More Grounding Questions

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?

Hey Al,
Very nice Jensen paper. I gave it to my son who is studying to be an EE. Even though the paper starts out a little technical, the conclusions and tips section at the end make recommendations to minimize ground loops pertinent to this thread.
Vet93- From a purely academic standpoint, that's a good question, "has the signal been degraded even if you can't hear it?" Unless you can get your equipment into a lab, you'll probably never know. Your ears are the ultimate instrument, maybe you should invest in The Isobar.

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. :-)

But I am not sure it (ground loop) does not hurt sound quality when the music is playing.

As I suggested, I think that the only way to be sure is to try it both ways (with and without cheater plugs), and compare the sound. I don't think comparing experiences with others will be helpful on that question, because it figures to be highly dependent on the components, the cables, and the AC power distribution.

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.

The Jensen paper explains that the root cause of ground loop hum and buzz is stray capacitance (and in some cases also designed-in capacitance) between the ac line and chassis. Particularly stray capacitance within the power transformer. If your two amps did not have identical transformers, and identical electrical and mechanical design of the the surrounding circuitry, wiring, and mechanical structure, there is no reason to expect their susceptibility to ground loop problems to be the same, even if their basic grounding schemes were similar.

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

If the chassis is connected to AC safety ground but not to circuit ground, it seems to me that any and all noise voltages that may be introduced onto the chassis from the AC safety ground wiring, or as a result of emi/rfi, will be free to couple via stray capacitances from the chassis to arbitrary and unpredictable points within the circuits. If the chassis and circuit ground are common, there will be controlled low impedance pathways for that noise to be shunted to ground.

I thought the Aiken paper was excellent; thanks! I note that he addressed the issue of isolated rca jacks that I had raised.

You may find the following paper and its references to also be of interest:

http://www.analog.com/static/imported-files/tutorials/MT-095.pdf

Best regards,
-- Al

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

Thanks all for the comments again.