Full review and test of the Torus AVR2 Mains Power Conditioner by Australian Hi-Fi Magazine. Free download.

I discovered a major failing of the Torus AVR2 power conditioner the moment I tried to remove it from the double cardboard box in which it was delivered. It’s too heavy! Also, it does not have handles. A product that is this heavy (35kg) and this large (it measures 430mm wide by 200mm high by 490mm deep) really needs to be provided with handles—two as a minimum, and preferably four, so it becomes an easy two-person lift.

I guess the only godsend was that I wasn’t reviewing the 20-amp version of the Torus AVR2, which is even bigger and, at 74kg, more than twice the weight!

The Equipment

The Torus AVR2 (the AVR stands for Automatic Voltage Regulator) is a power conditioner that removes voltage spikes and high-frequency noise from the mains power supply before they can get to the components in your hi-fi system. It also stabilises the mains voltage so there are fewer fluctuations, and keeps that voltage…to within ±10 volts here in Australia, with our nominally 240V supply. (In the US and other countries using a 120V supply, the Torus AVR2 keeps the nominal voltage to within ±5 volts). This prevents against voltage surges and brownouts. However, in the event that the mains voltage exceeds 262 volts, or falls below 170 volts, the Torus AVR2 will automatically disconnect your hi-fi components from the mains power supply to protect them.

Once you have wrestled the Torus AVR2 out of the box and placed it on your equipment rack… or the floor, it’s simply a matter of plugging your hi-fi components into the five empty 240V ‘medical grade’ mains sockets on the rear, plugging the Torus AVR2 into a standard 15-amp wall socket and switching it on.

The minute you switch the Torus AVR2 on, the small display at the right of the front panel will light up, with the top line showing the incoming voltage and the bottom line the outgoing voltage. I was a bit alarmed when I first turned mine on, because it showed an incoming of 242 volts and an outgoing of 270-volts. I rapidly switched if off, fearing something had gone wrong.

A careful reading of the manual showed that I needn’t have worried, because the output voltage shown on the front panel is not actually connected to the sockets at the rear until after the Torus AVR2 has stabilised the voltage, using a series of relays, and this process can take up to 20 seconds. So I switched on again, and watched the output voltage slowly drop from 270 volts to 238 volts, after which that exact voltage was applied to the rear 240V outlets.

The Torus AVR2’s front panel display shows not only the level of the input and output voltages, it also shows total current being drawn by your system (in amps) on the same display. If you push the button below the display, it will then show both average and peak power. Push it again and it will show the time and date. Press it once more and it will show the power outlets on the rear that are drawing power. For some reason these are called ‘active zones.’ Press the button once more and the display will show the IP address of your Torus AVR2 (only if you’ve connected it to the internet).

As you have probably guessed by that parenthesised comment, you can connect the Torus AVR2 to the internet, using the Ethernet port on the rear. If you do this, a whole new raft of features appears.

Once your computer is connected to the Torus AVR2, you can check its status from anywhere in the world, as well as operate it from anywhere in the world. And, once a computer is connected, you can individually switch the rear power sockets on or off. You can do this switching manually, or you can program them to turn on and off at specific times, on specific days of the week. You can also program the Torus AVR2 to send you an email if the AVRs experiences what the instruction manual calls ‘an issue’, in which case it will send you an email notification of the specific fault condition that took place.

Although these capabilities are impressive, I wondered why all this functionality had been provided. If I am on the other side of the world, why would I want to be able to switch my system on or off, or have it do so in my absence? Whilst pondering this, I discovered that whenever the Torus AVR2 switches on, it will then switch on each power outlet (aka ‘zone’) in order, starting with A. This is really useful, because it means you can connect (say) a disc or network player to A, your preamplifier to B and each of your mono power amplifiers to C and D. This will correctly sequence your system power-up pattern to prevent potentially damaging turn-on transients from reaching your loudspeakers. However, I have to note that this won’t be so useful if the components in your system switch to standby power when they’re not being used.

Later on I also found that with your computer connected you can actually calibrate the Torus AVR2, but since this process necessarily involves using an expensive calibrated voltmeter and the operator of the voltmeter potentially being exposed to lethal voltages whilst measuring, this process is not included in the otherwise totally comprehensive Owners’ Manual.

