The circuit design is modified based on the McIntosh preamplifier and the design values are optimized. It uses three 12AX7 vacuum tubes for amplification and uses one pentode-triode vacuum tube 6F3P (6BM8) as voltage regulation. Vishay 1N5062 forming a bridge provide for full- wave rectification. The resulted ~300V DC. A low dropout regulator LM1084 is used to supply the filament. As all resistors and capacitors are low-noise with good channel matching, the sound quality should have low distortion.
1. Three vacuum tube 12AX7 for amplification and one 6F3P (6BM8) for regulation.
2. Use of WIMA MPK10/ Solen capacitors, Nichicon Audio capacitors, Philips / BHC Averox capacitors, and Dale resistors.
3. Built-in rectification and regulation circuit.
4. Dedicated power and ground rails for tube power and tube filaments.
5. Symmetry in layout design for both channels.
6. Power requirement: one 260V AC(100mA), one 18V AC (1A), and one 6.3V AC (1A).
7. PCB dimension: 110mm x 250mm, thickness 2.5mm and 2oz copper, two layers.