Alieno LTD 250 Amplifier

Ron Resnick

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Alieno LTD.jpg





I want to start a new, dedicated thread focused on the Alieno LTD 250 amplifier.

I became aware of this amplifier after bonzo75 heard it and wrote about it.

I then became very interested in this amplifier when I saw it and heard it myself in the dedicated listening room of Audioquattr in the Netherlands.

The amplifier is described in marketing literature as an OTL, but that was controversial from the beginning of the discussion.

For this dedicated thread I will start by re-posting my post about finding on an Italian audio forum a link which led me to a technical description of the Alieno.
 

Ron Resnick

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I spent about four hours using Google translate to translate from Italian to English dozens of posts about the Alieno 250 LTD amplifier on an Italian audio forum. The translated posts did not tell me anything.

But then I found this:

http://www.audio-activity.com/si-audio041114.html

. . . a large excerpt of which Google translated to English as follows:


The LTD implementation has nothing to do with the traditional circuits, let alone with those defined hybrids that require the use, in addition to the tubes, also of the semiconductors in the amplification line.

The hybrid amplifiers, in fact, try to reconcile the softness of the tube with the imperiousness of the transistor, entrusting the first to the amplification in voltage and the second to the current one. In doing so, however, the "magic" of the tube sound is only partially expressed, since only the modulation of the voltage supplied to the loudspeaker has a valve imprimatur, while all the current supply remains the typical one of the transistor (of course with all its pros and cons).

The new technology LTD is inspired, instead, to a different design philosophy: the valve section, Single Ended in pure class A, provides the load as much voltage as the current, the latter supported by a particular process of power supply semiconductors.

Short technical study

We report in the attached figure an extremely simplified circuit that helps to understand how the LTD system works. Let's start by examining the right half of the circuit, the most innovative one. The output current from the final pipe drives the load through a very low value resistance (in the figure indicated with "R"). The voltage drop at the ends of this resistance is used to control the modulation of the output current at the power supply section (which therefore works as a current and not voltage generator). The output of the feed section, as shown in the figure, is connected to the load in parallel with the output of the final valve. By operating in this way, the tube drives the load both in tension (directly) and in current through the sophisticated feeding system indicated above.

On the left side of the circuit you can see the extreme simplicity of the signal path, which crosses only two stages, the one equipped with the driver valves (ECC82), configured in asymmetric SRPP, and the one using the 300B finals (one per channel, in Single Ended Class A configuration with cathodic output). The coupling between the stages is direct, without any capacitor. Finally, the KT150 (high power and latest generation valve), used as an active current generator, feeds the 300B in the most linear way possible, allowing it to express itself in the best possible way.

Last technical note: the mass (indicated with GND on the extreme right of the circuit in the figure) has the particularity of being floating: it preserves the safety of the speakers as it inhibits the transit of the signal in the event of any functional anomaly.


Alieno.jpg
 

Ron Resnick

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I interpret the translation to mean that the load (i.e., the loudspeaker) is seeing current delivered to it directly by the transistor power supply.

I think I would characterise this design as a "semi-hybrid" design in that the voltage side is tube driven with a tube output, and the current side is tube driven but with a solid-state output. I think this topology is somewhere between a hybrid amp and an all-tube amp.

I would not call it an OTL.

My understanding is that the speakers are connected directly somehow to the voltage output of the 300B, while the current output of the 300B is fed to a solid-state amplifier.

The solid-state stage amplifies the current output from the 300B. The speakers are connected directly somehow to the current output of the solid-state amplifier.

Somehow the voltage output of the 300B and the current output of the solid-state stage are summed, and the summed effort is connected to the speaker terminals.
 

Ron Resnick

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Then Stavros, the famed Designer and CEO at Aries Cerat, commented on the information about the Alieno, and I was very grateful for Stavros' thoughtful and gracious input:

Stavros wrote:

A hybrid amplifier would use tubes as voltage gain,driving a SS output stage.
Ron, SS are "OTL" (well there are exceptions) but the term is not used for Solid state designs.They do not use OPT as it is not needed.

This design,though it is not wise to comment on other designer's work,does not work like usual hybrid designs.

In hybrid designs,the tube stage only delivers drive to the output stage and not to the load.
In this design,the 300B does deliver current to the load(although it is limited to it's max 50-70mA ) which only is enough for a few milliwats for a normal speaker.The SS section of the output stage ,"sample" the current of the 300B which drives the load,and "boosts" the current.Now,the SS section, does in a way,mimics the transfer curves of the tube,so the distortion and sonic footprint of the amp is leaning more towards the 300B not the SS.

We have experiment in this technology,and a (distant though) member of this technology is the Ianus.

Having designed and lived with many examples of similar tech,it is not a surprise if the Alieno does indeed sound like a tube amp and performs marvelously if.

Cheers

Stavros​
 

Ron Resnick

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I look forward to Gian hearing this amplifier in the system of his friend (who formerly had a top-of-the-line CAT amplifier), and I look forward to Kedar hearing it again as well.

While traditionally I am ideologically opposed to solid-state amplification (except, possibly, to drive Apogee ribbon speakers) my ears trump my ideology.

I thought this Alieno sounded great! I find the circuit design -- in which you are getting directly the voltage side (and the sound) of a 300B and indirectly the current side (and at least the flavor of the sound) of a 300B -- innovative and fascinating. Getting the sound and flavor of a 300B with the voltage delivery directly from the 300B and with the current delivery of a solid-state output stage seems, in topology, closer to a tube amp then a conventional hybrid amplifier the entire output stage of which is solid-state.

I am very seriously considering this amplifier, as well as a high-power SET amplifier, for the Pendragon ribbon panels.
 

bonzo75

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His friend previously had CAT, top of the line
 

Ron Resnick

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Ah, okay. Thank you.

I corrected my post above.

CAT versus Alieno actually is a very interesting comparison in that CAT is, I think, a very neutral sort of tube sound.

Maybe Gian can find out from his friend more listening impressions of CAT versus Alieno.
 

Ron Resnick

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Brad (Morricab), You are such a fan of the KR Kronzilla (and with excellent reason!) I wish you could compare it directly to the Alieno!
 

Ron Resnick

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Allegedly 250 wpc
 

LL21

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Brad (Morricab), You are such a fan of the KR Kronzilla (and with excellent reason!) I wish you could compare it directly to the Alieno!

I was just reading up on KR...saw that their DX monos are 100 watt SETs and their DXL monos are 140-watt push pull. Presume you are still after minimum 150watts for the mighty Pendragons?
 

Ron Resnick

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Yes, Lloyd. I am looking to solve my SET puzzle with about 150 watts, but not push-pull. So I am focused on AM Audio 833S Ultimate.

KR is great, but it is a conventional reverse hybrid — fewer tube stages than the Alieno.
 

LL21

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Yes, Lloyd. I am looking to solve my SET puzzle with about 150 watts, but not push-pull. So I am focused on AM Audio 833S Ultimate.

KR is great, but it is a conventional reverse hybrid — fewer tube stages than the Alieno.

Got it...look forward to your decision.
 

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