Ampli con le 300b di Daniele
Prefazione: Complimenti Daniele hai costruito un amplificatore che e' un punto di arrivo per tutti gli autocostruttori , un vero caplavoro estetico e sono sicuro anche sonoro. Bravissimo. e se avete aggiornamenti , richieste, consigli , su questo tipo di amplificatore scrivetemi che amplio l'articolo Davide www.audiocostruzioni.com
Allego qui sotto le mail ricevute da Daniele
Carissimo Davide prima di tutto mi complimento per il sito, sempre aggiornato e ricco di preziosi spunti .Ci siamo sentiti sul forum per le casse da abbinare al mio integrato di 300b autocostruito.Non sto a darti caratteristiche varie che tutti potranno consultare sul sito(di cui ti allego il collegamento) dove io ho preso il progetto. http://indigo.ie/~walton/300bpartslist.html
Rispetto all'originale io ho fatto una versione stereo con alimentazione sdoppiata a partire dall'induttanza di filtro e alimentazione dei filamenti di 300b in continua.Tutti i ferri sono Hammond eccetto il trafo di alimentazione acquistato sul sito Autocostruire.it dell'amico Alessandro.Devo dire che rispetto al mio precedente S.E. di el34 di Nuova Elettronica è veramente altra musica!! A proposito dei diffusori ho trovato molto interessante il progetto di Nardi(di cui condivido pienamente le idee riguardo all'alta fedelta')pubblicato sul n67 di chf ,le G-Glass che utilizzano due woofer Vifa M21WG-02 custom Audio Note ed un TW Audax TW 034 X0 .Al proposito mi piacerebbe sapere un tuo parere.Questo è tutto,spero di non essermi dilungato troppo.Ti saluto e a risentirci presto.
Carissimo Davide ti ringrazio per i complimenti e t'invio lo schema del mio ampli. Ricordo che non è farina del mio sacco,io non sono un tecnico ,ma un amante della musica con l'hobby del far da se. Le modifiche che ho apportato sono: lo sdoppiamento dell'anodica a partire dall'induttanza di filtro,la capacità dei condensatori di filtro portata a 50mf,il condensatore di accoppiamento fra il driver ed il finale da 1mf in luogo dello 0,22 previsto,doppio avvolgimento a 5v del tr.d'alimentazione per il filamento delle 300b(ha gold)e raddrizzato con un semplice ponte di diodi e filtrato con un condensatore da 10.000 mf e due resistenze da 10ohm 1 w (questo schema è derivato dall'alimentazione dei filamenti 300b del famoso Triodino). Le 300b le ho acquistate via internet su un sito tedesco ad un prezzo molto vantaggiso http://www.tubetown.de/hallo.html ,provare per credere! Parlano pure italiano!!! Al momento l'ampli sta dando voce a dei diffusori autocostruiti su progetto di Alberto Bellino, i Singer ma che non ritengo all'altezza di questo apparecchio. All'inizio di tutto il discorso c'è un vecchio lettore cd Nad 522 che sostituirò appena le mie finanze lo permettono. Non mi hai risposto alla domanda se hai letto l'ultimo numero di Costruire hi-fi a riguardo i diffusori G-Glast proposti da Nardi, a me sembrano intriganti.Mi piacerebbe conoscere la tua opinione. A presto
300B Mono Block Parts
Quantities are for dual mono construction - i.e. two amps.
· Angela Capacitors are manufactured in Denmark by Jensen, as indeed AudioNote are and weather they are marked Audionote, Angela or Jensen they are identical except for the label thereon. They are an paper in oil, aluminium foil type, but I have used the paper in oil,copper foil one for the siganl bypass section. For the power supply section I have used Angela Polypropylene and oil which is manufacturered for Angela by the same company - ASC - that supplies the like of Conrad-Johnson and are highly regarded in the Japaneese audiophile ranks.
· Jensen Tobias Jensen Ltd. was established in 1917,... thats 84 years ago, in the same year the Great October Revolution laid the foundation of the Soviet Union. Today the USS don't exist anymore, but Jensen are still manufacturing electronic capacitors, which have been developed through the decades of the electronic age. Over the years, good quality, high reliability and long life expectancy have become the central part of the company philosophy. Many years of experience, a staff of qualified experts, an advanced production equipment supported by an extensive control system (ISO 9001) guarantee a high level of quality.
· Black Gate Heart of Music as they say and though everyone has their preferences , most will agree that these are amoungst the finest electrolytic capacitors available. Superior construction and the use of fine grained particles give them a lower ESR ( by about 10%), lower noise floor lower distortion,greater bandwidth and a lifelike musical reproduction..no wonder that Audio Note use them by the truckload.
