OTL amp owners

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
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#81
Dear Stavros,

Thank you for your candid and detailed reply. It is refreshing to hear (ah, read) a designer being thoughtful and intellectually honest about the ideal and less ideal speaker matches for his amplifier.

It is comforting to learn that you understand and agree with the sonic character I hear from some OTL models. I think a single-ended OTL likely is (for an appropriate speaker) the "holy grail" of tube amplification. The Collatio II may very well be the best-sounding amplifier ever made for horn loudspeakers.
 

LL21

Active Member
Dec 26, 2010
10,550
2
38
#82
Hello Ron
Thank you for the compliments.
Happy to be among the company here at WBF.

I do tend to agree with you on the basis that ,at least to the OTL models i have heard,there is a certain leanness or absence of richness to say it better in OTL sound in general.

I have to state in front that the Collatio is a current amplifier,and not a voltage amplifier which is the norm.The majority of speaker drivers(dynamic drivers usually) will not like that. There is a certain niche of speaker drivers/technology which like and prefer to be driven by current amplifiers.Compression drivers are one of them.Some ribbons(usually transformer coupled,like the ones we use),some very low Q dynamic drivers as well do like current amplifiers.

In other words the Collatio is not designed to be an all around amplifier,but specifically designed to drive a certain category of speakers.

That said,i can say that the Collatio does not present the normal OTL sound traits.You may attribute this to being SE (the distortion spectrum is vastly different),the fact that is a current amplifier,or that carries a lot of iron in the signal path(being choke loaded parafeed) ,or even having a big DHT as driver tube.Any of these design choices could deviate the sound of Collatio from the normal OTL sound,but i cannot separate the effect that each of these parameter have, on the end result.

In any case it does not sound like a lean amplifier ,but at the same time it is not an amplifier we would recommend to speakers which would not be happy with current drive.And the majority of commercial speakers are just that .

Cheers
Stavros
Amazingly great post...intellectually honest, super informative, fun insights into the alchemy/science of building a system and understanding WHY things happen scientifically.
 
May 30, 2010
13,970
42
48
Portugal
#83
(...) Thank you for your candid and detailed reply. It is refreshing to hear (ah, read) a designer being thoughtful and intellectually honest about the ideal and less ideal speaker matches for his amplifier. (...)
Ron,

Just to remember that Ralph Karsten of Atmasphere also wrote long posts in WBF debating the current amplifier / voltage amplifier subject in OTLs, how they should measured and which speakers should / should not be used with OTLs. See our old and long thread http://www.whatsbestforum.com/showthread.php?11452-Constant-Power or mainly for speaker advice: http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
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#84
Thank you for reminding me!

Ralph has been very generous here with his time, his experience and his intellect!
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
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48
Beverly Hills, CA
#85
Has anyone made any progress on understanding the Alieno Ltd. 250 OTL?
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#86
My friend bought Alieno 2 months ago and sold Convergent stereo and is happy
Do you know which Convergent amplifier your friend had before the Alieno?
 

GMKF

VIP/Donor
Aug 15, 2017
320
3
18
Munich
#87
Has anyone made any progress on understanding the Alieno Ltd. 250 OTL?
I thought about quite a bit...
After reading about it, I found something while on Google.

I may be totally wrong here.

It's a OCT/OTL with both tubes working in cathode follower 'mode'. The trick is that the powersupply is left floating and moves up and down with the voltage of the output signal. (In my opinion this also explains the solid state power supply) That's probably were you get the juice.

image024.gif

I think the top tube is the 300B and the bottom tube has been replaced by a tetrode (KT150).
 

gian60

Active Member
Apr 17, 2016
1,255
13
38
#88
My friend had JL 5 Black Pack stereo
Wanted to change to buy mono JL Statement,but expensive and difficult to have so listen Alieno and bought and told me is much better than his Convergent
I will go to visit my friend with Ked when will come to my home end of february and to listen Torqueo
I never listen and saw Alieno even if company producer is in Naples but worldwide distributor is my friend living half an hour by car from my home

My friend has pre Convergent black path with TAD R1 and Sme 3012 and Lenco
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#90
I thought about quite a bit...
After reading about it, I found something while on Google.

I may be totally wrong here.

It's a OCT/OTL with both tubes working in cathode follower 'mode'. The trick is that the powersupply is left floating and moves up and down with the voltage of the output signal. (In my opinion this also explains the solid state power supply) That's probably were you get the juice.

View attachment 38158

I think the top tube is the 300B and the bottom tube has been replaced by a tetrode (KT150).
Why haven't more amplifier designers employed this design, do you suppose?

Is this design similar in result (if not in topology) to a hybrid amp with solid-state output stage?
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#91
My friend had JL 5 Black Pack stereo
Wanted to change to buy mono JL Statement,but expensive and difficult to have so listen Alieno and bought and told me is much better than his Convergent
I will go to visit my friend with Ked when will come to my home end of february and to listen Torqueo
I never listen and saw Alieno even if company producer is in Naples but worldwide distributor is my friend living half an hour by car from my home

My friend has pre Convergent black path with TAD R1 and Sme 3012 and Lenco
Thank you, Gian.
 
