More Grounding Questions

Would opening the grounds let RF noise in the system,that may be getting grounded now?Just a thought that occurred when reading.

I definitely would not connect the AC ground to the Chassis. The designer would have done so if he wanted, and may have in fact. I would only plug the component into AC as directed.
Likewise, I would not connect the signal ground to chassis, again, the designer would have done so if he wanted.
You may be confusing ground loops with Ground Loop Potentials, which cause hum because the interacting components do not share the same power ground.
If you have no hum, relax and enjoy the music. Please check your previous post, I added a section on controlling surges and line noise.

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.....

Thanks Heyraz. Let me provide more info. My main power amp has both AC ground and signal/circuit ground wired to the chassis.

I don't think I've ever seen that in audio gear.If someone used a cheater plug that can reverse the neutral,and the hot phase line,that would give 120 volts to the chassis.Zap the user,plus fireworks possible.I can see them tying the green ground to the chassis.I don't think I would experiment either.

Maybe,I'm thinking your reference to the AC ground as the neutral.Hopefully,It has the outlet supply ground tied to the chassis.I'm still thinking,if it isn't broke,don't fix it.

Vett93
This new post of yours has a lot more going on than the original (ground rod placement and ways to minimize noise). And by the way, everything I suggested was from personal practice after consulting EEs and Union Electricians. Being a retail pharmacist has it's advantages, I get to know a lot of knowledgeable people and pick their brains.

Why do you think your secondary power amp hummed when the signal ground was isolated from the chassis?
If I'm reading you correctly, the chassis of your secondary power amp was internally connected to the input signal ground as well as the power ground. When you isolated the input signal ground from chassis (and AC ground), the hum disappeared. How did you do this? If I read you literally, you were able to do this while leaving the AC ground still connected to chassis. I have seen equipment with "ground lifting" switches, but never used one in practice, nor do I fully understand it. Perhaps another reader can explain further.
Have you been able to obtain schematics of your equipment?
Did you open it up to verify that the power was proper polarity with regard to hot and neutral? Have you checked for leakage?
What equipment do you have exactly? Perhaps other readers have had personal experience. I read a post a few weeks back regarding a preamp/poweramp mismatch. Without getting specific, the two were literally oil and water, one passing DC to another unable to handle it. Perhaps your situation is basic design incompatibility.
I'm no EE but I have built a few kits, fixed a few rigs, and can read schematics well enough to trace a circuit.
Please provide more specific information, I'm intrigued.

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.

Will ground loops degrade sound quality even though it does not hum?

In addition to producing hum, ground loops can also result in high frequency noise and buzz, by coupling harmonic distortion components and/or noise that is typically present on the ac lines into signal return paths. However, if you don't hear that when no music is playing, or if any low level buzz or noise that you do hear is the same whether or not the equipment is temporarily floated with a cheater plug, I doubt that it would have any effect on sound quality. I suppose it is slightly conceivable that inaudible ultrasonic noise that is introduced by a ground loop could somehow intermodulate with the music and have audible effects, but it's easy enough to rule out that possibility -- just compare the sonics with and without the ac safety ground temporarily lifted via a cheater plug.

When you "float" your power amp, do you float the signal/circuit ground from the chassis or you float AC ground from the chassis?

I would never isolate circuit ground from chassis, assuming the equipment was designed with them common. And I'm not sure how it would even be practical to do that, unless the design had them connected together at only one point, and the rca jacks were the type that has isolated ground sleeves.

Assuming that circuit ground and chassis are connected at more than one point, isolating those connections would most likely result in significant impedances, especially at high frequencies, between circuit points that should be common. In other words, grounds at different points in the circuit would no longer be truly common. Also, stray capacitances between various circuit points and ground would be different than those which were present when the initial design and development was performed, in effect changing the design in unpredictable ways. Also, instead of the chassis functioning as a shield, it would very conceivably function as a path for emi/rfi to couple into internal circuit points.

Of course, as you probably realize floating the ac safety ground is in principle not a good idea either, due to the safety risk it creates. Although a lot of people do it anyway. As far as I am aware the only way to break a problematic ground loop that is both effective and completely safe is with something like a Jensen Isomax.

This Jensen paper will probably be of interest, if you haven't seen it already.

Best regards,
-- Al

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.