In Use and Listening Sessions

There are many very obvious reasons you might want to use a power conditioner. First would be to stabilise the mains voltage reaching your components because there’s a possibility that surges and low-voltages could do them some harm. It is, however, only a possibility, as most components are built to cope with surges and low-voltages. 

Another reason for using a power conditioner would be to eliminate high-frequency noise spikes from the mains power, as this can adversely affect the operation of digital-to-analogue converters, for example… though, once again, most components that could be sensitive to noise on the power line are designed to remove that noise themselves, to ensure proper performance.

However there is one not-so-obvious reason for using a mains power conditioner, which is to remove audible transformer hum from your components. 

Transformer hum used to be quite an issue in the past, particularly here in Australia, because most transformers were made by laminating plates together and winding coils around those plates. The problem was that most transformers were designed for operation at a mains frequency of 60Hz and a mains voltage of 120V. Here in Australia, when those same transformers (with different taps to accommodate the increased voltage) were used, the higher voltage combined with the lower mains frequency (50Hz) caused the laminated plates to vibrate, causing an audible hum at 50Hz. In some cases the transformer vibrated so much that it actually caused a buzzing sound.

It was largely because of this hum problem that most equipment manufacturers have switched over to using toroidal mains power transformers, which are not made by laminating plates together. Which is not to say they made the switch to toroidals simply to solve this issue…toroidal transformers have many technical advantages over standard transformers, plus a smaller form factor, so using them also allowed manufacturers to cut costs.

However, although toroidal transformers are intrinsically acoustically quiet (very little hum) when fed from an ideal 240V source, they can become noisy under adverse line conditions, which will result in the components they’re being used in to generate audible hum in the listening room… usually at 50Hz, but sometimes also at 100Hz and 150Hz. If your components produce an audible hum when they’re operating as a result of sub-standard mains power, using a power conditioner should reduce or eliminate it. One complication with assessing audible hum is that the level of hum will vary depending on the music being played, and the volume at which it is being played, because hum levels will always be higher when a transformer is being stressed, than when it’s not.

Another reason you might want to use a power conditioner is if you’re running a high-power amplifier. In many cases, depending on the supply voltage in your area, if your amplifier is running flat out, it could be pulling so much current from the mains that the mains voltage will drop, resulting in reduced amplifier performance. A power conditioner such as the Torus AVR2 will maintain the correct supply voltage, even under conditions of peak demand.

Yet another reason is ground loops. If your mains connections are such that there are multiple paths for electricity to flow to ground they may form a ‘loop’ which may then pick up stray current via means of electromagnetic induction, resulting in unwanted current in a conductor that’s connecting two points that are supposed to be at the same electric potential. The result of a gound loop is hum. With all your components plugged into the AV2, all the earths will be at exactly the same potential, eliminating the possibility of hum-generating ground loops.

In Use and Performance

I thought I’d check the Torus AVR2’s voltage control ability before I commenced my review, so I connected it to a variable mains power transformer (Variac) I use when I am reviewing 120-volt products, as it allows me to adjust mains voltage from 110 volts up to 270 volts. I first set the Variac at 230 volts, because this is the voltage the mains is supposed to be here in Australia. I say supposed because although the Australian government committed to switching from 240 volts down to 230 volts to harmonise with the European mains voltage several years ago, it has never happened. Or, perhaps, it has happened in some regions or with some suppliers, but not in others… and certainly not in my suburb. Anyway, with the Variac set at 230 volts, the Torus AVR2 put out a constant 235 volts. This seemed a little strange, and after a few emails with the Australian distributor, it transpired that the operation of the Torus AVR2 is somewhat dependent on the load that’s connected to it, and for my initial tests I’d connected a load that was drawing only 0.1-amps. When I increased the load to 2.8-amps, the voltage dropped back to 230 volts, right on the money.

With the bigger load connected I ramped up the Variac to 234 volts, for which the AVR delivered 237 volts. I then wound the Variac right up to 240 volts, at which there was a click from within the Torus AVR2 and the voltage dropped back to 233 volts. I then increased the mains voltage again, from 240 volts through to 258 volts, and watched the output voltage of the Torus AVR2 climb from 233 volts to 240 volts. With an input voltage of 260 volts, the Torus AVR2 put out 243 volts, slightly above its ±10V rating, but presumably if I had increased the load, it would have dropped it down to 240 volts. At 262-volts, the AVR disconnected all the loads connected to it, and displayed ‘High Voltage’.

