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Some rear space was saved to accommodate an accessory bay for upcoming digital inputs or the optional phono board. This obliged the designers to relocate the power IEC just beneath the three RCA inputs, not the ideal location if you use power cords with massive plugs. Even so the tight spacing between audiophile-type interconnects and AC cord created no traumatic issues during my review save perhaps pique audiophile superstitions. To complete the description of the back panel, a single stereo pair of well-spaced WBT binding posts accept speaker cables with virtually any kind of termination. The front panel controls include 5 source selection buttons on either side of the logo, one polarity inverter, an overly sensitive volume knob on the right and the very exclusive StormFocus knob on the left. The remote controls the main functions, polarity and StormFocus. The RI-70 outputs 125wpc into 8Ω and 220wpc into 4Ω (StormFocus @ 0Ω). It claims THD of <0.015% at 8Ω/1w and <0.03% at nominal power into 8Ω; 350mV input sensitivity with impedance of 35KΩ for the standard line inputs; and a S/N ratio of better than 105dB. Frequency response is given as 3Hz ~ 200kHz ±1.5dB.

Stormaudio has based its technical strategy on the aforementioned StormFocus, a rotary control that allows the user to match the amplifier’s output impedance to the speakers to deliver significant sonic benefits. The StormFocus knob works over a range from zero to 16Ω. At zero Ω the RI-70 will drive the speaker mostly in voltage mode while at 16Ω it operates quite exclusively in current mode. Stormaudio advises to start setting the StormFocus control to the loudspeakers’ nominal impedance, then adjust by ear. Another method consists in listening to the complete opposites (0 vs 16Ω) and moving the knob progressively toward the best balance. Practically there is no rule. Two speakers with the same nominal impedance may require completely different StormFocus settings. Considering only the technical implications, zero output impedance should make for an ideal voltage amplifier whose amplitude won’t adapt to changing loads. Voltage drive maintains a constant voltage across the load while current drive will produce exactly the same current into the load. Neither approach is perfect. Voltage drive will produce greater power as load impedance falls since the voltage remains constant simply asking for more current. Current drive will produce greater voltage to maintain the same current when the load impedance rises. The StormFocus design is thus supposed to deliver an ‘in-between’ solution, albeit one that is closer to common current drive.

Voltage drive supporters would likely argue that most modern speaker systems are optimized for voltage drive, high damping factors and that current drive is a quite inappropriate design for hifi power amplifiers. In many cases this argument might remain an overly optimistic consideration since loudspeakers are not completely predictable and their loads are far from stable. The load a typical driver presents is very complex and theory alone will hardly be helpful to tailor an amplifier to a specific loudspeaker without any practical assessments. Stormaudio accommodates the latter by modifying its output impedance with a circuit that's slightly different from what seems to have been published previously.

The main idea is to reproduce a signal very close in fact to valve or zero feedback amplifiers but more precise and neutral. Other prestigious companies have experimented with this kind of approach already. My own Orpheus Lab monaural amps use a similar but automated process designed by Anagram Technologies called Power Loop. Both companies believe that adjusting output voltage and current results in better transient response as a key factor for musicality. They claim that their solid-state realizations’ behavior is closer to tube-based amplifiers with high output impedance due to their intrinsic design but also claim far lower distortion. The main differences between these two circuits is the constant power delivered by the Orpheus amps regardless of the load (not the case for Stormaudio) and the automatic monitoring of the amplifier’s output against the loudspeaker inputs with the Swiss amps.

Because most speakers are designed for amplifiers with constant voltage and very low output impedance, they will certainly not react predictably when fed by a constant current amp. That means variations in their frequency response. Stormaudio assures us that these deviations will have a minor impact relative to the usual room perturbations and that the compromise between this and the improvement in transient response delivers more benefits than negatives. Obviously this kind of amplifier will react differently from speaker to speaker to make the StormFocus adjustment very useful to come up with custom calibrated settings.

Inside the cabinet the RI-70 uses a traditional balanced circuit and short signal paths with one massive toroidal power transformer. The power supply voltage has sufficient reserves to allow the amplifier to increase output voltages and face with serenity the various fluctuations in impedance amplifier and loudspeaker encounter. The output stages are powered by a double push-pull complement of high-grade Sanken transistors with integrated diodes for better thermal regulation. The preamp section is mounted on its own dedicated PCB and protected from power transformer radiations by a shielded roof [below].

In comparison to previous Vertigo models the now remote-controlled StormFocus is said to have improved accuracy particularly between left/right channels where the first generation suffered slight but audible offsets from potentiometer variations. The accuracy of the impedance settings has been improved as has internal wiring and vibration damping to deliver lower ground noise.

Before fiddling with the left knob, you will want to control the easy stuff - electrical and signal polarity. The former will be set only once, the latter depends on each recording. Then it’s time to experiment with StormFocus. The company proposes various listening criteria for this adjustment which were carefully selected after several listening sessions to identify repeatable sonic consequences from output impedance shifts. Stormaudio suggests to listen specifically to drums, bell harmonics, voices and orchestral works.

The obvious danger here is getting lost in a sequence of unperceivable differences and illogical results. I won’t have been the only reviewer or audiophile to squander precious time chasing performance changes without involving my amplifier’s output impedance. So you can imagine the maze I entered between zero and 16 ohms without a precise road map. It is furthermore quite impossible to make etched-in-stone sonic pronouncements on any device that is this variable with the speaker interaction. That’s why I chose to use my Chesky Ultimate Demonstration Disc to monitor as precisely as possible the sonic changes affected by StormFocus and why this review of the Revelation RI-70 will confine itself to a description of the basic sonic characteristics that defined its sound and were shared among two different speakers. I would strongly recommend that future or present Stormaudio owners acquire this Chesky demonstration disc. It seemed very helpful to track the output impedance setting changes. Given that my Orpheus Lab reference amps employ a similar scheme I felt somewhat prepared in knowing what to look for.

With my simple Triangle Acoustique Magellan Duetto two-way monitors, the RI-70 were faced by a quite pronounced saddle response typical of ported alignments but here stretched across a 25-ohm window. All Magellans love power and require sufficient grip for optimum control of their heavy drivers. The new Duettos are no exception.