# DIY RCA cables, mic cable or coax?



## DonutHands (Jan 27, 2006)

does it matter?


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## chad (Jun 30, 2005)

If you don't plan on going balanced...... COAX with the highest percentage shield you can find and still be workable.

Chad


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## Rudeboy (Oct 16, 2005)

And how about solder vs crimp or compression. I've used solder but am really curious about Canare and F-Conn. I like the idea of a single system that can produce a variety of configurations. Any input on the relative merits?


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## Jimmy D. (Sep 1, 2005)

> Not really. I use the canare star quad for most of my rcas and headphone cables, markertec.com (sp) has pretty good prices on supplies. Wirecare.com has all the techflex, heatshrink, etc you could ever need to dress up whatever you make. I picked up some eichmann bullet plugs with cardas cable just to try out some higher end stuff but I'll be suprised if I notice a difference.


Ditto that. The star quad makes very good ICs for car or home and the price is right. Also this cable is very flexible and easy to route. i would not use the Eichmann bullet rcas in a car though due to cost and care needed to solder. Get some rugged standard RCAs from Parts Express or other.

Jim


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## DonutHands (Jan 27, 2006)

originally i was going to use canare starquad and make 2 channel cables. but now as im sitting down and getting ready to start making some cables i find that the RCA ends i have are made to accept coax, not mic cable. really a bummer for me as i have to have twice as much cable routed around my trunk.

and im not buying different rca ends, i got these off ebay for super cheap.


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## chad (Jun 30, 2005)

You don't really need quad to do 2 channels, just standard balanced microphone cable.


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## DonutHands (Jan 27, 2006)

just use the 2 conductors, then the shield as the ground?

then what is this i hear about using a pair of the white and blue cables as signal and ground, then grounding the shield on one end of the cable for noise rejection


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## MiniVanMan (Jun 28, 2005)

internecine said:


> just use the 2 conductors, then the shield as the ground?
> 
> then what is this i hear about using a pair of the white and blue cables as signal and ground, then grounding the shield on one end of the cable for noise rejection


A good twisted pair cable will offer good noise rejection, on the signal side. I see no reason to ground another twisted pair. Star Quad is used for redundancy in live, and studio applications. It's designed for balanced applications where you ground the shield, then you connect + and -. I can't think of any benefit it gives you in a car environment, especially when running unbalanced. Another point against is the fact that it's got pretty high capacitance. 

If you're looking for an easy to terminate, relatively inexpensive per foot, low capacitance cable then look at this.

Here's a 100% shielded cable. It's very inexpensive. Capacitance is a good deal lower than Quad Star, and it's easier to work with. Not much in the way of bling, but it will do the job very well. 

http://www.gepco.com/products/proav_cable/analog_audio/singdual_22_M.htm

Here's a link to some pricing. Here you have to buy a minimum of $75.00, but it's better than your typical 1000' reels. Anyway, at $0.13 per foot, you get approximately 576 feet. Probably more than you need, but you can also sell some off. 

http://www.systemsstore.com/Merchan...ode=ss&Product_Code=61801&Category_Code=gepco


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## DonutHands (Jan 27, 2006)

does it matter if the coax cable has a foil shield in addition to the copper braid?


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## MiniVanMan (Jun 28, 2005)

It shouldn't. The foil shield should help in rejection before the stray rf even gets to the copper braid.


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## DonutHands (Jan 27, 2006)

well i think im going to pick up some cable without the foil shield. its got 95% coverage from the copper braid and a stranded core so its flexable.

thanks for your help on this one.


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## Thumper26 (Sep 23, 2005)

if you did want to use coax, you'd just heatshrink two pieces together if you needed a 2 channel run?


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## less (Nov 30, 2006)

Just built some using Star Quad and Viablue connectors. The price was right. They sound great. I have no issues with noise at all.

I suggest not connecting the shield to the ground at either end of the cable... just let it float. I've heard from very good sources who've done a lot of expirementation that connecting the shield for some reason seems to actually attract noise - sort of acting like an antenna. That is why I tried mine that way and they work great - silent.

