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GrubDAC Tweaks

All electrolytics (polymer and aluminum) have leakage current. This is the current that passes through the capacitor to keep it charged. It is given in specs as a current rating in microAmps (uA). However, apparently this current makes a capacitor "noisy."e;

You can read the formula off the datasheet.
For a Panasonic FM: I <= 0.01CV
For a United Chemi-Con PS-A: I=0.2CV

So a FM is an order quieter than a PS-A. Now how does this affect the grub? Well C1, C5 and C15 are part of a low pass filter to keep out noise. We want the largest cap possible to get a good effect from the ferrite/capacitor combo, but we want quiet as well. The PS-A gives us larger value, but is noiser.

So a tweak, for those not building a cable DAC would be to use aluminum electrolytics. Panasonic NHG is available in good values (470uF in a 6.3 x 11.2) for all three positions. FM and FC are available in 330uF. Nichicon at Mouser also has quite a few good options (UFW, UKW)

Note that this would also apply to the Bantam C12 position. Being a mid-rail decoupling cap, you want low noise here.
file last changed:Friday, July 2, 2010 7:00:00 AM
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