彙整 | 八月, 2009

SS 高峯在 VFET , Lateral FET 後继無人之ニ

31 八月

若说 V-FET 是日本在經濟高峯週期攞A grade 的遊戲之作( 大把錢 RnD, 咪燒吓銀紙囉 ), lateral MOSFET 都算有個 B , 而且 日立藉這個 second best 揾咗一大筆, 當年 D 2SK149/J49 (或 2SK150/J50) 賣到全球通行, SS amp 给 lateral MOSFET 撑起半壁江山。

同時代的東芝本來在技術上一D都唔輸蝕, 而且有 ring emitter 科技在手, 但無奈 MOSFET 有許多 gimmicks, 其一就是話佢 tube-like,点 tube-like ? 旺記觉得除了 FET 係 square-law device 之外, 別無技術支持呢句 statement, V-FET 就唔同, V-FET 絕對係 triode-like !

講番東芝, 在斯人獨憔悴之後终於姗姗來遲推出音響用 MOSFET,不過唔知是否知道已是水尾, RnD 縮水, 出嚟嘅 MOSFET 同 日立有距離。當年旺記用日立 MOSFET, 的確覺得佢冇 BJT咁拮耳, 而且中頻明亮, 至于東芝的MOSFET声較淋較懞, 今日許多廠家仍選用大概因冇得揀而已, “高掹"以前都一直用 2SK149/J49, 及後也挶住轉了東芝。姑且引一段玩咗大半生 FET 的 Borbely 的 comment :

“… for me these( 旺按:即 Hitachi, Borbely 就係 Hafler DH-220 designer) sound the best of all MOSFET types. At low bias they sound kind of soft, and come very close to tubes. They have relatively low Gm but the negative tempco is a plus. Vertical types( not V-FET, but vertical MOSFET) such as the Toshibas have higher Gm but a positive tempco, which makes it more difficult to stabilize the quiescent conditions. They can sound quite good as well, especially in the bass department, although for full-range I would always prefer the Hitachis.And the Hitachis can sound good with only 100mA, while the Toshibas would need at least double that."

講到呢度, 不得不讚 Nelson Pass, 將非音響用的 IRF MOSFET 加深度 bias 玩得咁好, 由睇住 Nelson Pass 嘅 A40 到 Threshold 到 First Watt , 一句, 真神人也。