1. The premise .
I state that I have never been, in my passion for hi-fi, particularly interested in tube amps. I had always regarded as a thing of the past, a sort of Jurassic universe created by old fans, unable to give evidence of progress, represented by FET transistors, and various amenities.
I've never even been a fan of electronics, except in fairly superficial, searching in the solid construction and good sound equipment, rather than the refinements circuit at any cost.
so happens, quite by chance that one day last year (2003) find me to read web pages of the site www.audiocostruzioni.com , a site that shows very young then several pages of DIY, doing, as they say, drop the eye on the achievements of Giuseppe Marotta, enterprising fan from Sardinia, with an obvious passion for the valves and circuits OTL (Output Transformer Less ).
The enthusiasm that the few lines they are send to the player who decides to contact him, helped by the interest in this plant from hearing a friend of Brescia, made with ARC tube pre, tube monoblocks Unison Research (with 845) and high-efficiency speakers DIY.
The interest of the undersigned is directed (God only knows why) on two monoblocks based circuitry and power valves Cyclotron 6C33C-B, valvoloni Russian military dimensions exaggerated. But maybe the size is, unconsciously, in making decisions.
are taken the necessary agreements between the parties and the project starts with the basic requirement tied to the construction of an amplifier (two, but ...) capable of driving the best two speakers B & W Nautilus with 90 dB sensitivity.
Here are a few clicks on the initial draft, with the description of the designer.
OTL 6C33C
I've always been attracted to the readings on the tube amp otl, describing amplifiers with low distortion, with an extremely wide frequency response with low damping and extraordinary. Otl amps are significantly different from all other valves, starting from their typical pattern used by most of the output transistor and the highest technical level due to its lack of output transformer. Of course, in a spirit of DIY I switched from reading the facts and as the first prototype I built using a final four 6AS7 OTL stereo per channel the scheme used has been published in Glass Audio 02/90 by Bruce Rozenblit.
The end result was considerably above what I expected! so much so that when I did listen to its present owner, my friend Antonio who wanted aIl'istante, the prototype is working for about four years and drives a pair of BW 801 series in the first suspension of 85 db efficiency, and notoriously difficult to drive, the sound is the highest level.
Encouraged by the excellent results I have gone to study a scheme and to build my final two otl monoblocks using Output configuration Cyclotron patented Electro and recovery from atmasphere and Graaf.
I used as an input 12AX7 preamp-sfasatrice followed by a voltage amplifier and 5687 as a pilot in that 6S4A cathode follower configuration 6C33C finals, the first three stages are DC coupled and ' single coupling capacitor is between the 6S4A and 6C33C.
otl Configuration is pure, without capacitors between the power tubes and speakers, and how to use a fast fuse protection that stops in the unfortunate event that it inhibits one of the final.
The sound is immediately striking for a bandwidth very extensive, with significant benefits in mid-high range and bass amp with a damping from a transistor. Among the great qualities of sound and space and depth with incredible detail, listening to the lyric soprano voice is exciting, with no inflection in moments of high dynamic range.
After I listened to the various configurations of tube amps are my favorites and have been operating for two years without any failure or replacement of valves.
2. The implementation of the project.
The project therefore originated from the preliminary draft, but will the small adjustments during gestation (long enough for different problems).
12BH7A A valve replaces the original 6S4A (from single to double triode) and 5751 (selected) replace the 12AX7. For the rest of the pattern remains unchanged.
Discussion "aesthetics" of the project is large and involves a variety of choices which will then be abandoned for the sake of simplicity and cleaning circuit.
Carry some photos of the construction of the final.
3. and there was light ...
Finally, after much discussion with regard to the final product and a long wait by the undersigned, the finals are completed in May 2004 after a long test of goodwill on the part of Joseph to fully evaluate the functionality and meet the design parameters.
I finally arrived at my house in June, ready to be tested on my system. In fact, compared to damage caused by the transport of cargo to our place (sic), the first week will be spent as a self-test on the installation of my son, to verify that the damage found is the one and you will not others are ... Trust is good, but ...
Here are some photos of the finals, in order to highlight also the circuitry interna.
4. listening and judging.
my total inexperience in the field tube led me to believe that a tube amp, needed a break after all modest to express their credentials and their sonic characteristics, as well as experience in transistor led me to believe.
It took three months instead because the amplifier could be considered stable in performance, without significant changes in overall timbre and detail ... You learn something new.
should be noted that in the meantime, I was also equipped with tube preamp (Conrad Johnson). But its origin from the flea market had apparently made no use running in, sviandomi from these fundamental aspects of amplification and tube.
