Analog Forum Krefeld 2014

english version at the end


Hallo,

nun war es wieder soweit, nachdem im Sommer in München mit der "High End" bereits mit Beharrlichkeit und lauten Beschwörungsgesten der unaufhaltsamen Sättigung des Absatzmarktes HiFi durch das audiospezialisierte Nischengewerbe entgegnet werden sollte, öffneten sich nun auch wieder die Tore des Analog Forum Krefeld 2014 für den ambitionierten Besucher. Das Analog Forum ist eine Veranstaltung der Analog Audio Association, einem Verein der schon vor langen Jahren mit dem Ziel gegründet wurde, den Artenerhalt der aussterbenden Spezies "Vinylschallplatte" mit der Nachhaltigkeit und sektiererischen Frische von Spielzeugeisenbahnherstellen und deren typischem weltoffenen und innovationsfreudigem Habitus Profit zu schlagen mit einem Forum entgegen zu wirken. Vor einigen Jahren hatte ich mich über einen längeren Zeitraum bemüht, in einem ihrer Zentralorgane, nämlich ihrem Webforum,  über den Stand der Dinge dieses Themengebiets regelmässig zu informieren und auch auszutauschen. Das habe ich dann doch ganz schnell wieder eingestellt, zu offensichtlich war es dann doch, das ein offener Austausch im Bemühen um qualitative Entwicklung zumeist von kleinkariertem "Besitzhabitusdenken"gelenkt und bestimmt wird. Nach wiederholter Erfahrungen dieses Umstands, habe ich mich dann spottend aus der Diskussion um die Qualitäten der Vinylschallplatte aus dem von mir vortan nun "Dualforum" geschimpften Plattform zurückgezogen.

Nun also sah ich es als meine Pflicht, wenigsten einmal den "Freunden der Spielzeugeisenbahn" Liebhabern aufwendig verchromter, komplex gravierter, mit umfänglich vorgegebenen Einstelloptionen für mindesten drei Tonarme versehenen (davon mindest ein 16-Zöller, am besten einpunktgelagert) und folgerichtigem dreistelligem Nettoversandgewicht ausgetatteten Analoglaufwerken (früher Plattenspieler genannt), einen Besuch abzustatten. Ich mache keinen Hehl daraus, das mir ehemalige Veranstaltungen schon solcherart suspekt allein als medial vermitteltes Ereignis erschienen, das ein Besuch für mich überhaupt nicht zur Frage stand. Das mag man für arrogant halten, aber schließlich kannte ich genug hinlänglich "Interessierte", die mich auch immer wieder darin bestätigten, einen Besuch dort nicht als "zwingend" einzustufen. Zum anderen weiss ich nur zur gut, das kommerzielle gewerblich orientierte Interessen mit meinen Erwartungen an ein hörbares Ergebnis, sagen wir es bescheiden, sich nicht wirklich zweckdienlich zueinander verhalten. Schließlich habe ich ja auch seit etwa 25 Jahren keinen HiFi-Laden mehr betreten, immer wohl wissend, das mir da "schon geholfen wird".

Nun gut, 2014 TrueFi goes Audiofair. Ich war überrascht, wieviele Menschen sich an einem Feiertag in engsten Hotelzimmern drängen, um sagen wir es salopp, eine Stereoanlage zu hören. Schnell war man in der ersten Runde durch die meisten angerichteten Räume, jeden Zweiten musste man wegen Überfüllung auf die Folgerunde vertagen. Aber auch deshalb schnell, da es unabhängig von Aufwand, Marken und Equipment eigentümlich ähnlich tönte. Man brauchte dafür kein sonderlich geübtes Ohr, das allgemeine Niveau der Aufführungen war sehr, sehr ähnlich und ich sage es vorsichtig mit Rücksichtnahme auf die HinterbliebenenAmbitionierten sehr, sehr bescheiden. In schon krass zu nennendem Kontrast zum Aufwand der dort getrieben wurde, klangen die Ergebnisse seltsam befreit von aller musikalischen Substanz. Schnell konnte man zumeist schon beim ersten Basston oder in der Grundtondarstellung vernehmen, das das Gebotene andere Ansprüche bedienen wollte, als dies meine sind. Nach selten mehr als einer Minute gesellte sich beim überwiegenden Teil der Aufführungen auch die Erfahrung eines meist sehr vordergründigen, oft auch harsch bis spitz vorgetragenes oberen Frequenzbandes dazu. Und Summa Summarum in Verbindung mit den meist auch blass und farblos vorgetragenen wichtigen Mitten, wurde das "HiFi-Soundbild" schlüssig abgerundet. Ich weiss nicht ob dies ein bewusst eingesetzter flacher, vordergründiger Sound ist, der sich besser verkaufen lässt? Jedenfalls mit Musik, derer analoger Eigenschaften und emotionaler Darbietung, hat das in den wenigsten Fällen noch nicht einmal vordergründig zu tun.
Es mag daran liegen, dass die räumlichen Bedingungen natürlich nicht optimal sind, jedoch war bei einigen Anbietern auch diesbezüglich höchster Aufwand betrieben worden, Raumakustikpanele im sechsstelligen Bereich waren aufgebaut, dazu die übermässige Fülle menschlicher Absorber. Ich vermute jedoch als eigentlichen Grund für das einhellig kraftvoll unattraktive Auftreten, starke Affinitäten zu unseren Lebensmitteln. Der überwiegende Teil der Produkte der sich so nennt, hat ja auch nichts mit Leben zu tun, – ganz im Gegenteil.

Es war schon mehr als erstaunlich, das einzig ein kleiner unauffällig vorgetragener Beitrag eines Schweizer Anbieters (wer hat's erfunden?) als einer der ganz wenigen Lichtblicke die gängige Trübe Aussicht aufzuhellen im Stande war. Mit einer Stereoanlage, die mich massgeblich an einige meiner eigenen frühen Anlagen erinnerte, mit einem modernen Thorens Subchassis-Plattenspieler, fast technisch identisch zum Klassiker TD160, hübsch und sinnvoll ergänzend kombinierten Röhren-Modul-Komponenten und einem kleinformatigem Breitbandlautsprecher, zeigte die Vorführung von Swissonor Eigenschaften, die auf keinem anderen Stand so nachvollzogen werden konnten. Feine, durchnuancierte, atmende Musikdarstellung mit einer geradezu im Vergleich bescheiden anmutenden Kette. Alle anderen scheinen gerade den umgekehrten Weg eingeschlagen zu haben, nicht kleckern, auch nicht klotzen, – rüpeln scheint die Devise. (jetzt muss eigentlich wieder meinen Klassiker zitieren, der die Parallelen im Kaufverhalten von SUV's und den jeweilig anderen Produkten als gleich benennt)

Auch Wolf von Langa's winziger dipoliger Kugellautsprecher "Sphere" ist einer der wenigen positiven Versuche das dort Gängige in Frage zu stellen und mit einem einfachen Produkt zu überantworten. Vermutlich auch das ein Versuch, seinen zurückliegenden vermutlich negativen Erfahrungen geschuldet, auf solchen Veranstaltungen mit aufwendigstem Equipment zu punkten, nun marktkonform ökonomisch anzugehen. Schade, hatte ich doch gehofft dort einen der aufwendigen DHT Verstärker von Thomas Mayer in der Vorführung zu erleben zu dürfen, leider wurden die "sphere's" mit japanischen PP-Amps angetrieben.

