Alieno 250 LTD MkII

Reference 3AB Stereo 250W Power Amplifier

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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 250 LTD is frankly a ground-breaking product that has no peer. There is simply nothing else in the world that has this technology or can deliver this performance. It is the first and only amplifier in the world utilising two 300B tubes generating 250W per channel. It is an OTL-OCL (Output Transformer Less & Output Capacitor Less) Single Ended, pure Class A amplifier. It is not a hybrid tube/transistor amplifier.

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.

Alieno 250 LTD

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). With 250W per channel and generous amounts of current, the Alieno 250 LTD ensures authoritative control of speakers in any dynamic range, precisely tracking the complex impedance load demands of even the most difficult to drive loudspeakers, allowing the full freedom to choose their typology.

Alieno 250 LTD

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.

Allowing an Unlimited Choice of Speakers

The Alieno 250 LTD can drive any speaker, including the brands and models that are considered to be the most difficult speakers to match with an amplifier. With a damping factor that exceeds one hundred and a managed output current of approximately 200A, Alieno have created an output power capability that is enviable even for a transistor amplifier, let alone a single ended tube output stage. All this with NO negative feedback. Audiophiles who wish to enjoy the ultimate immediacy and purity of the Single Ended Triode sound quality are no longer restricted to a small selection of high efficiency speakers. You can now enjoy this sound on your favourite loudspeakers!

Alieno 250 LTD rear side

Fuss-Free Tube Management

The Alieno 250 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 300B power tubes. This design places very little stress on the tubes and they will last well beyond their typically rated five thousand hours. The Alieno circuitry results in a dissipation of the 300B tubes of about 20W which is half of the maximum expected by tube manufacturers. 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.

A Monumental Achievement!

The Alieno 250 LTD is a no-holes-barred attempt at making the world’s best power amplifier. It 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 250W of power giving the owner the freedom to choose any speaker are not just rare attributes – this is the ONLY amplifier in the world which can do this.

Putting aside it’s 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 250 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. Mind blowing.

Alieno 250 LTD side view


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Product Specifications



Item Vacuum Tube Stereo Power Amplifier
Type Pure Class A, Single Ended OTL-OCL
(Output Transformer Less & Output Capacitor Less), with proprietary LTD technology.
The acronym means: “Loudspeaker Tube Direct”.
Tubes are used exclusively for amplification circuitry and solid state exclusively for the power supply section. No hybridisation of tube & solid-state technology.
Transistors are utilised for power regulation, stabilisation & safety circuitry ONLY.
Power Output 250W RMS continuous per channel (@ 3 Ohms)
Distortion Average 0.1%, Max 0.5% from 20 – 20,000Hz
Frequency Response ± 0.5dB from 5 – 100,000Hz
Internal Bandwidth > 1 MHz
Gain 22dB
Input sensitivity 2.5V RMS
Input Impedance 100 kOhms (irrelevant capacity)
Input Connectors RCA and XLR
Optimal Load Impedance 2 − 8 Ohm
Signal to Noise Ratio > 100 dB
Damping Factor > 100
Negative Feedback Negative feedback is totally absent (zero)
Slew Rate > 300 Volts/Microseconds
Output Current > 100A peak per channel
Tubes required per channel ECC82 x1 – Preamplifier and driver tube.
KT150 x1 – Stabiliser tube.
300B x1 – Output power tube.
Tube Management Constant optimisation of all tube operating parameters, including bias, over-voltage and over-current protection along with real-time output impedance management.
Auto adjustment of balance differences between each tube in the circuit.
Imprecisely matched tubes or individual tube lifecycle issues are wholly compensated by regulation circuits.
Protection features Thermal threshold independent for each channel.
One AC main fuse and five fuses on each power supply section.
Protection for wrong connection between power supply unit and amplifier unit.
Double timer for a gradual loading of the charge on AC power grid.
Each protection has its independent warning LED, including the fuses.
On/Off “thump” eliminated by delay relay transient protection.
Infallible loudspeaker protection circuitry.
Dimensions (including cables plugs on rear panels) Amplifier Unit
450mm (W) x 500mm (D) x 280mm (H)
17.7″ (W) x 19.7″ (D) x 11″ (H)Power Supply Unit
450mm (W) x 600mm (D) x 270mm (H)
17.7″ (W) x 23.6″ (D) x 10.6″ (H)
Weight 100 kg (220.4 lb) Net