Tweakers' Asylum

Worthless

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djk

In Reply to: RE: Is this inductor bad? posted by dave789 on February 12, 2009 at 00:11:08

The inductance values in this series will be way too low to be of any use in audio.

For line level circuits you will be looking for values in the 100mH~1H range, with as low of DCR as possible.

Follow Ups:

RE: Worthless - dave789 07:26:20 02/12/09 (2)
They are useless for audio band tone control circuit etc., but they can be used to cut down noise MHz region to reduce RF interference.

For example, it is not hard to find an amplifier with input capacitance 200pF. 200pF gives about 800 Ohm at 1MHz. So if we connect the above mentioned wide band choke in series, it will increase the cutting of above-1MHz noise.

I saw some 100mH~1H range inductors. Their inductance are usually measured at 1kHz, and they seem to pass through above-1MHz signals because of the capacitive effect in the coil.
- RE: Worthless - rick_m 08:37:11 02/12/09 (1)
  They can be super at getting rid of RFI. Like you say, they have excellent ultimate attenuation at high frequencies. I routinely use similar ones along with feedthrough caps for filters in gear for repeater sites.
  
  However the highest perm material is pretty non-linear and if you maximize the cranks they have loss well below 100KHz which is getting rather close to hi-fi for comfort. So, at the risk of stating the obvious, I suggest that you listen to make sure that they don't adversely affect the sound before permanently installing them. If they do, and your interference isn't too low, go with ones with less perm, besides being less reactive, they will be more linear.
  
  Glad to see that you are trying to address problems at the right points in your system.
  
  Regards, Rick
  - Excellent advice. - Al Sekela 11:02:24 02/12/09 (0)
    The chokes may work well for RF noise reduction, yet have objectionable effects on the audio band. One pitfall that is easily overlooked is the mechanical isolation. Placing these things where they can vibrate may introduce unpleasant acoustic feedback, with peaks depending on the mechanical resonances of the choke body and how it is suspended. Sticking it down with something gooey may then introduce a nasty dielectric.

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