The Factual Cable Thread

[DocG]

Hi guys,

Frankly, I would never have thought I would start a cable thread, but here goes...

I want to keep it polite, areligious, and well, yes, factual ("Where's the fun in that", I hear you think!). RCA or XLR? Long interconnects and short speaker cable or the other way around? Dos and don'ts to avoid ground loops... But not the Ultrablack Kryptonite Plus versus bog mains lead. You get the idea!

Let's see what happens...

 

[chebby]

"Where's the fun in that", I hear you think!

Get out of my head!

 

[DocG]

Well, I guess I could go and ask elsewhere...

Carry on squabbling...

 

[Anderson]

You can strap this XLR to the mains cable no problem, XLR with appropriate equipment will reject interference.

 

[Vladimir]

Just use shielded XLR cable.

 

[andyjm]

In the good old days, when transformers were used to balance and unbalance a connection, the common mode voltage didn't really matter. These days, balancing and unbalancing is done with semiconductors, and particularly for the unbalancing bit, the differential amplifiers used to unbalance will have a maximum common mode voltage they can cope with before they run out of puff.

In layman's terms, modern balanced connections will put up with a certain amount of noise, but there is a limit you can push them past that they won't be able to cope with. Short of winding both the mains lead and signal lead in a nice coil together, strapping them alonside each other is about as bad as a thing you can do, so in the worst case, be prepared for some hum.

 

[andyjm]

I was being ironic. Running two cables in parallel maximises the chance of interference. The only thing worse would be to make a transformer of the cables by winding in a coil together*

*some smart fellow will no doubt point out that coiling the cable has no net magnetic effect as the flow and return currents balance out, but given the comment was ironic, I am allowed that.

 

[DocG]

I see. Glad you made that clear

. Ignorance is bliss (or so they say...

).

And would coiling the two signal cables together, leaving the mains cable alone, reduce the risk of hum/noise? Is that the reason for twisting the cables inside the chassis (like in the picture)? Or is that only useful when using non-shielded wires?

 

[andyjm]

Just as a 'for what its worth', the whole gig with balanced interconnects is not stopping noise, but ensuring that exactly the same amount of noise is picked up by both the inverting and non inverting conductors.

This is usually done by twisting the two conductors together inside the cable, so if there is noise around, it is picked up equally. There aren't an infinite number of twists however in the cable, so in certain physical arrangements one conductor may pick up more noise than the other.

In situations with low signal level and long runs (microphone cable for example) 'Starquad' cable is used. This has 4 conductors twisted together in a precise spiral form. Imagining the cable as having a square layout of conductors, opposite corners are connected together to create the inverting and non inverting paths.

Having four conductors greatly reduces the chance of different amounts of noise being picked up by the two paths, and may help if you have hum issues.

Starquad should be available from any good pro musician store - sold as high quality mic cable.

 

[DocG]

See? A friendly, polite cable thread, that helped the OP see the light (or a glimpse of it, far, far away...)!

It is feasible! Thanks, Andy! *drinks*

(Now let's quickly abort the thread, before it gets nasty... )

 

[andyjm]

I see. Glad you made that clear . Ignorance is bliss (or so they say...).

And would coiling the two signal cables together, leaving the mains cable alone, reduce the risk of hum/noise? Is that the reason for twisting the cables inside the chassis (like in the picture)? Or is that only useful when using non-shielded wires?

Didn't see this post when I wrote my last one.

Yes, its good practice to twist pairs of cables together to minimise noise pickup (or noise transmission come to that). Cat5e is twisted pair, and it is always advised that in structured installations (patch panels and the like) that the twists are maintained to the last possible moment to minimise crosstalk.

Keeping the signal cable away from the mains cable is always a good idea, but I don't understand the bit about twising the signal leads together. The twist is inside the cable (a balanced interconnect usually has two cores twisted tightly together with an overall screeen). If the two signal leads you mention are the balanced connections for left and right, it would be best to run them parallel, don't twist them.

Again for what its worth, I have the same type of setup. I have Krell amps located closer to the speakers to minimise cable runs and allow for cooling, and run balanced interconnects from a Krell processor to the amp. The mains leads are kept at least two or three inches away from the signal leads at all points. There is no noticable hum.

 

[DocG]

Keeping the signal cable away from the mains cable is always a good idea, but I don't understand the bit about twisting the signal leads together. The twist is inside the cable (a balanced interconnect usually has two cores twisted tightly together with an overall screeen). If the two signal leads you mention are the balanced connections for left and right, it would be best to run them parallel, don't twist them.

The two leads are for the signal from XO - power amp module - tweeter, and XO - power amp - midbass. It would be an active set-up, with a DEQX-module as the active XO. So two XLRs left and two XLRs right, each feeding a Hypex NC400 module.

But if the cores inside the cable are tightly twisted already (as you can see, I have no back-ground on the subject at all), I guess it's probably not sensible to also twist the two cables together...

 

[DocG]

I'm planning a new living room system, that will combine all I like in hifi gear. I started a thread about it a couple of years ago. Basically, I want active planar magnetics, with a good DSP correcting amplitude, phase and timing (and if necessary even the room). It will be something like Oppo 105 - DEQX HDP-4 - power amps - Magnepan MMGs. I haven't found the proper power amps though, and now I'm considering a DIY project with Hypex NCore 400's, sitting at the base of the speakers (thus keeping the speaker cable as short as possible). Hypex's Bruno Putzeys insists on using balanced interconnects with his amps and hence my question:

Can I strap-tie a mains cable, carrying 220 V, and two XLR-cables together, without ruining the sound? The system will be in the living room, remember? And it would be tidier than three seperate cables running from the cabinet to the speaker...

