Alieno 100 LTD OTL-OCL 2A3 Tube 100W Stereo Power Amplifier
With the same innovative technology used for the progenitor ALIENO 250 LTD, also ALIENO 100 LTD is the first and unique tube amplifier with two 2A3s that delivers 100 Watts per channel.
ALIENO 100 LTD is an OTL-OCL (Output Transformer Less & Output Capacitor Less), Single Ended, pure Class A. ALIENO 100 LTD is not a hybrid tube & transistor amplifier.
The LTD exclusive “Loudspeaker Tube Direct” technology allows the tubes to be used exclusively for the amplifier circuits, while the transistors are used exclusively for the power supply and protection circuits. No hybrid tube/transistor sound!
In addition to the two 2A3 amplifier tubes, ALIENO 100 LTD differs from the more powerful ALIENO 250 LTD for the single cabinet that contains both the power supply and the amplifier sections. For all the other choices of circuits and components, ALIENO 100 LTD adopts the same “no compromise” construction philosophy of ALIENO 250 LTD.
This extraordinary amplification system is virtually the definition of extreme high-end audio. Audio engineer & inventor Fulvio Chiappetta conceived the theoretically perfect amplification system but his ideas were considered impossible to implement. What he wanted to achieve had never been done before – design an amplification system with the purity, refinement and emotional communication of a single ended triode design however with the power to drive any real-world speaker without the use of an output transformer, a hybrid design or a solid-state device in the signal path. Many designers in the history of audio have tried to achieve this ‘Holy Grail’ type of amplifier but it was deemed impossible. After 30 years of experimentation & development, Fulvio unveiled his Alieno amplification system, which consists of a preamplifier and a choice of two power amplifiers. The audiophile world is still trying to make sense of his achievement and the lucky few who have heard the Alieno sound are saying it’s genre redefining.
The Alieno 100 LTD was launched at the Rome Hi-Fidelity Show in November 2021 and follows in the footsteps of the acclaimed 250 LTD. Whereas the 250 LTD is a twin chassis design that uses a pair of 300B tubes to produce 250W, the 100 LTD is a single chassis stereo power amplifier that uses two 2A3 tubes to produce 100W.
To be frank, these two power amplifiers are ground-breaking products that have no equal. There is simply nothing else in the world that has this technology or can deliver this performance. They are the first and only amplifiers in the world using an OTL-OCL (Output Transformer Less & Output Capacitor Less) Single Ended, pure Class A topology delivering high power. They are not hybrid tube/transistor amplifiers.
At this point, you cannot be blamed for thinking “Impossible, this is some kind of marketing hype!”. Spend a moment listening to this amplifier and you will realise that 30 years of uncompromising development has yielded something very special. The secret here is the proprietary LTD technology (Loudspeaker Tube Direct) which allows the use of tubes exclusively for amplification circuitry with transistors used exclusively for power supply and protection circuits.
Eliminating Output Transformers
Output transformers are used in most tube power amplifier designs and have a significant influence on the sound which is why so many high-end designs place a lot of emphasis on the quality of this transformer. When listening to OTL (Output Transformer Less) designs which have eliminated the output transformer, you can hear the absence of the transformer (however traditional OTL designs have other issues).
When a signal moves through an output transformer, it is converted into a magnetic field and subsequently
re-converted back into an electrical signal. These two transformations result in a degradation of the signal which is heard as a loss of purity and immediacy in the sound. Eliminating the output transformer from the signal path is therefore extremely important if you are searching for ultimate transparency. In its absence, the true sound of tubes can be expressed in all their fullness. In fact, some of the flaws generally attributed to tubes, such as slowness, lack of impact & poor low frequency control, are to a large extent caused by the output transformer, not the tubes themselves.
Single-Ended Triode Circuitry
Single Ended Triode (SET) circuitry is renowned for its magical musicality and notorious for its lack of power. The ideal amplifier for purity and clarity should combine the positive qualities of single-ended outputs with the elimination of an output transformer. It should also have sufficient output power to drive any reasonable load.
These desires were Fulvio’s motivation for inventing the innovative circuitry of the LTD design. Output power comes from the power tube, while supplies to the load (voltage & current) are supported by Alieno’s unique semiconductor power supply process (current).
Not a Traditional Hybrid Design
The Alieno LTD technology differs profoundly from traditional circuits defined as ‘hybrid´ which in addition to the output tubes, also include the use of transistors. In a hybrid system, after voltage amplification by the tubes stages, the signal is then delivered to the solid-state section for current amplification.
In hybrid designs, the tube is tasked with increasing the signal voltage only, but not its current. This generates a partial, but important, loss of the tube signature on the sound. This precious purity and tonal structure are the desirable aspects of single-ended sound which must not be lost if aiming at ultimate sound quality. The ‘magic’ of tube sound is thus only partially expressed in hybrid designs, since only the voltage modulation supplied to the loudspeaker has those tube qualities while the current supply adds the signature typical of transistors.
