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Old 28th September 2006, 11:19 AM   #11
torzsok is offline torzsok  Hungary
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Oh well, it seems that I have to experiment with this.

Please confirm my understanding: any sort of shielding should be connected to the chassis ground, and nowhere else, right?

thanks again,

torzsok
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Old 28th September 2006, 07:04 PM   #12
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Default ...

" ... any sort of shielding should be connected to the chassis ground, and nowhere else, right? ..."

Yes, although there may be a ground path from audio ground back to chassis ground (a commonly used topography), direct connection between the metal chassis and the shield plates or shield screens is the better procedure = isolating the primary side of the transformer (which references to the power line ground and/or common power line).

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Old 28th September 2006, 07:48 PM   #13
torzsok is offline torzsok  Hungary
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Hi Eddy,

I will have a chassis ground (power supply ground), and a separate audio ground (power+signal).

Any guidance to information sources or research suggestions are still welcome.

torzsok
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Old 28th September 2006, 07:57 PM   #14
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Default first, connect to ...

... connect to the chassis ground any and all shields ... this is safest and best for quality audio.

If at some point you feel the need or your technology dictates, you can run a jumper between the audio signal / pre-amp / amplifier input signal ground and your chassis ground(s).

It is axiomatic that ground loop problems develop when using a common signal ground and chassis ground = a signal ground of the "star" configuration is prefered, a common, independant central point for all signal grounds that is completely different and completely isolated from a "daisy chain" of chassis grounds.

Chassis grounds are meant for power protection isolation shields (usually meant to protect the power lines from the outside world and shield the power supply noise from the audio signals) ... audio signal ground is meant as a signal reference and signal return path (and rarely for power line protection and/or shielding ... as then the audio signal can be corrupted by power line noise).

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Old 28th September 2006, 08:07 PM   #15
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Default transformer shield newbie q

Hi,

I am just looking for the solution on the similar case, and I have learned that a copper plate can't shield a Magnetic field, only the electric field. You will need some magnetic material like mu-metal to attenuate the magnetic field. Please check the following link:

http://www.lessemf.com/mag-shld.html#276

Besides, the famous S&B TX-102 transformer is casted in the mu-metal to shield any external electromagnetic field.

Regards,

Adam
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Old 29th September 2006, 03:48 PM   #16
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Default True ...

" ... copper plate can't shield a Magnetic field, only the electric field. You will need some magnetic material like mu-metal to attenuate the magnetic field. ..."

True enough ... copper does the best job of shielding EMF ... but copper is very poor at shielding magnetic fields. ... But that's why we all try to use torrid transformers, because of the lower & more efficient configuration of the magnetic fields = less magnetic shielding required.

It is also true that the best comprimise for shielding both, EMF and magnetic fields, is the mu-metal material ... unless obtaining it is not cost effective for your project.

Look: you can spend your time & money trying to shield everything in the local, physical universe including the Earth's own magnetic field plus all the EMF in the neighborhood, or you can do your best to install decent, effective EMF shielding and then spend your time & resources of better circuit designs, designs that don't really need much shielding. Proper circuit design and layout covers a world of sins. The use of torridal transformers, good circuit board layout and component positioning, the use of shielded data lines and shielded low level signal lines ... etc ... can negate the need for any magnetic shielding as well as extra EMF shielding.

(Chasing that last 5% costs as much as getting the first 95% correct.)

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Old 29th September 2006, 05:28 PM   #17
AndrewT is online now AndrewT  Scotland
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Hi,
we are reaching a concensus that copper and other non magnetic shields do not reduce magnetic fields.

But, you do not have to fit very expensive mumetal shielding.

Thick magnetic steel will attenuate the magnetic field (not non magnetic stainless steel).

I have seen a thick ring of steel around the outside of toroids on two different units (a power amp and a pre-amp). The ring of steel almost closed the gap between the floor and lid of the chassis.
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Old 29th September 2006, 06:53 PM   #18
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Default OK .... no problem-o

" ... we are reaching a concensus that copper and other non magnetic shields do not reduce magnetic fields. But, you do not have to fit very expensive mumetal shielding. Thick magnetic steel will attenuate the magnetic field (not non magnetic stainless steel). ..."

I don't have a problem with any of this ... except:
" Chasing that last 5% costs as much as getting the first 95% correct. "
... and ...
" Proper circuit design and layout covers a world of sins. The use of torridal transformers, good circuit board layout and component positioning, the use of shielded data lines and shielded low level signal lines ... etc ... can negate the need for any magnetic shielding as well as extra EMF shielding. "
... and ... it seems like a whole lot of extra effort to do both or either when the need may not out way the effort.

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Old 29th September 2006, 08:02 PM   #19
Nordic is offline Nordic  South Africa
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Yeah, I don't see how if you do your layout and design properly it would become such a big issue, unless it is a sensitive high gain device or maybe a radio transmitter or the like...
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Old 29th September 2006, 08:29 PM   #20
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Default a big score ...

... I just made a great score:

I obtained a heavy duty, but broken, Crown 200W stereo amp for about US$50. I gutted the circuit board (now its a frisbee) and some other parts, keeping the torrid transformer, power switch & fuse, output to speaker connections & filters and some other stuff. The huge space inside the steel case allowed me to install two power supply filter boards and two 150W amplifier modules several inches away from the torrid transformer. Since all the new boards are mounted horizontally (parallel & in the same plane) to the magnetic lines of force of the torrid = no magnetic interference worries, mate = .

In fact since the unbalanced inputs to the amp(s) are also far away from the torrid, I could (but I won't) use unshielded input cable ...

(+/- 65 VDC PS rails through aussieamplifiers.com NX-150 amp modules = ~185 Watts into 8 ohms and less than 0.003% THD ... and the specs check out so far with the transformer unshielded from the rest ... )

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