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看过其 EV400  A30  A50 的电路 放大和推动比较普通 但功率级比较有特色

输出变压器是接在阴极 哪位能否解释一下其原理和优缺点

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2010-4-6 15:59 上传

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早在半導體元件被發展出來以前的真空管電路時代,Circlotron電路就已經被發展出來了!

首先我們先來了解一下Circlotron電路的基本原理。
下面這個電路圖是一種三極真空管的Circlotron電路,負載是接在真空管的陽極。
2009-11-11 12:01 上传
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Circlotron電路的基本原理在於電源在電路中的電流必須構成封閉的迴路,
也就是說一個電路中的電源從正端流出的電流,不論在任何情況下都必定等於從電源負端流入的電流!
下圖顯示出電源V1的電流迴路:
2009-11-11 12:01 上传
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由於電源V1的電流迴路I1流經真空管U1,所以V1的電流I1完全受到真空管U1的控制。

下圖顯示出電源V2的電流迴路:
2009-11-11 12:02 上传
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由於電源V2的電流迴路I2流經真空管U2,所以V2的電流I2完全受到真空管U2的控制。
而I1跟I2在負載RL上重疊,所以負載RL上的電流為 I1減掉I2(或者也可以說是I2減掉I1,就看你的相位怎麼訂定),
電流I1完全受到真空管U1的控制,電流I2完全受到真空管U2的控制,
所以形成真空管U1跟真空管U2以推挽的方式在驅動負載RL。

Circlotron電路除了可以將負載接在真空管的陽極,也可以將負載接在真空管的陰極,
像下圖這樣。
2009-11-11 12:02 上传
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一般將負載接在真空管的陰極通常都會接成陰極隨耦電路,
像下圖這樣。
2009-11-11 12:02 上传
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然而上圖中,V1和V2相對於輸入信號的地而言是浮動的,因此真空管U1跟真空管U2的偏壓Vgk無法確定!
由於真空管U1跟真空管U2以推挽的方式在驅動負載RL,
若要將真空管U1跟真空管U2的偏壓Vgk確定下來,必須抓出負載RL的中點電位做為地電位,
像下圖這樣。
2009-11-11 12:02 上传
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當然,也可以用具有中央抽頭的輸出變壓器來抓出負載RL的中點電位做為地電位,
像下圖這樣。
2009-11-11 12:02 上传
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在半導體元件中,FET跟真空管一樣都是電壓控制的元件,
所以FET很容易就可以套用到前面所介紹的真空管Circlotron電路。

下圖是負載接在洩極(Drain)的MOSFET Circlotron電路:
2009-11-11 12:01 上传
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Circlotron電路是一種推挽輸出電路,可以工作在A類、B類或AB類的狀態。
上圖中,電源V1和V2是24V,所以這個電路可以輸出的最大峰值電壓是24V,
但如果考慮MOSFET和其源極電阻所可能吃掉的壓降,輸出的最大峰值電壓估計大約在20V左右。
負載是8Ω,輸出的最大峰值電壓是20V,所以最大的輸出峰值電流為2.5A。
推挽輸出電路,是兩邊各輸出一半的電流,所以MOSFET的偏流必須設定在1.25A以上才能工作在A類狀態。

下圖是負載接在源極(Source)形成源極隨耦電路輸出的MOSFET Circlotron電路:
2009-11-11 12:01 上传
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相較於高輸出阻抗的洩極輸出電路,低輸出阻抗的源極隨耦電路在工作在AB類時有顯著的優點,在此特別加以仿真說明。

下圖是加入交流訊號並將MOSFET的偏流降低,使其工作在AB類的洩極輸出MOSFET Circlotron電路:
2009-11-11 12:01 上传
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下圖顯示出兩個MOSFET的電流以及負載上的諧波失真。
2009-11-11 12:01 上传
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下圖顯示出兩個MOSFET的合成電流以及負載上的諧波失真。
2009-11-11 12:01 上传
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下圖是加入交流訊號並將MOSFET的偏流降低,使其工作在AB類的源極隨耦輸出MOSFET Circlotron電路:
2009-11-11 12:01 上传
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下圖顯示出兩個MOSFET的電流以及負載上的諧波失真。
2009-11-11 12:01 上传
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下圖顯示出兩個MOSFET的合成電流以及負載上的諧波失真。
2009-11-11 12:01 上传
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從上面的仿真比較中,可以看出低輸出阻抗的源極隨耦電路在工作在AB類時,
電流較大的MOSFET會在另一方截止時自動加大輸出電流,補足因對方截止所缺少的電流,
所以失真遠比高輸出阻抗的洩極輸出電路還要低得多!


接下來如果用雙極性電晶體BJT來做Circlotron電路又如何?

