Archive of the former Yahoo!Groups mailing list: MOTM

Hi Ken,

 

The exact MOTM part is the muRata BL01RN1.  I don't believe Mouser carries this part... however, Allied does!  www.alliedelec.com The Allied part number is 711-4101.

 

I did a little homework on ferrite beads a few months ago - amazingly droll stuff.  Anyway, humor me whilst I give some overly simplified comments...  oh, and I would be grateful if someone would let me know if I get it right (or wrong).  ;-)

 

Choosing a bead is a function of what freq range you are trying to conquer.  The basic selection criteria is material type and physical dimensions.  Different materials have different suppression qualities.  (As you would suspect, no material is the best at all frequencies.)  Usually, a given bead is spec'd as some impedance (in ohms) @ some frequency.  Actually, at the manufacturer's site, there is a chart for each bead product that maps impedance, reactance and resistance vs. frequency.  Check out this article for more info: http://www.fair-rite.com/CUP Paper.pdf

 

As it turns out, I chose to use Fair-Rite part 2743004112 (Mouser #623-2743004112) instead of the standard muRata part for the Oakley midiDAC2.  This is due to all of the "noise generators" on the PCB - I didn't want any of that crud to get back to the power supply.  The reasoning for my decision is:  The muRata bead BL01RN1 is spec'd at an impedance of 70 ohms @ 100Mhz.  The Fair-Rite part I chose is 110 ohms @ 100Mhz.  Now, what I did was to compare the frequency charts of the two parts at 10Mhz, since this is the frequency of the clock on the midiDAC2.  (I believe there is also a 2nd harmonic component at 20Mhz, so I compared this as well.)  The muRata part is 40 ohms at 10Mhz and 50 ohms at 20Mhz, while the Fair-Rite part is 55 and 75 ohms respectively.  I would have gone with an even better part, but the 10mm lead spacing on the PCB prevented it.  I'll probably end of using this part for other projects as well.

 

Happy Holidays,

George