[SoundStage!]Synergizing with Greg Weaver
Back Issue Article
May 1998

"Ferrite"-ing Out RFI

This month’s sonic solution deals with a surprisingly effectual remedy for a problem that, to varying degrees, affects just about everyone. It is a cost-effective way of corralling those grating and detail-robbing perpetrators we know as the two-headed menace of EMI (ElectroMagnetic Interference) and its resultant compliment RFI (Radio Frequency Interference). EMI, which we find in abundance everywhere, is the radiated spurious energy that susceptible devices (your stereo equipment) receive as RFI. What do I mean by saying that they are everywhere? I mean exactly that. But first some history is in order.

My first practical experience with EMI came back in 1971. One of my best friends had just gotten a new handheld programmable Hewlett-Packard calculator. This thing was the bomb in its day. Keep in mind now, it’s spring of 1971. A desktop calculator about the size of a regular school text book—with stacked register displays, only one memory and the square root function—cost my high school’s science club $400. Yeah, I thought that might put it into perspective. But man, what a gadget this HP was. It actually had a crude, embryonic form of microprocessor inside. And, by using its magnetic-strip memory system, you could load a 21-step program into its on-board memory and really go to town a number crunchin’.

As cool a device as this HP calculator was, I just about completely lost it the first time my friend inadvertently placed it beside my stereo receiver while it was spinning its gears. Talk about noise. ERR, EEH, AHH, OOH, ERR, FRIP, RAA. A continuous string of discreet screeching pulses, all being emitted by the unshielded infant ICs buried deep within this early super calculator. Hell, with a little practice he got to the point where he could, with some degree of certainty, play rudimentary tunes with the haze of EMI this thing radiated into the air in all directions. While this was a gas and we had lots of fun with it, RFI and EMI management now took on new meaning for me.

My research has revealed that the impedance of free space to electro-magnetic fields is given as 377 ohms. Now, an antenna is merely a device built to match that impedance at the frequencies of interest, much like a transformer. Since all conductors are antennae, and we have many, many such conductors in our audio system, the more mismatched the impedance from free space (that 377-ohm figure), the less electromagnetic-field pickup will occur. Since most preamps are wide-band devices, they will amplify the detected electromagnetic field picked up along their cables and wiring. This can cause added IM distortion, depending on how non-linear the amplifying device is to the electromagnetic pickup. In some extreme cases, it can be quite prevalent. Ever hear a CB radio broadcast on your stereo, even when the stereo was off?

You should have by now realized that this means that practically every electronic appliance in your home is basically a transmitter of sorts. All those electric motors in things like your refrigerator and washing machine, as well as some of the ICs and digital displays in things like coffee makers and microwave ovens, generate their own radio frequencies and broadcast them indiscriminately throughout your household. Don’t forget that CD player/transport with all those ICs inside. And does your player/transport have a florescent display? Ah yes, I thought so. Even more possibilities for encroaching radio transmissions. And jeez, look how close it is to your sensitive preamp/receiver/FM tuner. Aaahhh!

The impetus for this month’s column comes more from my inadvertently reminding myself of the audio analyst’s fourth audio axiom (through forgetfulness) than directly planing to write it. That fourth axiom says "The effects of any substitution/addition to a music system become most apparent upon removal of that substitution/addition." It had become necessary to remove all the ferrite shields I had installed on my Silver Signal Tape in order to facilitate the cleaning/destaticizing that I wanted to do. Well, it wasn’t necessary, but I’m fussy like that. Believe it or not, some close friends, including my significant other, have chosen to describe me as anal. Can you believe it?

