Hi all, Hi Steven

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LONG but read it:
I dunno if i'm right now, but i think there are some basic misunderstandings on decoupling the "mains earth" from the amp circuit.
A METAL enclosure or METAL chassis surely must be hard wired to ground. Directly - with NO resistance inbetween the chassis, metal parts that could be touched by a user and the mains earth - where i presume that "mains earth" is the grounding from the power line. A circuit breaker or mains fuse in the household can not trip with a resistance that is connected between the AC line and the breaker. Before this happens, the resistors or caps burn down as they can not withstand 120VAC @ 16 A for a second... A pure short circuit has a power of 2000 Watts (in our location it's 3600 Watt). What should a 100 to 150 Ohm resistance do here? Nothing else than fail!
Connect one 150Ohm / 5 Watt resistor, one 10A circuit breaker and a switched 60W light bulb in series and see what happens.. Don't forget wearing your protection glasses! Even the fact that an AC current is rated as impedance and not as ohm's resistance doesn't help in any way. I hope that makes sense..
Any resistance between AC powered devices and chassis or enclosures made of metal must be avoided. In any case. Transformers and transformer screens, line filters, output transformers must be connected to earth too. Anyways anytime. Even if you use chassis or enclosures made of wood or plastic.
A short circuit on the "DC side" basically is protected by the main-transformer's primary or secondary fuse, if the current of the load overrides the fuse's current rating. The DC circuit also has NO reference to mains earth. The DC circuit is isolated from earth by the main-transformer. This is beacuse the secondary transformer windings have no point where they are connected to earth, thus they have no reference to ground. Take a PSU and a DMM and a wire with clamps. Connect the DMM to the DC output of the PSU
and the DMM COM to the mains earth and measure the DC. You'll get no measurable result because of the fact that there is no earth reference - as meant before.
But, HV circuits are also attached to the mains ground for several reasons. One of the reasons is the GCFI protection. If a short occurs there is also a chance that the GFCI will trip. The circuit breaker surely doesn't.
What and why?! - Because the mains earth / power line earth and the NEUTRAL basically have the same reference. Earth and the NEUTRAL are 0 (NULL). But - they are splitted in the household.
The NEUTRAL works as "0" in a circuit breaker and GFCI balancer (The GFCI is a magnetic, balanced switch which shunts to earth). The earthing connects all to earth and at the end to the power line. If a AC / DC current (40mA - 80mA) runs into the neutral, the GFCI will break the mains power in the household at the point where the GFCI is mounted.
So - why the heck do some builders or schematics use resistors and capacitors to decouple the DC GROUND from MAINS EARTH??
Because it's OK and works. AC hum and buzz is an pretty much unbeloved child in the amplifier world.. Everyone tries to get rid of it. If you have coupled the DC grounding with the mains earthing the chance of hum and buzz is very high. There are ground loops and device loops (potential differences) which cause hum in several cases. Now - here comes the point why DC ground decoupling is used.
We can decouple the "DC ground" from "mains ground / earth" by using an 100 to 150 Ohm resistor and 100n / 630V cap. That will say that the DC circuit ground is connected by using an resistor and cap to the point where the mains earth connects to the chassis. At only one point. This will provide a way of secure amplifier (GFCI trip) and also decreases ground loops. That's the only way to use the resistor and cap. Nothing others.
Now to the conclusion:
The PSU from this project and the connections are OK! Bruce did the same like i mentioned before. He decoupled the amplifier ground (DC ground) from the mains earthing / grounding. This is not very unusual and works fine to me and for many others. As you can see on the schematics, a mains filter is used in the circuit. The filter package is directly connected to earth and the chassis, thus the chassis is directly hooked up to earth. The amplifier ground is attached to the earth via the decoupling network. There is NO resistance between earth and the amp!
I hope that makes sense to you.
Have fun
