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[求助]LM3886套件,音量調整問題

為了能更清楚的區分,特別開闢這個專區,希望發燒同好能在這個討論區分享你們的心得。也希望有專長於這個領域的”大大”們,能多多幫忙參與解答大家在音響方面的問題。

[求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週二 4月 05, 2016 10:31 pm

不好意思,小弟只會拿烙鐵焊接,電路原理完全外行,上來發問麻煩各位,還請見諒~
小弟最近剛裝了一套站上的LM3886套件,感覺調音量時轉一些就很大聲了,大概是以7點鍾位置是0音量來看,只要調到8~9點鍾位置就很超大聲了(是A Type VR 100K),不知到有什麼辦法可改變,比方說調大或小VR的阻值,有人跟我說在VR輸入和接地並一顆3.3k或3.9k的電阻就可以,不知正不正確?
謝謝大家。
chuan0711
 
文章: 10
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Re: [求助]LM3886套件,音量調整問題

文章xaudio 發表於 週二 4月 05, 2016 11:42 pm

如果訊源是音效卡、DAC、DVD player 等,請將 R6 由原本的 1K 改成 10~20K 試試看!
xaudio
 
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週三 4月 06, 2016 12:43 am

感謝您的回應,目前的音訊來源用手機播放mp3或wav檔,暫時使用家裡現成的藍芽傳輸器連接TUNAI Firefly http://www.tunai-creative.com/?mode=grid#!tunai-chinese/x6win
過陣子要來改wifi無線傳輸了音質才不會被壓縮掉~~
另外~剛查看零件表敘述Ra6,Rb6,影響前級放大倍率 ,所以我就是改這兩顆就對了?上面寫改成2k放大倍率為6,改成10~20k不會差太多嗎?謝謝您~~
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章xaudio 發表於 週三 4月 06, 2016 1:57 am

非反相放大器最小增益是 1.0,即使拿掉前級放大倍率也夠了,輸出最大功率沒問題。
改成 20K 和改成 20M 差不了多少。
本站的 LM1875 及 LM3886 比較特殊,放大倍率不好計算,需要寫個程式才能確定答案。

LM1875 之前已經計算過了:
請教一些LM1875的問題
LM3886 應該很類似 LM1875,只怕還是太大聲,不會有音量太小的困擾。

By the way:
還在聽 MP3 和 WAV 檔嗎?
由聲譜看 Lossy Compression 對音質的折損
Lossless Audio 已經步入第 20 個年頭,音樂的工業革命似乎近尾聲啦! :D
xaudio
 
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週三 4月 06, 2016 6:37 pm

有損壓縮音樂還是有他的方便性啦,光檔案小方便傳輸就夠它再稱一陣子了,不過聽過無損的WAV就回不去了 :D
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週五 4月 08, 2016 8:06 pm

感謝xaudio大大指導,剛好有10K的今天把就R6電阻改成10K的了,感覺音量有小一些了切到9點鐘位置才比較大聲,之前才切到7~8點鐘位置就超級大聲的,改成10K還是有點保守,應該再加大阻值,不過我不敢再改了,因為吸錫器太小管很難拆焊,焊點又小,搞了一小時才清掉殘錫,深怕板子被焊槍燙壞搞爛 :?
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章xaudio 發表於 週日 4月 10, 2016 8:04 pm

chuan0711 寫:改成10K還是有點保守,應該再加大阻值,不過我不敢再改了,

LM3886 也計算出來了,這是扣掉前級由 R8 輸入的放大倍率:

4Ω = 20.535238
6Ω = 23.709020
8Ω = 25.694610


後級擴大機靈敏度一般是 0.775Vrms (0dBu),50W-8Ω 需要的放大倍率為 25.8。
因此後級放大倍率剛好符合 8Ω 標準,前級倍率大於 1.0 是多出來的。
R6 = 20K 前級倍率約 1.5,仍超出需求 50%,只是比較沒有那麼保守而已。

lm3886.zip
(611 Bytes) 被下載 175 次
xaudio
 
文章: 1838
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週五 4月 22, 2016 10:17 am

