Phono stage picking up radio signals?

Audiofankj,

I have emailed James before and he has always responded in kind. I did email him about the RFI issue and given the fact that he is 8 hours ahead of me and it's the weekend I'll look for his response Monday. Also, I plugged in the phono stage without any load resistance plugs and it still picked up a radio signal. While the plug theory makes sense I'm at a loss as to why the unit would continue to exhibit the problem without the plugs being utilized.

I have also tried to work through he dealer who I bought this unit from (used) and he was somewhat helpful, but insists it is a problem with my tonearm cable or the position of the unit. I know it is not the tonearm cable as I've done many tests, and as for position, I only have so much room to manuever and nothig has worked do far.

Hopefully James will have an answer.

Nsgarch,

I was seeking out shielded ICs and referred back to one of your posts. You mentioned a floating shield, meaning the IC is shielded on one end only. I have seen some double shielded ICs which are shielded on both ends. I'm assuming this won't work based on your post but was curious as to why.

Thanks

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.