S.I. Audio is a Neapolitan company and an Italian fine reality. Its founder, Eng. Fulvio Chiappetta, started his business designing and selling DIY kits. In next to no time, he felt the need of adding a complete and available production of audio equipments, becoming very soon a benchmark for the enthusiasts of tube amps and mains conditioners.
The product reviewed by ReMusic is the S.I. Audio Cult/I, a class-A stereo integrated amplifier with 75 watts per channel, which adopts an OTL and an OCL tube technology.
I have always appreciated the Output Transformer Less (OTL) technology. It was devised around mid twentieth-century by the designer Julius Futterman. During the boom of the transistors circuitry - which can provide high lab performances thanks to massive feedbacks - he preferred avoiding, in the vacuum tubes, the use of the output transformer. In fact, this one was considered harmful because of the reduced wave band and the introduction of negative rotations of phase. From the sound point of view, I think that the OTL technology can put together the purity and the transparency of the single-ended triodes - TSE - with the power of the transistors, and the result is a splendid blending between dynamic force and naturalness in the emission. Whereas is very simple to design and realize any transistor circuitry without output transformers, it is very hard to do it with the tubes. It entails lots of experience to handle at best the high electric powers at stake. In several realizations by S.I. Audio, in conjunction with the OTL, there is also the OCL technology which requires the elimination of the coupling capacitors. Doing that, it is possible to limit the negative intervention of the capacitors on the signal path.
Even though being a stereo integrated amplifier, the Cult/I has two chassis with separated power supply. The Cult/I weighs about forty kilos and that says a lot about the commitment of the enthusiasts, when they have to solve the handling difficulties of the earth/volume and the related filled spaces. Actually, the main chassis mounts fourteen power and driver tubes, so it needs plenty of air, mostly on the top, as the heat emanated from the eight Sovtek 6C33 tubes, has not to be underestimated.
The case dedicated to the power supply weights a lot indeed. Therefore, when you put it on the ground, keep it possibly far from external electric sources, so to avoid any negative interference.
At this point, you can easily realize that also the packing box is very accurate. It consists of two wooden cases, with inside reinforced blocks, screwed in attachment points. This system appears very complex and not very intuitive, so to envisage a brochure with instructions for packaging. A separate protected wrap contains the tubes, previously selected and calibrated in the factory. Since they are numbered, that can be placed exactly in the - also numbered - ceramic sockets.
Same thing for the three pairs of driver tubes: two ECC83, two E88CC and two ECC82.
It is very simple to put the tubes into the ceramic sockets, thanks to the high quality of these connectors. Of good quality are also the gold-plated RCA pins for the inputs, one of which is a balanced XLR. Particular attention deserve the excellent output connectors, which allow the screw clamping also for the 4 mm banana pins and therefore a high security standard.
Extreme care has also been put in the power supply, which is separated for the two channels in order to define the totally dual/mono circuitry of the Cult/I.
The Cult/I has an original look. When switched on, the black frontal panel in Plexiglas becomes light blue all around the three knobs, made by hemispheres of lucid heavy metal. The eight triode tubes turn into red and reflect themselves in the polished mirrored stainless steel of the top panel. At their back, five 4.700 microfarads capacitors - black, bulky, pricey, and of excellent quality - built by the British BHC. They seem to be on sentry duty!
The small wooden sides refine the line making it lighter and less techno. At a glance, the device looks less heavy than it actually is.
The Cult/I has an actual tube preamp stage, testified by two pairs of ECC83 (12AX7) and ECC82 (12AU7) tubes, used as active preamp and buffer, and the E88CC (6922) tubes, used as output stage. We can hence affirm that the CULT /I is a preamp plus a power amp in one chassis only.
The eight amplifying tubes are the Soviet 6C33, which deliver a power of 75 watts, but I consider this data underestimated, as, at the listening, they seem more, in terms of control and dynamic impulse. The 6C33 are very strong and silent and they used to be employed on the Russian MIG jets. Their heating up is indirect so, notwithstanding the immediate warmth they produce, they can be considered operational only after one hour of functioning. The complex and delicate industrial production of these kind of tubes, determines a quite large tolerance, so it is quite expensive, in terms of money and time, making ready a match of eight tubes with similar electric characteristics. The manufacturer calibrates the bias directly, so it is automatically kept constant by the machine without needing any further realignment or correction.
I must admit that I like the charm of the illuminated tubes that, in my room, seem truly enchanting.
However, the most captivating thing is the sound coming out from the Cult/I
In the classical music, there is a beautiful sense of transparency, as though the soundstage has been polished and wiped, with no grain of dust that could stain an imaginary see-through glass. This amazing feeling continues also with the lowest notes of the timpani, the bass drum and the double basses. These instruments seem playing in a very clean and fresh space, without altering the low tonalities and the tone colour of the single instruments.
While listening, I have the idea of a very quick transient response, so I decided to make a test with the rock music. I started with Bob Dylan followed by Guns ‘n Roses.
I have been astounding in catching the perfect attacks and releases of voice, guitar, electric bass and harmonica, which are performing in a musical setting, punctuated by tune and synchronism.
The Cult/I has great dynamic skills and is able to give back the micro information. That means that this good integrated amp reproduces the musical details in a sober and polite way, with a fair richness of particulars. The macro dynamics is of excellent fabric and succeeds in involving the psyche in a careful but mild and relaxed listening, nonetheless complete and fulfilling.
With jazz music, you can appreciate the output of the musical message in your environment. The sound stage is large and evenly deep, but not so deep to loose detail and transparency. The control is remarkable and expresses itself, at the same time, with the emission of both bass and high frequency notes.
I am looking for some faults but I cannot find anything. Maybe I can say that the micro contrast is just a bit less than the excellent macro contrast, but I am also sure that you can reach the right balance by using speakers more efficient than mines (“only” 87 dB!).
In this sense, I want to stress the great driving capability of the S.I. Audio gear, which is given with sureness, resolution and decision. A real champion among the OTL tube amplifiers, whose technology notoriously suffers the sensitiveness variations of the speakers, but not the efficiency. So, you can dare beyond any limit and match the Cult/I with speakers that you have never thought to connect to tune amps.
The best quality of the Cult/I is, with no doubt, the ability of beating time and rhythm with naturalness and spontaneity. During the test, you cannot avoid to beat time with hands and feet.
As to the cables, I have used the White Gold as signal cables and very neutral cables as speaker cables. I must admit that the Cult/I is not so idiosyncratic to cable changing, but I suggest to employ cables that can exploit the great transparency and dynamic skills of this integrated S.I. Audio. For example, any cable with a silver conductor.
Finally, this S.I. Audio Cult/I is a great device, appreciable for its excellent transparency and dynamic skills expressed in a timbric contest of absolute rigor.
Moreover, it does not surrender to hard driving speakers, so you can insert it in every audio chain without any problem of interfacing.
High recommended if you are looking for purity, control and class-A tone in tube amplification.
Official current price in Italy: 3,900.00 euro
Associated equipment: to Roberto “The Rock” Rocchi's system
