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Old 18th April 2012, 01:24 PM   #22351
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Quote:
Originally Posted by vacuphile View Post
What I wonder is, and I hope someone can fill me in on this one, what difference would it make in an electronic circuit? Faraday's law of induction produces the same result for all conductors, magnetic or otherwise. So, what is the mechanism that could cause magnetic components to sound worse than non-magnetics?

vac
A material with a relative permeability greater than 1 will "attract" the flux lines in the area, and will change the reluctance of the path the flux lines take. (I am attempting to keep this simple, but may not succeed well, sorry).

Any cylindrical conductor carrying low frequency current will store magnetic energy within the conductor via it's internal inductance, roughly 15 nH per foot times the magnetic permeability of the conductor. If you use a magnetic material like the iron I use at work with permeability around 3000, the internal inductance will be 45 uH per foot per wire. Typically, I would expect a mu of 100 to 1000 for magnetic materials, so figure 150 nH per foot to 1.5 uH per foot.

Another problem is linearity of the material. Most typical magnetic materials also have a hysteresis curve, a non linear relationship between B and H (magnetic stimulus and response). For example, if you have a magnetic wire which stores energy via inductance, and you put it into a magnetic field which is also time varying, you will modulate the wire inductance. Using the previously exampled wire, at low signal levels, I'd expect 45 uH per foot...at 1 ampere, that stores 22.5 microjoules. If I subject it to a magnetic field that causes it's permeability to halve, the wire will give up 11.25 microjoules due to permeability drop.

If you use a magnetic plate to separate a low signal high sensitivity area from a high magnetic field area, and the high magnetic field modulates the wall permeability, the result can be a mixing of signals on the low level side.

Care must always be taken when materials which exhibit non linearities as a result of stimulus, are put into an environment which allows that stimulus.

j

Last edited by jneutron; 18th April 2012 at 01:29 PM.
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Old 18th April 2012, 02:04 PM   #22352
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Default CMCL

Quote:
Originally Posted by godfrey View Post
[...]
>Originally Posted by Bonsai View Post
>...I thing we have to look to Edmond Stuart for inspiration.

Dunno about that.
Huh? Never heard about a CMCL?

Quote:
I remember Olivier trying to follow Edmond's advise in this thread. After nearly a year, he still hadn't got it to work.
[...]
At least Andrew understands why it took him so long.

>inspiration
I'm not sure to what Andrew was referring. It could be a CMCL, but also the Super TIS, as both configurations solve the common mode TIS current issue. Indeed, a CMCL does add to complexity (4 to 6 extra trannies). The Super TIS, on the other hand, is far less complex, as it doesn't need a CMCL at all.

Cheers,
E.
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Old 18th April 2012, 02:07 PM   #22353
Bonsai is offline Bonsai  Taiwan
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Common mode control loop. Maybe it should have read CMCCL for common mode current control loop.

Apologies for the confusion.

:-)
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Old 18th April 2012, 02:10 PM   #22354
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No apologies needed.

edit: By now, I've abandoned the CMCL concept, as the super TIS is better and simpler.

Cheers,
E.
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Last edited by Edmond Stuart; 18th April 2012 at 02:19 PM.
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Old 18th April 2012, 02:21 PM   #22355
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jneutron,

Thanks for your very informative response, it all figures!

Vac
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Old 18th April 2012, 02:48 PM   #22356
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gk7, this is where we part company. We have found some things to be important just from listening. Not my listening, but other peoples' listening. It is not just ONE factor that turns a potential stallion into a dog, it takes a lot of things. Excessive iron in series or proximity of quality audio signals is but one of them. Would I have believed this 40 years ago? Probably not. This is why it is so difficult for me to even give this advice, even though following it has certainly helped me make more successful audio products.
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Old 18th April 2012, 03:07 PM   #22357
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We don´t need to part and I certainly do not ignore your experience and advice. I was just asking what _could_ be an explanation to the mechanisms that make this possible. jneutrons explanation for example describes
how magnetism can have an influence, next would be to think about how to measure
and to quantify this influence. This is how progress is made, I believe.
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Old 18th April 2012, 03:13 PM   #22358
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Progress is made by putting hypotheses to the test and either running with them or abandoning them, depending on what good, rigorous experiments tell you.

Marketing to a hobby or fashion niche is a totally different matter. The story is important, evidence is not.
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Old 18th April 2012, 03:16 PM   #22359
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Well, good luck trying. Of course, there is some advantage to making a measurement in this case, but you might be surprised how small the distortion is, at least with normal test signals.
I have measured proximity effects of mu-metal shielding, and there is an AES paper done some years ago on magnetic materials in audio equipment, done by a Japanese company, back more than 10 years ago.
I suspect that it is not just the permeability of the material making the conductor 'compromised' but other factors as well.

Last edited by john curl; 18th April 2012 at 03:27 PM.
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Old 18th April 2012, 03:19 PM   #22360
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the bare fact of a physical mechanism like magnetic material hysteresis isn't however an explanation of the audiophile recommendation to avoid magnetic materials in circuits

as a precision instrumentation designer, having read extensively on the subject of analog circuit design for precision applications over a 30 year career I have never seen mention of steel core component leads, resistor end caps as a limitation to at least -120 dB on measured distortion products in low level analog circuitry

I recall one reference to Ni plated connectors giving -130? dB distortion products in kW RF connectors

there are several accounts of magnetic field leakage from air core inductors interacting with steel chassis, ect giving measurable distortion so I suppose you could "see" magnetic component leads in the leakage path of an inductor - so we have one avoidable condition that may have measurable effect
Bruce Hofer related an anecdote that the steel lid did give some measurable distortion in an AP analyzer's oscillator circuit - not wanting to give up on the external magnetic field shielding they added a thin Al plate to the inside of the lid over the sensitive circuit and the Eddy current "shielding" was enough

I don’t recall Williams, Edgar mentioning “magnetic” resistor leads as a limitation in their designs of ultra low distortion audio oscillators


and of course there is the further logical conundrum of transformers and electrodynamic drivers often at both ends of the recording process with clearly measurable distortions from magnetic material nonlinearity
with our analog circuitry with basically immeasurable effects from magnetic component leads in the middle

it would be far more convincing if there were actual measurements showing these hypothesized "audible" magnetic component leads, endcaps, connector plating distortion (IM too) magnitude, spectrums...

Last edited by jcx; 18th April 2012 at 03:30 PM.
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