Phil's lab understanding how to choose a ferrite bead

Question

I'm trying to understand what ferrite bead he chose as shown in the picture. It says it is a 120R ferrite bead but from what I understand, when looking for a ferrite bead, you have to know the frequency you want to filter be in the resistive range on the component's ZRX chart.

So what frequency range is he filtering here? And is this the correct way to notate a ferrite bead, as opposed to labeling the component something like "60 Ω @ 50 kHz"?

I am a bit new to the electronics field so excuse me if I am missing something obvious. The schematic is from Phil's lab's YouTube channel showing how he made an amplifier with NE5532 op-amps.

Answer 1

There are other parameters that are important for the component. Current rating, for example. Also package size. Not all of that stuff needs to be on the schematic.

100MHz is very commonly used as the frequency at which the impedance is specified for ferrite beads so omitting it does not subtract so much from the understanding of the schematic and makes it less cluttered. I would assume 100MHz unless otherwise specified, to be verified from the database of course if ordering parts or whatever.

Personally, I do put it on there, like "1K @ 100MHz" but Mr. Salmony appears to have less tolerance of clutter.

Answer 2

The nominal impedance is usually specified @ 100 MHz. I agree that just labeling the ferrite bead with "120R" is not good practice and something like "120R@100MHz" would be a better way to do this.