- #21 [kit271], 17-12-17 09:17
- #22 [kit271], 17-12-17 10:14http://colin5881.pixnet.net/blog/post/425500361
push-pull不是隨着時間由0-180-360嗎?
Balance是同一時間輸出輸入整個正相和反相的訊號.
說成push-pull, 不如說bridge amplification仲好
文中的THAT opamp是非一般的, 它不是普通opamp, 是專門用來做balanced interface的IC, design很好, 我也很喜歡用, 有研究過它是無法與AD SSM214x or BB DRV134比美
最後修改時間: 2017-12-17 10:27:53 - #23 [wontun], 17-12-17 21:55綜觀各位師兄意見,可否歸納如下:
1.上級機種是真平衡設計輸出,下級機種最好繼續用真平衡制式;
2.如果不能,下級要轉RCA,最好用opa或isolation transformer 做轉換,不要用adaptor;
3.反之,上級機種是RCA設計做輸出,下級就最好不要轉平衡輸入;
4.如果上級機種本身線路是不平衡設計,就算有平衡插做輸出,都最好不要用,用回RCA做輸出. -
- #24 [kit271], 17-12-18 09:34Re #23
其實"真平衡"這個名詞好抽象, 簡單說即起碼要四份放大線路去獨直處理正相和反相訊號
1. 比我會敢玩, balanced connection一接到尾. 最好係由DAC的數碼部份已加上反相訊號開始, 通常線路都要用多一倍DAC零件, 貴DAC先會敢做.
2. 下級只support RCA之話, 買隻external convert牛或有源opamp converter, 條RCA線最好1呎左右, 貼近個destination. 千祈咪用adapter.
3. 無錯
4. 另一個講法, DAC個XLR output RMS voltage唔好低過4V
以上係小弟玩balanced既經驗.
最後修改時間: 2017-12-18 10:05:16 - #25 [zoneaudio], 17-12-18 11:05玩平衡XLR就在平衡嘅層面較聲,
玩RCA就在RCA嘅層面較聲,
無話邊個好,
好多時成套機玩開RCA較好晒,
跟住屎忽痕見有XLR又插來玩下,
唔.....都係RCA好D........,
因為你嘅setup是RCA調較而產生誤判,
由RCA轉玩平衡要重新調教setup一次才有好效果 - #26 [peter827], 17-12-18 15:53Balance原本係長線傳輸時避雜訊做法,不過DAC發展中因利成便做出嘅正負相輸出卻有著隱藏優勢,i/v轉換後正負相對地各有4點幾v,正負相之間嘅電壓差就係8點幾v,這8點幾v嘅訊號量相對rca舊標準2v多4倍,好好利用的話往後電路可減少4倍增益而保存最多原訊息。
- #27 [kit271], 17-12-19 09:45這隻就是Jensen出的balanced isolation transformer(INPUT), 放左DAC去preamp之間隔離高頻noise經由DAC singal-ground去preamp singal-ground, 又可防止groud-loop, 呢個就係用transformer而唔用opamp converter既例子
最後修改時間: 2017-12-19 09:46:07 - #28 [waterman], 17-12-19 10:04#26
...
8點幾v嘅訊號量相對rca舊標準2v多4倍,好好利用的話往後電路可減少4倍增益而保存最多原訊息
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同意
假設: 平衡輸出8VRMS/600ohm, RCA輸出2VRMS/75ohm, 低內阻既RCA可輸出既電流多平衡2倍。 好好利用既話也可以保存最多原訊息
小弟以為"平衡輸出"同"RCA輸出"各有長短, 問題係"可唔可以好好利用?" - #29 [Kkkkiu], 17-12-19 12:35#28
認同,其實去到數碼年代,2v輸出已經很大了,到了前級音量還要衰減超過一半,何況8v?!衰減帶來的失真都算了,本來一件事要分幾個人做,就像單端及推挽一樣,還來的相移問題,前者就損失高頻細節,後者就損失泛音,咁多壞影響點解取難不取易? - #30 [Phil.ng], 17-12-19 13:46有D DAC 有5V,前級 我set 去6db gain. 幾夾
- #31 [dkyyu], 17-12-19 14:07With 5V to 8v output, suggest brother to try try passive pre amp. Even the cheapest resistor type will work pretty well. With nore bdget, the transformer type passive pre amp will even be better.
最後修改時間: 2017-12-19 14:09:04 - #32 [Kkkkiu], 17-12-19 14:31那不是脫褲子放屁?電壓升到咁大,卻又降到咁細增益,增加了相移問題,又犧牲動態,為何?
- #33 [dkyyu], 17-12-19 14:50That's why a passive pre-amp has a higher chance to work much better by avoiding unnecssary secondary gain when you have a high output front end source.
- #34 [Phil.ng], 17-12-19 14:58試過set 去 0 db, 行電阻volume, 無動態
- #36 [kit271], 17-12-19 16:22動態同分析力都是基於DAC output current再佩合i/v.
i/v之後再因正反相合成而倍增的電壓, 倍到幾大是沒有意義!
最後修改時間: 2017-12-19 16:27:35 - #37 [peter827], 17-12-19 16:42i/v之後出嘅電壓唔算係放大出來的,可以話係DAC原生嘅第一級電壓訊號,而一般解碼出rca就要降壓到2v這傳統標準,因為你唔跟標準的話燒咗人啲嘢就大鑊,btw識唔跟標準做嘅話就點都得,不過當然後果自負。
- #38 [dkyyu], 17-12-20 18:47試過set 去 0 db, 行電阻volume, 無動態
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Dear c-hing,
Not logical.
Assuming you are using speakers at normal sensivity, say 87db, the high sound level will burst your ear piece if the output is over 5V and volume setting at 0db. There must be some kind of attenuation in between. Suggest to try the passive preamp. - #39 [phil.ng], 17-12-20 19:03是0 db gain, 前級有gain 校、然後只用機內的 電阻matrix volume.
即是將有源前 變成passive - #40 [dkyyu], 17-12-20 20:20是0 db gain, 前級有gain 校、然後只用機內的 電阻matrix volume.
即是將有源前 變成passive
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I think there is some confusion. An active pre always remains as an active device even when sound volume level and gain control are set to 0db or whatever value is.
Most of the time, the "前級有gain" acts as a variable resistor base attentuator to offsetting or changing the default pre-amp gain, it is still working as an active pre with gain (either in Voltage or Current). In other words, both volume control and gain control are attenuators. A typical example is found with Nagra PLP.
I guess you can hardly change an active pre to passive without bypassing all the active devices and associated circuits. Setting to 0db doesn't mean bypassing active to become passive.
Usually a passive has no active component in signal circuits, only passive input selector and volume control switch (typical resistor or step-down tranformer type) are found.
Hope this help.
最後修改時間: 2017-12-20 20:24:29 - #41 [Phil.ng], 17-12-20 20:36Thanks, but....
前是用jumper 去select gain, 如 set 去 0db gain , 就會bypass the gain module, 只有 remote and volume 會function.
最後修改時間: 2017-12-20 20:40:39 - 下一頁 (2 of 3)
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>>方間的平衡轉RCA的adaptor, 是將反相訊號與地端接通而成RCA同軸輸出,是否反相訊號會因接地而消失了嗎?
是, 而呢個conversion係最差的方法. 用opamp或transformer比較正路, 各有所長.
簡單d講, opamp可做到低output impedance, transformer做到isolation.