ECC822 tube OTL headphone amplifier

In the circuit shown in the figure, a double triode ECC82 (equivalent to E802C, E82CC, North American 12AU7, and domestic 6N10 type) is used as the amplifier. This type of pipe has the characteristics of excellent indicators and long service life. The preamplifier needs to produce enough signal amplitude to drive headphones. The transistor part of pins 1, 2, and 3 amplifies the signal. The input signal reaches the circuit board through the 50kΩ volume control logarithmic potentiometer P1 (P1 is not shown in Figure I), and then is directly transmitted to the preamplifier stage through C1 and R1, while R1 and C1l provide the necessary negative gate bias. Gain is essentially determined by R8. The maximum input voltage is determined by R2. R9 is determined like this. That is, the static anode current is selected in the largest possible linear part of the characteristic curve. The input signal, which is inverted and amplified at the anode, is coupled to the second-stage gate via C2. The second-stage cathode resistor is divided into two parts, R5 and R6. R5 and R6 are connected in series to form a load resistor. Its voltage dividing effect selects a correct value for the gate bias voltage. The gate bias voltage is decoupled and stabilized by R4 and C3 before being applied to the gate. The anode current determined by the gate bias and the corresponding characteristic curve forms a voltage drop across R5 and R6, which is strictly proportional to the current. This voltage is then fed to the headphones via coupling capacitor C4. In order to avoid clicking noise when the headphones are plugged in, connect R7 to keep the output at the DC signal ground potential. The above only introduces the working principle of the L (left) channel circuit. The same is true for the right channel.