Bleibt zu erwähnen, das die überall allgegenwärtigen Lakritzschnecken auch nicht die emotionalen Fehlerwartungen befrieden konnten. Natürlich könnte ich nun schreiben, ich habe es immer gewusst, dass sich mein Anspruch an Musikreproduktion und deren akustischer Umsetzung mit gängigen HiFi-Komponenten nicht befriedigen lässt. Natürlich könnte ich jetzt schreiben, das der organisierte Unfug auf einem Laufwerk 18 verschieden bestückte Tonarmrohre "on the fly"im Wechsel unterschiedliche Abtaster hörbar machen soll, schon mit einem einzigen Einpunkttonarm, schon als grob fahrlässige Täuschung bewertet werden muss, oder kennt jemand ein einpunktgelagerten Tonarm in einer wirklich funktionieren Kette, – wohl kaum? Nein, diese Liste der Schmähungen kommerzieller Exzesse in Krefeld will ich nicht führen, mir geht es um Wichtigeres.
Aber die Problematik geht ja doch noch etwas tiefer, – muss man seine eigenen Ansprüche im Angesicht dieser präsenten Durchschnittlichkeit, aber auch ihre unverfroren selbstherrlichen Vermarktungspraktiken wirklich in Frage stellen? Ich weiss es nicht, schlussendlich ist dieser Konflikt auch der Grund warum ich diesen Blog gegründet habe und dazu benutze ein Forum für ähnlich denkendende und handelnde Menschen mit komplett anders gearteter Erwartungshaltung zu erreichen.

So verliessen wir einigermassen irritiert die sehr gut besuchte Veranstaltung, verzichteten auf den Kaffee im Mercure-Hotel und tranken diesen dann lieber als kurzen Zwischenstopp auf dem Heimweg bei Mike. Dort wurde der kleinen Gruppe mehr als augenfällig in Erinnerung gebracht, worum es uns allen eigentlich geht. Gute Musik und deren Wesen zu transportieren, ihre inneren Emotionen, ihre Ausdrucksfähigkeiten und Spannungsbögen ohne vordergründige Technikwahrnehmung vermittelt zu bekommen. In einem Kontrast, der grösser nicht sein konnte, gelang dies mit Mikes Anlage im Nachvollzug dieses kurzweiligen November Nachmittags. Das Wetter war eigentlich sogut, dass es die Jahreszeit hat vergessen lassen. Einzig die spätere Erfahrung und Vorführung von Mikes Setup, diesmal mit Tungar PSU für die LM-Treiber, war einerseits mit ihrer saisontypischen Vorweihnachtbeleuchtung der Tungarröhren auch Anlass sich der Jahreszeit zu vergegenwärtigen. Die Performance dieser Anlage muss ich an dieser Stellen nicht mehr hinlänglich beschreiben, mit dem gängigen Vergleich der "Welten, die sich da auftun", ist der Unterschied zum kommerziellen Gestöpsel in Krefeld so unzutreffend beschrieben, das mein Bemühen dafür noch die richtigen Begriffe zu finden, auch die Unmöglichkeit beschreibt, auditive Musikdarstellung in Worten zu fassen.


Bis bald, Volker




english version:

Now it happened again, after the summer with the Munich-High End-Fair, already the inexorable decline of the audio specialized niche industry should have been countered with perseverance and loud summoning gestures, now Analog Forum Krefeld  2014 opened again the gates for the ambitious visitors. The Analog Forum is an event of Analog Audio Association, a club that was many years ago founded with the goal of typical preservation of the endangered species "vinyl record" with the sustainability and sectarian freshness of toy train manufacturers and their typical cosmopolitan and innovation-habit to profit to counteract with a forum. Some years ago I did try to inform regularly and exchange about the state of things of this subject area, in one of its central organs, namely their web forum  I did stop quite quickly, it was too obvious that a an open exchange mostly was directed and determined by a "possession habit of thinking". After repeating experiences of this fact, I decided to withdraw me from the debate about the qualities of vinyl records from what I henceforth did call "Dual Forum".

So now I saw it as my duty, at least once the "Friends of toy train" lovers consuming chrome, complex engraved provided with circumferentially set options for at least three different tonearms (including minimum one 16-inch model, at best with point bearing) and consequent three-digit net shipping weights, equipped analog decks (earlier called phonograph) to pay a visit. I make no bones about it, before the times of such events already appeared suspicious, such a visit did never stand for me to question. That may grow arrogant, but eventually I knew enough "interested", which also repeatedly confirmed that a visit is not "mandatory" for life. Secondly, I know very well the relations between commercial business-oriented interests to my expectations of an audible result, we say it modestly, are not really useful relate to each other. Finally, I have also missed to enter for about 25 years any hi-fi shop anymore, always knowing that they were no helps for me since.

Well, in 2014 TrueFi goes Audio Fair. I was surprised how many people are crowded on a holiday in closest hotel rooms, to say it bluntly, to hear a stereo set. Quickly the first round was done by leaving out every second room because of overcrowding for the following second round. But also rapidly because it sounded strangely similar regardless of expense, brands and equipment. It requires not a very trained ear, the general level of the performances was very, very similar and I will say it with careful consideration of the survivor's very ambitious with modesty. In pretty wicked to call contrast to the effort driven there, the results sounded strangely exempt from all musical substance. Quick one could usually hear with the very first bass note or in the lower frequency representation, what is offered would serve other claims than mine. After rarely more than a minute, the experience of a usually very superficial, often harshly pointed to rendered upper frequency band joined them in the majority of the performances. And summarized in combination with the usually pale and colorless middle frequencies, the typical "high fidelity sound"was presented conclusively. I do not know, if this is the typical deliberately shallow, superficial hi-fi sound is, that it needs to sell? In any event, with music which features analog and emotional content in a foremost performance, the shown attitudes do not even represent superficially this values in most of the cases.
It may be fact that the spatial conditions of course are not optimal in hotel rooms, however, for some providers the highest rate of respect has been operated into room acoustic, panels in the six figures rate were constructed. However, I suspect as the real reason for the unanimous powerfully unattractive appearance shows strong affinities to our food. The majority of the products of the so called, has also nothing to do with life - quite the contrary.

