RH84 Build

[johnf]

I am building an RH84.

Can anyone tell me if the circuit shares a ground to chassis with mains earth or "floats" e.g. like the ST-35.
Many amps have a star ground or ground bus which connects with a single point to the chassis along with safety ground.

This is a hard wired amp

Any thoughts greatly appreciated.

http://www.tubeaudio.8m.com/RH84/rh84.html

[nyazzip]

well, i am a rank amateur but i grounded mine to chassis. works fine, very quiet

[Alex Kitic]

Can anyone tell me if the circuit shares a ground to chassis with mains earth or "floats" e.g. like the ST-35.
Many amps have a star ground or ground bus which connects with a single point to the chassis along with safety ground.

Generally speaking, I prefer a single ground connection to the chassis.
I build my amps with some sort of a star ground which is connected to the chassis, possibly in that same point.
Furthermore, I do not "earth" or connect the amp chassis (ground) to earth -- actually, the preamplifier is the only component which is "earthed" in my system.
Most probably you would not experience any problems unless it were about turntables and MC cartridges.

In short form: the power amp should be "floating" in respect to the earth connection; the preamplifier should be "earthed", thereby connecting all other equipment to earth in one point.

[kheper]

Can anyone tell me if the circuit shares a ground to chassis with mains earth or "floats" e.g. like the ST-35.

Look at the schematics. Both the amp and the power supply are tied to ground. See the symbol near the 470K resistor in the amp schematic and the symbol near 220uF cap in the power schematic?

[Alex Kitic]

Look at the schematics. Both the amp and the power supply are tied to ground. See the symbol near the 470K resistor in the amp schematic and the symbol near 220uF cap in the power schematic?

There are two terms here:
1) ground
2) earth

Every circuit must have a ground connection to work -- in the sense that the ground connection is the negative (-) as opposed to the B+. Even more so with circuits that have both a negative and a positive power supply. Therefore, yes, both the amp and the power supply are connected to ground - OF COURSE - and the question was, as I understood it, whether the amp should be earthed (i.e. connected to the earth terminal of the power grid) as well, or left floating (not connected to earth) (as I said, I prefer earthing just one piece of equipment and letting all the other pieces be earthed through their ground connections via cable to the earthed piece of equipment, preferably the preamplifier).

Another part of the question was probably related to the "ground buss vs. star earth" issue (whichever solution you choose it should work for you, i.e. if no hum is audible you have chosen the right one) - and the "multiple chassis connection vs. single chassis connection" issue, i.e. whether the chassis shoud be grounded, or not, and in how many points (not as simple, single chassis connection should be prefferred).

I hope this clarifies it for everyone who has doubts - the solutions are mostly design choices, but one has to choose a solution.

[kheper]

Probably a terminological muddle happened here.

The ground symbols on the amp and power supply go to chassis ground. They do not "float" above ground. Whether they go to real earth, e.g. through a green lead of a three pronged plug, I cannot say. That is the builder's choice. Sometimes you can pick up hum from another component with the green lead connected, but an amp can probably be earthed without concern.