When I reduced the voltage to 226 volts, the Torus AVR2’s output voltage dropped to 229 volts, and for an input voltage of 224 volts its output voltage dropped to 226 volts and so on, delivering ever-reducing voltage until it was delivering a 220 volt output for a 218 volt input. Then, when I reduced input voltage to 216 volts, a relay clicked and the Torus AVR2’s output went back up to 227 volts. When I got all the way down to an input voltage of 170 volts, the Torus AVR2 again disconnected the components connected to it, but this time displayed the words ‘Low Voltage’ in the front panel display.

So overall, my tests showed that with the load I used for the tests the Torus AV2 will maintain an output voltage of between 220 volts and 240 volts for any input voltage between 172 and 258 volts. The results of my tests are shown in Graph 1, below:

My first sonic trial with the Torus AVR2 was with an 80s vintage amplifier I keep for sentimental reasons (don’t ask, or you’ll be like my wife, who’s always asking me why I don’t get rid of it!). It has a toroidal transformer that hums so loudly I could hear it from the listening position (just one of the reasons I no longer use it). After taking it down from its usual resting place on the top shelf of my home office I was a bit surprised to find the amp even worked, as it hadn’t been switched on for something approaching 15 years, but when I plugged it in, away it went, and it certainly hadn’t forgotten how to hum…. at least it hadn’t when it was plugged directly into the mains power socket on the wall. However, when I connected it to the Torus AVR2’s output, the hum all but vanished… at least I could no longer hear it from my listening position—though I could still hear some hum if I put my ear close enough to the amplifier’s case.

Somewhat surprised by this outcome, I tried another amplifier which uses a standard EI transformer, not a toroid, from which a slight hum has always been audible if I put my ear right up against the case. When it was connected via the Torus AVR2, the transformer hum was still present, but to my ear it was at a distinctly lower volume level.

My third sonic trial was simply to hear whether the Torus AVR2 had any effect on amplifier sound quality, using two different but identical hi-fi systems, but with one system connected directly to a mains wall socket and the other to the Torus AVR2. In the set-up I used, both systems did share a common source component (an SACD player), in order to simplify the A–B switching process.

In these sessions, during which the voltage of the wall socket remained fairly constant at around 242–244 volts (and the output voltage of the Torus AVR2 also remained fairly constant, but at 234–237 volts) I found it extremely difficult to tell the two audio systems apart, such that I fancied the differences I heard could equally be due to the necessarily different locations of the speakers in the room. Which is not to say that I didn’t have quite a few ‘aha!’ moments, when I definitely thought I’d found a musical passage where I thought the sound from the system connected via the Torus AVR2 sounded clearly better, but when I then replayed that passage multiple times through both systems, I again found it hard to hear the difference I first heard. This happened quite a few times, as I said: indeed so often that I began to wonder whether it was because of transient noise spikes on the mains that existed for a short period and had been removed by the Torus AVR2, but had dissipated by the time I went back to do my double-checks. Unfortunately, I have no way of knowing.

My last experiment with the Torus AVR2 was to intentionally reduce the mains voltages to both systems to just 217 volts, so that one system was getting a true 217 volts, but the other one (thanks to the Torus AVR2 automatically boosting the voltage to it) was getting around 230 volts. In this last experiment I clearly heard that the sound of the system connected to the Torus AVR2 was superior, particularly during transients, where the sound was cleaner, more dynamic, and with less distortion.


The problem with drawing conclusions in any review of a power conditioning product is that the effect of adding a power conditioner to a hi-fi system will vary significantly depending on the quality of the mains power being supplied to that system in the first place, the supply voltage, and the design of the power supplies in the components in that system.

For example, if you’re lucky enough to be living in a house that is supplied with clean, stable mains power, and the power supplies in the components in your system already have their own filtering and voltage regulation circuitry built in, I think it is unlikely you would obtain any audible benefit from adding a power conditioner.

If, on the other hand, you live in a home that has a less-than-perfect mains supply and/or the components in your system have little in the way of filtering and voltage regulation—or none—then using a power conditioner could certainly provide tangible benefits. #