Ground Loops - Article question , confirmation

[stefanobilliani]

Hello All ,


From the pass diy article " Ground Loops " , Kent English wrote :

" If you ar running unbalanced cables, always run 2 conductor shielded wire .
(...) Shield ground should not be connected on the source end of the wire , only at the input component end "

Do I interpret it right just as is in the picture attacched or is it viceversa ?


Thank you .

[Zen Mod]

you got it right

NB that vice versa is sometimes even better

[stefanobilliani]

Originally Posted by Zen Mod

you got it right

NB that vice versa is sometimes even better

Really??

[Speedskater]

It's also a very bad idea! What really matters is having a very low shield/return resistance.

Bill Whitlock of Jensen Transformers writes:

In engineering terms, a high-performance cable for unbalanced audio should have low capacitance and very low shield resistance. A good example of such a cable is Belden #8241F. Its 17 pF per foot capacitance allows driving a 200 foot run from a typical 1 kOhm consumer output while maintaining a -3 dB bandwidth of 50 kHz. Its low 2.6 mOhm per foot shield resistance is equivalent to #14 gauge wire, which can significantly reduce common-impedance coupling.

[Nelson Pass]

I think Bill is referring to the common shield / 1 conductor variety of cable.

The earlier reference is to shield plus 2 conductors.

[454Casull]

Yes, two conductor plus shield is better than coax... make sure the shield is a good one, though.

Though I would guess that if EMI is a particular problem in your area, the coax might be the lesser of the two evils since coax cables tend to have better shield characteristics...?

[dave_gerecke]

If I remember correctly from various readings of datasheets, etc. over the past few years, the shielding isn't some much due to whether it's a coax or a two conductor pair with separate shield, as it is with the particular cable. You have to look at the datasheet of the particular cable to see what the shield coverage is. Some are only ~70% range. The better ones will list a shielding of ~95% range or better. As you can see in the picture, some even use a full wrap aluminum shield, with a separate drain wire to connect the shield when desired.

This is all assuming that you are concerned with RF shielding in your area.

Peace,

Dave

[454Casull]

Originally Posted by dave_gerecke

If I remember correctly from various readings of datasheets, etc. over the past few years, the shielding isn't some much due to whether it's a coax or a two conductor pair with separate shield, as it is with the particular cable.

Peace,

Dave

No, there is nothing that says that a coax means good shield and non-coax means bad shield - but it seems as though applications that use coax cable seem to be a bit more intolerant of interference (and they can't be used balanced), and so coax cables usually have better shields.

A foil shield will give 100% coverage but may not perform as well as a braid because of its higher resistance.

[sesebe]

I know about what you speak stefanobilliani.

The main idea is to not have a current flow thru shield, can induce noise on signal. The current should pass thru an additional conductor.

This current is generated by ground diference between used equipments.

[stefanobilliani]

Originally Posted by sesebe

I know about what you speak stefanobilliani.

The main idea is to not have a current flow thru shield, can induce noise on signal. The current should pass thru an additional conductor.

This current is generated by ground diference between used equipments.

yes , my question was if it was correct to connect the shiled ( 2 conductors cable ) on the " amp " side <or> to the CDplayer side , since I was a bit confused with the "source " and "input component" terms .
Anyway in my little pratical experience , it seems that 2 conductors + shield performs a bit better .

Thanks