- #21 [niceday009], 22-09-28 00:52
- #22 [hahayanyan], 22-09-28 00:57#21
希望 將來有 悠閒的心情 以及時間 自己去diy 體驗這些分別
落手落腳 from 線路圖撞下板..make mistake from sample.. Etc.. 應該就會印象深刻明白
Niceday, thx for sharing
總是忘記可以接五極...
最後修改時間: 2022-09-28 00:59:41 - #23 [thomasc2], 22-09-28 01:05#20 好可能你根本完全唔知 人地講緊乜, #1講的是擴音機的bias current 偏置電流.
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- #24 [Kenny], 22-09-28 01:09嘻嘻 ....
晚安! - #25 [richmond168], 22-09-28 02:07From some who designed audio amplifiers before:
When I designed my amplifier (long time ago), I started at targeting what would be the lowest impedance it would drive besides the output power.
If I was designing a class A amp, say capable of full power into a 2 Ohm load, I would make sure the bias, the output devices, power supply including the transform are all capable to do so, with enough margin.
So, when the amp is driving a 8 Ohm load, it is in Class A. It will still be in Class A down to 2 Ohm. It will be working in Class AB mode when the load impedance drops below 2 Ohm.
So #1 May be true or not true, depending on the design of the Amp. - #26 [niceday009], 22-09-28 10:16#2
呢個問題好多人問過我,我試下用簡單方式回答,但起碼你要知一條公式係功率Watt = I xI xR ( I係电流,R係喇叭电阻)
一部推挽Class A 原子粒amp為例, 標明50 watt RMS Class A 於8 ohm輸出意思係兩個條件:
1. 对於8 ohm喇叭,部amp可輸出2.5A 通過8 ohm load就達50watts輸出, (算式係IxIxR, I係电流 R係8ohm,等於2.5x2.5x8 = 50watts),呢樣嘢係classA, Class B, Class D都一樣
2. 但对class A推挽机係有一指定特徵,甲類amp之功率原子粒自己耗电係長時間維持同一數值高电流,例如部甲類50 watt机係細声輸出或大声到50watt仍係甲類,amp 之功率原子粒係長期維持約正3A,及負3A之原子粒工作电流 (Class AB就沒有大細声耗此大电流,佢冇声或細声時功率原子粒可能只耗0.5A电)
你嘅問題係此50watt Class A amp若果load 4 ohm喇叭是否都可以輸出50watt Class A動作,答案係Yes or No.
Yes係部amp之power supply設計夠电流以及amp之輸出級原子粒並聯數量足夠. 按數式watt=IxIxR,4 ohm喇叭負載扯到50watt輸出係要求更多电流,因為4ohm 喇叭扯到50watt等於 IxIxR 等於3.54 x 3.54 x 4= 50watt.
而家你睇度4ohm 喇叭係要扯3.54A电流而8 ohm喇叭只係扯2.5A电流. 所以部標明50watt 8 ohm Class A机是否可以同樣Class A動作出50watts 係4ohm 喇叭係視符power supply 之設計
No嘅意思係某部Class A amp 標明8 ohm 50watts 等於佢用8 ohm 喇叭出到50Watt 係class A电路動作,但係用4 ohm喇叭佢只可以最多出到35 watt係Class A動作(因為power supply已唔夠电),而出到50watt係處於Class B動作
最後修改時間: 2022-09-28 10:32:40 - #27 [niceday009], 22-09-28 10:49所以#1內文冇講清楚部amp是否係任何load都可以維持甲類出3.54A
若果部amp係4 ohm仍然可以甲類動作出3.54A电流俾喇叭,等於4 ohm 一樣可以出50watt 甲類功率,因為3.54Ax 3.54A x 4 ohm = 50 watts - #28 [MDLP], 22-09-28 11:09又係轉載
上一個 post 好多朋友唔係好明,所以出多一個 post 深入 D 解釋 :