· Riken Ohm Resistors are a Japaneese audiophile grade resistors, that have a huge following with tube fans in their home country, with gold plated leads that have a 1% tolerance ( produced by depositing a thin film of carbon on a ceramic former) and has the sound combination of an Allen Bradley and a good metal film type, together with very low noise floor and will not suffer from temperature drift.
· DaleThese ceramic wirewound resistorswith aluminium heatsink, from one of Vishays subsideries, are a popular choice for power suppies... users include, Pass Laborities
· CTS Clarostat are a N.O.S. 2W military specification wirewound pot with a locking shaft for the hum balance of the power tube filament supply
· Mains Transformer is Angela Instruments Universal Mains transformer which is a 380-0-380v 200mA enclosed type, with additional 6.3V at 3.5A for the power and input tubes as well as 5V at 3A for the rectifier filament. They reckon that it's so good that they carry a 5 Year guarantee
· Choke choice here has been for the Hammond type for no other reason other than it is availabe from Angela also and has the necessary qualities required, being of the same heritage as the output transformers and it is nice to maintain the continuity where possible. It is an enclosed type though it has a lower ohmic value than what was specified in the original circuit and a higher load value too.
· Output Transformer Oh dear.....there was a lot of thought into this one. There are so many opinions out there that it can be a minefield to the inexperienced like myself. I spent so long debating it that it held me up for months as my initial feeling was to go for one of the more expensive, more upmarket makers, assuming that they real good ones are more expensive. But it just kept me from ordering and it was getting silly , so instead I opted for a sensible choice in the form of the Hammond 1627SE, which has air gapped laminations and weights 11lbs. The use of interleaved windings helps to maximise the high frequency responce and have an excellent bass responce.
Hammond traces its roots back to 1917 - some 84 years ago, co-incidentially the same as Jensen above - and was incorporated as Hammond manufacturing in 1927 and currently has a turnover of $166million and employs 1,200 people. In the 1930's, Hammonds previous years experience was to put them in the forefront of the manufacture of magnetic components during World War II for communication transmitters and very specialized transformers and the beginning of the Cold War in the 50's thrust upon the Company significant volumes of military transformers, especially as a result of the construction of extensive early warning radar systems across Alaska, Canada and Greenland.
Their ratings are for full power at the rated plate current and their specs are +/ -1dB rolloff points - 20-20KHz , again at full power, as well as having a tested HV rating of 2000VAC. These models use a "distributed air gap" to eliminate core saturation and high quality M6 grain oriented silicon steel laminations.The multiple interleaved secondaries allow 4, 8 or 16 ohm load impedances .
· Power Tube The 300B....First developed by Western Electric as an audio device in 1935 is still one of the most linear audio tube ever made - need I say more. For the first 6 mths I used the JJ Tesla but have replaced it with Western Electric...beyond belief and worth every penny.
· Signal Tube General Electric 6SN7GB.....Good alround tube, though somewhat lacking in the lower octaves and is a little forward and somewhat "in your face"
RCA Red Base 5692.....a sweet alternative to the 6SN7GB and one that some will say is the very best of its type. Absolutely superb and my best recomendation for this amp. Though very expensive, it has a wonderful midrange and better bass tonal definition.
RCA Black Base 6SN7 GT ....they all have their own benifits and while this is a sweet tube with a good extended top, it is no match for the Red Base
· Rectifier I have used the 5U4GB General Electric tube for this amp but have also tried a Mullard GZ34 and found that there are some benifits brought with it in terms of bass definition and an increase in the top end , presumably because of the increased B+ due to the lower voltage drop across it of around 20v - I finally setttled on the 5U4GB for better sonics and what seems like better drive overall. The 5U4 GB has a voltage drop of 44v across it and is 1970s vintage.
· Angela Instruments... Have been in operation for 24 years and are well versed in mail order business. Their shipments are insured in transit and offer a 7 day return policy if not satisified. Their service in my opinion is impeccable and were very fast and efficient and went to great trouble when I had a query.
Useful links for this project
So, all you have to do is to ask yourself if you can connect together sixteen parts in a compedent manner. Then do that again - and then have a go at the PSU. So you see, if you look at it in individual parts of a greater picture then it is not so ...err...daunting a proposition.
This schematic is from Angela Instruments and is otherwise known as the J.E. Labs 300B.
WARNING.......The usual warning must be acknowledged - that herein this circuit contains letal voltage that can KILL.... We are talking serious damage !!! Do Not Mess with it unless you are familiar with good electrical safty practices.
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