Isolated ground in dedicated room/new construction?

Immatthewj- Just for your reference then if you ever sell it that is the SLA-70B Signature version 2. If you add high quality coupling caps and a beefed up power supply (more electrolytic capacitance and big polypropylene bypass caps) it’s very good still. I have custom fully balanced SLAM-100 mono blocks with separate mono block power supplies running KT150’s. Very nice amplifiers.

@harpo75  , actually mine is a SLA-70B Signature, which may be the reason it has  the bias pot and the bias jack accessible behind the transformers?  That must have been a pita to bias!  I don't remember what all the differences were with the Signature vs the SLA-70B (nonsignature) . . . 6550s instead of EL34s, and it has a standby switch on the rear apron that maybe the nonsignature version didn't come with.

I get it down every once in a blue moon when my other amp goes down, and you are correct--it is still a swet sounding amp.

Immatthewj- That was/is a good little amp.  The bad thing was having to take the bottom off the amp to go in and bias it.  Never could figure out why Dennis did that. Hopefully you drilled a hole in the chassis and mounted the bias pot and mount a couple test point terminals on the outside also.  Makes it much easier.  Did that for several people.  Sweet sounding amp!

Another informational interesting thread.

Among other things, this got me taking a look back in time at the manual for my first tube amp (which I stilt own & have owned for going on 30 years,a Cary SLA 70B) and under "GND" the manual states that;  "For "audio-purists" this should be connected to an earth ground rod via the shortest lead possible - this is not essential for proper operation.  This ground will help insure immunity to RF interference and AC ground loops."

I have a vague recollection of speaking with a representative of another audio manufacturer, who shall remain nameless, who suggested that I "float the ground."

On that note, a couple of years ago I upgraded my digital to the Marantz SA10, and it has a two-blade receptacle for the supplied two blade power cord.

 

 

 

@jea48 

Excellent idea. I’ll try that this weekend. 
Happy listening !

Ron 

Would you please explain to me the reason for not using metal boxes?

I would have thought (just guessing) that a metal box that is grounded by the conduit would act as a shield around the outlets.  What is the reason for plastic boxes?  Thanks!

Would it present as sounding grainy /static? I figured the recordings that have some grain were from the recording.

 

Possibly.

For a test, turn off the circuit that feeds the dimmers and LED lights at the electrical panel. Then listen to your audio system if you can hear any difference.

(Turn off the circuit that feeds the dimmers? If the dimmers have internal back lighting they still spew garbage onto the AC line. Even if the dimmer switch is turned off. If you do hear a difference for the better from your audio system then turn on the breaker at the electrical panel and listen again. You may find with the dimmers turned off with their switch the dimmer does not put out enough noise to affect the sound of you audio system.)

If you do hear a difference for the better then just use a table lamp with an incandescent light bulb for general light in the room for serous listening to music.

@jea48 

Thank you for the info. I didn’t think about that when I built my room. I have LED track lights on dimmer switches. Would it present as sounding grainy /static? I figured the recordings that have some grain were from the recording. 

@ronboco

Yes, and that includes the branch circuit wiring from the load side of the switch to light fixture(s). When can lights are used in a ceiling it can be a challenge to route the new dedicated branch circuit cable(s) from the parallel running lighting branch circuit wiring. Same for maintaining a distance from the can(s) that house the LED lights.

@jea48 

Do you mean the romex from the panel to the outlets should not be in close proximity to the romex from the panel to the lighting switches? Thanks

 

Ron

I would steer clear of 2-wire Romex. The hot and neutral run parallel along the flat length and this creates an RFI antenna. I use 10/3 Romex (orange sheathing) because the three wires are twisted, which helps attenuate common mode noise. I use the third conductor as a ground (make sure to tape the visible ends green) and clip the bare copper grounding conductor. This also has the added advantage that it can be converted to a 240V branch circuit in the future.

EDIT:

Also avoid running the three dedicated circuits parallel to other branch circuit wiring.

