彙整 | 十一月, 2009

一個 Class A advocate 的啓示

27 十一月

意猶未盡,继續講吓 Nelson Pass 的思路。

Pass 由 day one 出嚟發表文章, 就一直堅持 class A, 我印象中他没 publish 過 class AB 的 design。如果用耳仔收货, 其實好简单, 攞部 class AB amp, 聽一陣,然後將 biasing 调去 class A, 就会明白為何要用 class A。 旺記當年用部通用 mosfet amp 特登谷大 biasing聽class A 直至燒机為止, 明知 over rating, 但實在好声不能自拔,眼巴巴 睇住 D epoxy 顶唔順爆出嚟,都幾爽。

不過 Pass 係美国人, 一定会砌 D 理據嚟 justify 佢嘅取向,且把(憑我記得)他的理據表列 :

1. Class A 更 linear  , 最重要喺 open loop 的 linearity , 因為只有  open loop 的 linearity 才可保障 intermod 的 performance ;

2. 要 SE ! Pass 话 声波 by nature 係 SE, push-pull 係 人造嘅, 人聽唔惯 odd harmonics, 所以 amp 都要用 SE 減少 odd harmonics  — 呢点幾有趣,有 D  zen 意 ;

3. 要用 linear device, or triode-like device, 因 triode 條 operating curve 上下疊埋就係一條直綫。

4. 要用高压既 device 才会好声 — 我唔知佢喺唔喺喱埋玩 SIT 之後的结論,之不過高压低电流 — 旺記一早講咗呢个喺胆机好声嘅 major reason,冇嘅, Pass 賣石机, 唔通佢会话眾裡尋她千百度, 原來50年前嘅 device 至好声咩 !

半導体生意難做

26 十一月

近日歐美音响界之熱事,不可不说的自然是 Pass 老大掀起的 Depletion mode  FET 熱潮。我講喺"歐美", 因为玩 depletion mode, 日本 70年代末就玩嘞,就喺旺記在此 blog 晨早講到口水都乾埋的 V-FET。V-FET 比现代 depletion mode 更好玩的, 並非它在 deep class A mode 更 linear, 而喺 更型似 square law device , 即 triode-like !

不過, 東西方建立知識的方法論有別, 東方人以神來之筆跳躍出知識,西方則以邏輯加實踐一步步行上去,所以當東洋知道了三極之神的存在後便死攬不放, 而且不断找尋擬三極管的物体, 最後成就了 V-FET。西人則唔信邪继续探索,到了今天,终於認为单端最好声自然,Pass 自已就講過, 试晒所有 depletion mode FET, SONY D V-FET 喺唔同 D。我唔知 Pass 玩過 Tokin D SIT 未 ! Anyway, Pass 一步步行出嚟我都好佩服,不過比日本遲咗卅年 ! 而且, Pass 嘅玩法未夠燒, 要知乜嘢叫發燒, 睇吓 Digital-Do-main 和 Maxonic D V-FET amp 就明白。講开知識方法論, 旺記在美资公司任職時有个老鬼, 好精嗰隻, 一日同旺記吹水,旺記又响度亂車廿四發表建立科学知識之我见, 美老鬼陰陰咀笑着说, 你認為牛頓和愛因斯坦喺大量實驗之後先得出他们的理論咩 ?

一棍卜落嚟, 我記住你。

Anyway, 差 D唔记得咗,我喺想講半導体生意難做, SemiSouth 被  Pass 寵幸後竟然出 news, 大佬, 你出 SiC 喺 commodity, Pass 出小眾产品, 咁都殺埋 ? 真替他们的錢/前途担憂。不過咁, 聽闻當年 NS 全靠 diy友 一窩峯玩LM3886養起一大棚人,人民力量不可欺也。

 

SemiSouth 篇 News, 原文照錄,我就觉得幾攪笑。

SemiSouth Laboratories, a silicon carbide (SiC) power devices provider, announced that its product, an SiC JFET, has been adopted by a Consumer Electronics company for use in a new audiophile- quality power amplifier.

The new J2 Power Amplifier, designed by audio specialist Nelson Pass for First Watt, an amplifier provider, features SemiSouth’s SJEP120R100, a normally-off, 1200 V, 100 m-Ohm SiC Vertical Junction Field Effect Transistor (JFET), the company said. Nelson Pass is founder of First Watt and also Pass Laboratories.

Pass said, “These new JFETs have a very low distortion characteristic that makes them superb for use in linear amplifiers. In apples-to-apples comparisons with MOSFET-type power transistors, they can achieve 10 to 20 dB improvements in distortion performance. When a better transistor like this comes along, it can mean getting the same distortion performance with a lot less feedback, or lower distortion with the same amount of feedback. The J2 does amplifier does both, and that helps make it a better sounding amplifier than the best of its predecessors."

Dr. Jeff Casady, SemiSouth’s Chief Technology Officer and Vice President of Business Development, said, “We are really pleased and honored to be working with a designer of Nelson Pass’s caliber, and pleased he chose to use the highly linear, low-noise characteristics of our JFET in this new exciting product. It continues to show the versatility and performance of our cost-effective SiC JFET transistor technology."

 

睇到揸鑊鏟D人靜咗年靚又風光過, 真喺….唉。