It was more than amazing, that a small inconspicuous adduced post from a Swiss manufacturer was one of the very few bright spots, able to lighten the common turbidity view. With a stereo set, which reminded me to some of my own early systems, with a modern Thorens subchassis turntable, almost technically identical to the classic TD160, pretty nice and useful supplemented with a modular tube  amp component system and performed with a small-sized duplex speaker, the demonstration of Swissonor showed properties, that could not be tracked in any other state such. Refined, nuanced and breathing music notation with a downright modest compared sounding chain. Everyone else seems to have just taken the opposite path, sheer mass and glossy surfaces seems the motto. (now it would be time for my classic quote, that names the parallels in the purchasing behavior of SUV-cars and the respective products other than actually equal again)

Even Wolf of Langa's tiny dipole ball speaker "sphere" is one of the few positive tests to bring the major offers there into question and to respond with a simple product. Probably also an attempt, presumably his past negative experiences due to score at such events with lashivly equipment, now with the market to address economically. Too bad, I had hoped to be able to experience one of the most elaborate DHT amplifiers from designer Thomas Mayer in the demonstration there, unfortunately the "sphere's" were presented with japanese  PP amps.

It remains to mention the ubiquitous licorice snails  everywhere also could not pacify the emotional fault maintenance. Of course I could write, I've always did know, that my claim to music reproduction and its implementation with standard commercial hi-fi components can not satisfy my requirements. Of course, I could now write that the organized mischief of 18 different stacked tonearm wands to be changed "on the fly" to make different pickups audible, even with a single one point bearing tonearm might be a project of predicted failure, or does somebody know a one point bearing tonearm in a chain really work, - hardly? No, this list of insulting commercial excesses in Krefeld I do not want to lead forward, I am concerned with more important things.

But the problem is indeed still something deeper - you have to make own claims in the face of this mediocrity, but also to question their unabashedly brazen commercial marketing practices really? I do not know, ultimately this conflict was also the reason for me to start this blog and to found a forum for similar thinking people with completely different type of expectation about audio to achieve.

So we left somewhat irritated the very well-attended event, gave up the coffee in the Mercure Hotel and then made a stop over at Mikes house on the way back home to have it there. There, the small group was brought over evident in memory, what it all comes to us actually. To transport good music and its essence to convey, without superficial perception of technology to take care to their inner emotions, their expression skills and suspense. In contrast, the greater could not be, this was achieved with Mike's investment in the enactment of this entertaining November afternoon. The weather was actually so nice that it has the season to forget. Only the subsequent experience and demonstration of Mike's setup, this time with Tungar PSU for the LM-driver, one hand, with their typical seasonal before Christmas light the tungar tubes gave an opportunity to recall the season. The performance of the system I need no longer sufficiently to describe here, with the usual comparison of the "worlds that open up there," the difference from the commercial clatter in Krefeld is described as inaccurate, that my endeavors to ensure even the right words see, also describes the impossibility to describe auditory representation of music with written words.


Read on soon, Volker

The Aa Line Preamplifier IV – The Power Supply Part I

Hello,

to everybody. Today I will continue the series about the Aa-DHT-Preamplifier, I assume some people are waiting for the completion of the series. In late summer I did use the good weather to concentrate on other topics than audio, I did start a new blog with a totally different topic, so the work at the preamplifier did stick a bit. Everybody might understand without real pressure the continuing is low since I do use a almost the same preamp for a longer time already. But we will see if this "final" version is able to preserve new experiences.

The same Hamond enclosure like the line amplifier, painted with the same hammer tone silver painting. Lots of wholes  and cut outs were necessary for the quite complex power supply .

I did use the same steel case from Hamond like with the line stage for this power supply. If it would be just a PSU to feed for the line stage stand alone, the expenditure would be very comprehensible. A classic anode supply with rectifier tube and a charging and filtering chain of capacitors made up with the choke would do the job already perfect, since the design of the line preamp is completely class a. But the filaments of the directly heated triodes need to get a well made supply each, since their sensitivity for hum and other unwanted restrictions is a lot higher, than with any indirect heated tube. As already shown in the preamp descriptions I do use for that reason Rod Colemans constant current supply boards. These need each a own raw supply made up from separate secondary windings of a transformer, able to supply quite solid currents, here with two Aa in parallel we talk about 1 ampere each side. Conservativly spoken the transformer should be able to deliver a good 1.5 amperes for safety, noise and long term operation. To work out the final 3.8 volts at the cathodes of the Aa tubes a 12 volt transformer will be a good choice. It has to be determined exactly, otherwise higher voltages need to be burnt down and will create unwanted heat in the enclosure. In the first stage a typical rectification stage is necessary. I will use four 1N5822 fast recovery diodes for that job and low esr capacitors for the filter chain and  dropping resistors per channel to feed the boards.

But with the additional planned phono amplifier I need a more complex power supply. Since this second preamplifier will be realized with indirectly heated tubes, a higher degree of complexity for the anode supply is necessary, but in reverse with such tubes the filament supply will be quite easy to be realised. So my anode supply will divide behind the first filtering cap for a second rail with additional choke and a tube regulated output stage. Here a the integrated tubes of the ECL82/84/85 line (combined driver and power tube in one glass envelope) together with a 90C1 as stabilizing device are a smallest possible physical design for such a stage. This stage needs to supply less than 20 mA of regulated current output. The tube sockets and a extra capacitors are already installed for this later needed output stage.

In order to keep the grounding issues under control I did made a perspex board where all capacitors are mounted off the chassis and can be separatly grounded to avoid hum loops. I did expect to have a quite complex switching schematic, so I will install two separate switches for the different heater modes and anode voltages for both amplifier parts indicated with lamps.

MoD Parmeko mains transformer with typical sealed oil isolated enclosure and porcelain contacts.

