An electronic superior and more elaborate, considerable budgets for research and development of the audio industry at that time, an analysis and design of circuits of RF (Radio frequency) more meticulous with a production in mass of semiconductors ( BJT and JFET) of high reliability and of high gain and low noise, resulted the development of amplifiers of RF (Radio frequency) of very high features during the 70´s and 80´s.

Two of the secrets that makes higher sound and less distortion possible in older HI-Fi amplifiers is the use of JFET (Junction Field Effect Transistors) and dual power supplies. Technology of 4 decades ago that has not been overcome and follows in force in the present. The modern and present integrated amplifier Yamaha A-S3000 employs transistors JFET so much in the pre-amplifier (Line-Amp) as in the Main Amp or power stage. The modern Home Theater Receiver Pioneer VSX-820K lets see in its schematic diagram two JFET transistors in the Input stage. The circuits with JFET transistors of ultra low noise and high gain are usually placed in the input of the control section of the pre-amplifier and in the input of the section of the Main Amp-Power Amp that is to say the power stage of a integrated amplifier or stereo receiver. The characteristics of these JFET transistors are, among others: low noise and distortion, less heating, higher overall performance that the BJT (common transistors) improves the characteristics of phase and transient distortion, resulting in a brighter tone of greater pitch and clarity and an extremely wide frequency response. The old, ingenious, outstanding and dependable technology Hi-Fi still in force in the modern equipment of today.

Better sound was achieved with dual power supplies one for each channel, which improves Crosstalk Dynamic, which refers to signals from one channel that are filtered to the other.


Though it is certain that the excellent technology of audiofrequency of use of transistors JFET of decades ago still continuous in the present, the careful and detailed design of circuits of the previous Hi Fi equipment united to the outstanding electric properties of the semiconductors of the epoch -some of them discontinued- gave for result components with characteristic singular and prominent upon the new equipment -;this is verified doing a comparative analysis of the leaves of specifications taking in consideration five main parameters: the different distortions: harmonic (THD), intermodulacion (IM distortion), transient intermodulation distortion (TID),frequency response, signal to noise ratio, power bandwidth, effective power (RMS) per channel, factors where the equipment of some decades ago register better qualifications than the modern.-go to the section in this same blog- ¨How can 30-year-old receivers sound better than new ones?¨


Circuit symbol of the JFET transistor where two of its terminals form right angles of 90º in comparison with the transistor BJT where two of its terminals are inclined 30º aprox.



The old and ingenious Hi-Fi technology still in use in the present. Partial view of  ¨Funtion¨ 2/2 schematic diagram of the modern integrated amplifier Yamaha A-S3000. Identifying JFET transistors type 2SK209 highlighted in blue.



Partial view ¨Main¨ or power stage of the modern Yamaha A-S3000, L (Left) and R (Right) channels. JFET transistors type 2SK880BL highlighted in blue.




The modern Yamaha A-S3000 of actual production.




The old, ingenious and dependable Hi-Fi technology still in use in the present. Partial schematic view Input Assy of the modern Pioneer Home Theater Receiver VSX820K. JFET transistors type 2SK117Y highlighted in blue.



The modern Pioneer Home Theater Receiver VSX820K.




Why the excellent sound on old Hi-Fi equipment? Identifying JFET transistors in schematic diagrams.


Kenwood KA-7100 DC preamplifier schematic control circuit board. JFET transistors identified in the diagram as Qi1 and Qi2 highlighted in blue. JFET transistors type 2SK68A.



KA 7100 DC schematic power amplifier circuit board. Dual JFET transistors highlighted in blue of type µPA 63H.



µPA 63H is a Dual JFET discontinued. Extremely difficult to find, only a few of the original NEC manufacturer were located in distant Japan.



Pioneer SA-8800 schematic Tone Amp Pre-amp circuit board. Dual JFET transistors highlighted in blue identified in the schematic as Q1 and Q2 of type 2SK129A.



Marantz 1180 DC schematic Power Amplifier Main Amp circuit board. Dual JFET transistors highlighted in blue of type 2SK109.