Adding Input Capacitors to the Amanero Board
Continuing from the previous post, I decided to consider some mods to improve its performance. Looking at the schematics [schematic 1][schematic 2], the input capacitors to the regulators are implemented as per-spec at 1 uF in value. I decided to add a larger capacitors to both of the regulators. Used 100 uF Oscons mainly because I had a bunch of them handy. Furthermore, using large input capacitors for regulators seems to be a “normal” thing to do for audio applications. Look at the Buffalo II board use of 100 uF OSCON SVPs as input capacitors into its 3 LT 1763 on-board regulators:
For the Amanero board 3.3v regulator, I added the capacitor to the first capacitor in the PI network (C27). This further improves the filtering of the USB power. C27 is a “mere” 4.7 uF. At first I thought it was 47 uF and wrongly thought that it provided good filtering… maybe good but not as good as adding a 100 uF :-).
For the 1.8v regulator, I paralleled the 100 uF capacitor with its input capacitor (C31).
For C27, it was convenient and easy to piggyback the 100 uF capacitor. First add some solder to the pins of the capacitor, “mount” it to C27 and reheat the pins
For C31. the capacitor is too small (for me to work with), but there is a nearby ground via where I installed the (-) lead; for the + lead, I scratched off the solder mask in the power trace into the regulator, and soldered it there.
Doesn’t seem like a good solder joint since I only scratched a tiny bit of the solder mask but I tested it by wiggling it and measuring the continuity with the power input pin of the regulator.
The results are very encouraging. No longer do I see a “lingering” low level unlocks. The number of unlocks settles to zero after about one hour. In addition, the number of unlocks decreases at a faster rate than the Musiland, at least in the two tests I’ve done on the Amanero board.
Here is a plot of the results (44.1K sample rate, DAC DPLL set to “LOWEST”):
The test shows that the Amanero board, with the additional input capacitors performs as good, if not better than the Musiland 03 board. Same disclaimer applies: I’ve done just two tests…
For those interested, this is how I count the number of unlocks: [link]
Decided to another tweak before doing a “long term” measurement: adding a small value capacitor to the USB power line.
There is currently a 4.7 uF capacitor on the USB power line. I have already added a 100 uF capacitor.
Adding .022 uF film capacitor seems to be a good idea in order to provide further bypass to the input power line. The capacitor can be installed under the board across terminals 1 and 4 of the on-board USB connector (top of the diagram is the connector side)
Now we have the following add-on capacitors to the USB power line:
Hmmm… Some “disturbances” in the morning hours. The last test I did on the Musiland, was cleaner. (Usual disclaimer… small number of tests…)
I did remove the piece of putty I had put on the top of the Crystek oscillator. Perhaps the problem is compounded by the vibrations? Maybe I should work on damping and mechanical isolation.