Application analysis of field-effect transistors in audio digitization 1

The application range of field-effect transistors in audio digitization is becoming increasingly wide. The principles, advantages, and common knowledge of its use have been extensively discussed in some reference books and newspapers, and will not be repeated here. This article illustrates the reasonable application of field-effect transistors through two key points that are easily overlooked by audiophiles, especially beginners. At present, field-effect transistors (MOSFETs) used in the audio field include junction transistors (JFETs) and insulated gate field-effect transistors (MOSFETs), which are further divided into LDMOS, VMOS, and recently emerged UHC, IGBT, etc., and are still constantly developing and improving.

1. JFET lacks complementary tubes within pairing tolerance

The maturity of bipolar transistors manufacturing technology today has reduced the pairing error between NPN and PNP complementary transistors to a level that is widely accepted by professional manufacturers and audio enthusiasts. In contrast, the selection of field-effect transistors is much more difficult, and JFETs used as amplifier input stage transistors lack complementary pairs that meet the requirements (which is determined by the current manufacturing level). The attached table lists the main characteristic data comparison of Toshiba's DualFET K389/Jl09. According to the attached table, the difference between K389 and J109 is VCC and NF, where the difference between the values of C and C, as well as the difference between the N and P channels, is five times greater. The author once purchased 8 pairs of K389/J109, but the test results before installation were quite disappointing: ① The so-called twin tubes only have the same performance between two tubes in the same tube shell, and the difference between the N grooves in the 8 pairs of tubes purchased at the same time is quite large, and the difference between the N grooves and the P grooves is even greater; ② The Idss, gm, and Vgs of K389 and J109 are different, and the actual waveform testing is also asymmetric.transistors