I was interested in the Eichmann plugs but they seemed much better for home use, with the plastic being responsive to temperature changes. These Viablue plugs are similar and have some nice features. First, instead of having a brass core like 99% of rca's have, the made the core 81% copper ... the 99.999 oxegen free variety. Second, they have a nice locking mechanism. Third, they are very well made - high quality in every aspect. Fourth, the cost is $20.00 for 4 (av-outlet.com) which for a top quality RCA plugs is a good value. Lastly, i just like the way they look.

As far as capacitance goes, you really don't have to worry about the Canare cable until you get over 13 feet or so. Capacitance can effect the transmission of you highs. Even by the roughest standards I've read, the Canare star quad doesn't reach a high enough value to impact the high end until after that level.

Remember that cable manufacturers all use their own standards for measuring capacitance and all other electrical properties of their wires. I'd put my money on Canare having standards and measurements that are much more rigorous than Good ol' Joe's Cable Co. Personally, I'd rather use a cable manufacturer that has a quality name and is well known in the industry. Canare is still used in studios and on stage in demanding situations.

Just my 2 cents...

Less


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## chad (Jun 30, 2005)

less said:


> I suggest not connecting the shield to the ground at either end of the cable... just let it float. I've heard from very good sources who've done a lot of expirementation that connecting the shield for some reason seems to actually attract noise - sort of acting like an antenna. That is why I tried mine that way and they work great - silent.
> 
> Less



Not a good idea, if connect at least ONE end, that way it won't carry current but still acts as a screen. If it's properly bonded it cannot "attract noise."

Chad


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## Thumper26 (Sep 23, 2005)

so yeah, i'm looking for the smallest connectors i can find. part of the reason is b/c i plan on getting an audison 5.1k, and there doesn't look to be a lot of room to connect rca ends inside/under the amp...the amp has it where you mount everything underneath it for a clean install.

right now i have a crazy idea of using RG174 coax with some markertec ends b/c they'd be very small and very low profile, but Chad is helping me to see everything wrong with trying to do that as a first time DIY effort. We'll see what happens. I still have time before I get into all that.


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## chad (Jun 30, 2005)

Thumper26 said:


> so yeah, i'm looking for the smallest connectors i can find. part of the reason is b/c i plan on getting an audison 5.1k, and there doesn't look to be a lot of room to connect rca ends inside/under the amp...the amp has it where you mount everything underneath it for a clean install.
> 
> right now i have a crazy idea of using RG174 coax with some markertec ends b/c they'd be very small and very low profile, but Chad is helping me to see everything wrong with trying to do that as a first time DIY effort. We'll see what happens. I still have time before I get into all that.












You see that lack of hair?

RG174 is the root cause of that


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## Thumper26 (Sep 23, 2005)

lmao!

the whole 'meat grinder' comment got the point across as well.

do you know of any other stubby rca ends i could look at?


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## less (Nov 30, 2006)

chad said:


> Not a good idea, if connect at least ONE end, that way it won't carry current but still acts as a screen. If it's properly bonded it cannot "attract noise."
> 
> Chad


Silence is golden. If I get noise some day, I may give it a try.

Less


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## Daishi (Apr 18, 2006)

I've used Canare Star Squad 6mm OD cable now for 10 pairs of RCA's with great results. I actually use both white and both blue wires for one RCA, so I'm not sure how that affects the RLC compared to a double run. 

I have done exactly what chad has suggested which is connect the shield to one side of the cable...always going towards the source. That way any noise should be grounded previous to any amplification (at least I think so). 

1312-110 and 1312-109 are the RCA connectors I use. They're pretty tiny (which makes soldering a PITA) and they look decent. I found no point in spending gobs of money on more expensive connectors except so things looking prettier


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## thehatedguy (May 4, 2007)

Coax in the car is a bad idea and adding foil to it would make it even worse.


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## chad (Jun 30, 2005)

thehatedguy said:


> Coax in the car is a bad idea and adding foil to it would make it even worse.


Please elaborate.


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## thehatedguy (May 4, 2007)

The noise rejection in twisted pair come from the close proximity of conductors to each other, the physical twisting of the conductors with the alternating signal. Coax is like an antenna laying on the noisy chassis. There is no crossing of the conductors and thus no means of noise rejection, and adding foil to it is like making the antenna larger...thus more prone for injection of noise.


