Torus Power RM20 Audio/Video Power-Isolation Transformer
For this review, I was supplied with Torus's RM20 ($3000), a PIU that uses a single 2400VA toroidal transformer to supply 120V and 20 amperes to the 10 AC outlets on its rear panel. It also has a 20A circuit breaker for its On/Off switch and uses a massive, 14AWG detachable AC cord rated at 15A/125V.
Torus PIUs use transformers twice the size found in typical amplifier power-supply toroids and buffer the amplifier's peak current demands. The PIU transformer's primary, attached to the home AC line, is decoupled from the secondary attached to the amplifier, allowing what is claimed to be a more complete attenuation of AC line noise, from 1kHz to over 1MHz. Torus PIUs also provide substantial surge suppression, and are available in either single 120V input or dual 120V (balanced) inputs.
Installation involved placing the RM20's 95-lb chassis where it would get adequate ventilation: atop my Velodyne DD-18 subwoofer. I then used all 10 of its AC jacks for my audio components. Not only did the PIU provide a central place to plug in all my audio gear, it helped me eliminate extra extension cords and other line-cord clutter.
My approach to listening tests borrowed heavily from Brian Damkroger's review of the Audience Adept Response line conditioner in April (Vol.30 No.4). Like BD, I found it easiest to hear the Torus PIU's benefits by removing it from the setup after having lived with it and the Bryston 28B-SSTs in my system for two months. The PIU greatly enhanced subtle details of tone, timbre, and imaging when dynamics were extreme or volume was loud. Removing the PIU shrank the soundstage, making my system sound flatter and less detailed. This was most evident when I listened to "Deeper Wells," from Emmylou Harris' Spyboy (CD, Eminent 25001-2). The massive synthesizer sounds that open the track dominate and obliterate the sounds of Harris' voice and any instruments. Reinserting the PIU in my system focused the sound of the churning, roiling synthesizer on a spot at the front and center of the soundstage, allowing me to hear Harris' voice and the drums separately, farther back in the stage.
I highly recommend the Torus Power PIU to increase any serious audiophile system's powers of musical resolution and imaging.—Larry Greenhill