDo
      November 8, 2012 at 19:23

      I know, I know 🙂

  2. November 8, 2012 at 22:28

    To get good decoupling on 74AC devices, you will need to solder two or tree caps with different values directly on IC’s power pin. For example, get first larger one ceramic cap (trough hole) of 0.1uF then solder rest of SMD caps on its pins (1nF + 100pF) and all that solder directly on IC’s power pins. Do this on every fast CMOS/TTL ICs.

    The red cap as you shown on picture do not make big difference because they are quite “slow” and will do decouple on lower end of frequency spectrum. Ceramic capacitors X7R or NP0 (several values in parallel) will do the job much better in higher frequency spectrum. This is another RF tips & tricks 😉

    In general, every capacitor have frequency dependent ESR, so if you working with some fixed frequency, you can choose exact capacitor type and value which have almost resonant response (lowest ESR) on particular frequency and that will do “perfect” decoupling.

  3. November 9, 2012 at 04:56

    Great work – I echo what mikikg says – that red cap isn’t having much effect as a decoupler on such a fast chip. It has too long leads and too much internal inductance to operate at higher frequencies. I reckon your biggest improvement comes from using the ferrite which stops the noise getting out and minimizes the ground bounce. X7R and X5R caps are best for decoupling I find – NP0 can be very good too (even though more expensive) though has higher Q (lower loss) so watch out for potential resonances.

    • BlogGeanDo
      November 9, 2012 at 06:11

      Hi Richard, thanks for the comment. I guess this mod is really crying for a custom PCB with a good Gnd plane and smt components. I’ll have to rework the cap…

  4. qusp
    November 9, 2012 at 07:18

    haha excellent, finally i’m not alone on this stuff! I resisted being more explicitly critical, because i’m a little bit sick of being ‘that picky downer guy’..

    • qusp
      November 9, 2012 at 07:29

      I do know its a dry run, however many will only do this much and those pretty red caps have an ildeserved reputation as good digital/HF decoupling caps

    • BlogGeanDo
      November 9, 2012 at 15:22

      Hi Qusp,
      Holding back good feedback will not change your reputation 🙂

  5. qusp
    November 9, 2012 at 07:21

    a PCB would be great, but you could get pretty effective results just be sticking a solid layer of copper foil under the PCB and drilling through, or using blank copper clad Fr4 and drilling through to make vias

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