Grounding an Integrated Amplifer

@j-wall - yes I do. I was trying to explain to the OP in an overly simplistic manner. But thankfully others have cleared up the confusion, which is a good thing. 

@chayro do you have any idea why turntables need a ground? 

Confusion comes from the one word, "ground". The word, "ground" is used in different ways. That alone causes confusion and pain in the HiFi universe.

SAFETY ground is the third pin on the AC power plug. It is intended to prevent an electrical fire or electrocution. The fact is, one safety ground may indeed have a volt RMS or more on it, relative to another same-building safety ground. Putting a *battery-powered* oscilloscope between the ground connections of two separate outlets will often show that. BUT, that variation in potential does not make SAFETY grounds ineffective. One volt here or there is not generally dangerous to property or life.

SIGNAL ground, that terminal on the back of many pre-amplifiers or integrated amplifiers, is another thing. It is intended to be used as a reference (and ergo for noise suppression) in connections made to a low-level source -- most often a turntable. TT AC cords do not generally have a third ground pin because that configuration may well lead to a GROUND LOOP -- two electrical paths back to a common point -- here, the safety ground. The two paths cause an ambiguous (unsteady) ground current and voltage, and hum is the common result.

This notion becomes absolutely critical in neurological research, in which electrical signals *much* smaller than cartridge outputs are to be monitored. More than once I have come into a lab and separated safety and signal grounds, immediately changing extremely noisy electrophys setups into textbook data collection sessions.

Safety ground plugs into the AC power connection. Signal ground is a reference for low-level signals. Designers of audio equipment, and designers of small-signal equipment in general, know that. Let argument rest.

@OP As Fuzztone says above, the ground connection from the turntable grounds the TT chassis and tonearm to the chassis ground of the amplifier. It is a completely separate grounding system from the mains power supply to the turntable's motor.

Sounds like confusion between. electrical grounding (safety) and source grounding (for noise control of weak signals from phono pickups.)

@calgarian5355 - all the turntables I have owned use a separate ground wire. But Rega, and possibly others, run the ground through the interconnect, so no separate wire.  So it can be done. 

@chayro 

Well. That seems to make total sense!  Now I feel stupid asking such a newbie question.  So here’s a follow up question:  why aren’t turntable manufacturers making their components with grounded plugs?  

+1 chayro

The 3-prong power cord grounds the amplifier. The ground connection is probably for a turntable ground wire. Or, if the amp doesn’t have a phono input, for another component that might require external grounding. But it’s likely for a phono if there’s only 1. My amp has a separate phono and chassis, but that’s not the usual.  The instructions are telling you not to lift the amplifier ground with a cheater plug, which you shouldn’t do.