Big Iron: The AC Voltage Regulator

There are a lot of different things called a "power conditioner."  Often these are little more than power polishers which can have very little effect on the power you get from your wall outlet but among the devices which actually do something the AC voltage regulator is the one that does the most actual work. 

Many audiophiles are familiar with the PS Audio line of power regenerators, which definitely qualify but there are many good regulators out there at a fraction of the cost.  To give you an idea, the Furman M-8x AVR costs around $750, but list on the cheapest PS Audio regenerator is $5,400.  That's a very big difference, and not entirely justified by performance.  See more details here.

 

I'm going to focus on the Furman M-8x AVR (Automatic Voltage Regulation) in this post, which is I believe one of the cheapest suitable for audiophiles but you can definitely find voltage regulation in a number of units from Furman and others priced between the M-8x AVR and the PS Audio regenerators.  The great thing about this unit is that it makes an excellent add-on to an existing conditioner.  Read more to understand how this works.

What exactly is an AC voltage regulator? 

An AC voltage regulator attempts to keep the voltage coming out of the wall socket stable despite changing input. The idea is that by maintaining consistent voltage your gear will perform optimally no matter what is happening to the voltage inside the home.

99% of "power conditioners" out there do not include voltage regulation, including most units sold by Furman. The way these "old school" units work is by using a transformer with multiple output taps.  It is this big transformer that makes them heavy and expensive and why I titled this blog post "Big Iron."

 

The Furman M-8x AVR was originally intended for industrial (i.e. professional) environments which suffered from unreliable power.  Elevators, lifts, large heating and air conditioning plus lighting systems all put a strain on the incoming power and the M-8x AVR was designed to ensure that no matter what happened the audio gear had stable power.

 

The regulator constantly watches the incoming AC voltage and if it changes too much it switches to a new tap on the transformer that gives a better range of outputs. Look below at this chart, borrowed from the M-8x AVR's manual: 

 As you can see, as the incoming AC swings between 105 and 130 Volts the unit keeps the output steady between about 118 and 122 volts.  In other words, your voltage is always in the butter zone.    Further, if the voltage gets too high or too low it will shut itself down to protect the gear that relies on it.

 If you look at the business end of the unit, on the left, the INCOMING VOLTAGE meter tells the story. So long as any of the green LED's are lit your gear gets AC voltages in the sweet sweet zone of 118 and 122 (or thereabout). 

Do I need a Voltage Regulator? 

Fortunately in the United States most of us live in an area with really stable voltage and we almost never have to think about it, but the range of what is considered acceptable AC voltage is pretty wide, from about 110V to 127V, a pretty wide range of around 15%.  Some of us know we live in areas prone to sagging voltage or unreliable power.  In this day and age when everything is electric, like the stove, hot water heater and air conditioning, we put more demands on our household electrical service than ever before. A Furman voltage regulator will give you peace of mind and ensure your listening experience is always the best possible while keeping your gear safe. The regulation is about 3x tighter than the industry standards for wall power. 

 

For everyone else it is hard to say without observation if a regulator could help you so my suggestion is if you aren't sure get a plug-in VAC meter and watch it for a week to a month.  If you see the voltage dip below 117V or higher than 122V you might consider one.  These meters are cheap (< $20) and safe since there are no exposed wires.  Here is a typical unit:

 

 

 

It was in fact looking at the voltage on my Furman power conditioner that caused me to get the regulator.  Living in a modern apartment building in around 2018 in San Francisco we were hitting 130V often.  It took PG&E a couple of weeks to correct the problem but after this I never took the regulator out of my stack until I moved out. 

Choosing a Voltage Regulator

As a voltage regulator, by itself, the M-8x AVR is an excellent unit, but it's pretty bare bones.  No additional noise filtering and just basic surge protection. Most audiophiles are used to being bombarded with features beyond mere voltage regulation.  In my case I use the voltage regulator before a fancier Furman conditioner and you can do the same thing as well if you already have good surge and noise protection. 

 

If you don't have an existing conditioner or want to have an all-in-one, Furman has the P-2400 AR that has top-tier surge protection (SMP) and linear, active noise filtering (LiFT) for about half the price of an entry level PS Audio unit: 

 

Is this as good as a PS Audio Unit?

For the rest of us, a Furman with LiFT, SMP and voltage regulation will keep your gear safe and performing near optimally and leave a lot more money in your pocket.  Looking at the technical reviews of the PS Audio regenerators, the Furman may be better for two reasons: 

• Introduces less noise below 200 Hz vs. PS Audio
  
• Cleans up noise above 3 kHz better vs. PS Audio thanks to LiFT and SMP
  

The one feature where a regenerator really excells is in keeping the voltage to within 1V vs. 5V for Furman. 

There are a couple of downsides too.  Look, I use Furman in my home and am super happy with them, but be aware that the auto-transformers have a slight mechanical hum (not through your speakers) and that as they switch voltages you'll hear the relays click.  I hear this happen maybe once a month.  If you are in a situation where you expect this to happen regularly you may want to place your unit with this in mind. 

For the money, I'd rather get a Furman with AVR, LiFT and SMP and spend any remaining cash on iFi power adaptors for any devices that need them than a PS Audio regenerator.

What about Instant Current? 

Some audiophiles get obsessed with not having anything between their amps and the power station a hundred miles away.  Here's the way to think about it: 

Nothing limits performance more than sagging AC.

Put another way, if power is being choked off the voltage will sag.  That's how the math works, and this is exactly what a regulator will prevent. 

 

Pretend you are playing classical music and a 24 Hz note hits.  Do you think the peaks and valleys of this note are going to coincide with the peaks and valleys of the 60 Hz signal coming out of the wall?  Of course not.  The best we can do is make sure that the voltage coming out of the wall is consistent no matter whether it's a sweltering summer day and the AC is running full blast or you are pushing your amps to their limits, and that's exactly what a voltage regulator will do.  

Other Brands

When comparing options one thing to keep in mind is how tight the output regulation is. As mentioned, the Furman keeps output within about 5V (118 to 122) , but I've seen much less expensive brands with about twice the tolerance for output voltage, and no real idea what happens above or below.  These are designed for point-of-sale equipment and keeping gear running in industrial buildings. Make sure you have good specs to understand what it will do from 110V to 130V when comparing.  

APC also makes several UPS / Conditioners that claim a sine wave output.  Check the reviews related to their reliability.  The extra circuitry which converts a normal PC grade UPS to audio grade seems to not have the same level of reliability as their normal UPS units.  I have had no problems at all with their UPS units for PC's and my internet hardware though.