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Discussion Starter #1
I am in the process of making a batch of RCA/RCA line level audio interconnects. These will be used to connect hi-fi components.

I have looked over the web and need some advice. What is the best cable to used for audio interconnects? I have so far found 3 options, and will list what I have found for them.

- 2 or 4 conductor mic cable
This allows one conductor for signal, one for ground and the shield can be disconnected at one end of cable, to allow low noise and hum.


- Coaxial
This has very high shielding against noise and very low capacitance, but there is a debate on Characteristic impedance matching, being 75ohms and not 50ohms. By the way, I have found discussion that RCA connectors are not 50ohms.


- Standard screened single conductor cable
This seems to be the standard configuration. Single cable to signal and shield to ground on plug.


I have a longish run of 30ft, so I am keen to avoid noise. I am also loathed to spend big bucks on shorter interconnects, when I have a soldering iron.

Any advice on the best type of cable would be helpful and appreciated.
 

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Elite Shackster , HTS Moderator Emeritus
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For a long run, I would only use shielded coax cable. It has fantastic noise rejection and low loss. Plus, IMO it's easier to do than soldering those tiny RCA connectors.

For brands, I like Canare, but Belden and Carol are widely used and recommended. Just make sure the ends you use are rated for the cable. Usually the cable is RG59, RG6, or RG6 Quad shield. Some of the quad shield stuff won't work with connectors, and 59 is completely different than RG6. The ends are usually well marked as to what size works with them.

Good luck
 

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Any advice on the best type of cable would be helpful and appreciated.
Really, any well-made cable with a good shield will work fine. And yes, most RCAs are 25-ohm connectors, so there's no reason to get bent out of shape about impedance for audio signals.

Check out my DIY soldering guide (link in my signature) for recommendations on cable and RCA connectors.

Regards,
Wayne
 

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Discussion Starter #4
Great, thanks guys.

It seems that coaxial is the recommendation. The only thing I was left wondering was if mic cable would be less better at shielding, but less problematic with potential ground loops, as the shield can be disconnected at the terminating RCA plug.

I'll also check out the coaxial cables suggested.
 

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Elite Shackster , HTS Moderator Emeritus
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Hmm, I just tried to find the old site I used for a reference.

It was by Chris White and had a great instruction set (and listed all you needed to buy) on making cables using the Canare wire and RCA ends. It's not at his homepage site or at the now defunct HomeTheaterTalk.

If anyone knows where this page moved, please post it. It was a good reference (but not as good as Wayne's soldering tutorial :) )
 

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Discussion Starter #6
I have read for hours on Characteristic impedance, to find out that it isn't relevant for an audio connect - I am not producing a transmission line with matched impedance of 75ohms.

I am still unsure about the winner of mic vs Coax able. Coax is wins on the sheilding, but mic cable allows return cable and shield to be separated (I am assuming that the shield will be unterminated on destination RCA). Coax is normally double or triple shielded, where mic cable is 95%+ copper braid shield and this is still quite good.

Which is the bigger benefit, highest shielding on coax or separate ground return and shield on mic cable.
 

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Discussion Starter #8
Common sense always prevails in the end. You are most probably right, as long as it has low capacitance and good shielding, it is just an efficient piece of wire at the end of the day.

Ground loops won't be an issue on short runs, so I'll go for coax for some shorter cables, and take it from there.

It was a pig of a job to get my head around characteristic impedance. It shows how far we have come, as a few hours on the web would have been a whole day down the library years back.

Thanks guys for your wise heads.
 

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I am not producing a transmission line with matched impedance of 75ohms.
An audio interface is a high impedance circuit. You don't need to be concerned with the characteristic impedance of the cable or connectors.
Indeed, both the digital and video interfaces in your systems are fairly close to 75 ohms and require cable impedance matching because of the possibility of reflections, but not the audio interfaces.

There is just no possible transmission line theory that would support any type of reflection on a piece of coaxial cable at audio frequencies in any length less than many, many kilometers. In fact the characteristic impedance of a piece of coax is only valid at high frequencies - audio doesn't qualify.

At audio frequencies the wavelength is very long. So, for example, as far as standing waves on a 1 meter piece of coax, when we're dealing with a 10 kilometer wavelength, well, the 1 meter portion appears as DC. No reflections possible.

The audio interface is a low level, high impedance connection where almost no current is drawn and we want to present a relatively low voltage to the amplifier input with as low a noise floor as possible. The preamp acts as a voltage source. The main concern is noise and to a lesser degree cable capacitance. A properly shielded cable is important. Wouldn't matter if it was 50 ohms or 200 ohms characteristic impedance. So don't get concerned.

I was left wondering was if mic cable would be less better at shielding, but less problematic with potential ground loops, as the shield can be disconnected at the terminating RCA plug..
How would the mic cable be less problematic with less ground loops or noise? The single ended circuit still has the signal and the ground connected at both ends to complete the signal path. The shield is still connected at one end to that signal ground.

