One step further: Piotr's 405-project
Piotr, from Poland, revised his 405 with the Dada-kit ... and some other components:
-Dada Electronics basic revision kit on OPA604,
-mains voltage selector removed,
-double power supply with common zero (chasis),
-8x10000uf/63V BHC power supply capacitors,
-WBT speaker terminals,
-Cardas Rhodium RCA sockets,
-Furutech pure copper ICE socket,
-3N silver, gold plated wire for most power supply connections (plait),
-new rear panel, moved backwards to fit in with lots of capacitors,
-Cardas 3%Ag solder used,
-all PCB pins shortened and resoldered,
-Ultralink Challenger 2 signal cable (6N OFC),
-C1 caps removed (short),
-abandoned PCB fuses .
-1,2V input sensitivity
-Minimum connections - zero connections except primary fuse, PS capacities, and ground to case screws.
-Power supply wiring made of silver wire is constant, uncut, unsoldered, no connectors, handmade plait - from "source" to "target" (rectifiers to PCBs passing capacitors, case to speaker's zeros, all zeros passing one crossing)
I didn't meet any serious problems. Almost didn't test the unit before run. Started from the first time. Results are stunning. Believe me. No partial distortions. Perfect, stereophonic, focused sound. Pleasant and reach at the same time. Pure black background with natural, creamy recording's noise. Much more agressive, faster, precise but still natural, rich, transparent sound to live with. Bass not foggy. Similar bass shape and depth like before but this is not coffee with milk anymore. This is more like.. dark brown, thick espresso that you can feel, but you cannot touch.