Application analysis of field-effect transistors in audio digitization 2

Finally, the author can only select two tubes with an error of 3.8% from K389 as single-sided differential input stages (in the past, it was not difficult to control the error of the same polarity tube within 1% when using bipolar twin tubes, and the pairing error of the opposite polarity tube would not exceed 3%). Through the comparison of the above data and actual testing, the following insights can be obtained: when JFETs are used for complementary input stages, the discreteness of V and I-1 will cause a significant offset in the static operating point of the circuit, thereby deteriorating the stability of the circuit; transistors The inherent differences between gm, Cis, and Cis have a greater impact on the dynamic indicators such as waveform symmetry and transient response speed of the entire push-pull stage. Regarding this point, some well-known foreign manufacturers have already formed a consensus, such as Tianlong, Malanshi, and others. Field effect differential input stages made of K389 are often seen in their products, but it is always difficult to see the shadow of J109. Perhaps K389/J109 was originally a "loose fit".

Compared with JFETs, MOS transistors are easier to achieve higher withstand voltage, power consumption, and transconductance. In addition, the complementary pairing requirements for the parts of the amplifier other than the input stage (such as the driver stage and output stage) can be relatively relaxed, and some pairing defects can also be overcome through careful circuit design. Therefore, the application of MOS transistors in the final stage of power amplifiers is not a big problem. The problem with MOS transistors used in power amplifier output stages is not complementary pairing, but rather low efficiency.