- #41 [mm452], 22-05-29 17:02
- #42 [Cominox], 22-05-29 17:30我唔想聽什麼靘線設計為之好,我窮人買唔起幾千蚊條,diy1505只是90蚊,90蚊對黃金線放在唱頭放大器我話超正,又唔好話秒殺咩咩牌子,我覺得非常滿意己經足夠
- #43 [kmita2006], 22-05-29 19:37正如#38,
雙導体RCA audio cable 都可以用平宜的鴨寮街車佬綫來DIY。
Remark, twisted pair的 RCA cable 阻抗會變成約110 ohms 不宜用作DAC的 75 ohm coaxial input.
最後修改時間: 2022-05-29 19:39:55 -
- #44 [藍晶晶], 22-05-29 20:43其實將條BELDEN 線加返個網就已經搞惦晒. 但加左無非是濾雜訊電磁波, 我又唔會做了, 因為而家條線咁已經好清好靜.
- #45 [LaLaLam], 22-05-29 20:48其實Belden好多款正式的 audio音頻線,效果都係非常不錯,例如下圖的 9451,仲平過 1694A,1506A等,唔明點解一定要用高頻同軸線。
- #46 [LaLaLam], 22-05-29 20:56Belden 1694A, 我哋都用好多,係好東西,不過只能用於高頻,幾個GHz, 可以用作大功率發射,但用於音頻就好奇怪了,又貴。
- #47 [freeman062], 22-05-30 00:201694A 是同軸75 ohm ,設計出來作為高頻天線及數碼視頻傳送等用途是非常不錯,但如用在音頻上是不太適合,設計作為音頻訊號傳送的線材多的是,何須捨本逐末呢!
- #48 [mm452], 22-05-30 07:40係呀,都係揾返audio線DIY會好啲!
- #49 [落雨路], 22-05-30 20:05做數碼線應該唔錯
- #50 [落雨路], 22-05-30 20:13如果鐘意用同軸天線DIY, 鴨記有隻maspro牌天線,design for HDTV, 用料畀曾sir介紹的Beldon更好,屏蔽用上銅膜+銅網,介質物料起碼高一個層次,但價錢仲平過Beldon, made in Japan
- #51 [藍晶晶], 22-05-30 23:11何解咁多推斷, 行動自己插來試下, 再比較不同同軸線當AUDIO 線音效, 更勝理論.
- #52 [shektau6], 22-05-31 05:27#36 低頻 用 Belden 1505F應該好聲D
- #53 [mcc2018], 22-05-31 07:38用高頻同軸線做音響線也是非常不錯,尤其用作喇叭線,經過試聽多種不同形式的接法,如下圖般的open ladder line接法有突出表現,不過要在不同位置套磁環,也要用兩線距離調聲。
- #54 [etsang3], 22-06-04 18:39當線在一個頻率或更高工作, 線長超過那個頻率波長, 阻抗(impedance)才會有效,
才要匹配(使到信源阻抗=負苛阻抗, 獲得最少(也一半)的損失))
如所用的線長度, 以工作頻率計, 不夠半個波長,未起阻抗(例如SPDIF和FM在一呎內的阻抗根本不是75Ω),
不用考慮要阻抗匹配, 用50Ω,75Ω, 600Ω 也無分別的
所用的各種用途的接線超過以下長度, 就要看線的阻抗特性去買去匹配
反而我們要注重線的電容, 總量超過150pF 便不好了
最後修改時間: 2022-06-04 18:42:21 - #55 [ich], 22-06-04 20:01#53
下面有詳細介紹點樣用同 Belden 89259 85 ohm同軸線做一條喇叭線,十幾年來有好多人(包括我)造過,平靚正:
https://diyaudioprojects.com/Power/Belden-89259-Speaker-Cables/
最後修改時間: 2022-06-04 20:02:15 - #56 [yourcousin], 22-06-04 20:50關於 clock cable (SPDIF ?) 長度甚短,如幾米以內,無須理會抗咀75ohm, or 50ohm, or whatever, 從科學上解釋,非常對。
幾天前,遇到一個thread。話2018(2017?), 有幾個互不認識的發燒友,各自在家內,用自己各自的系統,用咗幾個月,做blind test.
佢地的試後評語,只交去organizer。Organizer 集合所有評語,再交回給所有testers.
