It all started about a year and a half. Infected with enthusiasm about the tubes by Bojo and Stoy40, I decided to start an amplifier based on tubes. I figured it would be easier to start with something simple like headphones amplifier. It turned out that I was definitely mistaken. Naturally I started looking for ready solutions on the internet and then I came across to painfully familiar to all of us http://headwize.com. I liked this project described there:
I owned one E88CC and Bojo gave me 6H13C which is similar to the 6AS7. The original version of the amplifier sounded awful, of course. The bias point of two tubes in the scheme were totally confused. In a nutshell - everything from scratch. With Stoy40, who helped me to the end and we formed a team, designed the new circuit and put all the tubes in normal bias point. Naturally, the improvement was noticeable, but definitely not satisfactory. After several attempts we decided to use SRPP as a first step. Then tried and IXCP in the SRPP of the first triode.
In this version the amplifier sounded decent, so we went with it, put in a computer chassis, to the Spring Expo 12-13.04.2008. in St. Zagora, where some of you saw and listened it.
Naturally, this does not satisfy us and we countinued to look for improvements. We decided finnaly get out the awful extremely hot cathode resistors from the output tubes and so we came to the decision to use the second triode of the tubes. It became to look as a modified version of the popular scheme of Morgan-Jones. For the driver we returned to the SRPP variants with 6N30P tubes. So we got to make the V6 concept resembling the "V"-shaped internal combustion engine.
In the power supply we used again tubes - for each individual channel separate rectifier. Filtering is a standard CLC scheme. There was a separate toroidal transformer for the tubes' heatings. From the beginning to this point was passed about a year - a time for experimentation and improvement. With this version we went to the autumn Audio Expo at Technical University - Sofia 2008, where the amplifier was heard and liked, even there was interest to purchase. As at this stage the amplifier couldn't be sold, we thought it would be necessary to make elaborate to perfection, uncompromising commercial version.
In this version we used 6H30P - driver in SRPP, 6N5S - in the final stage as cathode repeater and EZ81. Passive elements was replaced entirely with audiophile ones. Gain control was made of 24 positional switch ELMA breadcrumbs with 3 micron gold plated contacts and connections, resistors for it was from the Japanese company SUSUMU, thin film, 0.5%, 50ppm. The other resistors in the amplifier were PRP, Mills and Allen Bradley, EVOX - RIFA for the filter and the output capacitors. Oxygen-free copper-solid core with a lacquer-insulated pipe was used for the wiring of the amplifier.
The basis of the amplifier was a piece of mahogany polished with wax. Strips under the lamps were made of inox. The spikes and the gain regulator, which resembles a pulley of an internal combustion engine were hand made of stainless steel.
For input connectors we put silver plated Neotech, for the headphone jack - Neutrik with gold plated contacts.
Plaque again in inox - laser engraved.
This the path that was traveled by my initial desire for a "simple" tube amplifier for headphones (whose idea was to get me back again to the tube technique) to create a V6 Nitrocharger.
Amplifier sounding could be described like this: Tight and dynamic bass, precise mids and airy high. Accurately recreate the music scene with real location of each instrument and correct representation of micro details in music.
Due to its low output impedance the amplifier can handle dynamic headphones from 32 ohms up to 600 ohms without any problem. In the development process we used headphones Grado MS1 - Oma 32, eventually final settings were made with the AKG K-701.
I want to thank all friends who contributed to the creation of the amplifier. Special thanks and appreciation to Stoy40 as part of the team's ideas, shared knowledge, the wasted nerves and sleepless nights.