Phono stage picking up radio signals?

Clio09: "shielded on both ends" or "shielded on one end" is not the correct terminology. A shield, whether it's braid or foil (sometimes both,) encloses the cable from one end to the other.

If the shield is connected to the ground pin (in the case of power cords or balanced IC's) or to the outer ring (ground) of an RCA plug at only ONE end, it is said to "float" (at the end where it's NOT connected.) This is the best way. It's like putting a grounded box around the cable, but since it's only connected to ground at one end, NO CURRENT CAN FLOW THROUGH IT.

When shields are connected to ground at both ends, they still shield, BUT they also form a loop -- the other half of of the loop being the negative signal conductor inside the cable which, of course, is always connected at both ends (or you'd get no music signal!)

This loop acts like a kind of antenna (but usually not Radio Frequency, RFI, like radio stations) instead it picks up nearby Electomagnetic Radiation, EMI, usually 60 cycle, generated by power lines, power cables and transformers.

Many highend manufacturers sell their equipment with perfectly good shielded power cords. Unfortunately, UL approval requires that the shield be connected to ground at both ends (I don't know why) but this defeats the purpose from an audiophile standpoint! It's easy to fix though.

As for interconnects. It was Bruce Brisson (owner of the company that makes MIT cables) who originally put MonsterCable on the map with his "shotgun" interconnect design. It's called "shotgun" (double barreled!) because, unlike single ended IC's previously, which had a single + conductor in the middle, surrounded with a braided - conductor-cum-shield (coaxial, or coax), he used TWO signal conductors + and - (shotgun) inside, connected at both ends of course (to the RCA pin and ring), to carry the music signal, surrounded by a shield connected at only one end (the "arrowhead" end) which therefore carried no signal, but protected the internal signal conductors from interference. With a few exceptions (Kimber, Nordost, and a some others) this is the cable topology (conductor layout) used by most of the manufacturers today. Some, like Straightwire, even put a separate shield around each signal conductor and tie the two shields together and connect them just at the "arrowhead" end.

Now, this business about the "arrowhead." The reason it points to the (one) end where the shield is connected to ground, is so that if you point it in the direction of signal flow, the shield will be connected to ground at (usually) the preamp end. That is where the best ground potential (usually) is, and therefore the quickest, easiest "drain" for any interference the shield picks up. The exception, is the pre-to-amp interconnect, where if you've lifted the ground on your amp PC, you should point the interconnect arrow "backwards" to the signal flow (or toward the preamp) so that the shield is still connected to ground at the preamp end. (Notable exceptions to this convention are Purist and Magnan, but they have unconventional topologies.)

I could go on, but your eyeballs are probably falling out by now, so I'll quit. Let me know if you have any questions :~))

Neil

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Neil,

Thanks for the explanation. I was looking at the VH Audio Pulsar ICs and according to Chris Ven Haus in addition to being grounded at one end, the shield is also carrying the ground/return. So if I understand your explanation correctly this would not be the best method as it is not a floating shield.

I'll take a look at some of the other recommendations you have made for cable vendors. Could there be a situation where using floating shield ICs on the phono stage will require using them throughout the system? I'd like to just make this one replacement and be done with it.

Thanks,

Tony

RE VH IC's: If the shield is only connected at one end, then it can't be carrying anything. The term "ground return" is sometimes used to mean the negative signal conductor.

You can mix shielded and unshielded in the same system if you want to.

I still advise you to try some inexpensive cables first, just to make sure that it really is the unshielded Nordost that is causing the problem. Cheap Monster, Audioquest, Straightwire, or MIT should do the trick.

Neil, great explanation of "shotgun" topology, and the purpose of the "arrowhead". Most people I know think the arrowhead indicates the directionality of interconnects caused by the grainular structure of the conductor. You have cleared it up.

Zargon, thank you. There are some cable manufacturers who, especially in their speaker cables (which aren't ever "ground shielded",) orient their arrow direction based on "wire draw." Which simply means the direction the wire was pulled through the dies during manufacture. Supposedly, the orientation of the metal crystals as a result of the drawing process makes it easier for the electrons to flow in one direction than the other.

Others who produce spkr. cables and IC's which are symmetrical as far as orientation goes, often include arrow
indications so that (according to them anyway) you'll be able to orient the cables in the same direction, should you have to remove and re-install them after they've been broken in. Personally, I think it's just a "me too" marketing ploy.