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ericcoleridge
Joined: Jan 16, 2007
Posts: 889
Location: NYC
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 Posted: Mon Nov 19, 2007 4:39 pm Post subject:
Coax Cable for Audio Jack connections?
Subject description: Do most people here recommend using Coax for audio? |
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I have been reading, I think in user guides from Oakley and SynthTech, that coaxial cable is recommended for all audio jacks? Just wondering if people here have practical experience on this subject?
I thought I'd try it out, but I'm not even entirely sure what the grounding in the coax gets soldered to? it gets soldered to ground on one side, but not the other? |
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blue hell
Site Admin
Joined: Apr 03, 2004
Posts: 24423
Location: The Netherlands, Enschede
Audio files: 297
G2 patch files: 320
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| Posted: Mon Nov 19, 2007 4:46 pm Post subject:
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Coax is a bit of a big word for shielded cable, but yes it is coaxially built indeed.
For normal audio connections you have to use shielded cable to avoid pickup of hum and radio signals. Usually the shield is connected to the earth terminal of the plug on both ends of the cable.
Is this for use as patch cables for a synth?
_________________
Jan
also .. could someone please turn down the thermostat a bit.
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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Posted: Tue Nov 20, 2007 10:44 am Post subject:
Re: Coax Cable for Audio Jack connections?
Subject description: Do most people here recommend using Coax for audio? |
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| ericcoleridge wrote: | | ... in user guides from Oakley and SynthTech, that coaxial cable is recommended |
I've built some MOTM-kits and couldn't resist laughing.
Of course, input cables from the jacks are coaxial.
You think "shielded - oh thats good". 
But the next moment you connect the input attenuating pot - just from the point where the shielded cable bumps into the pcb, the wires for the pots go away from the pcb. And these are unshielded. 
You know ? The same signal coming from the jack leads shielded to the pcb and from there to the pot - unshielded.
That's a joke.
But looks very professional.
To be serious:
In a module, where a few audio connections wired to jacks over a short distance, you don't need shielded cable. The levels of the signals are usually high and you don't have to expect disturbing influences.
But -
Say you built a mixer module with many audio connections, perhaps lying parallel to each other - shielded cable may be a good thing.
I've built such a mixer at first without shielded wiring.
I've got very little crosstalk between the channels. Not that much, but it bothers me.
I switched to shielded cables (coax, RG174 - it's the best) and there was silence on all channels.
Another example:
I have internal wiring in my cabinet, it's a really big one, the wiring goes over a long distance in parallel (it's a multiple system over several rows).
I also have done it at first with unshielded cables.
What a mess !! Absolutely unusable.
It took two days to remove it and replace the whole system with coax.
Now it's perfect.
You don't need to connect both ends of the shielding to ground except you have to ground both sides ( connecting a jack which is isolated mounted at the faceplate for example).
For the effect of shielding its sufficient to connect one end to ground.
cheers,
Bernd |
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ericcoleridge
Joined: Jan 16, 2007
Posts: 889
Location: NYC
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Posted: Tue Nov 20, 2007 4:20 pm Post subject:
Re: Coax Cable for Audio Jack connections?
Subject description: Do most people here recommend using Coax for audio? |
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| Serenadi wrote: |
Say you built a mixer module with many audio connections, perhaps lying parallel to each other - shielded cable may be a good thing.
I've built such a mixer at first without shielded wiring.
I've got very little crosstalk between the channels. Not that much, but it bothers me.
I switched to shielded cables (coax, RG174 - it's the best) and there was silence on all channels.
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Thanks Serenadi,
This sounds like a pretty convincing argument to use coax wiring (where it's appropriate).
Obviously, anyone can do whatever they want, right?, but I'm wondering if I should anticipate owning a pretty noisy cross-talky instrument if I don't use coax.
However:
| Serenadi wrote: |
You don't need to connect both ends of the shielding to ground except you have to ground both sides ( connecting a jack which is isolated mounted at the faceplate for example).
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Not sure I understand everything you wrote.
both sides but not both ends? |
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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Posted: Tue Nov 20, 2007 9:25 pm Post subject:
Re: Coax Cable for Audio Jack connections?
Subject description: Do most people here recommend using Coax for audio? |
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| ericcoleridge wrote: | | ...but I'm wondering if I should anticipate owning a pretty noisy cross-talky instrument if I don't use coax. |
Thats right.