Ground loops won't be an issue on short runs
Ground loops can be generated on any length run.

brucek
 

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Discussion Starter #10
How would the mic cable be less problematic with less ground loops or noise? The single ended circuit still has the signal and the ground connected at both ends to complete the signal path. The shield is still connected at one end to that signal ground.


brucek
The reason I was wondering about mic cable was because I wondered if there was an advantage to keeping the noise currents on a piece of wire separate to the ground 0v wire. I always wondered, and recently saw an unbalanced cable by Monster which had separate signal, ground and one ended shield. This prompted me to seek advice from the forum.

I do recognise that the Monster cable may be a load of marketing tosh, with no foundation in science, but I wanted to check.
 

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I wondered if there was an advantage to keeping the noise currents on a piece of wire separate to the ground
But it's not separate to the ground, is it? It's attached at one end. So, it's still connected. How could this make a difference? :)

brucek
 

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But it's not separate to the ground, is it? It's attached at one end. So, it's still connected. How could this make a difference? :)
Well, supposedly it’s the twisted conductors that makes a difference. Maybe you’ve seen DIY cables like this, that the tweaky audiophile-types are fond of:




In lieu of a shield, the twisted conductors are supposed to accomplish the noise rejection, due to the signal (+) and (-) continually flopping 180˚. The two conductors in mic cable are twisted, so theoretically you should have improved noise rejection over single conductor shielded cable, if you configure it so that the signal (+) and (-) is traveling on the two conductors. This is accomplished by lifting the shield on one end, or not connecting it at all.

So the theory goes. Sounds wonky for sure, but there must be something to it or those cables pictured above would buzz like the dickens. Personally, I wouldn’t use any cable without a good shield. The main reason I like mic cable is that you can tie the two center conductors together and have a more robust cable – i.e., if one of them breaks the other retains continuity and you still have a functioning cable.

Regards,
Wayne
 

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Hmm, I just tried to find the old site I used for a reference.

It was by Chris White and had a great instruction set (and listed all you needed to buy) on making cables using the Canare wire and RCA ends. It's not at his homepage site or at the now defunct HomeTheaterTalk.

If anyone knows where this page moved, please post it. It was a good reference (but not as good as Wayne's soldering tutorial :) )
Is this what you were looking for?

http://web.archive.org/web/20080131074852/http://white.hometheatertalk.com/diycable.htm
 

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Elite Shackster , HTS Moderator Emeritus
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Ah yes, that was it. We should contact Chris White and see if we can republish (or if I get ambitious write one up myself). It would be a good "crimp" primer to go with the soldering tutorial.

As for shielding, that's the primary reason I like coax -- good shield and no screw ups in assembly. I can do the soldering, but in the field, you want to just strip, crimp, and go.

That being said, I had a customer once who wanted a very slim cable to run to his subwoofer that couldn't be in-wall and had to run along the base of the stairs and a door frame (exterior with one of those wood threshold strips). I ended up making him a wire with Canare 4 conductor mic cable. It's not twisted directly but keeps the wires around a + in the middle. That and it has the tightest braided shielding you've ever seen. I had to use a dentist pick to comb out the strands one at a time. Soldered Neutrik RCA ends. Turned out great, just took a lot longer to make than the crimped coax.

summary: shield is my first priority, then I choose crimp over solder for convenience. (for video always use coax but that's another story).
 

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Discussion Starter #15
Thank you for taking the time out to find the link - it was very interesting. I didn't realise that the gentleman in the article was crimping, and funnily enough I was looking at Paladin crimping frames last night.

I think I'll stick to solder, as time isn't as critical for me, and I can use my existing equipment.

What are the grey boxes on the pics of cables Wayne posted?
 

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What are the grey boxes on the pics of cables Wayne posted?
Those are called Ferrite rings, and they basically are small magnets used to suppress high frequency noise in electronic circuits and can be found on PC monitor cables and other cables like USB as well.
 

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Discussion Starter #17
I have found an article which I am sure some, if not many, here may have read.

http://www.bluejeanscable.co.uk/articles/humrejection.htm

I don't know how objective Bluejeans are, but my gut feel says pretty objective, as they seem to scientifically explain how they think. As a novice, I sometimes have trouble filtering the hi-fi mumbo jumbo from valid arguments.

Bluejeans blind tested coax against mic cable. They seemed to imply that coax was good, and there was a clear lag in noise rejection of the unbalanced mic cable.

Coax it is then.
 

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Elite Shackster , HTS Moderator Emeritus
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For reference:
My cables are LV-77S for audio, digital, and some video. I use the V3-5CFB (3 cord bundle of L-5CFB) for component video.

The RAM electronics cables I just tested (review above in the sticky section) were Belden 1505F

I have no problems with noise pickup from my cables.

Great article. Blue Jeans Cable is a pretty straight shooter. They like science and simplicity over marketing.
 
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