Since the middle of the 1990's I did collect at ebay parts for tube amplifiers, which were almost impossible to find before without the web as source. The perfectly made Parmeko transformers are one example of these rare and obsolete parts for the use within tube  amplified devices. With c-core laminations and oil filled sealed enclosures, porcelain isolated contacts and very conservative ratings, these transformers belong to the best made ones in history. The most of them are made for the British MoD (Ministry of Defense) and were used at professional or military equipment and there is nothing comparable made known from any other country. Even with Ebay it is not very easy to find the right values and specifications for all projects in mind, so it took several years to collect this set which is now used for this power supply. A mains transformer with a good variety of anode voltages (300-270-250-0-250-270-300V), a perfect rectifier filament winding with 4-5-6.3V and separate 6.3V filament windings is a very good choice. The two chokes with 30H and 50H are a perfect match for both anode supplies. Only the filament transformer for the Aa's is a modern torodial design.
With this mains transformer I can use rectifier tubes with 4 volts filament, this means I can use AZ1 or AZ11/12 which are easy and quite cheap to obtain even todays where the most rectifier tubes have skyrocketed their prices. There are some early types which are equipped with mesh plates, a sound wise perfect value for such a project with low current drawing figures.

Read on soon about the next part, Volker

La Platine Verdier – The Final Turntable

Hello to everybody,

after a long period of absence I did plan to restart this blog with another Aa-preamp part to be the next entry. The Power supply should be topic shown soon, but another case of death needs to be covered first – Jean Constant Verdier, the ingenious mind of the legendary magnet bearing turntable has died recently.

Talking today in 2014 about turntables has the same attitude than talking about car design. Both issues in terms of technical inventive creativity have disappeared, instead a solely ostentatious understanding of design issues hat taken place in both fields. The bespoken record player appeared in 1980 as one of the last great innovative designs at the audio market, first seen at Maison de L'Audiophile in Paris, France. "La Platine Verdier" offered several new design issues at the first time for record players, when it entered a almost saturated market, dominated from typical japanese mass production decks, mainly introduced as direct driven designs. Only a few other sub chassis designs had survived beside them, mostly light weight built, like the Thorens and several derivated like the Linn LP12 and others. The Verdier came out with a hefty mass of almost 50 kg with a completely new concept to find the best possible options for vinyl operated audio. Here it has to be named with reuse of 12 inch studio tonearms, low compliance cartridges and incorporating first a high mass platter, it did set the path for the current audiophile record player. It was designed to resemble the mass of the record cutting process platter to catch up the circumstances during the pick up process. Next a extremely solid (20 mm) sized axis with massive bearing housing was introduced as a controlled resistive element. But the main novelty of the whole design was the magnet decoupling mechanism, which kept the platter off resonances. In combination with a spring-air controlled pneumatic acting feet system for additional decoupling of the artificial stone base down to 3 hz, the separation of the motor unit into a own chassis and a very long and thin string, the Verdier  has set the pace in terms of suspension, decoupling and weight for a mass players. All features together opened a whole bunch of aural attitudes, which have not been archived before, nor they have been completely captured up by any later design.

As simple as it can be, clearly visible the two magnet housings and the 7mm air gap in-between.

Today it seem to exist strange relationships in the purchasing behavior of SUV-cars and between  turntables. Where attitude tops function, conspicuousness resembles modesty, their shear weight and size will do some job? Todays formal principles of chromed or gold plated surfaces for drilling rigg like designs, seem to have overtaken any functional issues for more gestural attitudes with representative character.
In opposition the Verdier turntable is a masterpiece of functionality, simplicity and material choices as perfect example of the "form follows function" theory of the early 20th century modernity. For lots of people it is ugly, but for some aestetical educated, it is may be the most beautiful design ever made, since it does not show any subtile compromise to more decorative ideas. Only the motor unit could have been designed a little better for the same basic understanding.
The so called "magnet bearing", which is technically seen the wrong designation, gives this player a unsurpassed bundle of aural attitudes. First there is the unexcited calm, which gives a unsurpassed view into the rhythmic performance and a precisely defined soundstage. The naturalness of dynamic abilities, timing and the finest resolution of micro details are bundled together like none. If you own this record player, you don't think anymore about other options, – it is just boring.

Here with Shindo Mersault Tonearm and dedicated cartridge mounted on top of bronze base with pneumatic cueing system. 

The Verdier will be definitely my last record player to cover my record collection (since 20 years), for the coming future it needs anyway other concepts to play digital stored music.

Thank you so much Jean Constant.

Try to get one since it is still possible, you never know what is coming next.

Read on soon, Volker

The Aa Line Preamplifier III – The Completion of the Amplifier Part

Hello to everybody,

today I want to show the completion of my amplifier chassis with the constant current filament regulator boards. As already stated I did use the predecessor of this preamp for several years with different battery types, since conventional dc regulation showed a lot of problems and did not sound as good as batteries. So I had to struggle instead with contact problems, broken cables and dying batteries for years, which was a real pain. I had started with lead batteries, later did I use conventional AA Nimh's, a pack of three makes 1.5 hours of listening possible. So did use several packs, the everyday use and charge cycles made life for them short, almost every year I had to exchange the most packs.
In 2010 I did learn about Rod Colemans Constant Current regulator boards, which have been designed for this particular dedication, the filament supply of DHTs and for the use in pre amplification stages as special option. These boards can be configured for almost any triode type, even the big ones like 211, GM70 or 845 with high current draw figures can be used. For each triode one board is needed separately, which means here in this case with two Aa's running in parallel mode as couple will be fed by one regulator. They don't run very hot, so they are quite easy to use in the amplifier enclosures.

The Coleman regulator boards are mounted to both chassis sides to dissipate the heat and to be very close to the filaments of both Aa couples, here shown with one board.

The regulators are dead quiet and don't show any deterioration of the sound structure, comparing them to batteries. They will be available though Rod Colemans web page and are a great help for everybody using directly heated triodes in audio amplifying devices. They need to be implanted with a raw power supply each, which should be designed to match the final preferences set by the tubes itself. Any extra power will be burnt down into heat by the regulators itself. As example for the Aa with 3.8 volts for their filament a transformer with separate windings for each raw supply with minimum 11 volts output is needed. Each Aa draws 0.5 ampere of current, together it is 1.0. The boards allow the exact setting of the current to match the variations of such old vintage tubes.

Since the Daven attenuators  are extremely difficult to find nowdays, which means it is almost impossible to find them as stacked stereo units in values like 100K or 250K, I did use one mono type for each channel. With everyday use of such a preamp, separated attenuators for each chanel would drive me crazy. With any control of volume you need to match the stereo balance again, a night mare if the amp is not positioned exactly in the middle of the speakers. In order to make the use more comfortable, I introduced a coupling system. With a o-ring both shafts are coupled together by wheels from a toy steam engine. The o-ring keeps both attenuators in balanced mode since I need to adjust one of them. If, I can hold one since I turn the other one where need. We will see if that system will do comfortable within everyday use, otherwise I have to design a spring supported clutch system…

O-ring coupled shafts for the Daven attenuators.

