Aries Cerat preamplifiers compared – Incito S and Impera Reference
Review sample supplied by Ultisone and Callas Audio
Retail prices in the NL including 21% VAT:
Incito S: 14.200 euro
Impera Reference: 22.000
Following my initial review of the Aries Cerat Incito S preamp and the Heléne DAC, Ron of Callas Audio had jokingly said that the annoying thing about Aries Cerat equipment was that no matter how great a model sounded, the model above it would be even better. The advice, therefore, was to not listen to a model that you can’t afford. Shortly thereafter, it was suggested by Michel of Ultisone to review the Impera Reference preamp, a model that sits above the Incito S. Michel concurred with Ron’s viewpoint but did not tell me anything about the relative differences, leaving this for me to find out. Expecting the Incito S and the Impera to be relatively close to one another, I suggested making the review into a comparison between the two models. To this end, Michel supplied the Impera while Ron once again supplied his Incito S.
Above: Incito S and Impera Reference power supply units sharing a level of the Artesania Organic Line Modular Rack.
Upon hearing the two models side by side, I quickly learned that there was no hyperbole whatsoever and that the two preamps do indeed inhabit two different performance classes. This being the case, I decided to put the focus for this review on the Impera Reference but with the Incito S added for perspective.
Impera models
The current Impera range exists 0f three different models, all of the “II” (2) generation. The basic model that I will be reviewing here is called Impera Reference but note that the preamp has “Impera II” printed on its front panel as well as on the power supply unit. Above the Impera Reference is the full-twin-chassis Impera Signature and above that is the Impera Limited Edition which is the current top model.
My “basic” Impera Reference is strictly speaking also a 2-chassis design but instead of the Impera Signature’s full-twin-chassis, the Reference preamp utilizes a small external housing just like that of the Incito S preamp for the power transformer. The umbilical cable between the power supply and the preamp carries AC from the transformer’s multiple secondaries. The AC is then rectified, filtered, and regulated locally.
With a 52 cm width and a 53.5 cm depth, the Impera is wider and considerably deeper than the Incito S. While the latter looked normally sized and even a little cute compared to the bulky CH Precision components, the Impera actually makes the Swiss blocks look cute. To put this into perspective, the Incito S is 48 cm wide and 35 cm deep while the Impera Reference is 52 cm wide and 53.5 cm deep. Those 4 centimeters in width may seem insignificant but when you see the unit in person, you will probably be shocked. Once you have recovered, try to lift the unit and you’ll be in for another shock! It weighs 65 Kilograms, so you better have a large and very sturdy rack!
Technical Differences
So just how does the Impera differ from the Incito S, you ask? Peeking inside, I see similarities such as the TVC volume control but also lots of differences, mainly in terms of the sheer amount of transformers and chokes inside the Impera. I think it’s safe to say that 4/5 of the unit’s internal volume is taken up by transformers while the volume control and active line stage take up the remaining 1/5 on two small PCBs.
There’s not a lot of technical information available. Such is the maker’s philosophy, it seems, that he does not want to dwell on technicalities but rather lets the audio component’s performance speak for itself. The European Aries Cerat website mentions the basic specifications and mainly focuses on the Impera’s Inverted Triode Technology, which I will detail a little further below.
Like the Incito S, the Impera utilizes Multi-tap input transformers as the attenuation method for volume control, along with the stylish Nixie-Tube input- and volume indicators behind a thick glass front panel. For the Impera Reference, in particular, it’s mentioned that the multi-tap input transformer has a special bifilar winding which results in excellent performance both in frequency and time domain. The 26 separate taps are switched by small-signal sealed relays.
The Impera Reference has what is referred to as a “Double choke-filtered quad power supply. So, 8 power supplies? From the looks of it, that certainly seems right! All four vacuum tubes are fed by special quality PSUs, with four individual choke filtered capacitor banks. There are 5 unbalanced inputs, an HT pass-through, and a single unbalanced output. Optionally, one can also fit balanced in- and outputs.
Inverted Triode Technology
Inverted Triode Technology is a vacuum tube innovation developed by Aries Cerat and utilized in the Impera II series. According to the manufacturer, the technology is different from any kind of vacuum tube used in audio and tube electronics in general. In the basis, three electrodes, a cathode, grid, and plate, are combined to give an amplification device completely different in operation from the classic vacuum tube.
Inside a typical vacuum tube, an electron stream emitted from a heated cathode is accelerated toward a positively charged anode, which has a flat plate structure. The electron flow is impeded by the grid, a negatively charged wire-grid structure, placed between the cathode and anode. This operation resembles a typical fluid control valve, hence the name “valve” tube.
Inside an Inverted Triode tube, the electron stream emitted from a heated cathode is accelerated towards the anode, now a wire-grid-like structure. The electron flow is now unimpeded since no grid structure exists between the anode and cathode. Instead, a plate-like structure, enveloping the cathode/anode assembly, called the control “grid” is shadowing the anode electrical field, having a very high negative electrical field itself, thus “pushing” the electrons away from the anode. This mode of electron flow control is completely different from the triode mode of operation.
The inverted triode actually acts like a virtual “vacuum state transformer”. Instead of having gain, the inverted triode has only a fraction of unity gain, just like a step-down transformer. The internal resistance is many times lower, and input capacitance is nearly zero.
The inverted triode has a 100 times lower plate resistance than a 6SN7 tube and zero input capacitance which gives the output stage superb measured performance and a 2 Hz-500 KHz bandwidth, figures that are apparently not achieved by other triode designs with a transformer output stage.
According to the manufacturer, another example of the Inverted Triode’s technical advantage over a typical vacuum tube such as the 300B can be found in a comparison of the two driving the same output transformer. The Inverted Triode tube presented a power bandwidth of 2 Hz-500.000 Hz whereas the 300B tube had a bandwidth of 15 Hz-100.000 Hz. Same transformer, same driver tube, but 5 times the bandwidth for the Inverted Triode tube.
The output stage is driven by the input tube with the help of an amorphous double-C core signal choke. The output stage then drives a high-quality double-C core output transformer with a bifilar winding technique, which gives the transformer supreme frequency extension and supreme transient signal response parameters.
Bias Adjustments
Just like the Incito S, the Impera II’s bias can be adjusted by the user to find just the right balance between warmth and control. Both Ron and Michel had made sure to adjust the respective preamps to their default settings. As I initially wanted to experiment with this for the Impera, I requested instructions for the procedure but as time went by, I decided that the factory setting was actually perfect and no adjustment was required. For those who want to experiment with this, the instructions are as follows.
Note that current Impera models have internal bias value displays but my earlier sample requires a simple volt-meter. The black ground wire should be connected to the Impera’s rear panel earth connection while the red “live” wire should be connected to the rearmost E280F tube’s pin 1 (first pin after the break) while adjusting the potentiometer. The procedure must be done for the left- and right channels individually. The minimum usable value is 150, the maximum is 180. Michel indicated that the minimum audible increment is 5 and that the factory-recommended setting is midway between these values, so 165. He left my unit on 170.
I owned the Accuphase C3900 solid state preamplifer, then replaced this with the tube Nagra HD Preamp HV. With the Nagra, there is a significant improvement in bass quantity and quality (for example bass textures), amongst other improvements.
It seems as if the “old saw” about tube units lacking bass when compared to their solid state counterparts (at least for preamplifiers) is no longer valid at the top level.