- 佢地看完評語,才發覺,佢地自己blind test 話,用75ohm clock cable 接去50ohm 10M clock, 比用50ohm clock cable 差。
個Thread 好長,請跳去
"01-08-2018, 02:17 PM"
https://www.audioaficionado.org/archive/index.php/t-31846.html
最後修改時間: 2022-06-04 21:01:32 - #57 [mcc2018], 22-06-04 21:07#54, Coaxial cable 其實也是必需用transmission line theory 去解釋的,如下圖示,一條同軸線的簡化等效線路係不單止電容,還有電抗,詳細數學算法不在此談,大家可以 google找到,簡單而這當這LC係 Lumped elements, 無限微分然後積分的結果,於是coaxial cable的特性阻抗分成三段頻率,低中高,其中高頻段(>100K ohm)的特性阻抗characteristic impedance Zo = sqt L/C, 接近常數,正是我們常說的 50,75,100 ohm 的特性阻抗,和 cable的長度無關,但 cable還有一個糸數叫 velocity of propagation VoP 或 velocity factor VF, 就和 cable長度非常有關,頻率波長和特性阻抗無關,但與 VSWR, 電壓/電流駐波比非常有關。
- #58 [mcc2018], 22-06-04 22:08"同軸線短的話不需理會特性阻抗是否 50, 75ohm... ", 這點不大同意,下圖是一條只有1m的 spdif 75 ohm 同軸線,放在一套50 ohm的矢量分析儀(VNA)所測量到的結果,發現 1.VSWR = 1.77@13.39MHz, 阻抗 75.3 ohm, 電壓駐波比大於正常 50 ohm線 70%, 於是有嚴重駐波反射,加上線的 velocity factor, 於是系統發生 jitter 抖動,有趣的是,這種抖動形式上與 dithering非常類似,在聽感上是少了一種令人煩噪的數碼聲,多了一種像黑膠的圖潤感,這類 dithering抖動降噪原理可以 google 找到,例如:
https://zh.m.wikipedia.org/zh/%E6%8A%96%E5%8B%95_(%E6%95%B8%E4%BD%8D%E8%A8%8A%E8%99%9F%E8%99%95%E7%90%86)
最後修改時間: 2022-06-04 22:17:10 - #59 [etsang3], 22-06-05 12:29
恕小弟財疏學淺,上網溫書之後,把我對"阻抗匹配"的關注長更正為大於1/4波長
線長達到運送頻率的1/4波長時,線的阻抗為最低,約等如它的電阻值,
線長未到頻率的1/4波長,信號的衰減以線的電阻值計算(如DC衰減計算),未有阻抗不匹配的"反射反相"問題,
線長大於頻率的1/4波長,線的阻抗會有最高和最低的變化(從信源看出去), 那麼"反射反相"問題會出現影響信源
https://www.omnicalculator.com/physics/wavelength
https://www.emisoftware.com/blogs/cabling-affects-emi-unexpected-ways/ - #60 [Yourcousin], 22-06-05 12:49
我地點樣去解釋 這幾位人兄 從 各自Blind test 中,得到75ohm/50ohm 不月的匹配,是有分別的呢?
(本人,冇任何preference, 因在學習中)
"01-08-2018, 02:17 PM"
https://www.audioaficionado.org/archive/index.php/t-31846.html
"Summary: The way I read the testers’ output and my own is that without exception all testers' experience was more or less of the form that 50-ohm cables on 50-ohm circuits result in the best overall sound quality, precision of the overall musical experience and note-by-note precision, duration, size, color, musicality, etc.....
AND using 75-ohm on a 50-ohm circuit resulted in degraded sound quality, less precise and accurate imaging, bass articulation in particular, etc...
Furthermore, using a proper 50-ohm cable on a 75-ohm circuit actually sounded better in several ways that a proper 75-ohm cable BUT not the reverse config.
There were interesting results with 50-ohm cables with 75-ohm BNCs on a 75-ohm circuit BUT the reverse (75-ohm cable with 50-ohm connectors on a 50-ohm circuit) was to be avoided due to detrimental effects on the sound, imaging, etc....
In short, through this exhaustive test seemed to prove that despite what even Esoteric is saying today, 2 years after the discontinuation of an Esoteric 8N-A2000 pure 50-ohm cable which is still one of the finest in the world (during whose manufacturing & sales years Esoteric was singing a VERY different tune and advised clients that it DOES matter), it seems that using the properly rated cable on a given circuit DOES make a difference regardless of length due to the frequency at which these signals occur."
最後修改時間: 2022-06-05 12:55:02 - 下一頁 (3 of 5)
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1694a 做天線確係吾錯的!