The back shows several sockets for different dedication. From left there is the power input socket (6 pole) where both raw voltages for the Coleman regulator boards will be supplied. The other two contacts are for the filtered anode supply. Next to this socket are two output xlr-sockets, the two main output terminals of the amplifier, these can be switches for the two corresponding rca sockets as alternative outputs at the other end of the back panel. All paired rca sockets in-between are four different input contacts, which are connected to the source switch, operated from the front panel. Four inputs should be enough nowadays, since the most sources are fed through one dac, like web radio, streaming clients, computers and similar. So there are three inputs for other sources like phono equalizer or a recording unit and here the second set of output sockets will be helpful.

After mounting the two potted chokes on top of the amplifier case and after connecting the tube sockets with four Aa tubes, the amplifier chassis is complete and is waiting for its complex dedicated power supply. When the power supply is completed and will work with the dedicated smooth anode supply of 200 volts and the two raw supplies for the regulator boards, I need to adjust these with a dummy load instead of the real tubes to prevent an overload of their filaments. But till there is quite a long way… As almost everybody knows, a good power supply is by far more complicated than the amplifier part. I will show it with an option of two different versions, a quite simple tube rectified supply with the three different voltages to keep this preamp a simple stand alone solution.

For the aficionados the series of articles will be continued showing a quite unusual pre-amplification concept, which will have the future in mind. Similar to german broadcast preamplifiers of the 1950ties I will show the build of different stages with different amplification factors. A gain amp (+50 db), a catch-up-amp (+25db) for compensation of losses and the already shown line amp for impedance matching to the power amp.
With these modules and a dedicated power supply almost any use in a modern audio set can be managed. For example a typical dac output stage will need roughly a amplification of +50 db, almost the same than a good phono stage before RIAA equalizing. When equipped with a input transformer with different windings and different ratio, like 1:10 or 1:25 (just to mention the extremes), the same amplification stage can be used for both sorts of applications. Since the former digital signal is now strong enough for the impedance amp (line), the phono signal needs further equalization with a RIAA filter with typical loss of -25db at a following stage. So another amplifier with +25db gain is here needed for compensation of the losses to level up for the line stage.

A multi voltage power supply will be needed for such a amplification chain. Such complexity needs to match highest standards and components, potted oil filled transformers and chokes would be first choice, but it is already difficult to find this stuff nowadays. The anode supply develops with tube rectification at the beginning, ideally made with a classic mesh anode rectifier tube lie RGN1054 or 1064 as perfect partner of the Aa tubes, to be continued with several chokes for HV and LV: 1. a well filtered B+ for the DHTs in the line stage; 2. two well filtered low dc-voltages for the Coleman Regulators; 3. a further filtered and tube regulated anode supply for the gain amps, and finally 4. a well filtered dc-supply for their filaments of all indirect heated triodes. I assume the weight, complexity and size of a well made power amp to get an idea about the case.


Read on soon,
Volker

The Aa Line Preamplifier II – The further Completion of the Amplifier

Hello to everybody

interested into the completion of my Aa-DHT-Preamplifier. As already stated, this line amplifier is a perfect solution for the mainly digital based systems, as it can be a exceptional supplement for any analogue chain with separate phono equalization. Implanted into a system with advanced dynamic attributes and with careful set up to harmonic structures, this preamplifier can open a window into the finesse of advanced audio performance, which I never have been able to obtain from commercial made line preamplifiers. A typical variety of incomparable attributes accompanied with directly heated triodes in small signal amplification stages are the base for such a extreme statement. DHT's for small signal output are very linear in their whole operation spectrum. They have a extraordinary refined character, sometimes show up with unique tonalities and exceptional dynamic abilities. Exactly like their more powerful sisters in power stages, but with a much deeper scaled effect because of the smaller signal ratio. The unbelievable attitudes of the Aa-Triode give a extra portion of refinement, linearity and tremendous wide open transparency, combined with harmonic detail I do not know second. Commercially made tube preamps could and can only be designed around available types of tubes, it was almost impossible to find bigger amounts of exceptional tubes since the renaissance of the tube amplifier in the 1980ties for hifi, nor it is possible today. The exceptional icons of indirect heated tubes for small signal amplification, independent of mu characteristics and impedance values, are mostly tubes made for professional dedication, like the WE 417 and 437, the red RCA's like 5691 and 5692, all the Telefunken special series like EF804s, EF801s and the red tipped types of all ECC types, the D3a's, C3-series, from other makes like Bendix, some former Soviet brands and uncountable lots of rare others tubes not named. All these exceptional quality tubes are not to be found in commercial audio amplifiers, where they could show their incredible qualities. But even these exceptional tubes cannot tame up with the same audible benefits of direct heated tubes, they are able to perform tremendous other benefits but rarely with such finesse of dht's.
The tungsten thoriated filament of directly heated tubes is acting as cathode in the signal part and creates very special peculiarities. On one hand responsible for such incredible aural benefits, but as well well for very delicate conditions in everyday use. Everybody common with DHT's in the power stage might be experienced with the typical sensitivities of such tubes for hum and vibration. In reverse to the amount of signal to ground ratio current, these sensitivities are ten times or more higher. This can make the use of such tubes very uncomfortable or even more, – it can be a real pain. I am using such tubes since almost ten years by now in such implementation for every day, within that time it has come sometimes to a point, where I just switched off my stereo, because I was unable to locate some reason for apparent hiss or hum. Completely exasperated after some time of search I decided to find reasons for the problems another day… In particular in the first years, when I did use flying batteries for the heating of the filaments, contact problems with broken cables, clips, battery containers, – flying batteries create here a permanent conflict zone. With a fixed and permanent installed power supply solution (constant current source) the most of such problems are now history. For those which are already on a shortcut, a  common or even complex regulated voltage supply is unable to support the aural qualities in the signal loop. It needs a complex constant current source with own complex (highly filtered with common mode choke) power supply per tube!It has to be said with impertinence, a direct heated triode is not a plug and go installation. If you want such a ease of use, you better should go for something else than tubes and in particular for directly heated triodes in general. Those respecting the extraordinary outlay will get gifted with the most colorful natural soundstage possible.

For those undaunted here a new life with audio might start soon. The Aa-Line Preamplifier its a fantastic solution for the digital chain. In combination with a good dac all the quite new benefits of digital stored music (i.e. better recorded standards, storage and organization improvements, a wide spread program of sources: world wide radio stations with lossless compression, cloud based streaming, etc), will find a exceptional natural sounding input stage, able to perform with a perfect holographic soundstage, if the following components (i.e. power amplifier and loud speaker) are able to support such a level of resolution. All regular readers of my blog have got already certain ideas how to get close to such a rare and uncommon performance. For me the exceptional resolution and the incomparable micro detailed dynamics are a base to operate a huge cone speaker like the Tannoy with wide medium frequency performance to a higher degree of resolution other designs can not support.