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## thehatedguy (May 4, 2007)

FWIW, Richard Clark went over this on Carsound years ago. And I had a few emails with John Risch, and he too suggested twisted pair over coax in the car. He didn't think the coax with shielding would be good in the car either.


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## chad (Jun 30, 2005)

thehatedguy said:


> The noise rejection in twisted pair come from the close proximity of conductors to each other, the physical twisting of the conductors with the alternating signal.




Works great with balanced, not as effective with unbalanced. With unbalanced the cold (ground) is merely acting as an ineffective shield.



thehatedguy said:


> Coax is like an antenna laying on the noisy chassis. There is no crossing of the conductors and thus no means of noise rejection, and adding foil to it is like making the antenna larger...thus more prone for injection of noise.


No sir, the foil/braid is tied to earth in a proper install, NOW IF it were not tied to earth to act as a screen, I could not agree with you more. Please note that your CATV coax does not float the shield  If it did you wold have a royal mess, the same thing would happen as you explained, tons of IM distortion due to the shield acting as a receiving antenna VSWR would also be thru the roof due to the shield actually resonating. when screened properly by bonding the foil helps by increasing the percentage of signal carrying conductor coverage.

Remember true twisted pair was popularized in telco which runs very much balanced, the key to it's success. In an unbalanced situation it's just two twisted wires with one carrying signal. Balanced, i have run signal MILES with no shield at all, a small impedance mis-match on one of the runs in the pair and you will quickly see what it's all about.

Chad


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## Abmolech (Nov 2, 2006)

The twisted pair cables have no "noise rejection" capabilities (Lets be honest we are discussing noise attenuation).

Coaxial cable have noise attenuation built in. They do this by a combination of manufactured design features.

Keeping the "hot signal" proximity a suitable distance to reduce Bl. (EMI)
Shielding to ground to provide RF noise attenuation.

For twisted pair cables to attenuate noise they require a CMRR circuit. Without this circuit (balanced) the cannot differentiate between induced and signal line voltage.

I challenge you to replace the coaxial cable for your antenna with a twisted pair.


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## chad (Jun 30, 2005)

thehatedguy said:


> FWIW, Richard Clark went over this on Carsound years ago. And I had a few emails with John Risch, and he too suggested twisted pair over coax in the car. He didn't think the coax with shielding would be good in the car either.


Car Schmar, what's the difference between a car, under a transmitting tower, next to a PD, whatever? Because it rolls does it somehow obtain some magical electrical properties?

I CANNOT BELIEVE that these folks don't know how shielding works, I mean hell, the name gives it away!

Chad


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## thehatedguy (May 4, 2007)

Sounds like the Eddy Runner stuff going on over here.


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## chad (Jun 30, 2005)

Although I don't agree with eddy on many things, well that's an understatement. He ain't an idiot about RF rejection, noise rejection, and shielding.


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## Abmolech (Nov 2, 2006)

You note they won't take the challenge.
 

Maybe car manufactures know a thing or to about noise attenuation for interconnects. I am sure the cheap effective coaxial cable can be replaced with twisted pair, cause they are superior in a DC environment. (Where do they dredge this nonsense up from? )

Please TAKE the challenge.

Pretty please..

I am begging you..

Yeah didn't think so.


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## bdubs767 (Apr 4, 2006)

Abmolech said:


> You note they won't take the challenge.
> 
> 
> Maybe car manufactures know a thing or to about noise attenuation for interconnects. I am sure the cheap effective coaxial cable can be replaced with twisted pair, cause they are superior in a DC environment. (Where do they dredge this nonsense up from? )
> ...


What challenge do you speak of? And who is eddy runner?


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## Abmolech (Nov 2, 2006)

Replace the coaxial cable interconnect from your head deck to your antenna with twisted pair.

Your cable goes through the "noise capital" of a car (the dash) and often in close proximity to a large RF inducer (petrol pump). It has to transfer MHz unmolested to your radio. So transferring kHz to a power amplifier should be like "falling of a log".

The challenge is to therefore
*replace this antenna cable with "superior" twisted pair*. 


So far no one has accepted the challenge, cause we all know that twisted pair are not "up for it".