所有放大元件都只能處理一個方向的電流,而音響電流有正負兩個方向,要處理晒兩個方向電流有以下方法:
單端A類:加偏流,例如將 +/- 10A 加 10A 偏流轉成 0 至 20A,就可以用一個元件去處理。
推挽B類:用兩個放大元件,不加偏流,一推一挽,推管處理 0 至 +10A,挽管處理 0 至 -10A。
推挽A類:線路同推挽B類一樣,但加偏流,變成兩個單端A類,推挽輸出。
推挽AB類:線路同推挽B類一樣,只加些少偏流,細輸出電流時是 A 類,大輸出電流自動變成 B 類。
純A 類放大器的偏流耗電量是輸出功率的雙倍,同樣功率,負載阻抗越高,輸出電流越細,偏流也越細,所以純 A 類擴音機通常以 8 ohm 負載定偏流,接 4 ohm 負載時,偏流不足,A 類變成 AB 類,而 8 ohm 的偏流,用於 4 ohm 負載時,只能提供一半的 A 類功率,其餘功率變晒 AB 類。
喇叭阻抗變化好大,任何情況都唔低過 8 ohm 冇乜可能,所以玩純A類擴音機要考慮這一點。 - #29 [LaLaLam], 22-09-28 11:11其實喇叭的阻抗並非純電阻性,而是如下圖虛線部份有感抗和容抗(例子是 Dynaudio的其中一款喇叭). 電功率=IxIxR 只可用於 DC 或 極低頻 AC. 交流功率 AC power係=VI cos(phase angle in degree).所以擴音機的推動能力和是否純甲類偏置是必須考慮在感抗和容抗的變化下是否仍然穩定。
- #30 [thomasc2], 22-09-28 12:21#27
知道甚么是峰值, 甚么是有效值吗?
3.54A 是峰值, 節算成有效值為 2.5035A, 2.5035A x 2.5035A x 4R = 25W rms
其它的得閒至睇 - #31 [hahayanyan], 22-09-28 12:38lala master
can i assume , if it is an AMP
example......it is 20W class A, and above 20 W and upto 50W class AB
such amp have to be Push Pull Class A, but cannot be done by Single END only ?
thx
also...#29
can i consider such speaker ...are typlical....
or is it any speak..or a lot of other speakers are less Dramatic ?
those 2 Mountains at from 20hz to 100hz.................. oh my god.......
最後修改時間: 2022-09-28 12:42:39 - #32 [niceday009], 22-09-28 12:43#29
用电動式喇叭阻抗會隨著頻率变化是一定,先唔講呢個參數當佢靜电喇叭去容易講解,標題係是否廠机50watt 8ohm甲類是否可以接4, 2, 1 ohm 仍然係50watt 甲類動作,用IxIxR 講解比較容易 - #33 [niceday009], 22-09-28 13:04如果部amp 標名50watt Class A push pull,可能8 ohm load 先維持到50watt Class A動作
8 ohm load, 2.5 x 2.5 x 8 = 50watt
4 ohm load, 3.54 x 3.54 x 4 = 50watt
2 ohm load, 5 x 5 x 2 = 50watt (你睇到接2 ohm要出5A电,那原子粉功率部分要長期耗約10A电先可以保持甲類)
有D机係只有8 ohm才全50watt Class A 動作
有D机係4同8 ohm都係Class A動作去到50watt,因為power supply 夠大
但冇机可以2 ohm 同1 ohm維持Class A動作出 50watt
日本人出机好尊重數據
佢地出一部甲類amp 50watt一般標明用幾多ohm 喇叭,例如8ohm
如果呢部机接4 ohm喇叭出100watt等於係Class B動作. 可能4ohm時只可以出36 watt Class A動作
最後修改時間: 2022-09-28 13:27:30 - #34 [jeffreylam98], 22-09-28 13:27吾怪之得 gryphon 同樣火數的class a 大過 accuphase 甘多,係咪因爲 gryphon 真係8 4 2 ohm 都係Class A, 所以power supply 好巨形
- #35 [DY2036], 22-09-28 13:34商家佬要介紹部擴音機,總要有一個大家公認嘅計算方法,例如在8ohm之下最大功率係幾多。
Class A機嘅功率輸出都只會說明在8 Ohm之下佢響標示嘅功率數字下部機仍然處於A類工作狀態,當阻抗降低嘅情況之下根據公式Power = I^2xR,因為偏置電流不變嘅情況之下呢個A類輸出功率亦都相應會降低,其實響牛輸出嘅推挽式膽機都有相同嘅問題。呢類數字同部機嘅音效和音色冇直接關係,但係輸出能夠隨阻抗降低而倍翻(可能已經進入咗AB類)可看出部機嘅驅動能力同潛力。
好似我部淘寶麼改機,Class A 石機輸出:
9W/8 ohm load
8W/4 ohm load