Today I will try to show some more completing of the amplifying enclosure. Now the rubber isolated perspex board has been mounted to the chassis, a distance of 20 to 30 mm between board and case is a quite good value since the Aa-tubes have a solid dimension, more known from typical power tubes of the 1930ties like coke bottled 6L6 types or similar. So the tube will be hidden with the socket inside, wile the balloon shaped glass will show out. The tube sockets are mounted at the perspex board with  some turrets to find place for the very few components and their connecting wires, which are necessary for the design of the line amp. This version of the DHT-lineamp is the "short wire version" of this topology. Since it incorporates plate chokes instead of output transformers (the long wire), the physical signal length from input to output sockets is less than 40 cm wire, with just a tube system (plate-grid-cathode/bias resistor, tubes in parallel mode), one oil-paper cap in-between. It is almost impossible to do any shorter design and this explains the tremendous influence to the final performance of the Aa-tube.

Solid silver wire with cotton hoses customized made near to the unwired socket board

Used components

To bring these 40cm to the perfect resolution I did decide to use solid 4-p silver wire (99.99%) for the signal path. I made up the wires myself from solid silver wire (0.5mm or 24 ga) and did isolate them with natural cotton hoses. The negative loop/earth path is made with thicker blank silver wires (1 mm or 18 ga) per stereo side, which get at one point together. The few resistors are carbon comp types of minimum 2 watts heat dissipation and 3 watts metal oxide types for the cathodes. The attenuators are classic potentiometers from Daven with switched 21-step carbon comp resitors for both sides. All capacitors (4 pc.) are oil-paper types, the chokes are Lundahl LL1667/10mA both coils in series (400 H  for 15 K at 30 hz), potted with wax into aluminum enclosures. The chassis for the preamp and the power supply are from the steel 14xx-series from Hammond. The used tubes are nos Valvo Aa's from war production in 1944.

Amplifying chassis from underneath: at top all input and output sockets; left and right Daven attenuators with input source switch in the middle; next level left and right coupling oil caps and b+-support capacitors; the board with input voltage devider, cathtode resistors and all silver wires; knobs with extension shafts for the front panel.

The used parts and components reflect my final selection for this amplifier type, I will definitely use the built sample for the next coming years. I did decide about the rare and expensive parts, till it might be my final line preamplifier and this is going to be a very important component in my audio chain as a result of increased digital format use. It can be made with similar parts and components (chokes, attenuators, resistors, switches, etc.), which are more easy available at a level of 95% of the same performance at the half of the costs. It might depend to the interest out there, may be I decide to make a kit with this design...
Within my next entry the amplifying part of the design will be finished with the inclusion of the regulator boards for the filaments. After this I will start to show the more complex design of the power supply for both pre amplifying stages, the line and the phono stage. Both stages need very different supplies, till the Aa tubes run in pure class a, so they need a quite simplified anode supply together with exceptional complex heater supplies per tube. A class b operated phono equalizer will benefit enormous from a complex filtering chain with chokes and a integrated tube regulation for the anode supply, combined with a simple dc heater design. If you want to follow its realization 

read on soon, Volker

Incredible close to music VI – A Evaluation of Foreign References

Hello

to all interested reading on about further experiences with Line Magnetic and Shindo amplified set ups. Today I want to make a short report about a visit in Frankfurt some days ago, where a very advanced and experienced audio chain with Shindo amplifying devices and Line Magnetic components is in use. The owner Claus is a long term follower of advanced audio concepts with triode and horn amplification. He started his interest into audio during the early beginning of the european triode movement in France with Jean Hiraga at Maison L'Audiophile as initial. It is obsolete to mention that Claus has owned already a tremendous amount of equipment during that time of 30 years. He always stayed or sold back his components convicted to find paths behind the curtain of the typical superficial audio presentation into a more harmonic and natural representation of music. One example might show his behavior quite well, the shown Shindo 300B Mono amplifiers in my article: Incredible close to Music I – The System Matching.  Exactly this pair has been part of Claus installation til the early 1990ties, when he did sell them presumably with his typical words: "I don't need them anymore". This quote shows a rare attitude: the ability to concentrate to the essential qualities, where a lot of us others would stay with components as proud ownership in mind he gets rid of for him anymore useless components. After one more owner these amps harvested 15 years ago at Mikes set up, just to close the circle.

A listening room were walls are covered with shelves containing records, lots of records (may be 2000), books and CD's. The positive benefits of such surfaces and their physical masses for room acoustics are known and a lot of audio enthusiasts use their record collections for that sort of effect as well. But this time it was the first time, that there was not anymore a dedicated record player…?! As I could hear he had a Platine Verdier player (what else?) and EMT turntables for years, now he uses streamed digital data, deliberated from a pure audio computer into a Line Magnetic dac. ("I don't need them anymore".)

Claus Line Magnetic horn set of LM22/597 is extended for low frequency support with dipole enclosures. Customized made from solid german oak, the enclosures are made similar in design to the "755" speaker from Auditorium 23. Inside he uses a fantastic delicacy, a pair of Microtecnica 15'' field coil speaker units. These are the most beautiful made low frequency drivers I have ever seen. They have been manufactured in Torino in the 1940ties by a company which concentrated to different precisely manufactured micro mechanic product lines, one line covered several products for the cinema industry like complete installations of projectors and sound equipment. Originally these wonderful speakers might have been used some time ago in a Italian cinema, presumably installed very similar to the well known Siemens Klangfilm Bionor sets, assembled with a front loaded integrated horn funnel in a huge wooden baffle board, together with high frequency multi cell horn dispersion on top.
Italian products of this particular time mostly show up with a typical exceptional attitude, where the finalized form follows highest ingenious standards in combination to a exceptional aesthetic expansion. This attitude has been rarely cultivated with mechanical produced components in other countries at this time. In the post Bauhaus era of the 1930ties other values did decide in wide parts of northern Europe about the form finding process in industrialized productions. "La bella macina", the underlying philosophical principle behind typical northern Italian (Piemont and Lombardy) industrial designs before war, was as well a cooperation between swiss immigrants of advanced technical expertise searching work in the most industrialized region of their culture. The term states the perfect combination of functionality, crafts and form. Exceptional motor designs, like made by Alfa Romeo or Gilera, with espresso machines by Faema, typewriters from Olivetti or bicycles made by Bianchi in these days, might remember of what I am talking about, even if a typical German arrogant purely ingenious based understanding of machines, neglects these facts persistently.

