Latest phono (RCA) cable craziness.

[Feek]

I needed to pick up a phono to phono cable for a subwoofer, no urgency, just something I'm going to need in the next few days.

I was passing a high street hifi shop who have around 25 branches so they're relatively well known and I popped in to grab one.

He asked me what it was for and so I told him. He said that he's got exactly what I want and offered me a cable for just under £30. I metaphorically coughed and spluttered at that price and asked what's so special about it.

He told me that it's made especially for subwoofers and that the ground isn't connected at one end to prevent earth loops. He actually said that it's 'floating'. He also said it should be connected so that the writing on the cable started at the TV end so that the floating earth end would be at the subwoofer.

I questioned this. I specifically asked if he meant that the outer wasn't linked between each end and he was adamant that was the case.

Incredulously, I took it out of the box and asked if he had a multimeter, expecting the answer to be 'lol, no' but he reached into his drawer and had one there! I checked continuity from one end to the other and of course, both inner and outer were connected.

It's not like RF where there would be a DC short across a balun, this is a straight phono cable.

I know some of these audiophile monkeys will believe anything they're told but seriously, to suggest that a phono cable won't have both connections is just taking the biscuit. How can people be so gullible as to believe this garbage?

Needless to say, I made my excuses and left.

 

[firstborn]

There may have been an outer shield over a construction containing two other conductors. One of the ends of the outer shield left floating.

 

[NickK]

Single ended rca.. only needs the correct inductance, capacitance and resistance plus shielding .. it doesn’t need magical jojo juice and diamonds.

just use a thick piece of shielded copper wire..

 

[Cryfreeman]

Don’t forget the upgraded power cable.

 

[Feek]

There may have been an outer shield over a construction containing two other conductors. One of the ends of the outer shield left floating.

It's a length of wire with one phono on each end with conductivity between the centre pins at each end and the outer at each end. Nothing could be floating, there wouldn't be connectivity.

it doesn’t need magical jojo juice and diamonds.

Ahh, according to the man in the shop, it doesn't need both cores connecting! That sounds quite magical

just use a thick piece of shielded copper wire..

Exactly! It doesn't need anything special.

 

[firstborn]

It's a length of wire with one phono on each end with conductivity between the centre pins at each end and the outer at each end. Nothing could be floating, there wouldn't be connectivity.

OK, think standard coax connected to RCA each end, but with an additional shield over the coax connected to the RCA outer only at one end.

 

[Feek]

OK, think standard coax connected to RCA each end, but with an additional shield over the coax connected to the RCA outer only at one end.

OK, he didn't explain it like that.

But what is that supposed to achieve (apart from acting as an aerial)? It can't be anything to do with an actual ground because both source and sub are powered by figure eight power cables so they're not even connected to the mains earth.

/edit - Ahh, I see this concept was 'invented' by Monster Cables. Well that explains everything really

 

[lucid]

Ah, this BS again about ground loops and floating shields.

A long conductor - which is what a shield wire is - that's connected at one end is.....

Spoiler: tah-da!!

an aerial.

People obsess about ground loops like it's some kind of boogeyman. They're actually quite rare, particularly as a lot of AV gear is now double insulated and so lacks a physical connection to the mains earth of the ring main. Without that there can't be a ground loop.

I'm convinced a lot of what people misdiagnose as ground loops is actually poor cable shielding, or subwoofer hum from either bad caps in the PSU or just poor design. Anyway, for a decent double-shielded sub coax look up "hum killer mini subwoofer cable" on Ebay. £30 will get you an 8m cable that's just 3.5mm diameter and yet better shielded then all the thicker cables plus more flexible than anything else I've seen in the cable market.

 

[firstborn]

Ground loop does not necessarily equal earth loop.

 

[mmj_uk]

OK, think standard coax connected to RCA each end, but with an additional shield over the coax connected to the RCA outer only at one end.

What do you mean by additional shield over the coax? like dual shield cable? conductor, insulator, braid then a layer of foil around the braid but not connected at one end? it really just sounds like a snake oil sales pitch to sell a £3 cable for £30.

 

[Feek]

What do you mean by additional shield over the coax? like dual shield cable? conductor, insulator, braid then a layer of foil around the braid but not connected at one end? it really just sounds like a snake oil sales pitch to sell a £3 cable for £30.

That's exactly how I read it.

That's not how it was explained to me in the shop.

 

[mmj_uk]

What the guy in the shop said sounds like even more of a rip off, £3 cable without the shielding connected at all? would it even work? doesn't the distance of the outer shielding from the conductor determine the impedance? if there's no ground connection both ends the signal won't travel properly or will it?

 

[Feek]

£3 cable without the shielding connected at all? would it even work?

He was clearly talking rubbish because I bleeped it and there was connectivity.

 

[firstborn]

What do you mean by additional shield over the coax? like dual shield cable? conductor, insulator, braid then a layer of foil around the braid but not connected at one end? it really just sounds like a snake oil sales pitch to sell a £3 cable for £30.

Only thing that would make sense would be another insulator between inner and out shield, then the outer shield would then be akin to a sleeve balun?

 

[NickK]

Surely a non connected “shield” acts like a choke. Only issue is that the choke is so small in he dies that it’s probably only going to filter VHF or UHF. Probably not that efficient either due to the lack of loops allowing maximum flux use age.
Probably more efficient to put a differential transformer at each end then run two conductors.

 

[JasonM]

Some of the better audio cables have an extra shield around them, this is not new as electric guitar cables have been doing this for years.

I believe the sales person was referring to a 'Pseudo balanced' cable where the extra shield is connected to only one end. Never used a 'Pseudo Balanced' cable so unable to confirm if they benefit or not.

 

[Frubeling]

Of all of this my main takeaway is damn, £30 isn't an expensive cable in the slightest

The guy in the shop's explanation seems a bit iffy though. The primary reason for a dedicated subwoofer cable is the meshed shielding to reduce power hum

 

[JasonM]

I use some RCA cables with meshed shielding and they reduce the hum on the active monitors I use.

I actually recorded this very basic test on a smart phone, showing the background interference between a Van Damme Silver cable (with mesh shield), and a Maplins Premier cable (no mesh shield).

To exaggerate the interference I've got the monitor gain set to +6. You can hear the noise difference when I switch the cables.

With the gain set as I normally have it, combined with the Van Damme cable there is no noise I can hear, however the Maplin cable (or any other standard cheap cable) there is always some noise noticeable.

People that have hum issues on studio monitors, some of the issues is cheap cable and not the actual monitors.

Again it's a pretty low quality video, however it demonstrates without a doubt better quality interconnects reduce interference, and this is my sole purpose for posting it.

And this is a photo of the two actual cables in above test. You can see the mesh shielding on the Van Damme cable.

https://lh3.googleusercontent.com/p...JEGyYE3o4tvkHwyDz1z9ZzYTJ0TSSvda=w799-h599-no