More Grounding Questions

Thanks Heyraz. Let me provide more info. My main power amp has both AC ground and signal/circuit ground wired to the chassis. One of my sources, SlimDevices Transporter, has both AC ground and signal ground wired to the chassis also. So does my preamp. They don't hum at all.

My secondary power amp had the same setup too but it did hum. The hum stopped after I disconnected the signal ground from the chassis.

My system does not have popping sound nor audible noises from the speakers. I am also an electrical engineer with lots of formal education in EE. But I'd like to learn from others who have practical hands-on experiences with their audio equipment. There are a lot of things in audio gears that school books didn't teach. Or I have forgotten most of them.....

Hifihvn, yes, AC ground (not AC neutral) is wired to chassis.

Heyraz, there was a ground loop between the preamp and the secondary power amp. (To be clear, I only use one power amp at a time). So it hummed. Then I isolated the signal/circuit ground from the chassis while keeping the AC ground wired to the chassis. The hum stopped because no ground loop is between preamp and the secondary power amp.

I opened up the secondary power amp to disconnect the wiring. I did check the polarity and it was fine. The manufacturer wouldn't give out schematic. But it is a simple KT88 PP amp and is easy to trace.

When I use the main power amp, there is still a ground loop between the preamp and this main power amp. But it does not hum.

Maybe I should re-phrase my questions:
1. Will ground loops degrade sound quality even though it does not hum?
2. When you "float" your power amp, do you float the signal/circuit ground from the chassis or you float AC ground from the chassis?

Thanks all.

Al,

Most amps I know use "star ground" or some variation of it for grounding various common points. In short, these various common points are wired together first and only goes to the chassis at one point. A good article can be found from:

http://aikenamps.com/

Click "Tech Info", then "Advanced (Aiken)", scroll down a little, and you can see "Star ground".

Adding Jensen transformers in the signal path may get rid of the ground loops. But I hesitate adding more components in the signal path.

So for chassis to act like a shield, do you have to wire the chassis to the signal ground or AC ground?

I cannot hear noises when the system is idle. But I am not sure it (ground loop) does not hurt sound quality when the music is playing. As an example, I couldn't hear any hum, buzz, or noises before I put a Shunyata PLC for the digital and preamp gears. But the Shunyata PLC does improve sound quality, IMO. So this is not an academic question. Rather, it is more like trial and error.

This is why I want to solicit opinions from others who have experiences in this area.

The Jensen paper may be technically correct. But it may not describe all real life scenarios. Take Figure 1 in that paper as an example. It tried to explain the hum voltage potential at the power amp and suggested that it would cause hum. This may well be correct. But both my power amps had the same grounding scheme before the mod. However, only one of them hummed. So his theory cannot be true at all time.

From a personal experience, the theory one learned at the regular University EE program has very limited areas of application in real life. In the MS and PhD programs, one would probably learn that there are other ways of looking at the same problem, and a theory/equation is only valid when certain assumptions are true. One challenge in real life is finding out which assumptions are true. :-)

I think you are right, Al. I'll have to try it both ways and determine for myself.

Thanks all for the comments again.