Hi,
I prefer the post7 grounding layout as it gives more consistently low hum compared to post5 for two channel amplifiers.
I also find that when using multichannel amplifiers that separating the PSU grounds helps as well. This requires the use of dual rectifiers for each PSU and then connecting the zero volt line from the smoothing caps to the star ground.
Finally, there is a safety issue that has been overlooked with the layouts posted.
The 6ohm disconnecting resistor between Safety Earth (chassis) and Audio Ground (Star Ground) does not comply with the mains safety requirement of most countries.
The exposed conductive parts must be permanently connected to the Safety Earth.
The reason for this requirement is to ensure that the mains fuse blows quickly, if the mains live lead during a fault condition contacts and/or connects to other low voltage parts of the equipment.
If fault current prior to the fuse blowing passes from Live to Audio ground then through the 6ohm resistor to Safety Ground back to distribution board earth the voltage appearing on the audio ground will be high enough to kill anyone that happened to touch the equipment at the wrong time. Further, fault current passing through the resistor will more likely blow the resistor before it blows the fuse, leaving the Audio ground at Live voltage and no effective connection to Safety Earth.
I recommend either of two solutions.
The first and safest is direct connection from Safety Earth to Audio Ground. This generally gives rise to hum loops in most connected equipment.
The alternative is to use a Disconnecting Network between Audio Ground and Safety Earth. This Disconnecting Network can consist of a parallel combination of:- Power resistor, inverse parallel coupled Power diodes, Power Thermistor, HF capacitor.
The Disconnecting Network MUST survive LONGER than it takes the mains fuse to rupture and for the arc to extinguish.