15'' Microtecnica Field Coil cinema loudspeaker in solid wood dipole enclosure

The Shindo 64B PP-Mono amps on top, left beneath the Mag-Amp beside at right the DBX active crossover. In Foreground the Shindo line preamp on top of the Line Magnetic DAC.

In difference to Mikes set, Claus positions his LM22 horns at the stereo base close to the center with the low frequency dipole enclosures mirrored to the outer sides. He uses a pair Shindo 64B push pull amplifiers in combination with a Mag-Amp by Lundahl for the active low frequency support. Each sides signal get devided by the use of a active Dbx 24dB filter unit, since the LM 22 and the LM 597 are cut off with a passive network. A rare and expensive paper capacitor from Western Electric supports the performance for the wide tone spectrum of the medium and high frequencies to a higher degree of refinement supplied to the field energy of both speakers.

Passive filter network for the medium and high frequencies, made up as flying installation with rare expensive paper capacitors from Western Electric (behind LM555W telephone).and some ordinary paper caps.

We did listen to a variety of Claus digitally stored music, with a concentration to contemporary jazz, but as well some large orchestral classical music. With good 30°C room temperature or more and high humidity it was not the perfect day to listen to tube amplified audio sets. Well, I didn't know at the beginning of the listening, – was it me, the climate or the set, I did hardly find into the music. For compensation I did drink a good liter of water during the first three tracks. The music did show all the signs, which are so typical for the projection of the wide frequency LM22 horn, but it was a good bit to dry for my taste and it was a bigger bit dryer than I do know the components already from Mikes or Hans sets. It was like with a exceptional wine, which was some years stored to long in the cellar. Like a Tignanello of 12 years age, of a well known year, it might take a good while to oxidate and open up, before its shows its exceptional complexity together with a refined harmony in the foreground. As well here, everything was there, it was just a bit to tight and dry… I do know these horns in the meanwhile very good and I know them better balanced. After a while Claus stopped the audition and asked: "Now I would like to change to a different power supply for the field coils of the Line Magnetic horns?"
It took a while to change all connections and we started to talk about several topics. I started as well to make some photographs of the set. A good hour later we came back again to listen to similar music and I thought: If I will be able in a foreign set up after a hour time to realize any difference of a power supply?
It did not take long, may be two minutes and I tried to evaluate, if we do listen with completely different settings, I had the feeling it was set with a lot higher volume level than before. But it was even more than volume settings, the whole soundstage had lost all the dryness and its shortness of breath. Instead the well known wide open dynamic soundstage performed with incredible detail, harmony and transparency. I did ask, is it true that there is only a different power supply for the field coils? And is it set to the same voltage? I could not believe the difference. I started to tweet my feet and started as well to like the music, which always points the major difference. Just a power supply, … for the field coils, unbelievable. There is not even some direct connection to the audio signal, it must be a foremost interaction between magnet and voice coil? Nobody can really explain this effect...

Now the chain had shown up with all the unique advantages the Line Magnetic horns are known for. For me it was really amazing to realize how small the differences of sets in the final performances are, even when whole parts of the chain can be different or the surrounding room is absolutely different, the general performance shows the absolute same advantages.
Here the only little difference in Claus set is the active 24db cut for the low frequency path. As a result the frequencies from 300 to 500 hz are less prominent, comparing it with Hans and Mikes set. Their 6 db passive filter brings a mild support in this particular frequency range. But these differences are far beyond qualities, they have to be seen with respect to different ideas and taste, performed harmonics and preferences of different owners.  As different power amps, like the Shindo 300b Mono blocks of Mikes set would have a influence to the presentation here, the Shindo 64b amps would do in reverse with Mikes set. At the end I could find completely back to what I already know about this speakers. As well here again the Line Magnetic set up confirmed my understanding to be one of the most transparent speakers for audio use. They are able to produce almost natural dynamics together with a refinement in harmonic detail, were other systems will be judged by. So they can offer the most advanced insight into well recorded music and can make the listener to forget about its origin. A pitty that the beloved Microtecnica speakers were on such a level of perfection, that I could not really hear them in the set, they just acted perfectly to be true invisible…

Later in the evening I had the chance to listen to the new A 23 loudspeaker "Hommage à Ken", made as a homage to the shortly faded away master Ken Shindo. Equipped with a totally new designed LM755 chassis, which in difference to the first LM version with field coil magnet, is exceptional close in all details to the rare an expensive WE755A. It incorporates as well a w-shaped alnico magnet like the original and a extremely similar made cone structure. Out there is a quite huge community relying to that first version to be the best full range speaker built ever. For me it was a first time to listen to such a alnico version, and it was the first time to evaluate such a speaker not to be operated in the classical baffle board.
Two things are remarkable from the first sight. This 8 inch cone can do real "full range" and it shows a exceptional refined resolution of musical harmonies together with all necessary dynamic abilities. Coming from Claus LM set, it was a very similar experience to find into its presentation. It is of course not a "full range horn", with all benefits of a little aluminum diaphragm, but it has a quite small cone and performs without any crossover on the other side. It brings out a similar tonality, so that the shallow listener would not see any argument to get such a complex system like the LM22/597 with LF-support, if a simple cone can do the same…?! Almost the same, to be honest….


Read on soon, Volker

The Aa Line Preamplifier I – The Mechanical Construction of the Enclosure

Hello to everybody reading my blog,

now after the end of the soccer world championship it might be time to start a new series of entries about the building of a DHT preamplifier as central component of a future orientated system. Several times I have quoted my extremely positive experience from my Aa Line preamplifier, which I do use since 2004. This was my first realized preamplifier incorporating directly heated triode tubes in the small signal section of my chain, namely the line stage of my set up. When I realized this concept almost ten years ago, I did not expect to be so much convinced one day that such a preamp will go to be my final word in the line amplification stage.
At the beginning it formed a extremely well sounding approach towards refinement, but in 2004 my chain was not in that developed stage, where it is today. The first remarkable side effect came when I started to rediscover my digital signal sources again. For more then a decade my Meridian CD player was into storage. With my Platine Verdier Record Player and my time living in the US, created a concentration into vintage vinyl as foremost signal source. But around 2005 the digital storage of music attracted my attention. I did start to record my vinyl for digital storage at harddisks. The combination of "lossless" storage and Apples hard- and software (Airport Express w. digital out, lossless format to be supported), formes a easy access to digital systems within my analogue tube amplified audio set up. Together with my new Aa-line amp it created a extremely refined sounding system, with lots of merits I didn't know from my analogue arm. In these days I did use my audio mainly to listen to my analogue jazz record collection, from time to time I made some recordings from vinyl just for storage issues. I didn't take the digital side to serious, I was a lot more shaped by my early experiences from the 1990ties, when early digital recordings and cheaply made transcriptions from vinyl to CD created my worse experience with digital and formed the decision to leave it for the "consumer".