每聲道輸出得一對大牛龜古董2955管,再加上輸出要經過四粒1000uF電容並聯才去喇叭(不是for audio grade),而家無論人聲、分析力同衝擊力都有唔錯嘅表現。所以我覺得有時數字係冰冷,要親身用耳聽先可作準。
最後修改時間: 2022-09-28 13:47:08 - #36 [niceday009], 22-09-28 15:38甲類amp用8 ohm去量度甲類動作已經好有良心,日本人大部份都用8 ohm
有D歐洲廠出机用40 ohm load度佢Class A 動作,以下呢款輕身机居然話有40Watt 甲類動作(我曾買过,Densen b350 plus),查清楚原來佢用40 ohm load至有40watt 甲類動作,但市面上边有40 ohm喇叭?
1 x 1 x 40= 40watt, 部机只需出1A电就可以,原子粒功率部份長期耗2A电就可維持甲類動作,但边有40 ohm喇叭?
最後修改時間: 2022-09-28 15:39:15 - #37 [DY2036], 22-09-28 17:31當然有40 ohm啦,如果佢講耳筒輸出就冇呃你囉。
- #38 [vinvin28], 22-09-28 21:07My understand of Class A is:
- The transistor (say output) is always biased “ON” so that it conducts during one complete cycle of the input signal waveform producing minimum distortion and maximum amplitude of the output signal.
- Therefore, your have to biase the transister to have constraint current flow-trough such to make sure the negative half cycle of your output signal are within the operation range
- bear in mind to drive your speaker is "voltage"...without any voltage, there will be no current pass through your speaker
- Your amplifer output power is some-how limited by your supply voltage (say 50W, 8ohm amplifer, you need a supply voltage around +/-29V) that allow you have sufficient voltage swing. If you put a lower impedence speaker, the major change is the output current.
- Assume you use a transistor that can withstand a continous power (Maximum Power Dissipation) of 200W with no issue.
- Either you bias it at a bit lower idle current situation that make the amplifer are having class A under 50W 8ohm and it will become class AB when the load impedence drop to 4ohm
- or higher bias (say mid point of transister) that will maintain class A at 4ohm
- both of the above is still a class A amplifer indeed....
- Therefore, whether it can maintain at class A at lower ohm loading is really subject to the design of that amplifer...
- - #39 [thomasc2], 22-09-28 21:16其實並非甚麼深奧的東西, 網上大把講解, 真想學的點解唔去認真去讀下而浪費時間去認為, 以為, 覺得,估計,差想....
..懶得逐個睇, 總結一下就算,
何為A類? 沒有交越失真就為之A類.
因此單端(可膽可石)就祇可以是A類, 情況就有如男人唔會生子宮瘤, 女人不可能有前列線增生 - #40 [DY2036], 22-09-28 21:31師兄真係一針見血,其實呢個題目同講阿媽係女人分別不大。
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都有好多combination
如果el34接5極, 單端兩枝可出22watt, 推挽可出40watt,但兩种到要用NFB
如果el34接三極,單端兩枝只可出12watt, 推挽可出20watt,但價值係佢可以唔用負回輸,声音分析力更高,而單端其中音出名靚