DIY 2A3 SE Amplifier
This is my first self made tube amplifier using directly heated tubes. Inspired by the Kismet 3 by Fabio Camorani, yet with different power supply and driver tube. The reason being that I did not have these components when I started the project. Obviously the versions presented here will not sound like the Kismet. The sensitivity is somewhat low for an 'integrated' amplifier. In my case this is not an issue, because the Lampizator after the CD player delivers enough voltage.
The first version with Sovtek 2A3 tubes and EH 6AQ8 tubes for drivers, sounded so clear and detailed that I thought every component change would be audible. I set out to experiment and tried out different driver tubes 6N1P, ECC85 and ECC83. The ECC83 from JJ I liked best. Later I also tried the 6N2P. Along with a Vita Q paper in oil coupling capacitor it sounded even better to me. Later I exchanged Sovtek's against EH Goldpin and finally against chinese 2A3C from Shuguang. This is it! (I thought ...). Once the 6P7S SE amplifier was finished, I understood that the 2A3 SE was not performing as it could. With the 6N2P it sounds very fine but lacks 'bite'. I felt that the driver circuit had to be modified.
Several months later I acquired some E180F tubes not really knowing what they were good for. Searching the web, I found a schematic at AudioRoundTable in which the E180F -wired in triode mode- is used to drive the 300B all by itself. I made several trials parting from this circuit, yet always with resistive plate load. Now the 'bite' was there. The sound impresses at first but I felt the mids and the tonal balance were not right. Several attempts to 'cure' the midrange resulted in the schematic presented here yet I was not at ease with the result.
Lately I tried 6N1P and 6N3P in SRPP with the biasing method used in the E180F driver, also switched back to the Sovtek 2A3. Now the sound mesmerises... There is no relation to the first version any more although the basic circuit design is nearly the same. Further very interesting driver circuits can be found here.
Pictures