由於BJT不同於真空館和FET,真空館和FET是屬於電壓控制元件,而BJT是屬於電流控制元件,
所以BJT理應由電流來驅動。

下圖是由集極輸出的BJT Circlotron電路:
2009-11-11 12:18 上传
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下圖是由射極輸出的BJT Circlotron電路:
2009-11-11 12:18 上传
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上圖由於是由電流驅動,所以並不能算是射極隨耦輸出電路!
射極隨耦輸出的BJT Circlotron電路應如下圖所示:
2009-11-11 12:19 上传
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上圖中,由於BJT的 Ie = Ic + Ib ,而Q1、Q2的Ib並不在V1、V2的電流迴路之中,
所以Q1、Q2的Ib會流經R4、R5而在R4、R5上造成壓降,這一點可以由下圖的仿真中顯示出來。
2009-11-11 12:18 上传
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下面五張仿真圖顯示出R4、R5對於Q1、Q2的Ib供應不足而造成Q1或Q2截止的現象。
2009-11-11 12:18 上传
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上圖顯示Q1、Q2的偏流設定在1.25A左右。
2009-11-11 12:18 上传
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上圖顯示出RL兩端輸出電壓波形明顯不對稱。
2009-11-11 12:19 上传
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上圖為測量Q1、Q2的射極電流Ie的電路。
2009-11-11 12:19 上传
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上圖顯示出R4、R5對於Q1、Q2的Ib供應不足而造成Q1或Q2截止的現象。
2009-11-11 12:19 上传
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上圖為Q1、Q2射極電流Ie的合成波形。

除此之外,這樣的電路如何維持Q1、Q2的偏流穩定、如何做偏流的熱補償也是個大問題!
因此發展出如下圖所示,以恆流源供應Q1、Q2的Ib的電路。
2009-11-11 12:00 上传
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上圖中的恆流源I1、I2在實際電路中可以是個阻值很大的電阻或用小信號JFET、BJT構成的恆流電路。

下圖為測量Q1、Q2的射極電流Ie的電路。
2009-11-11 12:00 上传
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下圖顯示出Q1、Q2的Ib供應不足而造成Q1或Q2截止的現象。
2009-11-11 12:00 上传
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下圖顯示出Q1、Q2的Ib供應不足而造成輸出波形削頂的現象。
2009-11-11 12:00 上传
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上圖這種輸出波形削頂的現象是由於恆流源所供應給Q1、Q2的Ib是固定的,
所以當一方截止時,另一方的Ib即達到最大供應量,以至於輸出電流無法繼續增加,而導致輸出波形削頂!

下面這張圖在Q1、Q2的B-E極反向並聯一個二極體,
當Q1或Q2的B-E極逆偏時,二極體順偏導通而提供額外的Ib供應,
使輸出電流繼續增加,而不致於讓輸出波形削頂!
2009-11-11 12:00 上传
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下圖顯示出Q1、Q2的Ib供應不足而造成Q1或Q2截止的現象,
但由於二極體順偏導通而提供額外的Ib供應,使未截止的一方輸出電流繼續增加。
2009-11-11 12:00 上传
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下圖顯示出負載RL上的電流波形沒有削頂。
2009-11-11 12:00 上传
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既然Q1或Q2的截止是因為Q1、Q2的Ib供應不足,
那麼只要讓輸出電流大的一方可以得到額外的Ib供應,就不會搶走另一方的Ib導致另一方截止!

下圖的設計使得輸出電流大的一方可以得到額外的Ib供應,但額外供應的Ib大小必須適當,
太大會導致Q1、Q2虛耗功率,太小會令Q1或Q2的截止!
2009-11-11 12:00 上传
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下圖顯示Q1、Q2都沒有截止。
2009-11-11 12:01 上传
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下圖顯示出負載RL上的電流波形失真很低。
2009-11-11 12:00 上传
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介紹到此,就大致可以了解Sumo-Nine放大器在Circlotron電路部分的電路設計。
2009-11-11 12:03 上传
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雖然Sumo-Nine放大器是使用Darlington電晶體,不過Darlington電晶體可以看成是β值很大的BJT,
所以前面有關BJT用在Circlotron電路的分析都適用於Darlington電晶體。

比較前面BJT的Circlotron電路和真空管及MOSFET的Circlotron電路的分析,
可看出真空管及MOSFET這種電壓控制元件用在Circlotron電路的效果較好,問題也較少。
BJT這種電流控制元件用在Circlotron電路的效果較差,問題也較多。
其實也可以嘗試用中功率的MOSFET驅動大功率的BJT,以這樣的架構用在Circlotron電路。
MOSFET驅動大功率的BJT的電路架構其實跟IGBT(Insulated Gate Bipolar Transistor)類似,
所以把IGBT用在Circlotron電路的效果應該也會很好。

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田庄的窝
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2#
田庄的窝
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3#

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This review page is supported in part by the sponsors whose ad banners are displayed below


Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S; Ancient Audio Lektor Prime; AMR CD-77
Preamp/Integrated: Supratek Cabernet Dual; ModWright LS-36.5 with PS 36.5; Wyetech Labs Jade; Almarro A318B; Melody I2A3; APL Hifi UA-S1; Trafomatic Experience One [on loan]

Amp: 2 x Audiosector Patek SE; 2 x First Watt F4; Yamamoto A-08s; Fi 2A3 monos
Speakers: Zu Audio Definition Pro; DeVore Fidelity Nines; WLM Grand Viola Monitor with Duo 12; Rethm Saadhana; Zu Presence [on review]; Mark & Daniel Maximus & Ruby Monitors w. OmniHarmonizer