May 30, 2010
13,970
42
48
Portugal
#92
I thought about quite a bit...
After reading about it, I found something while on Google.

I may be totally wrong here.

It's a OCT/OTL with both tubes working in cathode follower 'mode'. The trick is that the powersupply is left floating and moves up and down with the voltage of the output signal. (In my opinion this also explains the solid state power supply) That's probably were you get the juice.
(...)
I think the top tube is the 300B and the bottom tube has been replaced by a tetrode (KT150).
It does not seem possible - Alineo writes that the KT150 is for power supply stabilization for the 300b - probably as a series regulator, as used for example by ARC (6550) and Lamm in the ML3. ( one 6c33).
I would also like to know how they do it!
 

GMKF

VIP/Donor
Aug 15, 2017
320
3
18
Munich
#93
Why haven't more amplifier designers employed this design, do you suppose?

Is this design similar in result (if not in topology) to a hybrid amp with solid-state output stage?
There hasn't been much RnD in OTL amps... You also really know what you are doing when you sell OTL's commercially (blow up's are not good for customer relation's). Building a hybrid amp is probably easyer and you can still flavour the sound with tubes....

The design probably isnt similar in result as hybrid amp's, but the sound can't be told by it's cover.
The lack of lean-ness you explained in your "review" is probably due to harmonic distortion. For example the Einstein amp's have aprox. 0.02% quoted distortion, Alieno quotes' 0.1%.

Overall it probably measures mid way between a Hybrid/OTL and Non-OTL tube amp.

Specs in italian:

OTL/OCL con tecnologia proprietaria LTD
Potenza di uscita
: 250 Wrms per canale da 20 Hz a
20.000 Hz su di un carico di 3 ohm
Distorsione
: tipica 0.1%, massima 0.5% da 20 Hz a
20.000 Hz
Risposta in frequenza:
ingresso – uscita 5 ... 100.000 Hz +
0.5 dB
banda passante interna >1 MHz
Guadagno
: 22 dB (nota 3)
Sensibilità di ingresso
: 2.5 Vrms
Impedenza di ingresso
: 100 kOhm
 

GMKF

VIP/Donor
Aug 15, 2017
320
3
18
Munich
#94
It does not seem possible - Alineo writes that the KT150 is for power supply stabilization for the 300b
In my opinion the bottom tube can sort of be a power regulator for the top tube.... because the it regulates the cathode of the top tube. The cathode of the KT150 is controlled by the bottom floating supply.

I would also like to know how they do it!
Im just giving my best guess here. I hope someone could translate the italian brochure ;) https://admin.abc.sm/upload/4952/pagine-da-fds-249-alieno.pdf
 
May 30, 2010
13,970
42
48
Portugal
#95

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#96
Maybe Gian and Kedar can figure out more about the Alieno during that visit.

It would be surprising if the Alieno truly proves to be a unique and innovative design of which no one else has conceived. But Italians have pushed envelopes from time to time (e.g., Enrico Fermi, Enzo Ferrari).
 

GMKF

VIP/Donor
Aug 15, 2017
320
3
18
Munich
#97
Maybe Gian and Kedar can figure out more about the Alieno during that visit.

It would be surprising if the Alieno truly proves to be a unique and innovative design of which no one else has conceived. But Italians have pushed envelopes from time to time (e.g., Enrico Fermi, Enzo Ferrari).
That would be very nice.
I would imagine that the Alieno design team has come up with a well thought out design (based on stuff we know) if not done something brilliant.

Most of our modern ideals and ideas came out of Italy at some point when Italy was the center of knowledge (Renaissance).
So why not shake up the amp world ?
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#98
The distributor of the Alieno confirms that only tubes are providing both the voltage and the current amplification. Somehow the big power supply allows the KT-150 allegedly to generate the current for the 300B.

Does anyone have a theory as to how this could be possible?
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
#99
I just 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.



image.jpg



* * *

Would the electronic engineers here please get to work reading and understanding this description, and explaining the circuit design of the Alieno to the rest of us? Thank you!
 

Ron Resnick

Site Co-Owner, Administrator
Jan 25, 2015
5,075
30
48
Beverly Hills, CA
I thought about quite a bit...
After reading about it, I found something while on Google.

I may be totally wrong here.

It's a OCT/OTL with both tubes working in cathode follower 'mode'. The trick is that the powersupply is left floating and moves up and down with the voltage of the output signal. (In my opinion this also explains the solid state power supply) That's probably were you get the juice.

View attachment 38158

I think the top tube is the 300B and the bottom tube has been replaced by a tetrode (KT150).
GMKF, I think you are on the right path and getting warm.
 

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