글쓴이 : SOONDORI
진공관 앰프처럼 상면을 그대로 노출시키고 방열판은 전방에 배치하는, 특이한 구조를 취하고 있는 파워앰프.
이른 바 QUAD 405 스타일? 방열판 전면 배치는 입력~출력의 선형 Signal Flow를 염두에 둔 작은 아이디어일 것이다. 한편으로 조작부가 거의 필요 없는 파워앰프이기에 가능했던 디자인이기도 한데… 시각적인 안정감에, 꽤 그럴 듯하다.
100W@8오움, 1hz~100Khz, THD 0.01%, Damping Factor 100, S/N 120dB, 21Kg, 1977년, 당시 16만 엔.
* 관련 글 : SONY TAE-8450 프리앰프와 TAN-8250 파워앰프
(출처 및 기타 사진자료 : http://amp8.com/tr-amp/sony/ta-n7.htm)
(JFET 6개가 사용된 병렬 드라이빙으로 힘들게 100W. 그런 것이 1970년대 소자기술의 한계)
그나저나… Sony는 홍보자료에서 ‘V-FET 구동’을 재차 강조하고 있다. 무엇일까?
이 DC앰프 출력단에 사용된 2SJ18, 2SK60 FET 소자들의 내부구조를 암시하는 단어. VFET는 Sony와 Yamaha가 함께 개발하고 공유했던 일종의 JFET로서 ‘V’는 Vertical을 뜻한다.
(V자 계곡과 같은 내부 절연공간이 있기에 VFET. SIT(Static Induction Transistor)이라고 한다. 출처 : https://www.nutsvolts.com/magazine/article/fet_principles_and_circuits_part_1)
높은 주파수 신호들을 최소 왜곡으로 잘 취급하고 대출력 구현도 가능하다는 특징이 있다. 물론 MOSFET가 보편화되기 이전 시절에 그러했다는 것.
2SJ18 VFET의 실제 모습은 아래와 같다.
(일련의 VFET들이 중국 Fake 사업자들의 표적이 되고 있다는 카더라 통신도 있다. 출처 : http://www.agoraquest.com/forums/viewtopic.php?t=33590)
다음은 V-FET에 관한 소개와 설명을 담고 있는 문서의 일부. (The Sony VFET Amplifier 40 Year Commemorative – Nelson Pass)
This is about audio power amplifiers, more specifically about those made with a special type of transistor known originally as a VFET, now more commonly referred to as a Static Induction Transistor (SIT).
In the 1960’s silicon power transistors began to replace tubes in audio power amplifiers, being more convenient in a number of ways. The transistors themselves were smaller, less costly, more efficient and they needed less external hardware to make them work. There were some complaints about their sonic performance in audio amplifiers as compared to tubes, and some efforts were made to give transistors a more “Triode-like” character.(1) Similar efforts and discussions about them continue to this day.
In 1972 a U.S. patent application was filed by Junichi Nishizawa describing a special type of JFET (Junction Field Effect Transistor) where the “drain-current to drain-voltage characteristic simulates the anode-current to anode-voltage characteristic of the triode vacuum tube very closely.” (2)
Examples of “VFETs” were produced by Sony and Yamaha forty years ago and appeared in power amplifiers produced from about 1975 through 1980(3). These amplifiers are now prized for their exceptional sound, the credit popularly going to the linearity of the VFETs(4). They were called VFETs at the time because they have a vertical (not lateral) structure. The subsequent invention and dominance of vertical MOSFETs (Metal Oxide Semiconductor Field Effect Transistor) made use of the term confusing, so now they are generally referred to as Static Induction Transistors (SIT), except perhaps as reference to these original parts.
These transistors were also exceptionally fast as switches, and in 1976 Sony also produced an early version of the Class D audio amplifier, the TA-N88.(5)(6) By the 1980’s Sony and Yamaha ceased production of VFET amplifiers. Various reasons for this have been offered, the most likely being that production of these exotic parts was considered too expensive to compete with the cheaper vertical MOSFETs which appeared on the market. (기타 생략)
다음은 Yamaha 로고가 인쇄된 VFET 소자들을 사용하는 B-2 파워앰프 예시.
(출처 : https://i.pinimg.com/originals/71/af/72/71af72e080a33030cb348a75accde52d.jpg)
