Unbalanced cable "directionality"... mismatched instructions?!?!
- Thread starter lgo51
- Start date
lgo51 said:So, with all things considered, with a particular focus on equipment commonly found these days... Which is best?
Well, just make up a set of cables with the shield connected to just one end and try them both ways and see if one or the other way sounds better to you and if so, whichever way that happens to be, go with that one.
Hahaha! Good one!
Of course you may also consider dispensing with a separate shield entirely. Twisted pair, twisted/braided quad geometries are largely self-shielding to begin with.
Personally I think separate shielding is rather overrated for most situation.
se
sound engineering
I think the same issue remains with briaded wires, only 2 of 3 carry signal information. Regardless of geometry, one is still functioning as a 'shield'.
Possibly I was not clear with my request. In the end, I'm sure we all select what pleases our ears most. But here, given two references from qualified sources, we find opposing recomendations, and hence a dilema. What I am seeking now is sound engineering, not engineering for sound.
Cheers,
LarryO
I think the same issue remains with briaded wires, only 2 of 3 carry signal information. Regardless of geometry, one is still functioning as a 'shield'.
Possibly I was not clear with my request. In the end, I'm sure we all select what pleases our ears most. But here, given two references from qualified sources, we find opposing recomendations, and hence a dilema. What I am seeking now is sound engineering, not engineering for sound.
Cheers,
LarryO
Re: sound engineering
I don't know what sort or braiding you had in mind, but for the braiding I have in mind, all of the wires carry signal information.
Ok. If the issue is shielding, then the cable shield should be an extension of the chassis shielding and connected at both ends.
se
lgo51 said:
I don't know what sort or braiding you had in mind, but for the braiding I have in mind, all of the wires carry signal information.
Ok. If the issue is shielding, then the cable shield should be an extension of the chassis shielding and connected at both ends.
se
Re: Re: sound engineering
3 wires braided together...
Signal+ to Signal+
Signal- to Signal-
N/C to Signal- (connector shield)
I think that the 3rd, 'shield', wire only carries induced EMf/RFI currents. If i understand correctly the idea is to use the common mode rejection capability of the Target to cancel the induced noise on both the high impedance 'shield' and the high impedance Signal+ lines. Yes? No?
Cheers,
LarryO
Steve Eddy said:
3 wires braided together...
Signal+ to Signal+
Signal- to Signal-
N/C to Signal- (connector shield)
I think that the 3rd, 'shield', wire only carries induced EMf/RFI currents. If i understand correctly the idea is to use the common mode rejection capability of the Target to cancel the induced noise on both the high impedance 'shield' and the high impedance Signal+ lines. Yes? No?
Cheers,
LarryO
Nelson Pass said:
Thank you, Nelson.
All balanced would be heaven, but i'm wrestling with many unbalanced interconnects and just trying to get the odds going in my favor - and have a 'system' to rely upon as things get shuffled around, as they always seem to do.
Now if i could only get all the manufacturers to float the signal connectors off chassis ground and keep the mains safety ground away from the signal path entirely... and maybe win the lottery while i'm at it
Highest regards,
LarryO
Re: Re: Re: sound engineering
Typically in a 3 wire braid (which I've always thought rather silly except perhaps for balanced lines) the thrid wire is doubled up with the ground lead.
I was speaking of twisted/braided quads.
Carries them to where? It's not going to carry any current if it's not connected to anything at the other end. Gotta have a closed loop to carry current.
Which idea? The three wire braid idea? If so, I don't know what the idea is behind it with regad to unbalanced lines.
se
lgo51 said:
Typically in a 3 wire braid (which I've always thought rather silly except perhaps for balanced lines) the thrid wire is doubled up with the ground lead.
I was speaking of twisted/braided quads.
Carries them to where? It's not going to carry any current if it's not connected to anything at the other end. Gotta have a closed loop to carry current.
Which idea? The three wire braid idea? If so, I don't know what the idea is behind it with regad to unbalanced lines.
se
Re: Re: Re: Re: sound engineering
A current will flow in a conductor that experiences an [electro]magnetic field. Consider your radio or TV antenna, no physical closed loop there but it does have currents determined by the wavelength(s) of the impinging EMF. They are induced in the conductor and flow to "ground". No different than what we're speaking about in regard to interconnect wires. The higher the impedance, the higher the voltage developed by the induced currents... that's the law.
