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In Reply to: RE: 193L choke impressions posted by John Swenson on May 26, 2007 at 14:51:49
John,
Thanks for your subjective impressions. Now, what I'm really looking forward to hearing from you is the results of your empirical investigation into what exactly is going on with this shunt inductor, rather than speculation. While I've heard much discussion of what is going on, it seems that none of this is supported by any measurements (leastwise, that I've seen).
TIA,
Paul
Follow Ups:
The Hammond 193H is a smaller brother of the 193L. Both are specified as 5 henrys, but the 193H is for use at 200 mA instead of the 300 mA rating of the 193L.
It is reasonable to assume both use the same core material.
The core will limit the maximum frequency for which the device will act as an inductor. Above the maxumum frequency at which the core magnetic domains will follow the impressed current, the core stops participating, and the device has the residual inductance of the winding geometry, the parasitic winding capacitance, and a frequency-dependent resistance due to skin effect in the solid wire.
I don't have a 193L handy, but I do have a 193H. I connected it to a resistor and a signal generator, and swept the frequency. The choke impedance rises with frequency to 5 KHz, then it drops.
Many power transformers I've tested this way have a maximum frequency in the 40 to 100 KHz range, so Alan is correct that the Hammond chokes are superior as AC noise filters. However, the real reason they work so well is that their cores are not built for wide frequency response.
I would like to see the results of similar measurements on the 193L and 193M.
Given your explanation above, I'll rephrase and say that I look forward to Mr. Swenson's take on what underlying mechanism(s) is responsible for the efficacy of this component.
If its functioning as a noise filter, I look at it as a attenuation network with frequency dependant reactive elements terminated with a reactive/resitive load, a freqency dependant voltage divider.
If it is(also) fuctioning as a passive power factor correction interacting with the specific reactive charateristics of the load(s), I'd look at the line's harmonic content under appropriate load, both with and without correction.
I don't follow the logic of the explanations, unable to comprehend at this level of abstraction. It certainly doesn't behoove either you or Alan to actually measure anything in situi or appoximate. I'm not grasping how/why this durn thing works, and I'm just hoping that John might investigate its mechanism with additional tools and share those findings.
Bad form, no doubt, to re-post a post, but perhaps the link below helps.
In it I mention resonant frequencies in the MHz range, but it seems from Al's post that it is much lower--in the 5 KHz range.
Correct URL is http://www.audioasylum.com/audio/tweaks/messages/14/145002.html
or core magnetic behavior (or both). I suspect core magnetic behavior in the Hammond chokes, as transformers of similar size have much better frequency response.
All real capacitors and inductors are limited in frequency response by their parasitic inductance and capacitance, respectively. Getting an inductor that is useful at the noise frequencies that affect audio component performance is not trivial. Even so-called "RF" chokes with ferrite cores tend to have low self-resonance frequencies. I've found it necessary to make composite inductors, with several units in series, each one with smaller inductance and higher self-resonance frequency, to get broad-band coverage.
As far as I can see, the placement of the inductor across the line provides a low impedance at frequencies lower than the 60 Hz power line frequency, thus, it would attenuate low frequency disturbances on the AC power line below 60 Hz, with it's DCR the impedance at "DC".
While this may seem trivial, it helps to remember that almost all AC line filters, including my own DIY AC Line Filter & SS, filter out the HF's, and do nothing to the frequencies below some cut-off frequency. In the case of my AC Line Filter, it starts to cut-off up near the top of the audio band, depending on the exact source and load impedance.
As for how much AC power line content there is below 60 Hz, this is entirely dependant on your local power line conditions, and it is not uncommon for there to be residual "DC" present on the order of a volt or two, as well as frequency components between DC and 60 Hz. Most of those are the result of industrial equipment, unbalanced loads, and poorly designed and implemented power supplies that are sharing the AC line with your stereo equipment, esp. switchmode types. In a "perfect world", they wouldn't be there, but hey, we live in the real world, where Murphy thrives and rules.
Given that many of the classic audio components that are highly regarded for their sound also can have very simple/basic power supplies, and may be the most susceptible to LF AC line garbage, it would not be surprising to find that filtering out/attenuating those lower frequencies could provide a sonic inmprovement.
Whatever the choke does for HF's or RFI would be in addition to it's benefit at frequencies below 60 Hz.
Jon Risch
Thanks Jon - I hadn't considered it as a highpass shunt filter. I wouldn't think it makes a particularly good lowpass filter when its impedance finally falls below that of the line frequency. It would make a very expensive, ineffective X cap.
I still think its something to do with passive power factor correction, but I have no real or valid measurements to back up any suppositions.
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