Cables: Ocellia Silver Signature loom; Crystal Cable Ultra loom; Zanden Audio proprietary I²S cable; Crystal Cable Reference power cords; double cryo'd Acrolink with Furutech UK plug between wall and transformer; Stealth Audio Indra and Meta Carbon
Stands: 2 xGrand Prix Audio Monaco Modular 4-tier
Powerline conditioning: 2 x Walker Audio Velocitor S fed from custom AudioSector 1.5KV Plitron step-down transformer with balanced power output option; Furutech RTP-6 on 240V line feed
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio Vivid CD cleaner; Walker Audio Reference HDLs; Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro; Acoustic System Resonators and front wall sugar cube matrix
Room size: 16' w x 21' d x 9' h in short-wall setup, with openly adjoining 15' x 35' living room

Review Component Retail: €17.500/pr


American amplifier legend James Bongiorno holds US patent 4229706 for the bias circuit of a Circlotron transistor output stage. It was implemented in his Sumo 9. On his comeback project site Ampzilla2000, the narrative belabors the fact that no new amplifier architecture has been invented since JB's Great American Sound days: "Since his departure in 1982, there has been no conceptual topological discoveries whatsoever. None! Hard to believe but true. This is not to say that there aren't any fine amplifiers being made, as there are quite a few. However, virtually every one of them uses the same tried (or tired) and true circuits created by James way back when, with a lot of variations on a theme..."


Upon closer inspection, Bongiorno and his copy writer might grant an exception to the Thorens monos. Yes, they are transistor circlotrons just as certain Sumos were. However, the mid-power Sumo 9+ used 20 bipolar output devices, the high-power Thorens runs a single ultra-power Mosfet per phase of the cross-coupled floating output buffer that's at the heart of a Circlotron or parallel push/pull circuit. Uniquely, the Thorens then adds a 6-tube input/driver stage with complete DC coupling from input to output to avoid any and all coupling caps. And -- Bongiorno would appreciate this salient bit -- it gets away with a single variable current source to bias both half wave circuits. Just as Bongiorno's patent concerned itself with how to bias the floating counter phase circuits, so the secret of the Thorens lies in its three potted modules. They perform the precision servo biasing so critical to a high-power output stage that's not referenced to ground.


The Circlotron itself goes back to 1955 and Henry Wiggins' Electro-Voice circuit, a dual single-ended floating bridge affair. Cecil Hall was awarded a US patent for it around the same time. Another accounting lists Tapio Köykkä instead as having held the very first two patents for Circlotron architectures, albeit limited to his native Finland. His schematic published in the German radio magazine Funktechnik (issue 7 of 1953) to predate the Electro-Voice product. Then Jim Bongiorno used a Circlotron variation in his Great American Sound transistor amps during the 70s. The 80s saw Atma-Spere's OTL tube applications. BAT later joined that wagon with transformer-coupled circuits, Einstein with OTLs. And Gamut's high-power push/pull amps today use single Mosfets per phase to recall Thorens' "single-ended" massively monolithic 800W/300A monsters which eliminate the mismatches inherent in paralleled output devices.


When you consider the specific implementation which accredited electrical engineer Frank Blöhbaum of Saxony has dreamt up for the new Thorens company under Heinz Rohrer, you'll see that despite sharing aspects with other commercial amplifier offerings past and present, the exact string of ingredients in the Thorens monos is unique. A jubilant 2006 review in the German Stereoplay replete with top-notch measurements and their team's ongoing use of the test monos as their in-house reference amps is naturally a main feather in their cap. While the reborn Thorens is a Swiss company in Giebenach and the trademark and logo the property of Thorens Holding AG, Basel, the built-in-Germany aspect -- Thorens turntables and new electronics are manufactured in Malmsheim/Schwaben -- only added patriotic pride. Thus said review ended in a gushing "the Germans are world champions again", an obvious reference to the Teutonic obsession with soccer [original Stereoplay review graphics next].


While Thorens would be foolish to openly publish the schematic they licensed for exclusive use from Blöhbaum System, the following diagram by the designer shows the basic concept:


Such a patent-pending circuit contribution which still mandates closer inspection also begs a few other questions. The Thorens company's core competency and reputation we know and remember has always been with and for turntables. Not even the most presentient of industry pundits could have predicted the likes of the TEM 3200 under the Thorens banner. Who then is Frank Blöhbaum; how did he arrive at Thorens; and where is new owner and CEO Heinz Rohrer steering this company with the famous name going back to 1883 since acquiring and restructuring it after its 2002 bankruptcy? Any arm chair sleuth worth his slippers would smell an interesting story awaiting the telling. Cynics will insist that nothing new in amplifiers could possibly come from a small turntable firm; that any claims to the contrary will be marketing hype and bootstrap maneuvers in a challenging economy. By talking to both Heinz Rohrer and Frank Blöhbaum, a rather different picture emerged. To view Thorens' 1883 - 2008 time line, click here.


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