Cheers,
LarryO
Steve Eddy said:
A current will flow in a conductor that experiences an [electro]magnetic field. Consider your radio or TV antenna, no physical closed loop there but it does have currents determined by the wavelength(s) of the impinging EMF. They are induced in the conductor and flow to "ground". No different than what we're speaking about in regard to interconnect wires. The higher the impedance, the higher the voltage developed by the induced currents... that's the law.
Cheers,
LarryO
Hi,
I think that interconnects should be connected to the ground at the power amplifier side. The power amplifier is where the biggest transformation of energy happens and where all kinds of noise are likely to be generated. For that reason, the output amplifier's audio ground must be connected to the chassis ground and mains ground/earth. Sources like CD, preamps, etc. should have the chassis ground normally connected to the mains ground/earth whereas the signal-audio ground should be connected only to the amplifier signal ground. This principle allows us to avoid ground loops thru mains power connectors and remove the current which is induced by the noise in the shield internally (amplifier parts) and externally (all sorts of EMIs ) via the shortest possible path.
However, the level of EMI is reasonably low in a home environment so shielding interconnects isn't a must.
In professional systems (long multicore cable run), the shield is rarely connected to both sides (for example, between two radio control rooms and a master control room, where I always prefer connecting the shield at the master control room side). The only exception are cables for condenser mikes, which carry phantom power to mikes.
Also, a distinction should be made between unbalanced (usually using chinch connectors) and balanced connections (XLRs).
In unbalanced connections, the cinch connector's ground always represents the audio-signal ground and must be connected on both sides (with the cable's shield or second hot wire) because the ground carries the audio signal.
In balanced connections, XLR's ground pin (1) may be connected to the chassis ground and signal ground or not connected at all because the audio signal doesn't flow thru this wire (in correctly designed systems).
Regards,
Milan
I think that interconnects should be connected to the ground at the power amplifier side. The power amplifier is where the biggest transformation of energy happens and where all kinds of noise are likely to be generated. For that reason, the output amplifier's audio ground must be connected to the chassis ground and mains ground/earth. Sources like CD, preamps, etc. should have the chassis ground normally connected to the mains ground/earth whereas the signal-audio ground should be connected only to the amplifier signal ground. This principle allows us to avoid ground loops thru mains power connectors and remove the current which is induced by the noise in the shield internally (amplifier parts) and externally (all sorts of EMIs ) via the shortest possible path.
However, the level of EMI is reasonably low in a home environment so shielding interconnects isn't a must.
Nelson Pass said:
In professional systems (long multicore cable run), the shield is rarely connected to both sides (for example, between two radio control rooms and a master control room, where I always prefer connecting the shield at the master control room side). The only exception are cables for condenser mikes, which carry phantom power to mikes.
Also, a distinction should be made between unbalanced (usually using chinch connectors) and balanced connections (XLRs).
In unbalanced connections, the cinch connector's ground always represents the audio-signal ground and must be connected on both sides (with the cable's shield or second hot wire) because the ground carries the audio signal.
In balanced connections, XLR's ground pin (1) may be connected to the chassis ground and signal ground or not connected at all because the audio signal doesn't flow thru this wire (in correctly designed systems).
Regards,
Milan
Re: Re: Re: Re: Re: sound engineering
Well yeah, you can cause eddy currents to flow within the conductor. But that's limited to the conductor itself.
There needn't be a physical, i.e. DC path, closed loop (though most AM radios do use a closed loop antenna). The loop may also be AC. Put a capacitor across the output of a component. There's no DC path closed loop, but there's certainly an AC loop there.
But it is different.
In the case of an antenna, half the antenna is connected to the circuit's input and then to the other half of the antenna through a load impedance, the other half of the antenna being tied to ground.
However in this case, we just have a wire that's open at one end and the other end terminates at the ground node.
Now according to Kirchhoff, the current flowing into that node must be the same as the current flowing out of it. So if you've got current flowing from the wire into the ground node, where is that current going in order for it to flow out of that node?
se
lgo51 said:
Well yeah, you can cause eddy currents to flow within the conductor. But that's limited to the conductor itself.
There needn't be a physical, i.e. DC path, closed loop (though most AM radios do use a closed loop antenna). The loop may also be AC. Put a capacitor across the output of a component. There's no DC path closed loop, but there's certainly an AC loop there.
