Caros Foristas,
Apresento nestas páginas o resultado de muitos meses de projecto e implementação do meu último pre-amplificador.
Trata-se de um desenho "sem compromisso" utilizando os melhores componentes possível para este tipo de aplicação. Como expliquei noutro post, este projecto que considero absolutamente "hi-end", é o resultado da colaboração estreita entre vários amigos, desde o Thomas Mayer até ao Rui Pinho, pois este projecto como já expliquei tem um cunho profundo indirecto da RR Audiomanufatura.
O texto seguinte está em inglês, peço desculpa para o facto, mas como vai ser publicado num blog escrito nesta lingua, aproveitei.
Espero que gostem...para mim, tem sido um gozo poder dispor de um preamplificador deste campeonato.
My Type 26 Tube Preamplifier adventure – by Rui Lourenço (Portugal):
The project:
After several preamplifiers done in the past, I decided to try to build a direct heated triode preamplifier for my own reference system, to stand as the Ultimate. For that I had established some basic principles:
• It had to be a 2 chassis design
• Retro looking
• With valve rectification and non-electrolytic filtering
• I wanted to use SSHV2 regulators
• Dual mono (or almost)
• With output transformers
I studied several possibilities, but having seen in the past Ale’s first #26 implementation, after looking at the wonderful job Thomas Mayer develops, I knew I had to go this way, of course using also some of my predetermined ideas and principles.
The Schematics:
• HV supply is built based upon a Telefunken AZ11 (mesh plate) rectifier in graetz mode using to U4007 diodes. First cap is ASC X386 top blue line with 8uF; this feeds a Lundahl 1685 10H choke, feeding an ASC X386 normal line 50uF capacitor. The HV line then splits in two; feeding one Hashimoto 30H choke by channel, finally feeding one more ASC X386 normal line 50uF capacitor by channel, these last two capacitors have a 220K /5W Kiwame resistor across their terminals. Ground is common and arranged in star connection through a copper bar where all grounds connect together.
• Filament Supply uses a conventional design with Panasonic high ripple capacitors, three times 15.000uF by channel, plus 2 coil chokes by channel in a PI arrangement. The transformers are 15V/50VA Weiss manufactured, again one by channel. Rectification is done through rectification boards, built around YXYS Hexfred devices, all snubbered with 100R Kiwame resistors and 0,1uF capacitors.
• Mains transformer (incredibly good Weiss, built to Thomas specs), wood chassis (high quality real wood, no veneers), tube damping and output transformers came from Thomas Mayer in Germany.
• Main schematic:
o The HV lines coming from the supply chassis through an eight pin Neutrik connector, are fed in a custom made double 2,2uF/400V Kevin Morgan capacitor
o The two separate HV lines are feeding one SSHV2 regulator by channel
o These feed, one KK CCS by channel
o These then feed two VR75 type tubes in series, by channel, both by-passed by a Russian PIO capacitor, plus a 510K/5W Kiwame resistor on the top VR tube.
• I use one Rod’s filament supply by channel, fed separately from the above mentioned supplies
• The bias is set through five 50R/20W Dale resistors in parallel by channel to get 10R, and around 10V on their terminals
• The HV line is reaching around 145V on the 1R already mentioned resistor
• Again ground is very important, and the same implementation used on the supply chassis, is used on the main unit, using a chassis insulated copper bar, where all ground connections are linked. Chassis is connected to this ground in one point, and mains earth is connected through a separate line (also to the chassis via a 1M resistors and a by-pass capacitor), earth ground can be lifted through a switch.
• Both HV and filament supplies are completely clean on the scope.
• The all unit is DEAD QUITE, and you can’t hear any noise from the speakers, even with your head deep into the speaker units.
Some general information:
All used components are top notch:
• All internal power supply cabling is done with high quality copper, both using Nordost and Vandenhul wire
• Signal connections are Audio Consulting pure silver enamel cryogenic wire
• Solder is WBT
• All tube sockets are Yamamoto
• Volume control is TKD top level
• All screws and nuts are stainless steel and/or brass. All nuts are pure copper
• Resistors are Mills and Kiwame
• Capacitors are ASC oil caps, Panasonic, Kevin Morgan and Russian PIO
• Rectifier is AZ11 Telefunken Mesh plate
• VR tubes are Russian new old stock
• Type #26 tubes are Cuningham balloon type
• Iron from Thomas Mayer, Weiss, Lundahl (chokes and OTP transformers) and Hashimoto (chokes)
First impressions:
The first thing I am always very fundamentalist about, is the noise, again in this case, DEAD QUITE!!! Maybe due to all heavy artillery I’ve installed, the very good schematics, implementation, ground path, well, all counts.
The gain is for me perfect, meaning for my normal hearing level, with CD, and my 300W amplifier, depending on the level of the recording, I tend to go around 12 0’clock on the knob (best linear region of the volume control).
The sound is incredibly clean and tri-dimensional, very clean black back-ground and instrument separation with splendid dynamics and fast response.
All instrument timbres and vocals are very detailed with all the whispers and tonal qualities we could expect from top hi-end equipment, without any special effect normally related to tubes.
Bass presentation is very clear and tight, with great control.
Overall, this pre-amplifier performance is amongst the very best you can find. It was/is really worth the efforts.
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