The circuit design is modified based on the classical McIntosh C22 pre-amplifier. 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 capacitors, Nichicon Audio capacitors, 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(200mA), one 15V AC (1A), and one 6.3V AC (1A).
7. PCB dimension: 110mm x 250mm, thickness 2.5mm and 2oz copper, two layers.