Look at this one
http://www.serenadi.de/Modular/Modules/PAN/PAN2164-Back.jpg
Every audio connection is done by shielded cable.
But it is much more work and requires some carefulness.
Some people hurry to finish a module.
| ericcoleridge wrote: | Not sure I understand everything you wrote.
both sides but not both ends? |
Basically, every (asymmetric) audio connection needs two wires - the signal and the ground.
But if one end (e.g. the jack) is already grounded, you don't need the additional ground-connection thru the shielding at it.
In the above picture you see that the jacks are all mounted at the conducting faceplate and grounded thru separate silver wire.
So, actually you only need the *hot wire* from the pcb to the jack for the signal.
But for the effect of shielding a wire, it is necessary to connect the shielding to ground. This can be done on one side. |
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etaoin
Joined: Jun 30, 2005
Posts: 761
Location: Utrecht, NL
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Posted: Wed Nov 21, 2007 1:39 am Post subject:
Re: Coax Cable for Audio Jack connections?
Subject description: Do most people here recommend using Coax for audio? |
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| Quote: |
Every audio connection is done by shielded cable.
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Yes, but they connect to cheap unshielded plastic jacks and unprotected PCB traces, so it's almost the same "joke" as you mentioned above.
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http://www.casia.org/modular/ |
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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| Posted: Wed Nov 21, 2007 9:29 am Post subject:
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That's not the point.
1st - the jacks weren't as cheap
2nd - the pcb traces are *protected* in the way, that there are ground traces between the signal traces and the whole pcb is mounted on an alu plate which is grounded.
3rd - The point is that most of these wires are pretty close to each other, so crosstalk *may* occur.
As I also mentioned, with a mixer module I had some crosstalk using unshielded wires.
This is my Output-module with two PANs and a little mixer, very noiseless because of high quality OP-Amps and VCAs, so I didn't want to foul up this quality with *cheap* ( ) wiring. And let me say - the effort had been worthwhile. |
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Danno Gee Ray
Joined: Sep 25, 2005
Posts: 1351
Location: Telford, PA USA
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| Posted: Wed Nov 21, 2007 9:44 am Post subject:
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| I must say it looks extremely professional. |
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etaoin
Joined: Jun 30, 2005
Posts: 761
Location: Utrecht, NL
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| Posted: Wed Nov 21, 2007 10:49 am Post subject:
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| Quote: |
so I didn't want to foul up this quality with *cheap* ( Wink ) wiring.
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Okay, but why didn't you use shielded jacks then? I'm not saying it's wrong, I'm just curious why you go to such lengths and then use open, unshielded jacks and not shielded ones like these from switchcraft:
http://www.switchcraft.com/products/jack-102a.html
I can't criticize the perfection you are trying to achieve. My own modules are cheap in everything
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ericcoleridge
Joined: Jan 16, 2007
Posts: 889
Location: NYC
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| Posted: Wed Nov 21, 2007 10:57 am Post subject:
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Yeah, that's a beautiful wiring job, so neat and clean.
I'm aspiring to this level of professionalism-- but one problem I find on many commercially available boards I've assembled (especially EFM), is a complete lack of available points to tap a ground signal from. I often find no other option other than to tap into PCB traces-- which leaves me with messy wires soldered to various traces on the bottom of the PCB.
Is there a better, cleaner way to go about this? |
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Serenadi
Joined: Jul 03, 2007
Posts: 89
Location: Germany
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| Posted: Wed Nov 21, 2007 12:40 pm Post subject:
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Thanks to all for the comments.
The reason for this *perfection* is, that I like doing it that way.
I've built a Formant many years ago and I remember that I've lost the enthusiasm with it over the years, because of bad building quality.
Too many failures and functional disease.
Today I go the other way and want to create a really high quality instrument.
Maybe the claim is sometimes oversized.
@Etaoin
I don't think some millimeters of non-shielding in a jack have any influence. This is not high-frequency and low level stuff.
In fact, since I got this output-module (and of course the similar VCAs) my Modular is the most noiseless instrument in my setup.
@ericcoleridge
I see the problem with ground pads on many pcbs.
The best way would be drilling an additional hole nearby the power connector or nearby the point where the ground connection from the supply is connected to the pcb.
From there you can go directly to the components on the faceplate, where all pots and jacks are connected together that has to be grounded.
Use a thick wire for good grounding.
If you want to use shielded cable, the shielding can then be grounded at the faceplate-side, e.g. a jack or a pot. |
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