After powering it up and listening to it for around 2 hours on my dipole Fostex FE127E MLTL here are some initial thoughts.
- The bass, which on the FE127E is actually pretty impressive. It is nicely balanced.
- The iPod that I was using to power it, can drive the amp to clipping, especially on heavy bass passages. The mids and highs sounded okay, but the bass was definitive distorting and clipping.
- This amp does go pretty low and fairly loud.
- However, this is not enough power for my needs. 2W is definitely too low, unless I really use speakers over 97 dBW. The Fostex are 91 dBW and as a dipole around 94 dBW.
- The output noise on the Fostex is very, very low. On the multimeter VAC reading, it was 4 mV at the terminals. It was inaudible unless you were very, very close to the drivers.
- This combination with the paper full range give such a fantastic rendering on the voices.
- The voltages measured around 10% higher then design.
This amp took around 3 months to complete. The first was in ordering and sourcing the upgraded components. Also, the chassis design was undertaken. I then took a few months off due to having no time, and on a long weekend, I had the time to complete the amp. The staining and painting of the chassis was around half a day's work, but it spanned a day due to the time waiting for various finishes to dry. Up close, there are defects in workmanship and definitely learning lessons for the next chassis, but from normal viewing distances it does look quite smart. It took the better part of a full day to complete the PCB, and fix and wire everything up in the chassis.
After some false starts with grounding and connection issues, it was finally operational. A few notes. It takes about 10 to 15 seconds from power on for music to come through the speakers. The tube rectifier to thank for that. After some time playing, the chassis area around the power tube got warm. Not hot, but warm. Around the rectifier wasn't too bad.
The range of music that I was initially listening to was light (Dido, Missy Higgins, Coldplay, etc) but the sound was superb. With the Fostex, the sound stage was large, but could've been larger. The vocals, as I said before, were amazing. The bass, if it was a simple bass line was also impressive. There was a lack of very high end sparkle, that I was used to with my Mark Audio J6T, but that may be improved with a super tweeter. Overall, I am very happy with this amp. Much of the reason for building this amp was to further test and hone my skills in making high voltage tube amps. This proved that I could wire it up correctly, and test and find faults. It also proved to me that I can take a schematic and PCB making some minor changes, but still keeping the whole thing working.
However, it also demonstrated that 2W with my current speakers are not loud enough. Therefore, if I'd like an extra 3dB of headroom, and play it at most another 3dB higher. I would either need the same speakers with an amp of 8W or need the same amp with speakers that are 100 dBW. Therefore, if I built a 300B amp running around 8W, this would give me the flexibility of using the same speakers or using higher efficiency speakers. Conversely, I could use the 300B with slightly less efficient speakers and have the same 'loudness'. Any which way, this is an excellent amp for smaller rooms with high efficiency speakers. They produce a lovely sound, that should only get better with time, and have a wide range of differing tubes to be rolled and tested. It is reasonably priced and is an easy to build kit.
Highly recommended!
