Cable Asylum

RE: shield grounding on power cable between PS and phono stage

124.181.75.197

In Reply to: RE: sheild grounding on power cable between supply and phono stage posted by amos on April 09, 2008 at 13:59:51

I presume the PS of the phono stage produces +/-DC volts and ground, and you want to shield this between the PS case and the phono stage case?

If so, I would arrange earths as follows (this assumes you have a 3-wire mains setup in your house ... ie. there is "earth" at each wall outlet):

1. Inside the PS case, the earth tag of the IEC socket should be bolted to the case (a proper connection - scrape off all the paint/powder coating layer so you have bare metal under the nut).

This is a "safety earth" for the PS case and earths the metal case (so it protects the insides against RFI).

NB: I would *not* connect the "star earth" of the PS to this case - it should float.

2. As you say, if you use a shielded mains cord for this PS then the shield should be connected to the earth pin of the wall plug (in addition to the earth wire inside the cable).

3. The shield on the DC power supply cable (from PS to phono stage) should be connected to earth posts attached to each case (and again, scrape off the paint). This means the shield will be earthed (by virtue of its connection to the PS case, which is earthed) and also the shield will pass the earthing along to the phono stage case, so this will also protect its internals against RFI.

Regards,

Andy

PS: I had an amplifier setup until recently which had 13 wires between the "power supply" box and the "amplifier" box. Inside the "amplifier" box were 3 amp modules which each needed their own +/-/ground connections; the 13th wire was the ground between the two cases. I didn't bother to use shielded cable, though.

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