Should read:

Also avoid running the three dedicated circuits parallel in close proximity to other branch circuit wiring. Especially LED Lighting circuits as well as circuits with lighting dimmers. These circuits are the worse for inducing Harmonic Noise onto the Dedicated Branch Circuits.

.

Room will have have 3 dedicated 20 amp home runs for the system using 10 gauge 10/2 romex with ground, terminating with PS audio IG 120v outlets.

terminating with PS audio IG 120v outlets.

@frym

Did you run that by the builder’s electrician? Per NEC you can not install an IG (Isolated Ground) type outlet on a 2 wire with ground NM, (Romex is a trade name), branch circuit. FWIW, An IG outlet would serve no purpose whats so ever connected to the branch circuit wiring. None...

With this set up is there any point in setting up an isolated ground and how do I go about it?

By definition an IG ground wire must be an insulated green color ground wire. The ground wire is connected only to the receptacle outlet IG ground terminal and remains isolated all the way to the EGB, Equipment Ground Bar, in the electrical panel. The IG conductor must be part of the branch circuit cable circuit wiring. (NEC allows the IG ground wire to pass through a sub panel and connect to the Main Electrical Service Equipment Panel, (the sub panel is fed from), and connect to the Grounded Service Entrance Neutral Conductor.)

...Now with that out of the way...

The EGC, (Equipment Grounding Conductor, in the 10/2 with ground will work exactly as the described IG ground wire above provided the EGC is not bonded, connected to a grounded box, or what ever, from the ground terminal on the receptacle outlet to the EGB in the electrical panel. (Which you will have with a true dedicated branch circuit.)

House will have 400 amp service utilizing two 200 amp panels.

Each 200 load center panel will be a sub panel. Approximately how far, distance, is the sub panel, that will feed your three new dedicated branch circuits, from the main electrical service 200 amp breaker?

 

Approximately how far, distance, are the dedicated branch circuits from the audio room wall outlets to the sub panel? ( Measured, up, down, and around).

It is important the electrician does not run the dedicated circuits through the same bored holes through studs or joists. Nor should they be run along side any other branch circuit wiring through bored holes.

After the three dedicated circuits leave the electrical panel as soon as reasonably possible they should be separated from one another by at least 8"- 12" all the way to the wall outlet boxes. Also avoid running the three dedicated circuits parallel to other branch circuit wiring. Especially LED Lighting circuits as well as circuits with lighting dimmers. These circuits are the worse for inducing Harmonic Noise onto the Dedicated Branch Circuits.

 

See page 16. Read pages 31 thru 37

An Overview of Audio System Grounding and Interfacing

 

FWIW...

You might want to consider using solid core 10/2 with insulated green ground. (Solid core #10 conductors, NOT stranded conductors)...

Aluminum armored MC (Metal Clad) cable. (NOT AC Armored Cable.)

I prefer Aluminum Armored MC cable over NM sheathed cable, (Romex is a Trade Name). Especially if the branch circuit runs are long.

Per NEC you still can use a plastic wall box for the outlet for each dedicated circuit.

Why MC over NM?

Cable construction does a better job of controlling any induced voltage from either of the two current carrying conductors onto the EGC. Better than Romex can. Any induced voltage onto an EGC can cause ground loop hum. Especially on long run branch circuit wiring.

The construction of the three conductors are tightly twisted together in a spiral the entire length of the cable. What keeps them tight against one another is the outer aluminum armor.

 

Example Of Aluminum Armored 10/2 MC Cable:

 

All of the electrical grounds in a home must be bonded to the same ground point.  You’ll be violating all sorts of safety codes if you attempt to do otherwise and they are there for good reason. 

What you can do is dedicate grounds for your outlets (even running insulated ground wires) from the panel.

If you got an isolated service (independent meter) you could then use a truly isolated ground for things fed from that meter.

There are some in-panel ground isolators, which have a major downside. They are basically large inductors, that meet the NEC requirements for adequate ground current, BUT !!! They degrade the performance of most surge protectors.