The impact of the two units was therefore absolutely intense, deep, and extremely long time to get to give a serious assessment and ultimately to the units.
I require a final warm-up "important" by about half an hour, to express themselves better. Early plays can only raise concerns and stomach aches ...
The most immediately striking feature is the great sense of breath that the two objects return a scene open, airy space with a significant. Excellent reproduction of the depth of the stage and location of the various musicians and performers, of course, where records permit ...
This feature is one that puzzled me more, giving me a feeling of three-dimensional scene to which I was not accustomed ...
The mid-range, as expected, I think, by any tube amp, is wonderful, with an impressive sense of reality and dream at the same time. The voices, both male and female, are reproduced beautifully, with fine detail impeccable. I think the voices of Freddie Cole and Diane Schuur, rather than Allison Kraus or Dee Dee Bridgwater, absolutely real.
The treble is slightly behind the average, but with good extension and detail. This feature certainly helps to balance the issue in mid-high range of Nautilus, while giving a very convincing sense of depth. The extension above is absolutely correct, but how to give it to the listener is very gentle and never annoying.
The bass is the element, in my opinion, more convincing. After 30 years of solid state and a series of convictions related to the rubbery and the low accuracy of the low range of tube amps, I was absolutely thrilled by the quality of the lower end of these amps. Extension excellent, very good control and the "right" roundness in the reproduction of acoustic instruments, which means that even a musician to recognize the sound of their instrument as if he was playing. I do not think I can say that the bass is extremely fast, but I can say that have never been convinced that the low range, with particular reference to instruments Acoustic is faster. The important thing is that it is well controlled, without queues and unnatural that it is "real." I would say that in this case, the objectives are fully achieved.
Turning to an analysis of the behavior with the different musical genres, I can say that the traditional jazz and electro, with a preference for small groups, is the death of these amplifiers. I think the impressive realism of the Riverside recordings of Bill Evans with Scott LaFaro on bass seems that there in front of me ... Just as the trumpet of His Majesty Miles Davis' Kind of Blue "or the poignant sadness of that of Chet Baker in "Chet". The Realism is, once again, gorgeous, with an almost perfect reconstruction of the stage. Even incisions less efficient as the latest Diana Krall ("The Girl In The Other Room" or "Live in Paris") are still played with great consistency and realism, giving the voice of the Krall a little more ...
With serious music, classical to speak, the yield is also excellent, again, above all, the ability to create a virtual scene totally believable. Listening to one of my reference discs (Rodrigo - Concierto De Aranjuez - Carlos Bonnell - Decca) implies an emotional high. Bonnell's fingers move over the strings with a new grace, restoring the soul of the musician and his guitar. Also excellent performance of the reference discs Audio Review (Stork bravo!). Excellent performance of "Bolero" by Ravel from Reference Recordings, a growing absolutely perfect. With these tracks, turning up the volume to levels of risk to the health of the ears, make some sign of deterioration in sound performance, which is manifested by an increase in grain, a loss of fine detail and a slight hardening of the treble. Probably the limits of power combined with the sensitivity of the speakers play their role in this. Excellent yield piano, which has a breathing space and an absolutely remarkable. Also excellent yield of old instruments, from the excellent CD attached to a recent Audiophile Sound. As I said, are the major weak point of the full orchestral instruments, but only when played at insane levels of listening. Limitations intrinsic to a house, there are no problems ...
The yield with the pop-rock music is, as you can imagine, quite variable, depending on the gender play. Certainly fans of hard rock and heavy metal certainly prefer muscular final solid state, able to provide the infamous "slap in the face" but with other genres more "educated" the yield is still a high level. I think the inevitable TDSOTM or the beautiful voice of Peter Gabriel in "Selling England By The Pound" or "So", but also to the West Coast of CSN & Y or jazz-rock of Joni Mitchell. Also excellent yield with the music of our local author and I think Exalted "Anime Salve" De André or the beautiful "Songs crank" by Capossela, where the final two are able to re-create a sound space absolutely real and musicality.
At the end of all this talk, what to say? First an observation: the Audio AM my beloved are off since August, with a little 'of sorrow, but with no regrets or failures of type "music".
The two final OTL has improved greatly over time, demonstrating to the present quality music from all over: a great ability to reconstruct the virtual stage, excellent frequency extension, control, realism and ability to involve the listener ... What to say ? I am convinced that to treat one of the most well-chosen purchases of my career as an audiophile.
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