But it is different.
In the case of an antenna, half the antenna is connected to the circuit's input and then to the other half of the antenna through a load impedance, the other half of the antenna being tied to ground.
However in this case, we just have a wire that's open at one end and the other end terminates at the ground node.
Now according to Kirchhoff, the current flowing into that node must be the same as the current flowing out of it. So if you've got current flowing from the wire into the ground node, where is that current going in order for it to flow out of that node?
se
Re: Re: Re: Re: Re: Re: sound engineering
To "ground", maybe through the input stage of the device, maybe elsewhere. Point is that that junction is not "ground", regardless of its common label, and since there is current flow through the junction that "noise" now gets into the frontend simply because the signal reference has now "moved" and the Vin "seen" by the frontend has deviated from that which the signal-only would have presented. That's the theory as I understand it. And I'm willing, nay happy, to be shown the folly of my thoughts. Seems difficult to believe that this all to common issue has not been modeled by better minds and a definitive engineering perspective established. Maybe someone could point us to such a treatise?
Cheers,
LarryO
Steve Eddy said:
To "ground", maybe through the input stage of the device, maybe elsewhere. Point is that that junction is not "ground", regardless of its common label, and since there is current flow through the junction that "noise" now gets into the frontend simply because the signal reference has now "moved" and the Vin "seen" by the frontend has deviated from that which the signal-only would have presented. That's the theory as I understand it. And I'm willing, nay happy, to be shown the folly of my thoughts. Seems difficult to believe that this all to common issue has not been modeled by better minds and a definitive engineering perspective established. Maybe someone could point us to such a treatise?
Cheers,
LarryO
Re: Re: Re: Re: Re: Re: Re: sound engineering
Um, it's tied to the ground node, not the input stage of the device.
If the ground node isn't ground, then what exactly do you consider ground to be?
How has the signal reference moved? Moved relative to what?
That's a good thing. I'm not exactly saying you're wrong. But before I say one way or the other I need to understand exactly what it is you're trying to say.
I think the reason for the different recommendations has to do with those making the recommendations considering things other than the role of shielding and are considering things such as ground loop and other interchassis curents which have rather nothing to do with shielding.
From a purely shielding perspective, it seems to me that the shield sound be an extension of the chassis and connected at both ends. However this can bring about its own problems as mentioned above.
se
lgo51 said:
Um, it's tied to the ground node, not the input stage of the device.
If the ground node isn't ground, then what exactly do you consider ground to be?
How has the signal reference moved? Moved relative to what?
That's a good thing. I'm not exactly saying you're wrong. But before I say one way or the other I need to understand exactly what it is you're trying to say.
I think the reason for the different recommendations has to do with those making the recommendations considering things other than the role of shielding and are considering things such as ground loop and other interchassis curents which have rather nothing to do with shielding.
From a purely shielding perspective, it seems to me that the shield sound be an extension of the chassis and connected at both ends. However this can bring about its own problems as mentioned above.
se
I am sure that these articles will help you. I find them very informative regarding ground woodoo. 
http://www.rane.com/note110.html
http://www.rane.com/note151.html
AR2
http://www.rane.com/note110.html
http://www.rane.com/note151.html
AR2
AR2 said:
Thanks AR2 for the pointers. Spent the better part of the [ahem... work]day bouncing down the hypertext link nexus from there. Learned many things, and read other interesting stuff. Here are some of the take aways...
Following up on the conversation with SteveE, the folks at Rane stated the issue with more clarity than i did....
The lesson was that there is inductance and resistance in all the conductors we typically think of as "good conductors". Here's a snippet that puts some dimensions to that notion...
Given these physical realities, how does one deal with them? Well that was an open question, especially in the pro-audio world, for many years. Over the years many 'common practice' approaches were adopted, most of with where based upon trial and error in any particular situation. And, as many attested, the results were often less than wonderfully effective.
What I discovered was that the fog surrounding this subject was effectively lifted by the work of many in the AES, such as Neil A. Muncy and Ralf Morrison. And shown to be effective by Tony Waldron and Keith Armstrong who performed some key experiments that fully supported the proposed techniques. The later was a great read, here's an excerpt...
From all of this I jotted down a list of guidelines...
