Dedicated 20 amp circuit - Electrician laughed!

Now, I'm getting confused. Nearly every post on a dedicated breaker that I can remember has cautioned that a separate ground rod is a code violation? What gives?

A separate grounding electrode is legal per NEC 250.54 but ultimately the separate electrode must be connected to the ground of the main service per NEC 250.4 (A)(5).

An isolated ground receptacle basically means that the ground terminal on the receptacle is isolated from its yoke. In theory if you install an isolated ground receptacle and run the ground wire back to the breaker box, the ground wire will be isolated from the other ground wires and metal boxes on that circuit - up to a point.

Ultimately, every ground wire terminates at the same bus bar. Additionally, every single neutral wire is also eventually connected to the same ground back at the service. With that in mind, the only way for your audio system to be truly "isolated" from everything else in your home is to install a separate service.

That being said, having a dedicated circuit for your rig, as well as utilizing isolated ground receptacles, and paying mind to which circuits are connected to which phase in your breaker box can go a long way towards reducing unwanted noise, but it's not a cure-all or a magic bullet.

...take all of this with a grain of salt - I'm just a dumb electrician who builds amplifiers...

A separate grounding electrode is legal per NEC 250.54

Well that's a relief. 

but ultimately the separate electrode must be connected to the ground of the main service per NEC 250.4 (A)(5).

So... the electrode that goes into the ground must be connected to.... the electrode that goes into the ground. 

I must admit it sounds a whole lot more official with a bunch of letters and numbers but in plain English: 2 ground rods connected together. Right?

So... the electrode that goes into the ground must be connected to.... the electrode that goes into the ground.

I must admit it sounds a whole lot more official with a bunch of letters and numbers but in plain English: 2 ground rods connected together. Right?

Pretty much. Every service requires a grounding electrode. You can add a second one but it must be connected to the first one by a wire. At the end of the day, within a single electrical service, all of your ground wires and all of your neutrals are connected to the same ground at the service.

Millercarbon.  Multiple ground rods must be installed close to each other and be daisy-chained.  Different soil consists will produce different ground potentials.  This can have very bad implications... Problem is that many different locales have very different grounding capabilities.  Sometimes ground rods are welded end to end to reach down far enough to reach moisture that will provide a good ground. Corrosion enters into the issue.

My double ground rods are driven 4” apart close to a roof downspout to insure a “good” ground.  Even so, there is an extension of our drip system that provides constant moisture for a stable ground.

piaudiol - you're absolutely right

All single grounding electrodes must have a resistance to earth of 25 ohms or less - if not, you must add additional electrodes and "daisy chain" them together.