One things audiophiles love to do is upgrade their home wiring, but honestly many do so with absolutely no justification. They read about some Stereophile writer putting down $5k worth of new electrical work and an isolated sub panel with a ground field, yada yada yada, and they are immediately on the phone asking their electrician to run ten feet of cryogenically treated, but completely not NEC compliant battery cable for their amps.
I am here to announce that there is finally a simple to use meter that will tell you if you need to upgrade your wiring, and if so how much better you could make it and it's about $20.
Let me explain the magic here. This meter continuously displays the N-E voltage which is difference between the Neutral and the Earth or ground. With a little arithmetic we can use it as a proxy for how much voltage is sagging due to your wiring. In other words, if we assume that the hot and neutral wires have about the same resistance then they should have the same amount of voltage drop across them. Pretty cool, right?
One outcome of this testing may be that you realize that most of the variation in your AC voltage is not because of your wiring but because of the normal power company variations in performance. If that's true, a voltage regulator may be a much better solution for you.
Preparing for Testing
Before we get carried away lets make sure your house wiring is ready for this. Turn off every bit of gear on the branch circuit which your audio gear is connected to. Let's assume it is a dedicated circuit. Leave the breaker ON. Insert your brand new Kaiweets outlet tester. If any of the following are not true we already need to consider an electrician:
- The two left red LEDs on top light up, but not the third
- The voltage is reasonably close to 120V.
- The N-E voltage is 2V or less.
The LED testing is something an experienced DIYer can often fix, but fixing the rest of this probably is going to require a conversation with your power company or a certified electrician. Don't ask me for help, get a pro.
Assuming this testing is good, you are ready to begin evaluating your audiophile-grade AC circuit.
As you might surmise, you can do this testing with a good multi-meter but this unit is damn convenient, and safe since you aren't sitting there with probes in your hands and outlets. Still, if you have a good multimeter and comfortable probing your AC outlets go right ahead and use it, all the principles here will apply. If you want to probe your AC outlets with a meter that's between you and your health insurance.
Testing
Note the L-N and N-E voltage before you turn anything on. This is your baseline. Note it does change over time and while the Kaiweets outlet tester is relatively accurate, it may fluctuate a little over time. So if you see it say 0 or 1 V, call it 1.
Next we are going to estimate how much sag your AC branch circuit has under load. There's a couple of ways to do this, with music, or with a hair dryer. The latter will give you the most consistent measurement, but it will probably overestimate your sag by a lot.
Now, turn on all your audio devices, let them stabilize and warm up. Now let's play some music! As loud as you can stand it.
While it's playing (or while you have your hair dryer going) notice the voltage (L-N) go down and the N-E go up. Generally speaking, the difference you see in the N-E voltage is half your voltage drop due to the wiring. Lets go through an example.
Baseline: 118V / 2V
Playing Music: 115V /4V
The difference in the N-E between baseline and music playing is 2V. That's the voltage drop in the neutral. Since both the hot and neutral have about the same voltage drop we estimate the total drop under load is 4V. This means 4V is the absolute most you could get out of wiring upgrades.
But wait, how do I know this isn't the wiring from the utility company to my panel? Good question! You can assess this the same way. Put the Kwiweets on another, completely unused circuit. Bathroom counter outlets are usually great for this because by the NEC you can't put anything besides bathroom counter outlets on a circuit and each bathroom gets its own. Watch the N-E numbers there. Pretty much anything you see here (with nothing else on) is measuring the whole house N-E sag. If you see this going up and down significantly with say your AC or cooking or other appliances it's worth following up with an electrician. They generally say that anything over 2V on the house neutral is cause for discussion.
The Physics of Remote Measurements
You might be wondering how any of this can work, or why it works. It's worth talking a little more about. Consider a branch circuit in a home. Let's say it's very far away from the meter and main panel. Assuming there is little to no current, then the voltage at the outlet is nearly identical to the voltage at the main panel. The reason is that voltage drop is proportional not just to the resistance on the way here, but to the current as well:
V = Amps * Ohms
is the basic equation, so assuming we have a mediocre circuit, or a very long 14 gauge circuit. There's probably some resistance along the way. Maybe 2 Ohms. That's actually high, but let's assume it is.
If you draw 0.010 amps with your test meter :
V = 0.010 * 2 = 0.020 V difference
So as long as you draw almost no current, your voltage measurement at any point in the circuit will be almost the same as at the meter. This lets us "see" the neutral voltage for the entire house on any unused branch circuit.
This also helps us "see" the neutral voltage because the ground wiring should never have any current inside the home, so no matter where you are when you measure N-E you should be measuring the voltage of the neutral relative to the ground rod outside. Of course, sometimes this isn't true due to an appliance somewhere that leaks or has the Neutral and Earth bonded together but that's a whole other mess of problems.
Results
Audio gear has two kinds of power supplies today. Linear, and switching. Switching supplies are pretty immune to wide variations in AC voltages.
Linear supplies in source components usually have regulators which maintain constant DC voltages even as the voltage sags to say 110V or less.
Linear supplies in amplifiers however are almost all unregulated and therefore entirely at the mercy of the AC voltage for their status. While they filter a great deal of noise, a long term 5% drop in the AC voltage results in a 5% drop in the DC voltages on the other side of that linear supply. So if the amp's power supply normally has +- 50V, if the AC sags 5% it will only have 47.5V now. If that sag is caused by music you now are in a situation where the music playing actually makes the amplifier weaker, and limits dynamic range.
Ideally in these situations you should keep the voltage sag to about 3% or 4V or less to limit the amount of voltage drop which can affect your amps. However many of us have this kind of variation occurring all the time due to power company fluctuations. If that's you, you don't need better house wiring you need a voltage regulator, below.
Other Fixes
It is quite possible that you don't have a problem with your branch circuit but instead with the voltage at your home being very different at different times of the day but the utility company thinks it's OK. In that case you need a voltage regulator.
No comments:
Post a Comment