Furthermore, if we consider that although quantitatively inadequate to the direct driving of a speaker, the current supplied from a tube (not modified by the transformer´s influence) is at its core excellent for speed, impact and modulation, the ‘perfect amplifier’ would be designed with the ability to preserve 100% of these virtues and deliver them unchanged to the speaker connectors.
Fuss-Free Tube Management
The Alieno 100 LTD delivers a practical, stable, reliable and fuss-free ownership experience. There is no requirement for manual bias regulation thanks to the ingenious electronic circuit management of the KT150 tubes. All parameters are constantly optimised over the entire operating life of the tubes. In addition to the security and consistency of a system which is always perfectly fine-tuned regardless of electrical grid conditions and power tube aging, the control circuits allow “Tube Rolling” without worrying about bias regulation.
Another significant advantage for users is the extended longevity of 2A3 power tubes. This design places very little stress on the tubes and they will last well beyond their typically rated five thousand hours. Balances between various sections of the circuit are intrinsically managed and ensured through active circuitry and precise passive components selected for their sonic purity. There are no trimmers to adjust and no negative feedback – just the purity of the original tube sound.
What is the difference between the 100 LTD & the 250 LTD?
The Alieno LTD technology is at the heart of what makes these amplifiers unique and special. It allows the full sound of the power tube to come through, un-manipulated by output transformers & complex circuitry while producing enough power to drive real world speakers. The 100 LTD is not a cheaper alternative to the 250 LTD – it is simply another interpretation of the LTD technology with a different tube.
The 300B is undoubtably renowned for its sonic attributes. Interestingly, if you ask experienced audiophiles and tube aficionados to name the most musical tube they have ever heard, many also nominate the 2A3. However, due to the very low power output of this tube, 2A3 SET amplifiers are only used with extremely high sensitivity speakers (horns). After the success of the 250 LTD, Alieno decided to design an interpretation of the LTD circuit specifically for the 2A3 tube and the result is quite stunning.
The Alieno 100 LTD has a clear, transparent and dynamic sound just like the 250 LTD. Tonally, it can be described as very refined, graceful, charming….sophisticated. It has an immediacy that places the listener in the front row of the concert hall, giving the experience of a personal intimacy between the listener and the artist.
With 100W available, it can drive speakers with mid-high efficiency beautifully and even low efficiency speakers in smaller rooms. If you require the ability to drive low efficiency speakers with headroom, speakers with challenging impedance profiles, need to achieve high sound pressure levels or are using a large room, the 250 LTD is recommended as a more suitable choice.
A Monumental Achievement!
The Alieno 100 LTD is uncompromising in its design and incorporates multiple exclusive technologies and topologies to create a once-a-generation heirloom piece. The SET topology, lack of output transformer, lack of any solid-state device in the signal path and 100W of power giving the owner the freedom to choose from many speakers are not just rare attributes – this is the ONLY amplifier in the world which can do this. To do this with the exquisite sound of the 2A3 tube is a dream come true for many audiophiles.
Putting aside its unique design and no-expense spared build quality, when combined with the Alieno Preamplifier it is simply one of the best sounding stereo amplification systems ever created. It is sonically transparent to the source and facilitates nothing but the music. It has taken one man 30 years to develop and then hand-build a rare piece of audiophile utopia. There is evidence of engineering genius all over the Alieno 100 LTD and once you experience it, you forget everything you thought you knew. Considering how much money audiophiles spend over a lifetime of trying different amplifiers, the Alieno is a revelation. Meet THE destination amp. Sublime emotional connection.
Specifications
Power Output
100 W RMS continuous per channel @ 3 Ω
Distortion (THD)
Typically 0.1%, max 0.5% (20 Hz – 20 kHz)
Frequency Response
±0.5 dB from 5 Hz to 100,000 Hz
Internal Bandwidth
> 1 MHz
Gain
22 dB
Input Sensitivity
2.5 Vrms
Input Impedance
100 kΩ (irrelevant capacitance)
Input Connectors
RCA, XLR
Optimal Load Impedance
2–8 Ω
Signal-to-Noise Ratio
> 95 dB
Damping Factor
> 60
Negative Feedback
None (zero NFB design)
Slew Rate
> 200 V/µs
Output Current
> 55 A peak per channel
Tubes Required (per channel)
1 × ECC82 (preamp/driver), 1 × KT150 (stabilizer), 1 × 2A3 (power output tube)
Tube Management
Automatic optimization of tube parameters (bias, voltage, current), real-time impedance management, auto compensation for mismatch and tube aging
Protection Features
Independent thermal protection per channel; main AC fuse + 5 PSU fuses; PSU/amp connection protection; dual-stage AC load soft-start; per-protection LED indicators; delayed start to eliminate “thump”; full loudspeaker protection
Dimensions (W × D × H)
45 × 50 × 33 cm • 17.7″ × 19.7″ × 13″
Weight
45 kg • 99 lb
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