Installing A Dedicated AC Line Where the Existing Wiring is Already Pretty Good

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kentj1948

This past Monday, we had some sort of AC line glitch at our home.  I discovered this late in the afternoon when I found the refrigerator unwilling to dispense water or ice.  I had been in the listening room and nothing happened while I was there to alert me to any electrical issue.  (I subsequently discovered that the smart TV and computer also had been affected.  The TV flickered like something in a horror movie until it was cycled on and off a couple of times.  The computer had restarted.)

I referred to the refrigerator manual and found nothing useful troubleshooting my problem except the suggestion to unplug it for a bit and then power it up again.  There is no way to get to the plug in the wall so I turned off the breaker for a few minutes.  Fortunately, this worked and the refrigerator came back to life.  [Big sigh of relief!]

Looking around the breaker box got me thinking about a project that has been in the back of my mind since moving into this house: running a dedicated AC line to my stereo system.  My basement listening room adjoins the utility room so it is a straight shot from the breaker box to the wall behind the speakers.  I have a suspended ceiling in my listening room, which also provides a convenient place to run the wire.  After giving the idea some thought and finding no serious impediments to putting the line in, I decided to go ahead and give it a shot.
 
I think it is conventional wisdom in the audio community that a dedicated line is a worthwhile upgrade.  Yet most of the articles I have read have replaced old, dirty, outdated, often inadequate wiring.  What if the current wiring is in good shape and has nothing or almost nothing drawing current but the stereo?  Does a dedicated line still provide an improvement?

I have had dedicated lines in my last two homes, which also had basement listening rooms.  The more recent of these (2000-2014) was built from scratch so there was no before/after basis for comparing a dedicated to non-dedicated line.  The room before this was in use from 1993-1998.  I needed the new outlets so that I did not have to run any extension cords.  My father and I ran a length of ten-three wire and put in a subpanel with two circuits.  Again, there was no really good comparison possible but at least I didn’t have to worry about having enough current!  At that point my system was really not good enough to evaluate an upgrade in the AC line anyway.  I was still finding my way through interconnect and speaker cables.

The Work

I ran over to Lowes and spent a hundred bucks for what I required.  I had to buy a hundred feet of number 12 Romex (20 Amp) as I needed just over sixty feet, by rough measurement, and it is sold as either 50- or 100-foot rolls ($60).  I did not want a splice in the line so it had to be a hundred feet.  I bought underground Romex as it was, for some reason, $30 cheaper than the in-wall stuff.  I got a new 20 Amp breaker ($25), the best 20 Amp Industrial Grade duplex outlet Lowe’s sells, $7, and a plastic old-work box ($1).  I had a Romex connector and plenty of duplex covers among my miscellaneous hardware.

Running the wire through the dropped ceiling was straightforward.  In the utility room, I used cable ties to hold the wire to the cold-water pipes.  Overall, the installation looks pretty clean except for the wire running down the front wall of the listening room.  I think I can paint it and make it less obvious.

Clearly, this installation is not to code although it is safe to use.  If the time comes to sell this house, this line will be easy to uninstall.
 
I unplugged my stereo system before beginning work.

Putting in the breaker went fine. There is a subpanel and it has the extra openings that made adding this line possible.  I had to install the breaker using a flashlight but once it was in, and turned off, I could turn the lights back on in the basement, which made installing the outlet a lot easier.  The listening room outlets are controlled by one side of a dual 20 Amp breaker in the same subpanel.  The stereo is plugged into the fourth outlet on the circuit.

As near as I can tell, the wall outlets in my listening room are the only devices on the existing 20 Amp service so it is already a mostly-dedicated circuit.  The only thing that is on with the stereo when I listen is a lamp with an LED bulb in it.  It is plugged into the first of the room outlets.  I cannot detect any noise through my system attributable to the existing AC line.

At the listening room end, I drilled a couple of holes in the back of the old-work box so that I could attach it to the drywall with hollow wall anchors.  I put a few layers of blue tape over the tabs that normally anchor the box in the wall simply to keep them from dangling.  The box is reasonably secure but needs to be held in place when removing an AC cord.  I positioned it a bit lower and to the right of the existing wall outlet so that the mounting screws wouldn’t hit the Romex in the wall (!) and that my AC cords could still reach it.

The whole project, excluding the trip to Lowes, took a couple of hours.

The Results

All the components in my system plug into a PS Audio P5 regenerator.  It plugs into an MIT Z Duplex outlet in the wall.   The MIT outlet is a 15 Amp hospital grade and includes a mains filter assembly that attaches to its screw terminals.  I won this outlet in a raffle at Rocky Mountain Audio Fest some years ago.  At the time it cost $100.  Today it costs $150.  While the filter assembly is intended to offer some line noise reduction, its method of attachment to the outlet is kind of a pain.  It is designed to be held in place by one screw on each side of the outlet.  This works fine when the mains wiring terminates at the outlet.  But if the mains travels into and out of the outlet, getting the filter tightened so it fits properly is difficult.  The depth it adds to the outlet is also a problem.  Currently, I am using the outlet without the filter assembly because of these issues and because, frankly, it seems unnecessary given what the P5 does. (The photo is of the 20 Amp version, which is $200, but the 15 Amp looks exactly the same.)