Still with enough goading some of these people might get "owned" (whatever that means )

Of cause they could be open minded and ponder reality. 
This would be a MUCH better outcome.
Please cease and desist from suggesting twisted pair are inherently superior to coaxial. Sure if we use a CMRR circuit they have the ability to attenuate noise to a greater degree. (balanced line)


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## Rudeboy (Oct 16, 2005)

bdubs767 said:


> What challenge do you speak of? And who is eddy runner?


Eddie Runner


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## Abmolech (Nov 2, 2006)

Damn, a proper test? 

I thought mine was a little easier.


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## Rudeboy (Oct 16, 2005)

Abmolech said:


> Damn, a proper test?
> 
> I thought mine was a little easier.


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## chad (Jun 30, 2005)

It's just silly to assume that the same "technology" that is used to keep the "nasty" in a cable will not keep the "nasty" out of a cable. 

Car audio is the only facet of the audio industry that embraces this, no shielding, un-believable! I think these people see something somewhere, remotely correlate it to their situation, and then go to bed and have a dream. It's a mis-understanding on how things work, and the assumption that all interconnect structures work the same.

As of now, unless things suddenly changed while I was in my slumber, the industry standard for professional interconnect is balanced, twisted pair, WITH a shield. Or unbalanced WITH a shield. When all of my peers suddenly begin ripping the shield off of their interconnect cables I MAY change my tune but as it stands now I have yet to find a studio, stage, or anything else outside the car audio world that runs UTP with the exception of data and telco, and that's balanced, and sometimes shielded (the phone line coming into my home IS shielded  We also use shielded Cat 6 coming from Digital snakes ) If I have a sudden weird noise that I believe is cable related the first thing I do is A. Check the shileding B. find the noise source that it is VERY close to. 9 Times out of 10 I find a problem with A, and in the Civic I'll be damned if I found a problem with B.

This forum is comprised of folks that have been around the block, many that have first hand experience with RF transmission, which inherently means that they have experience with RF rejection if they have been doing it for more than 24 hours. RC built a fine sounding car, no doubt, but often times I question his claims for the use of obscure product in obscure applications and the assumption that it must work in all applications because he thinks it may. There is no substitute for cold hard facts when giving a rebuttal for such claims of superiority of a product or theory that is plainly out of place in it's application.

Chad


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## Guest (Oct 24, 2007)

maybe it's worth reviewing what a coax _shield_ is all about, and then its limitations in single-ended transmission in a car (or likewise noisy) environment will become more obvious  By the way ... read Ott  

Absent the shield, we've got a single conductor, naked to two types of noise :

1. Electrical interference. The model here is _capacitive_ coupling, from a noisy _voltage_ source into our precious conductor. It's actually a _noise current_, given by i=C*dV/dt, where C is the capcitance and V is the noise voltage in proximity to the conductor. Placing a coax shield around the conductor gives a shunt path to ground for this noisy current, effectively shielding the conductor  In this case, you really only need to ground the shield at _one_ end ... just make sure you have a low impedance to ground for the shield. Unfortunately, this tends to often be the lesser problem, compared to ...

2. Magnetic interference. The model here is _inductive_ coupling, from a noisy _current_ flowing nearby the conductor. That current flowing nearby will create a _noise voltage_ in our conductor, induced by V=M*di/dt, where M is the mutual inductance and i is the noisy current flowing somewhere in the vicinity of our conductor. Placing a coax shield around the conductor can actually provide a shield against this magnetic interference as well (even though it's not necessarily magnetic material) ... it works by allowing an induced voltage to occur in the shield, causing an induced current to flow in the shield as well. This induced shield current will create a magnetic field that actually tends to _cancel_ the primary noise field  For this technique to work, the shield needs to be grounded at both ends, in order for the "secondary" current to flow in the shield.

Sounds clever, and indeed it all is, but there are problems :

- a shield grounded at one end can also become an antenna, for noisy wavelengths less than the shield length. This is no longer a simple lumped-element model, and you can easily get noisy current flowing through the shield in a noisy environment 

- a shield grounded at both ends can cause a _nasty_ conductive (rather than induced) current to flow in the shield, by virtue of a different ground potential at each end of the cable/shield. This is particularly true in a car audio environment, where the ground at the trunk is often noisy compared to the ground at the dash.

