One of the largest and most complex amplifiers Sansui has ever built, and one of the most beautiful, both to look at and to listen to. Largely a BA3000 and a CA3000 fitted together in one box, everything fits together tightly like a 3D puzzle. All electrolytics replaced, all small transistors replaced, solved the preamp power supply board problem once and for all in the best possible way. LED illumination for the meters, taken apart and cleaned the rotary switches for the tone control, the mute and other switches. Placed a new bi-color LED for on/off/protection indication, fitted new 3-wire mains cable. A true no-compromise AU20000.
The preamp power supply circuit board is the same as in a BA3000, but since the AU20000 has a complete preamplifier section fitted instead of just a buffer amplifier in the BA3000, this preamp draws much more current than the buffer amp of a BA3000. Therefore the power resistors get much hotter and damage the circuit board. To solve this in a proper way I fitted replacement metal resistors on the inside panel opposite to the power supply board and made a short cable loom to connect them to the appropriate positions on the circuit board. This is a lot of work, but no other method will solve this problem in a way that will last for decades to come.
The beautiful stepped tone control rotary switches are often damaged by applying too much contact cleaner. The only way to make them work properly again is to remove them from the circuit board, take them apart and clean with thin machine oil on a cotton swab. The left one before, the right one after cleaning. I use a diamond polishing tool to clean metal contacts, like on the rotary arm of these switches, or relay contacts.
LED illumination for the meters can be a beautiful replacement for the original lightbulbs, but since LED’s have a much more directional lightbeam it is crucial to project this light forward enough and from enough distance to get an equal illumination without any ‘hot-spots’.
The mute switch also suffered from too much and too often applied contact spray. Only solution again is to remove it from the circuit board, carefully take it apart and meticulously clean each and every little contact. Put it back together again, re-solder it into the circuit board, fit the circuit board back into the amplifier and test it.
The complete pile of old capacitors and small transistors; more than 80 of each! I also replace most of the small transistors since they almost always have corroded (black) wires. Unfortunately, this corrosion continues inside the actual transistor and inevitably, it will become noisy over time.