Is grounding with RCA is safe?

I still have a question regarding your reply:
"In effect what you are most likely doing (depending on the designs of the components) is connecting the internal circuit ground of each component to the chassis of that component and to the chassis of every other component in the system"

I check the ground box from Entreq. It looks like to me that they do the same thing.

Could you help shed some light on this?

The internal circuit grounds of most components are connected to the ground sleeve of their RCA connectors. And since the components apparently have three-prong power plugs, the safety ground prong on those plugs is presumably connected to the chassis of the corresponding component.

So since you have connected the ground sleeve of an RCA connector to the safety ground pin on the power plug of each component, and the safety grounds of all of the components are connected together via the outlets and the associated AC wiring, you have most likely connected both the circuit grounds and the chassis of all of the components together.

I have no knowledge of Entreq products, but if in fact they do the same thing I personally would not want to use them.

I searched online and learn that ground loops can destroy audio gears in long run. Is it true?

I can’t envision a means by which a ground loop could cause damage, other than in the very unlikely scenario I described in my previous post. A ground loop could, of course, have adverse sonic consequences, and degrade the accuracy of the system. Which may or may not be subjectively preferable, however.

Regards,
-- Al

I wouldn't say it is unsafe, per se, but many designers deliberately lift the ground to prevent noise issues. Seeing a 100 Ohm resistor between the chasis, which is directly attached to the AC ground, and the signal ground is quite common. 
The quietest systems I've ever heard completely isolated the signal ground from the AC ground, preventing ground loops altogether.

I would not encourage anyone to start hacking this way.

In most components the circuit ground is directly connected to the chassis. And the chassis is connected to power cord ground. Pretty sure all common ground amplifiers are set up that way. You would not want to try your RCA trick with a non common ground amp.

So what you are proposing technically not make any difference, but anything goes with audio. According to the books what you are doing should make the system sound worse. You are supposed to ground everything in a component to a single point on the chassis via a "star ground". Grounding to different points is supposed to do bad things to the sound.

I would take a peek inside and make sure the circuit ground is connected to the chassis somewhere. The power cord ground should be connected to the same point. Then even though it goes against conventional wisdom......if your system sounds better go for it.

In most components the circuit ground is directly connected to the chassis.

I believe that is not true. And certainly, IMO, a **good** design will not connect circuit ground and chassis directly together, as it invites ground loop issues.

As Erik indicated, many designs have a resistor connected between circuit ground and chassis, and many others go even further in isolating them from each other. I know, for example, that circuit ground and chassis are not connected together in most or all Audio Research, Ayre, and Atma-Sphere designs, among others.

Regards,
-- Al

What you are doing is perfectly safe. The outside is ground anyway. Its real easy, with tube gear anyway, to look inside and see the one wire coming from the center of each RCA and going straight to the input selector. Only one wire. Don't take my word for it. Look and see. One wire. That's the pin, that's the signal, that's positive. That's why its insulated, and routed the way it is, away from noisy bits like transformers. That's why they lay them out the way they do.

Notice the outside of each RCA. They are not wired individually. They do not go to the input selector. On many amps they connect to a bus bar. Follow that wire, which notice is not insulated, it will at some point complete the circuit by being connected to ground. They may all come together at one point, I don't know, have only looked into and modded a few so there may be some exceptions. 

When there are you can be sure its for sound quality not safety. Mainly the problem is the way electricity works, running a signal through a wire generates a magnetic field around the wire proportional to the signal. While at the same time every magnetic field crossing a wire induces a voltage in that wire proportional to the field. This is how electricity is generated, be it in a Koetsu cartridge or Hoover Dam, and this is how transformers work too. And antennas. Same deal.

So if you're hearing an improvement that kind of makes sense. What you're doing is providing a more direct route to ground taking that one small part of the problem out of the amp. A little less is a little less and if you hear it you hear it. 

Count yourself lucky. The ground loop guys are right. Only thing they're missing is its a crap shoot. One guy does everything right, winds up with hum and hunting down a ground loop anyway. Another guy (that would be you) deliberately wires extra grounds which one would think ought to hum like crazy, and instead it actually sounds better. Go figure.