Armed with this info, what's the best approach? Best advice i know is :

- If at all possible, use purely balanced transmission for analog singals. There is no debate here ... twisted pair is your best friend. Each conductor has the same impedance to ground (that's what really defines balanced, by the way), and each conductor will experience the same noise ... rendering the noise to be common mode, which will be cancelled (or greatly attenuated) at the receiving end. A shield on the twisted pair may help, but is not necessary in most cases ... and you may benefit by experimenting with grounding the shield at one end or both.

- If you are stuck with single-ended transmission, the best cable _may_ still depend on your equipment. Does the amp in the trunk try to ground the RCA shield through a low impedance, or does the amp offer some differential "noise cancelling" on the RCA inputs? If you've got some degree of differential noise cancelling on the amp inputs, you may find that UTP (unshielded twisted pair) works best. If not, a coax may be your best bet, but _where_ the amp is grounded compared to the source at the dash will certainly have a strong impact on noise performance in this case.

- When all else fails, use a Jensen Transformer  In fact, it's simply not a bad idea to incorporate these in any case where you have single-ended audio transmission. There's no performance penality ... these can only help. The only downside is cost 

Oh yeah ... read Ott


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## chad (Jun 30, 2005)

werewolf said:


> maybe it's worth reviewing what a coax _shield_ is all about, and then its limitations in single-ended transmission in a car (or likewise noisy) environment will become more obvious  By the way ... read Ott
> 
> Absent the shield, we've got a single conductor, naked to two types of noise :
> 
> ...


Whitlock just wrote an EXCELLENT article in Live Sound regarding RFI rejection. I would prove excellent here in the tutorial section. I need to find it in electronic format and get the proper citations.

As for a differential input on amps, I just can't find them, AC was good about having the option on their processors, I have one and it WORKS! But getting the impedance matched betweent he hot and shield of an amplifier input seems to be at the bottom of most designer's totem-pole.

This winter I plan to impedance balance the outputs of my head unit to further take advantage of the differential input of the AC Matrix. I will certainly post results and how-to 

Chad

*edit* 

As for the grounding one end approach, yes, at less than one wavelength it can get noise currents, This is dependedent on the wavelenghth of the noise and if it is resonant to the cable length, if this becomes an issue often times a 50 cent ferrite or even a loop or two in the cable can do wonders. Not ALL frequencies under the wavelength of the length of the shiled cause issues. It's basically an end shunted antenna, which incedentally ARE resonant to a large degree.


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## Guest (Oct 24, 2007)

chad said:


> Whitlock just wrote an EXCELLENT article in Live Sound regarding RFI rejection. I would prove excellent here in the tutorial section. I need to find it in electronic format and get the proper citations.
> 
> As for a differential input on amps, I just can't find them, AC was good about having the option on their processors, I have one and it WORKS! But getting the impedance matched betweent he hot and shield of an amplifier input seems to be at the bottom of most designer's totem-pole.
> 
> ...


nice 

Allow me to add something, just a statement in defense of Richard Clark (RC). He's done way more for the car audio community than build a good-sounding car ... in fact, there's an endless debate over how much of that car he himself actually built  His real contribution to the hobby/sport, in my view, is the AutoSound Tech Briefs and lectures he gave with Navone during the 90's. He really did a LOT to help educate consumers and installers about car audio. And while i don't always agree with his conclusions in all cases, he typically employs a sound scientific method, coupling theory with practise.

On another note ... i like the idea of balancing the impedance output of a source unit  I wonder how many people realize that all you need is a resistor to achieve pure balanced transmission in car audio?  Of course, the receiver must have excellent CMRR as well. By the way, every latest generation amplifier in my beloved McIntosh line has a true, honest-to-goodness differential-to-single-ended converter as the very _first_ circuit on the RCA inputs  Well, every one except the 406M  Yeah ... i not only like McIntosh because they actually have things called _schematics_ for their products (many so-called amp designers don't have them ... cuz they don't know what they are ... cuz they tend to think "design" means "copy a PCB off-shore" ... but i digress), but also because they understand good electrical engineering 

Finally ... read Ott's book, and every damn application note and paper read by the dudes at Jensen Transformers to learn more than you ever wanted about noise ... sources, coupling, rejection, circuit techniques, etc.


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