Hours later, after removing all the ferrite shields and placing them in— rather than on— my record-cleaning station, I had completely forgotten about their removal. As the significant other headed out to work, I prepared for the evening’s ritual by firing up the old music system. I hadn’t even made it back to my seat before I became aware that something was amiss. At first I chalked it up to the fact that I had just powered up the system and it hadn’t yet had a chance to stabilize. The first sonic problem I qualified was that everything sounded "hazy," seeming to be a bit on the grainy side of natural. As annoying as this harshness was, I was also greatly troubled by the diminished dynamics and lowered resolution. But when, some 25 minutes into the listening session, the nature of the problem became obvious, I felt like one class-A dolt. As I approached the system from my listening position to turn the record, my eye was immediately drawn to the crossover. The blatant absence of the unusual shapes afforded by the snap-on shields attached to the Silver Signal Tapes just about screamed out to me in it’s obviousness. Duh, what a dummy.

At that moment I was able to recall just how pleased I had been when I first applied this tweak, reveling in the newfound resolve and quieter presentation, greater sense of ease, augmented dynamics and richer harmonics. But as with anything, over time I had grown accustomed to it.

Replacement was a snap (no pun intended) and five minutes later I was back in musical nirvana. What a delectable difference. There was a broad-band removal of fine "haze" from the background, providing a quieter environment from which the music could emerge. There was an overall calming of that slight edginess, allowing for a conspicuous smoothing effect on the texture of the voices of all instruments, yet without any loss of detail or micro-dynamics. Everything seemed more lively, more vibrant, more dynamic. Harmonically, things seemed richer, more robust and better fleshed out. In fact, these qualities seem to be illuminated considerably without artificially "spotlighting" them. The differences were not subtle by any stretch of the imagination.

By now most of you know I’m frugal. (Gee Greg, isn’t that just a politically correct word for cheap?) When searching to outfit my system with these devices in hopes of creating this grand refinement, I soon discovered that all pricing was not the same. You can order some of the spiffy-looking bright-red snap-on shields from Audiophile Company X to the tune of $99.95 for eight. You can run down to your local Radio Shack and buy ‘em singly (part number 273-105) for $4.99 each. Still too pricey for me. Time to get serious. Point your browser to Digi-Key, parts purveyor supreme, and fire away. You’re looking for the Steward Clamp-On Ferrites, part number 240-1001 ND (for white) or 240-1002 ND (for black). In quantities of ten, they cost $14.88, and that price goes down as you buy more. Ten seemed plenty for my adventures. Add $5 for handling please (because my order was under their $25 minimum), and another $3.36 for UPS ground service (your actual mileage may vary.) and you’re still under $24. Mine showed up in four working days.

The three brands of shields I’ve mentioned here are all virtually identical, being comprised of a formed semi-cylindrical ferrite material housed in a plastic snap-on case. Ferrite is nothing more than a magnetizable material made by combining and then baking ferrous and ceramic materials together to create a compound that offers low eddy-current losses at high frequencies. The recipe for the mix can vary, yielding different impedance characteristics, but essentially the stuff itself is pretty much the same.

More research on my part revealed the methodology behind the shield’s effectiveness to be fairly easy to comprehend. Radio frequencies (generally describing electromagnetic signals above about 70kHz) generate fields around them that are quite enormous. These large fields are free to couple to the multiple antennae—ah, I mean, cables—of your system. To reduce the effect of these large signals, the ferrite material in the shields creates a higher inductance in the cable, helping to attenuate the amount of electromagnetic pickup in the cable. By virtue of being partially magnetized, the material in the snap-on shields provides a source for magnetic loss, effectively creating a strong resistance to the coupling of the RFI to your antennae—er, cables.

The Steward clamp-on ferrite cylinders offered by Digi-Key provide 199 ohms of impedance compared to 247 ohms from the red ones offered by Audiophile Company X while 150 ohms is provided by the "Shack" versions, all referenced to 100mHz. Let’s see, $12.50 each for the pretty red ones from Audiophile Company X, $5 each for the ones from Radio Shack, or $2.40 each for the industrial-application Steward brand from Digi-Key. Hmmm. Let me think about this.