請教站長和前輩們,自從我把R6電阻改為10K後,雖然音量調整可以轉比較多一些些,但一直有個疑慮,改電阻降低前級op的放大倍率對於音質細節是否有影響?
記得以前有看過一個說法"前級放大倍率10倍,又稱10倍放大器",好像傳統都是這樣設計,也看到站裡LM3886擴大機的說明資料裡也提到設計放大倍率10倍,當初站長讓套件做此設定是不是有什麼特別因素?目前小弟改成10K感覺低頻部份好像變得比較薄弱些,或許音質真的有差,也可能是心理因素?因為不懂原理,還請海涵,謝謝。
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章georgeliao 發表於 週五 4月 22, 2016 11:22 am

chuan0711 寫:請教站長和前輩們,自從我把R6電阻改為10K後,雖然音量調整可以轉比較多一些些,但一直有個疑慮,改電阻降低前級op的放大倍率對於音質細節是否有影響?
記得以前有看過一個說法"前級放大倍率10倍,又稱10倍放大器",好像傳統都是這樣設計,也看到站裡LM3886擴大機的說明資料裡也提到設計放大倍率10倍,當初站長讓套件做此設定是不是有什麼特別因素?目前小弟改成10K感覺低頻部份好像變得比較薄弱些,或許音質真的有差,也可能是心理因素?因為不懂原理,還請海涵,謝謝。

理論上是不會改變音質的,我自己有試過!
以前大都用10倍放大來設計前級,但現音源輸出規格更多了, 我們老人們以前大都是1Vp-p的音源,現在有更高多的2Vp-p,甚至更高的都有,所以就常有覺音量調一點就變得很大聲!
George Liao.
[喬治查爾斯電子電路網〕
http://www.gccircuit.com/
email:georgeliao886@gmail.com
頭像
georgeliao
Site Admin
 
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Re: [求助]LM3886套件,音量調整問題

文章skyboat 發表於 週五 4月 22, 2016 11:35 am

前、後級放大倍率是依最前端的訊號源輸出波幅與最末端負載(喇叭)的需求而適當分配,這其中還得考量雜音、系統頻寬、音量調節的手感平順度等等因素。

整個系統組成單元都可能影響"音質細節",當音量調小了會感覺高、低頻都弱了是人耳本身的大問題,因此古人發明了多種控制電路來緩解這個聽感問題,例如:高低音增強或衰減的音質控制電路、結合音量調節器的響度控制電路,還有更高階的多頻段等化器,甚至為喇叭量身打造的特規等化器…,而這些硬體設備現在幾乎都軟體化了,有的內建在播放機內,或是個人電腦上跑的播放軟體內,善加利用啊~ :D
頭像
skyboat
 
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週五 4月 22, 2016 2:08 pm

georgeliao 寫: 我們老人們以前大都是1Vp-p的音源


站長您太幽默了:-D
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章chuan0711 發表於 週五 4月 22, 2016 2:11 pm

skyboat 寫:前、後級放大倍率是依最前端的訊號源輸出波幅與最末端負載(喇叭)的需求而適當分配,這其中還得考量雜音、系統頻寬、音量調節的手感平順度等等因素。

整個系統組成單元都可能影響"音質細節",當音量調小了會感覺高、低頻都弱了是人耳本身的大問題,因此古人發明了多種控制電路來緩解這個聽感問題,例如:高低音增強或衰減的音質控制電路、結合音量調節器的響度控制電路,還有更高階的多頻段等化器,甚至為喇叭量身打造的特規等化器…,而這些硬體設備現在幾乎都軟體化了,有的內建在播放機內,或是個人電腦上跑的播放軟體內,善加利用啊~ :D


飛船老師謝謝回應~我都忘了直接調整等化器就好,何必拘泥傳統硬體設定呢?
chuan0711
 
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Re: [求助]LM3886套件,音量調整問題

文章xaudio 發表於 週三 5月 04, 2016 7:27 pm

如果希望精準的設定 0.775Vrms 輸入靈敏度,單是改 R6 無法衰減,還有一個 R3 可調整。

preamp.jpg

假設 AV1、AV2 為前、後級放大倍率,Pmax、RL 為輸出功率、負載阻抗:

AV1 = R5 / (R3 + R5) * (1 + R7 / R6) ... 根據電路
AV1 = sqrt(Pmax * RL) / 0.775 / AV2 ... 根據需求


綜合以上算式得到:

R3 = (0.775 * (1 + R7 / R6) * AV2 / sqrt(Pmax * RL) - 1) * R5

範例一 (50W-8Ω),已知 AV2 = 25.694610,設定 R6 = 47K。
R3 = (0.775 * (1 + 10K / 47K) * 25.694610 / sqrt(50 * 8) - 1) * 100K = 20.75K。(20K)

範例二 (68W-4Ω),已知 AV2 = 20.535238,設定 R6 = 47K。
R3 = (0.775 * (1 + 10K / 47K) * 20.535238 / sqrt(68 * 4) - 1) * 100K = 17.03K。(16K)
xaudio
 
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Re: [求助]LM3886套件,音量調整問題

文章clibin009 發表於 週一 9月 17, 2018 1:30 pm

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