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In Reply to: RE: Odd harmonic ringing? posted by rick_m on May 26, 2007 at 18:34:07
Rick...it's fairly simple...all noise is caused by frequency imbalance. The incoming service into your house is fairly clean. Noise, harmonics, Rf, or whatever you want to call it is caused by the appliances (including your stereo) that are plugged into the circuits of your house. Ringing harmonics are caused by the cap / choke filter in 99% of your electronic components. What we are talking about here is the leakage from the first shunt capacitor in each component. The ringing could be caused by a uf value mismatch between component A, B, and C...or it can be too many at the same value causing a overlap in frequency (very similar to a crossover effect for the ac line).
As I mentioned before, everything on the line effects frequency. Ferrite rods shift frequency. Harmonic ringing caused by the shift can be fine tuned by moving the rod up and down the cable. In this case you are not fixing the problem, but altering / shifting the problem to another less noticed frequency.
I have been playing / installing the choke in various products that I design for the last couple of years. I have run into problems many times when combining the choke with normal single cap parallel filtering or ferrite beads and rods. Multi-valued cap filtering on the other hand has offered a nice step forward when combined with the choke.
My best advice to you is to install one choke per component. The choke will remove the ringing and offer PFC for the isolated component. At the same time it will offer parallel filtering for the other components plugged into the same circuit.
regards
Alan Maher
Follow Ups:
Hi Alan,
I appreciate the info and am trying diligently to understand it. My difficulty may be with the terminology as I think of "noise", "RF", and "harmonics" as largely separate things. Let me try this in Rick-speak and see if I'm close...
Is "leakage from the first shunt capacitor in each component" the voltage imposed upon the power line at the outlet due to processes within the component?
Does this statement describe the resonance situation? "The process of using L/C filters to reduce susceptibility and emissions can have the side effect of resonating at one of the harmonics of the power line which causes problems".
It would help my understanding a great deal to know within an order of magnitude the frequency range where you are seeing the ringing. It sounds like you've identified a band that causes the worst problems.
Last winter I tried connecting a honking transformer as a choke to my study stereo and heard no difference at all. Which tells me nearly nothing. The choke may not have had the right attributes, the system might not be susceptible to the effect, who knows?
Thanks, Rick
Ok...lets look at them one at a time.
"Is "leakage from the first shunt capacitor in each component" the voltage imposed upon the power line at the outlet due to processes within the component?"
A typical switch mode power supply has a very simple noise filter at the input. Capacitor-Choke-Capacitor is a very simple noise filter. In this design the capacitor is placed across the hot and neutral. The capacitor will leak on the neutral side. Simple parallel filtering is designed to create common mode rejection in electrical wiring (power cords) by altering the magnetic balance of the cable. The leakage from the capacitor is how the magnetic flux of the cable will be altered. Sounds simple...and it is...but, the value of the cap has a narrow band ringing frequency. The frequency is altered by the magnetic flux inside the cable...this is problem number two. By itself it causes minimum harm, but combined with multiple components and now you have a problem. Maybe component A has a .33uf cap and component B has a .22uf. Maybe component A and B both use a .33uf making it .66uf in parallel back at the wall outlet. Maybe the wall outlet is made out of brass and steel and ringings in the upper mids right at the same frequency as the caps. The odd harmonic ringing that has just been created is described by audiophiles as RF noise. RF in reality is the wave patterns (multipath) you see on tv or the radio station that is heard. What we are talking about is harmonics.
"It would help my understanding a great deal to know within an order of magnitude the frequency range where you are seeing the ringing. It sounds like you've identified a band that causes the worst problems."
We are addressing harmonics from dc to about 100KHz. The main area of concern for audiophiles is between 500Hz and 5KHz...well within the range of the choke. Lowering the harmonic ripple at this range provides true to life audio reproduction. The same can be said for people commenting about improvements to video. By reducing or eliminating the ringing in the lower band we are able to greatly reduce the ringing in the MHz and GHz range...which is why both digital audio/video and analog video are greatly improved.
"Last winter I tried connecting a honking transformer as a choke to my study stereo and heard no difference at all. Which tells me nearly nothing. The choke may not have had the right attributes, the system might not be susceptible to the effect, who knows?
I will ne honest with you...the transformer doesn't come close to the choke benefit. Some large (20A plus) transformers (isolation) offer small benefits from the added inductance, but most of that inductance is on the secondary and blocked by the center shield. The choke is different in every way.
Alan
Hi Alan, thanks for the details, it's a great help knowing that you are considering frequencies <100KHz.
Perhaps one of the reasons I noticed no effect last winter was because that system is rather old and only has linear power supplies in it as far as I know. Maybe adding the choke make more difference in systems that use switchers.
I think the main things I'm coming away with is to concentrate my efforts on stuff under 100KHz and to get one of the "right" chokes to play with. That's probably enough fuel for the fire for now...
Thanks for sharing your insights and experiences, I look forward to getting the chance to pursue this further,
Rick
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