These Stewards are a little over an inch and a half long, are about two-thirds of an inch in diameter and have a hole some .355 inches in diameter. These work perfectly on the SST’s (see February’s Synergizing in the Archives) and will fit all but the thickest of interconnects and power cables. If you want to go for the maximum inside diameter offered from Digi-Key, (and the maximum impedance, 234 ohms at 100mHz), try part number 10737 ND (in white) or 10738 ND (in black). Keep in mind that more is not necessarily better here because the more mismatched the impedance from free space (377 ohms), the less electromagnetic-field pickup will occur. But be warned, these guys are BIG, nearly twice the diameter of the 1001s or 1002s with an inside diameter of half an inch. If you are using big fat cables, or you just want to be sure you will be able to clamp on to just about any stock EIC power cord out there, order ‘em up. Ten of these bad boys will set you back all of $32.10 before shipping. Still mighty painless, given the degree of transformation they offer.

When they arrive, use them prodigiously; I did. The difference is similar to that afforded when looking through a window that hasn’t been cleaned all winter long, then looking through it again after a full cleaning and buffing. If you are experiencing low-level background hum, the ferrite shields may have a tremendous effect on lowering or removing it completely, so long as it isn’t the hum from a noisy transformer. They will likely impart a higher degree of smoothness overall, filtering away graininess and harshness you weren’t even aware you were hearing. Dynamic contrasts and low-level detail, with all this graininess removed, should come into better focus. If you notice that you have softened leading-edge transients or dulled inner detail rather than the positive attributes I’m describing, you can remove them a few at a time. I have only noted this detrimental system effect in one instance. Everywhere else, they bring their unique brand of magic.

The first place I recommend you try implementing them is your digital front-end. If you are using a one-box CD player, attach one clamp to each of the analog signal cables going to your preamp/receiver. That means one each for the left and for the right signal cable. You should initially try to position them about one to two inches from the back of the unit. I seemed to have achieved the best results with the shields mounted on the end of the cables nearest the sending unit rather than the end closer to the receiving unit. In other words, follow the direction of the signal flow (like from CD player to preamp) in the cables and place the shields nearest the "from" end. You may find a more optimum position for final placement with experimentation, but this seems to be a good jumping-off point in my experience.

If you are using an outboard DAC, in addition to placing the shields on the analog signal cables going to the preamp/receiver, position one on the digital cable about an inch or two from the back of the transport. You can do the same with the CD player or converter’s AC power cord. If the unit uses an outboard power supply, try one on the AC cord going to the power supply and one on the DC cord as well, again applying them one or two inches distant from the device (the DAC or power supply). This can help reduce the digital "glare" so often found in digital systems and can make some of the most grating CD players sound much more smooth and natural. And in an already exemplary system, this budget modification can work sheer magic. It is HIGHLY RECOMMENDED for any of you using the SSTs.

But listen closely. Some systems can be overly sensitive to these effects and you can destroy some of the fine detail and blur transients if you overdo it. As I mentioned, I have only found one instance where full-scale implementation of the ferrite clamps actually detracted from the overall system performance. There is no set number of ferrites which provide the highest degree of bliss; what may be too many in one application may be equally too few in another. So you have my written permission to experiment.

Don’t forget to try them on the signal cables between your turntable and preamp/receiver and between your preamp and amp, again applying one to each cable at about an inch or two from the "sending" device. Hey, add them to the power cables for those components as well. And have I mentioned trying them near the speaker input terminals on your speaker cables? In some applications I have found this to contribute more enhancement than on the signal cables, so be sure to try them there.

Over the years I have noted that the effects of this sonic supplementation can vary from having a fairly subtle yet positive effect to providing a breathtaking transformation. No matter what ferrites you select to manage EMI and RFI, and thereby remove the deleterious sonic trash from your music, be prepared for some overall system quieting and refining that cannot be obtained by any other means, even through equipment or cable upgrades.

...Greg Weaver

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