1) Never connect a circuit's "signal ground" to the chassis.
2) Never connect the main's "earth" line to the circuit's "signal ground".
3) Always connect the mains "earth" line to the chassis.
4) If using a "Y Filter" on the mains lines ("hot", "neutral") for common mode noise supression, reference the legs to the mains "earth" line at the point it connects to the chassis, and mind rule (2).
5) All signal interconnects should be fully balanced. If this is not possible (legacy equipment, circuit constraints, etc.), then noise performance will be compromised.
6) The "shield" of an interconnect should be connected to the chassis at both ends of the cable. And, that connection is best if it completely envelops the cable/connector junction (so called 360 degree connection) without the use of "pigtails".
7) It is best if each chassis is additionally strapped to a ground reference point by a very low impedance (inductance + resistance) connector.
8) Internal shielding to segregate noisy/dirty circuits is a good idea.
9) Contrary to conventional thinking, a "meshed ground" is better than a "star ground". This is true whether doing circuit board layout or lightning protection systems.
AND, the following related notes were taken...
1) 2) Should one 'correct' legacy equipment?
3) There is a branch of equipment design, called "double insulated" that intentionally does not adhere to this practice and it would be a bad/unsafe idea to alter such designs without specific expertise.
4) These filters use special capacitors that always fail to an open-circuit condition so do not think "audiophile" for this application.
5) This is the big hitch in the getalong. There is a gaggle of legacy and, sad to say, current equipment that does not support this highly logical principle. There are a number of possible solutions that can be applied to this situation. Note 110 from Rane, cited above by AR2, has a nice discussion of this and a handy table. The issue of floating one end of the "shield" is delt with extensively. I could find no solid engineering to form a rule for which end (source or target) to bond the "shield" to and which end to 'float'. I can say that more often I noted that the shield was tied to the target (input circuit) end of the cable. There was much said about the effectiveness of using a small (1 - 100 nF) capacitor between the "shield" and the chassis/signal ground at the 'floating' end of the cable. This completes the circuit for RF frequencies and blocks the low frequency 'ground loop' currents. Seems like solid concept and often recommended, but a challenge to implement physically.
6) The "360 degree" vs. "pigtail" connection techniques have more significant affects above about 30 MHz so for audio gear (sans digital circuitry) this level of attention may have diminushed return.
7) Lots of talk about this, especally related to lightning safety and in situations where there is significant distance between component equipment and the chance of higher "ground potential" (remember, there's no real "ground") differences is greater. One highly interesting point was that copper foil ribbon (say 0.011 x 2.0") has lower impedance than a #6 copper wire, and is much easier to handle too (remember to avoid sharp bends). For good discussions on this topic see the ARRL and other HAM sites.
9) This was one of those ratholes that I spent some time reading on as it was so contrary to what I thought I knew. Bottom line is that it works, and for good reasons. Trouble is that I have not (yet) found a good reference on "how to mesh ground" for general circuit wiring/layout techniques. Star grounding on the other hand has been addressed many times and seems almost intuitive.
That's what I gleaned from my little oddesy into the world of grounding and shielding. Maybe some of the more learned here will correct the things I've misinterpreted or help answer some of the open questions.
Cheers,
LarryO
Reading material
Here are some articles I found to be informative...
Designing for Interference-free Audio System Components
Design Techniques for EMC cables and connectors
Bonding Cable Shields at Both Ends to Reduce Noise
A Practical Interference Free Audio System (Part 1)
A Practical Interference Free Audio System (Part 2)
Grounding and Shielding Audio Devices
Sound System Interconnection
LarryO
Here are some articles I found to be informative...
Designing for Interference-free Audio System Components
Design Techniques for EMC cables and connectors
Bonding Cable Shields at Both Ends to Reduce Noise
A Practical Interference Free Audio System (Part 1)
A Practical Interference Free Audio System (Part 2)
Grounding and Shielding Audio Devices
Sound System Interconnection
LarryO
Larry,
You may also like to look at this:
http://www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
(ADI AN-202).
Not strictly about cabling and screening, but defitively On Topic.
Jan Didden
You may also like to look at this:
http://www.analog.com/UploadedFiles/Application_Notes/135208865AN-202.pdf
(ADI AN-202).
Not strictly about cabling and screening, but defitively On Topic.
Jan Didden