When I had to move my studio in 2010 I had to adapt new listening conditions. At the beginning I did start just to set up a digital streaming chain as first set, in order to have some music by hand. It came as is always happens, new room acoustics did create new courtesies, I started to like the digital arm of my set up quite well. Together with a new interest into actual and therefore newer recorded music, I realized a unknown conservated audible quality. It was very obvious that in the recording part of audio in the last decade a huge quality step was realized. Completely digitally recorded, mixed and finalized takes showed up with a remarkable close and accurate preserved soundstage, in a way of perfection I rarely didn't know from vintage vinyl. All the typical aural fingerprints, made by every analogue component in the recording chain, the microphone, its input transformer, the preamp, the mixer, the tape recorder, the amplifier and serveral other chained components seem now not any longer exist in a conspicuous way. Instead a much more homogenous and digitally corrected sound image seem to be the new standard of actual audio preservation today. A better focused staging with unknown lots of captured air is the typical side effect of modern well made recordings. All the former unavoidable phase shift effects seem to be gone with digital shaping, instead a wide, dynamic and refined window to lively recordings seem to be now some sort of standard. With the exceptional resolution of my line preamplifier, these qualities were the foremost sensual facts to be experienced, which I rarely did only know from a handful of my best analogue recordings. The DHT tubes combine a extreme musical coherence with absolute linear resolution in a way, indirect heated tubes don't show. The Aa Weitverkehrsröhren are exceptional top performers within the common known DHT's for small signal amplification. I did try other tubes as well like the widely used 26 tube ore the TM2 with similar success, as well with transformer coupling, but I will stay with the German Post Tube, since I like its extremely open, transparent and dynamic sound better than any other. They are made once for 10000 hour service in professional installed telephone relay systems and have some other mechanical advantages the most other DHT's don't show up with, because these typical US-american tubes once were made as consumer products for radio receivers in the 1930ties. The availability of German Post tubes is far better in my culture than any US-DHT and there is the variety of three different brands with different properties to find. The rare and expensive original early (from 1927 on) tube from Siemens (with tip and glass tree inside), the common Valvo type (globe type with mica spacers) and the last version made in the former East Germany by Neuhaus Röhrenwerke (with brass socket and coke bottled glass shape and ceramic spacers).

So I started after almost 20 years to buy again some CD's, giving me a new unknown listening pleasure on the first hand, but as well as streamed data beam digital sets a comfort and usability I never could establish with vintage vinyl recordings. Vintage vinyl is still unique in different fields, it wonderful large size covers, the printed informations and a typical liquidity in the timing of their sound, digital formats do not cary. Today I use both systems side by side with mating success, but the operability of streamed data sets the pace for the years to come. So the quality of the line stage is the key for that kind of use and needs to be of exceptional ability.

First  evaluation stage of my Aa-Line preamp in 2004, equipped with battery clips for the heaters and here showed with rare Siemens Aa tubes, identified by the tip.

Solid mechanical construction with complete relying at oil caps and solid silver wire for the signal path. On the left: the variacs for the lead batteries and a stepped attenuator for volume control.

But I will not conceal that there are some problems with the use of thoriated tungsten filament direct heated triodes, other tubes don't show. With directly heated triodes the cathode acts as heating element for the tube, which means the heater is part of the signal path. The most people know this problem from power tubes, where it creates sometimes hum problems, which can be solved quite easily, because of the higher signal to ground ratio. But at a lower signal levels and following further amplification, any little hum sign will be amplified up to solid levels. Here the problems needs to be solved completely. To get it work, it needs advanced solutions for the heater supply. In the beginning I did start with classic regulators (LM317), these bring a lot of radiated heat to the amp and don't sound very good. After burning my fingers at the chassis of my preamp I did decide to look for other solutions and ended up with a very uncomfortable solution, I did use lead batteries first. Now I had to charge every day my batteries in order to have enough energy for some hours of listening pleasure. I did try several different battery types, since the cheap Chinese lead batteries didn't last very long, after 100 loading cycles they lost  energy to be stored. So I switched to nimh-batteries. I got a quite good sound but only for two hours time with one set of batteries. So I had to buy several sets, which needed to be exchanged after a good year of use by charging them every day. I liked the sound qualities a lot, but hated the charging practice and the all around contact problems in practice. Always some hiss or hum happened needed some helping hand to fix the contact problems for further listening. Not comfortable.

In 2010 I switched to Rod Colemans CCS boards, which make life a lot easier. These constant current supplies are sounding as good as battery power and do not burn tremendous amounts of heat like other regulators do, when well implanted. These can be used with almost any DHT triode, independent of current amount with good success. So they are as well a good solution to be used with power amps.
Now after almost 10 years of use with this preamplifier and after final evaluation comparing it to other options with my new speakers, but as well in other chains, I decided to bing this concept into the next level and final stage. This will be accompanied with several blog entries.

It needs a well made mechanical design to find the long term usability. 

Now, in the final stage the line amp is going to be the switching center for all types of sources and needs several in- and output options. Only the best components are prefered for the job to be a final preamplifier, here with Lundahl iron, NOS Daven stepped attenuators and a Elma switch. Classic WE components are a good guide how to make a well organized amplifier.

For my new approach the Line amp becomes a central position in my chain. Beside the analogue system arm with my vinyl record player, the dac will feed the line stage with digitally streamed music using the comfort offered by wlan and with the iPad as a remote system, since all data are stored at the hard disk of my computer. For the future this is a important and foremost feature to be extended as main source? As well a recording option has to be kept be in mind, which will create other problems to be solved with tube amps.
I did try to listen again to some conventional line amps in the last couple of month. After this exceptional evaluation with very different amplifier concepts of advanced stage I was restless convinced about this preamplifier and therefore I did decide to bring it into a final state. For absolute perfection it needs a much lower output impedance to work flawless universal with every tube amp. With the high impedance of the Aa (30 K) it is almost impossible to match this preference, so some tube amps are not happy with the high load and connecting cables are getting a difficult choice. So, staying with the Aa tube and relying to its extreme unique sound qualities make a fundamental change of the implementation necessary. Cutting the internal resistance into half as a result of the doubled tubes into parallel mode, might be the way to get half of the output impedance. It should sound as good as before with much improved load into the most input stages of tube amplifiers.

Read on soon about the next steps, Volker