I'm hoping a balanced IC can reject/neutralize the noise a mains cable could introduce in the signal. Or should I twist the two XLRs to lower the noise?

I hope those in the know can give a comprehensive answer (as you can see, I'm certainly not one on them... *smile*)

Cheers!

 

[DocG]

In layman's terms, modern balanced connections will put up with a certain amount of noise, but there is a limit you can push them past that they won't be able to cope with. Short of winding both the mains lead and signal lead in a nice coil together, strapping them alonside each other is about as bad as a thing you can do, so in the worst case, be prepared for some hum.

You mean coiling the cables, like Hypex advice to do inside the box?

(EDIT: the site doesn't like the picture, I guess...)

Or rather braiding the cables like this?

 

[Vladimir]

Hmm, seems like things got unnecessarily complicated here. DocG, does or does not any of the two cables have shielding?

Shielding > Twisting, coiling, braiding etc.

 

[DocG]

Hmm, seems like things got unnecessarily complicated here. DocG, does or does not any of the two cables have shielding?

Shielding > Twisting, coiling, braiding etc.

Well, ATM the cables are still living in my imagination, as is the rest of the set-up.

But if I go this route, I need to order empty cases for both power amps, and I'm just considering where I could have the holes made for input and output connecters (IEC next to/as far as possible from XLRs -- WAF vs. noise risk).

I guess shielded XLRs should do the job properly. And I'd probably keep the IEC 2-3" from the inputs. Right?

 

[Vladimir]

All electronics should be kept inside a Faraday cage (metal case or a shield jacket connected to ground). That solves every potential problem with interference. With proper shielding you have no worries how close or appart your components and cables are. Without measuring it's unpredictable how much twisting two cables together will solve things due to inconsistencies like andyjm mentioned. Shielding solves everything perfectly 100%.

For DIY shielding you can use steel weaves from bathroom pipes or shower heads soldered to ground and the audio signal cable passing inside. You can cover that with a techflex jacket and call it a hi-end cable.

 

[Anderson]

Did somebody just mention cable?

There literally no difference between adequately constructed cables, can we please not then this into a cable debate. Also any points made to the contrary well be dismissed with prejudice! *diablo*

 

[steve_1979]

Did somebody just mention cable?

Really? You ask THIS question.

 

[Anderson]

Did somebody just mention cable?

Really? You ask THIS question.

Ffffffffff me. I thought I was replying to the new Codi marketing research thread. Oopsie. My point still stands.

 

[steve_1979]

Did somebody just mention cable?

Really? You ask THIS question.

Ffffffffff me. I thought I was replying to the new Codi marketing research thread. Oopsie. My point still stands.

We could do with a few more cable threads on hear. It's been a bit quiet of late.

 

[Anderson]

To be fair is funny the topic doesn't come up more often.

 

[DocG]

All electronics should be kept inside a Faraday cage (metal case or a shield jacket connected to ground). That solves every potential problem with interference. With proper shielding you have no worries how close or appart your components and cables are. Without measuring it's unpredictable how much twisting two cables together will solve things due to inconsistencies like andyjm mentioned. Shielding solves everything perfectly 100%.

For DIY shielding you can use steel weaves from bathroom pipes or shower heads soldered to ground and the audio signal cable passing inside. You can cover that with a techflex jacket and call it a hi-end cable.

Thanks, Vlad. That makes sense. I suppose I can get me some shielded cable in a pro-shop (not sure my wife will like the bathroom-in-living-room impression).

I have another - probably rather daft - question. Can you shield the power leads too? Or is that something for ICs and SC?

 

[andyjm]

All electronics should be kept inside a Faraday cage (metal case or a shield jacket connected to ground). That solves every potential problem with interference. With proper shielding you have no worries how close or appart your components and cables are. Without measuring it's unpredictable how much twisting two cables together will solve things due to inconsistencies like andyjm mentioned. Shielding solves everything perfectly 100%.

For DIY shielding you can use steel weaves from bathroom pipes or shower heads soldered to ground and the audio signal cable passing inside. You can cover that with a techflex jacket and call it a hi-end cable.

Thanks, Vlad. That makes sense. I suppose I can get me some shielded cable in a pro-shop (not sure my wife will like the bathroom-in-living-room impression).

I have another - probably rather daft - question. Can you shield the power leads too? Or is that something for ICs and SC?

The cable used for balanced interconnects, be it two core or 'starquad' comes with an overall shield. No need to strip the shower out of the bathroom yet.

Just a FWIW - for Vlad's Faraday cage to work completely, the cable needs to be shielded from both the electro and the magnetic part of an electromagnetic wave. Non ferrous metal (copper) won't help with the magnetic portion - hence I guess Vlad's reference to steel weaves.

I wouldn't bother worrying though. Give it a try with normal '2 conductor plus shield' balanced cable, if that hums try starquad, if that hums separate the mains lead from the signal lead. Simples.

A good place to buy balanced cable complete with connectors is a pro audio shop. Aim for mic cable as it will built to a good standard. Musicians don't stand for any of this magic cable nonsense and the prices may astound you. A quick search found a Van Damme starquad 5M mic cable with gold plated Neutrik connectors for £18 on Amazon. I am sure if you went direct to a pro supplier on the web you could get better prices than this.

 

[DocG]

OK, I was already considering some high-end Vola or Dornbracht shower hose

but maybe shielded Van Damme, Mogami or Canare leads are better VFM indeed!

Any added benefit if I buy shielded mains cables too?