K214 / J77single-ended headphoneamplifier----- K214 / J77 headphone amplifier

K214 / J77 single-ended headphone amplifier, K214 / J77 Headphone Amplifier Keywords: K214 / J77 single-ended headphone amplifier K214 / J77 single-ended headphone amplifier Single-ended amplification circuit is a model for efficiency, the circuit described below is the single-ended headphone amplifier made by FET and MOS control, and is suitable for driving sensitivity is not too low, low impedance headphones. First, the principle of circuit, can be seen from the figure, the entire amplifier can be divided into 4 parts: Be 1. Buffer circuit consisting of TR1 (K246), TR2 (J103): is used to isolate signal interference between the front and rear stages, improve the sharpness of the sound, this circuit is a complementary source outputter, and the input impedance is very high. The output impedance is small, and there are applications in many circuits in Japan's enthusiasts. Adjusting R3 can keep the output of the circuit to be left around 0V. 2, use a twin TR3, TR4 (NPD5566) to form differential amplification circuit: The advantage of the twins field effect tube is that the tube is symmetrical, omitting heavy complex pairing work. In the case of high current operation, the field effect tube can bear the working state of the large dynamic input signal, and is not introduced into high frequency noise due to the increase of operating current. The static current of this level is approximately 9 mA per tube. In order to cooperate with the NPD 5566's large current working state, the differential amplification load is an active load, and the Q1 (A1145), Q2 (A1145) constitute a mirror current source. 3, the output stage uses the sound quality and delicate K214 / J77 to do the output stage, and the configuration of the drain output is used in the circuit. 4, TR5, TR6 (NPD5566) The circuit provides a constant current source load for both TR3 and TR4 differential circuits, and provides a bias voltage for Q4, so that Q4 has a fixed operating current, providing a constant stream source load for output amplifier Q3. . Second, the working principle: The input signal is coupled to the buffer stage by input capacitance. After the buffer level isolation, input to the differential amplifying circuit, and the amplified signal drive Q3 is output to the load. Third, install debugging: Installation process, as long as the front element is measured, the welding is correct, there is basically no problem, focusing on the debugging process, the usual debugging process has 2 steps: 1, adjust the precision adjustable power resistance R3, make the output The potential is closest to 0V, and the output mid point can be controlled within 10 mV. 2, adjust the resistor R11, cause the output stage between 80 --- 140mA, which can be converted by measuring the voltage of both the resistor R13 or R19, that is, the voltage across the resistor is: 0.26V - 0.46V Practice has proved that the current is small, the sound quality is pure, and the current is very sound quality, and it can be adjusted according to the personal preferences.