NO !
as explained in post47
the coaxial cable is being used as a signal connection on both the core and the outer. Neither of these signal conductors gets tied into the enclosure.
The use of uppercase and exclamation points usually shows an argument defect.
Coaxial cable is used to connect signal on the core and signal reference on the outer which is ground.
In order not to have RF coming from the outer conductor going inside the amp, you must strongly connect the outer conductor to outside chassis.
If you don't want to have signal return connected to chassis, you have to use three conductors cable and three pins connector with the outer conductor connected to chassis.
Again, I would follow the views of Henry Ott and Ralph Morrison... A shield has to be connected at both ends for RF shielding, this is a fact gleaned from years of EMC engineering around the world, to avoid low frequency currents it can be connected by a capacitor or a ring of capacitors, but it still has to be connected at BOTH ends.
Some Henry Ott notes, I would recommend his views over say the Valve Guy...
http://www.hottconsultants.com/pdf_files/Audio Interconnections.pdf
http://www.hottconsultants.com/pdf_files/aes-2007.pdf
Foe unbalanced audio the shield has to be connnected at both ends for it to work as a shield...
Ground loops are created when two GND areas are at different potentials, play about with this all day every day, for the beginner there is no easy solution... there are numerous schemes that may or may not work, it depends on the topography of a given system. Having your designs and systems fully EMC tested will give you a practical guide to what works and what doesn't and after 30+ years of doing it you start to get an overview of what is going on...
To avoid ground loops always strive for a low impedance GND across the whole system, there are many ways of doing this...
Last edited:
Can you see that a coaxial cable used for a signal connection uses the outer and the core as signal conductors?
The outer is not an exclusive screen/shield. It is a signal conductor.
Here is H.Ott from the link provided by Marce:
I knew I did not make this up.
If this outer is not connected to the enclosure, then it does not conduct the noise current as described by H.Ott.
But when you do this
and make this extra connection to the ground/enclosure you are adding interference to the signal wire.
I see this as quite simple:
Keep the signal conductors separate from the enclosure. This applies to inputs and outputs and power.
Make each signal pair close coupled and preferably twisted or coaxial.
Last edited:
As far as I know, nobody said the contrary.
Then you don't need to use coaxial and its property.
And RF perturbations have an expressway to the device input. That's nice.
You have current only if boxes are not at same potential, if boxes are strongly interconnected it is not the case, the use of good coax cable is not forbidden.
There are no interference if boxes are at the same potential, which is the safest way.
Strongly connected boxes, connected ground connector to chassis, ground plane on pcb, multiple ground connections to the box is simpler and work at least as well.
If coaxial outer conductor is not connected to chassis, you have RF inside your device.
If you want to pick up an AC magnetic field with an electronic circuit then the usual options are a circuit loop (whether intentional or not) or a Hall effect device. If you believe that circuit loops don't pick up magnetic fields then there is no point in any further discussion with you and your experimental results can be ignored as they are based on faulty understanding. Please clarify.herve00fr said:
Depends on frequency. If you are trying to keep microwaves and high UHF (e.g. mobile phone signals) out of your amp then you may need the whole periphery to be grounded. If it is the local AM broadcast station then a cap may be sufficient.herve00fr said:
Much of the argument in this thread is about the conflicting requirements of audio with low hum and RF with low interference. Can people please recognise this? It might help the discussion.
Right. but "usual option" is not "the only way" and as far as I know Hall effect devices need a loop.
DF96, dear DF96,
1) Happy new year !
2) You are not allowed to make assumption on my belief or my understanding. Even if you are physics Nobel price, even if I am an idiot, unless I clearly wrote something which violates physics law, you are not allowed to make these assumptions. And even in this case, you have to clearly explain why I wrote something wrong.
Measurements I made are trivial : input of preamp is shorted, output is recorded, there are no place for misunderstanding.
Measurements results are facts, if you disagree, clearly tell why.
Results are not in violent contradiction with what I understand of physics law, if it not your case, you have to explain clearly why.
Clarify what ? I have not to clarify measurement results.
You repeat ad nauseum that magnetic fields should generate hum in the multiple points ground connection case. Tell me why.
In post 41 you said
This seemed to suggest that you believe that loops do not pick up magnetic fields, so in post 43 I askedherve00fr said:
Your replyDF96 said:
was still unclear so in post 66 I asked againherve00fr said:
Your replyDF96 said:
still leaves unclear your level of understanding of how magnetic fields interact with circuit loops, including ground loops created by multiple grounding. I don't know whether your failure to give a simple answer to a simple question is due to language difficulties, or technical difficulties, or plain awkwardness. You gave me the impression that you possibly did not understand a piece of basic physics relevant to this discussion, and you have been unable or unwilling to either confirm or deny this. So we still don't know whether you understand what is happening or not.herve00fr said:
Clarify your understanding of how AC magnetic fields interact with circuit loops, including ground loops introduced by multiple grounding of an audio circuit. I keep trying to avoid making assumptions about your level of knowledge, but you keep evading the issue.herve00fr said:
I am really sorry to give you this bad impression, but it seems to me that you invert the roles.
1) I invite you speak only on your name and not use "we", If other people do not agree with me, they are old enough to say it themselves, you are not the spokesman of the forum.
2) Once again, I made measurements, once again measurements results are not in violent contradiction with what I understand on the interactions between variable magnetic fields and loops. People have to explain why they agree with facts ?
You disagree with the measurements results. You disagree with facts.
You have to explain why, according to you, multiple connections to ground should have shown hum.
I agree with facts.
You disagree with.
You conclude I do not understand something.
Are you sure your logic is the right one ?
I note that you have not answered the question.
There seems to be little point in continuing this discussion.
No. I disagree with what you deduce from your results. I have tried, but failed, to determine why you make this deduction.herve00fr said:
No. Whether your stated results are facts or not is not something I can comment on, and it is not something I have commented on.
Ground loops. You seem unaware of this, but despite a number of attempts to encourage you to reassure us that you do understand the relevant physics you have chosen not to do so. I do not have to explain ground loops to anyone who understands the relevant physics, and I cannot explain ground loops to anyone who does not understand the relevant physics.
There seems to be little point in continuing this discussion.
As you did not.
Except that I bring numbers on what I say.
You don't.
My only conclusion is : multiple ground connection to box is simpler and work at least as well as ""classical audio method"", because measurements show that hum is under the noise.
I am afraid you disagree with that.
1) Ground loops is not a reply as it explain nothing.
2) I invite you to be a bit more modest and speak only on your name.
It is now clear that our understanding of electromagnetism laws are not exactly the same. As far as I know you never showed that your understanding is better than mine, as you never showed measurements or gave an undisputable explanation of your point of view.
I do not remember that you were declared "guardian of the physics law" by any scientific academy.
So until you clearly have shown you are right, I encourage you to keep your unacceptable assumptions on my knowledge in your pocket.
As you confirm that my measurements should have shown hum because of ground loops, you confirm that you are in disagreement with measurements, then disagreement with facts.
You have to clearly explain that.
Once again, I invite you to be a little bit more modest.
A person who is not able to explain something to "lambda people" is a person who does not really understand it.
This conversation has ended. If you are curious you can Google 'magnetic induction' or 'audio ground loops' to discover what I have been talking about.
- Status
- Not open for further replies.