Schematic help

[trem]

Sorry if I am missing it....
Page #2 of the schem, middle of page, there is a little "Ground Main" circuit. A couple of diodes, resistor and a cap.
It seems like the whole circuit is connected to ground.
What does this do.?
Thank You

[Enzo]

If you explore the circuit you will see the bold line for ground in the various circuits. What those parts do is reference the common circuit ground to the chassis ground. We often discuss grounding in Fender amps we build, and questions arise, should I ground to chassis or to the filter cap or whatever. These parts here are part of that same question. Instead of running return currents through the chassis, and potentially creating noise problems, we have the ground common, and then that is connected to chassis by these parts.

[loudthud]

The chassis and safety ground is isolated from the signal ground by the two diodes and the RC network. This eliminates a ground loop when the amp is connected to other equipment (like a PA system or effects processors) that has the signal ground connected to the safety ground from the mains.

[trem]

The chassis and safety ground is isolated from the signal ground by the two diodes and the RC network. This eliminates a ground loop when the amp is connected to other equipment (like a PA system or effects processors) that has the signal ground connected to the safety ground from the mains.

OK..... Thank You.
I do not think I have ever seen this before.
Guess it is not very common.?
Thanks Again

[Enzo]

In lots of recent era Marshalls.

[trem]

OK, that explains it.
I do not see too many modern day schematics yet in my "career"....
Thanks Again