I strongly recommend to build this amplifier only if you are already skillful with HIGH Voltages...Otherwise you'd better build something not LETHALif you make one mistake...
Francesca 2000 is my latest reachin the search of a "no compromise version" ofmy home amplifier. My mission is to find clearness and detail. Although Francesca 2000is the result of the many improvements in "Francesca 1999" under many views can be considered a *new* amplifier. These are the maindifferences vs.old "Francesca 1999"(seein the Schem. section):
- The use of the new 6C45P asfirst stage
- The use of a monoplate 2A3 as a drive stage in a fixed bias topology.
- The switch to a SV 572-3 tubeforthe output stage.
- The Redesign of Medium voltage section.
- The High Voltage section now uses a double PI filter.
Here is the Schematic:
click to enlarge
The best discover I've recently made is the new 6c45 Tube. This little monster si able to dissipate 8w, has insignificant noise and 900ohm Rp (!). From the 1st moment I saw the specs I've recognized this will be "the new millennium tube". I made the choice to use it in Francesca 200 to improve the 2a3 drive, lowering once more the Rp. Comparing to the parallel of EC97 there is more "punch" and also the highs are more clear. With a 5k OPT this tube can drive directly loudspeakers obtaining about 1,5W of pure sound. I'll also try this when my pair of hedlunds will be ready. We're also using it in Euridice with very good results.
The use of a sovtek 2a3 monoplate has improved a lot the clearness of the medium and low-medium register. Also the power of this stage has increased a bit thanks to this version of 2a3. I've turned to fixed bias with this tube, because of the better sonic results vs. self bias.
I also decided to try 572-3. This tube has lower bass punch compared to 572-10. But I've found that with my new 92 db Tqwt I didn't need all the power of Francesca 99. So I decided to turn to this tube for its very low distotortion when delivering high power (0.3% at 1w, 0.35% at 20W !!! ). This result in a very clear yet powerful sound. I've also bypassed all the critical polarized capacitors with a 100uf poliester "FastCap" made by Digitex. This has improved a lot the medium presence and the overall sense of speedness. All the most critical path of amplifier have been rewired using silver-teflon cables.
The power supply
Before starting I reccomend you to read the advices of contained the Francesca '99 ps. Besides the HV ps is almost the same (I've only added another LC stage) To give the right polarizing voltages,the medium-voltage p.s. (i.e. the part suppliing the 2a3 and 6c45) has been redesigned.
click to enlarge
As you can see I've extensily used Dc suppling for heaters. I' reccomend you to use in the most sensible partsELNA starget or cerafine Caps.
That's all folks, Listen and ENJOY!