The circuit design comprises of two stages: the first stage uses 12AU7 vacuum tube in common cathode configuration which provides moderate gain, minimum noise and high linearity to the amplified signal; The output stage uses 5687 or its equivalent 6N6-T as buffer to deliver sufficient power to the load. In additional to pre-amplifing input signal, this amplifier is capable to drive headphone directly whose impedance is often very low. The signal paths of this PCB layout is designed in symmetry for both channels. Dedicated power rails, ground, and signal paths, althogether are taken into considerations so that all are to minimize the parasitics, cross interference, and influence of RFI.
· One 12AU7 and two 5687 (6N6-T) vacuum tubes.
· Circuit design comprising two stages: common-cathode stage and followed by a buffer stage.
· Voltage Gain: 22dB
· Bandwidth: 850KHz
· Input Sensitivity: 1Vrms
· Input impedance: 100kΩ
· Ouput impedance: 75Ω
· Two single-ended inputs and two single-ended outputs.
· Symmetric layout design and signal paths with minimum parasitic.
· Dedicated ground and power rails layout design.
· Two large reservoir decoupling capacitors for power rails.
· Power requirements: one 260V(100mA) DC and one 12.6V(2A) DC.
· PCB dimension: 18mm (W) x 11.5mm (L)
· PCB thickness: 2.4mm, double layer, 2oz copper.
2. Headphone Amplifier
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