Last update: 26 may 2006

I bought my Audio Note Kit One in december 1996. The only tube amp I had before it was the Audio Innovations First (push-pull using 2A3). This amp has a good reputation but I immediately recognized the advantages of a SET after I finished the Kit One. A further big advantage of such a kit is that upgrades are easily performed. My changes in the course of a few years were: Black Gate elco's at the cathodes, Noble potmeter, Caddock resistors in the signal path, Ultratone silver coupling capacitors, silver wire in signal path and Elna Cerafine capacitors in the power supply. Each step was an improvement leading to more clear and detailed sound, the largest difference was probably made by the Black Gates

A different chapter is the replacement of the tubes as delivered with the kit. From the price of the kit you can understand that these are not top quality. My first replacement was the exchange of the 6SN7GT with a VT231 from Belmont. After that I changed the original (Chinese?) 300B tubes to Svetlana 300B's. After 3 years the 5U4G rectifier tube started to show blue sparks and it was replaced by a similar one. Later I heard that this problem arises because the capacitance of the power supply is quite high for this tube. A better tube is the GZ37 (or CV378). This tube further has the advantage of a slow turn-on heater. I bought a Philips NOS from Audio Note. For a rectifier it is expensive but the difference in sound is certainly worth the investment. The final tube to be changed was the 5687. I have obtained the 5687WB from Philips ECG. This set of changes makes the Kit One a different amplifier with much more detail, more extension to high and low frequencies and a big improvement in stereo space.

During the Christmas holiday of 2001 I rebuilt my amplifier because its housing became too small and rather messy after all the changes. I used the opportunity to make several changes. The most important ones are:

• Leave out the 6SN7GT input stage, this is advised in the manual if sufficient signal is available

• Replace the Noble potmeter by a DACT CT-2 stepped attenuator

• Leave out the printed circuit boards

• All wiring in silver, signal path as short as possible

The result is a much cleaner sound with more detail and spaciousness.

Update: october 2004

The final(?) step: Automatic Engineering transformersnovember 2003

After hesitating for several years I finally decided to buy these transformers with the amorphous core and silver wire on the secondary winding. I even informed about the price of silver on the primary side but that was way beyond the budget. It took three months before they arrived and they were much larger than I anticipated. With some effort I could install them on my rebuilt Kit One but it did not look very good. At the same time I again checked all the wiring and the soldering of the amplifier but I could not find any indication of something that could cause the hum problem that occurred indidentally. The only wayout of this was a second rebuild and I decided to prepare it in more detail than the first time. I did not use a metal plate but the alternative that I figured out turned out to be very impractical. One of the problems was that the space inside was limited making it to access it. My solution for that was quite drastic. I decided to make two frames, one for the power supply and one for the amplifier itself. The power supply nicely fits in the old Audio Note chassis and for the amplifier part I made a housing that fitts the new transformers very well. Another change that I decided upon after long thinking was a replacement of the DACT volume control. This was not because of its sonic quality but because it makes steps of 4 dB down from -30dB. Late in the evening I was quite often confronted with the situation that -30 dB was just too loud and -34 dB too low. Accidentally I came across an alternative: an attenuator that has 41 steps all of 1.5 dB. Its construction is in priciple the same as the DACT but it is much larger in size and therefore did not fit in my old housing. One month after I ordered this attenuator I took my amplifier completely apart expecting the attenuator to arrive soon as promised. This was a little too optimistic and I have had to spend almost three months without music. nevertheles, in the beginning of october it came and I installed it and became quite nervous. After a lot of checks I installed old tubes and ols speakers, connected a CD player and after two seconds I heard that only one channel was working. After a long lunch break I rapidly found a short circuit near the input of the right channel and also this problem was solved. After that the amplifier was placed in my listening room, still with old tubes. The first impression was already very good. I heard details on several CDs that I never heard before. The next day the good tubes were put in place and the sound was even better, some sharpness in the high frequencies vanished and the bass became even more controlled. Now, after two weeks of listening, I am still amazed about the improvement in the sound. The only new component is the Acoustic Dimension attenuator. Further I changes all the wiring, making the signal path as short as possible and the power supply is now half a meter below the amplifier, as you can see on the first photo below.

Update: 26 may 2006

Modified Audio Note Kit One