Before powering the system back up, I tried the P5’s power cord in both the MIT and Industrial outlets.  Subjectively, the grip on its prongs was pretty much identical with both of them.  I think one of the positives of most audiophile outlets (maybe the positive) is that they do grip the prongs of the AC plug more securely and this does relate to better sound.  This gripping ability is the difference between hospital grade and ordinary outlets.

When I finished installing the dedicated line, I had a set up with which I could make a direct comparison of the dedicated line to the existing line simply by switching between outlets.

I need to interrupt this narrative at this point.  My subsequent listening comparison concluded that the dedicated line was very slightly superior to the existing line, even with its MIT outlet.  As I was thinking about reasons why that might be, I realized a major problem with my methodology.  When I installed the new breaker in the box, I pushed it in place, pulled it out, pushed it in and did so several times to get a clean mechanical connection to the prong at the back of the box.  But I never touched the breaker on the existing line and it has sat there for a number of years.  So I shut things down, took off the cover of the subpanel, connected and disconnected both breakers five or six times, and doused the connections between box and breaker with Deoxit Gold G5.  I feel comfortable now that I am comparing both circuits with the breaker/box connections as identical as I can make them.  Back to the story.

I began my second AC line comparison with the system warmed up and plugged into the MIT outlet.  I again used Katharine McPhee’s CD, “I Fall in Love too Easily,” as I like this CD for its close-miked breathy vocals and excellent sound stage.  The arrangements are pretty spare so it is possible to concentrate on individual instruments as well.   I listened to Track 9, “It Never Entered My Mind,” a few times and then switched over to the dedicated line and listened again.
 
This time the differences I had previously heard between the two AC lines, while small to begin with, were further diminished.  I still felt, however, that the dedicated line offered a slightly more spacious sound stage and room reverberations were a bit more evident.  The saxophone located near the left speaker seemed better focused and more three-dimensional.  I could not discern any changes in Katharine’s voice, in the shimmery metallic sound of the cymbals, or in the bass performance.  The sound with either outlet was, in my opinion, extremely good.

I want to stress that these sonic improvements were pretty subtle and that I was listening for them using music that I felt would emphasize whatever differences existed.  I am also very big on sound staging and not everyone is.  And I also knew which AC line was being listened to and that may have influenced my perception.  It was not a blind test.  Having said this, there is still no question in my mind that the dedicated AC offered a very small but audible improvement in sound quality.

I can only speculate as to the source of the improvement as the existing wiring is pretty recent, has the theoretically better outlet, has no grounding issues (both lines share the same ground in the same breaker box), and is virtually dedicated.  My working explanation is that there is still some degree of oxidation and corrosion on the existing connections and that is enough to affect the sound.  It is also possible that the 15 Amp MIT outlet has somewhat less contact area than the 20 Amp Industrial outlet and that has some effect.  Even if that were to be the case, the MIT is hospital grade, which you would expect to be a plus for it. Possibly, there may simply be some synergy enjoyed by an uninterrupted monolithic line.

So, even if you have fairly modern circuits, you may still enjoy some sonic improvement from the installation of a dedicated circuit.  If you have older wiring in your home with various devices drawing current and feeding noise back into the line, there is even greater potential for hearing an improvement.  Even if I had heard no difference whatsoever between the two circuits, I would still be inclined to use the dedicated one as I am the sort of person who can’t resist the more purist set up.
 
I am not so sure about audiophile outlets.  I think a reasonable expenditure for a good quality outlet is well worth the money.  Replacing a worn outlet may in itself produce a worthwhile sonic improvement and would be the first thing to try if your stereo is serviced by older wiring. Spending a lot of money on an outlet that will be installed in aged wiring, though, seems questionable.  And as to whether some $350 carbon fiber duplex will give you enough bang to justify its cost, there, I am afraid, I am pretty skeptical.  But I would definitely try one if I had the chance.
 
Other theories and comments are welcome.

Thanks for taking the time to read this.

Kent





































brj

Nice write-up!

One thought as to a possible source of differences... are both the old and new circuits on the same phase?

When I had a dedicated audio subpanel put in several years ago, I had the electrician re-organize my mains panel so that every circuit that we could identify as feeding a device with a motor or half wave rectifier was on the opposite phase from that the of the subpanel.  I didn't have the luxury of an A/B comparison in that case, but it seemed like a good idea, though it has nothing to do with the age of the wiring.  (Though in hind sight, I should have checked for a few other devices that can be electrically noisy, like florescent light ballasts, etc..)

kentj1948

Thanks for your comments.  Actually, both breakers are on the same phase.  That wasn't intentional, just the most logical placement in the box. 

Kent 

Elizabeth

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One other point not covered is the fact the new Romex and other bits need to 'break in'.
The old wiring has had many years to mellow out. The new wiring? I would give it at least a MONTH of use then compare the two sets of wiring again.

kentj1948

That is an excellent suggestion. I will relisten in about a month.