Pass - The Zen Amplifier 自己做的一些功课，欢迎各位指点

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The Zen Amplifier   

ZEN 放大器

Nelson Pass   

纳尔逊·帕斯

Introduction     

介绍

一、“What is the sound of one transistor clapping?”

          单个晶体管发出的声音是怎样的？

      There are two mostessential principles to audio amplifier design. The first is simplicity. Thesecond is linearity.

           音频放大器设计有两个最基本的原则。首先是简单。二是线性。

         Einstein said, "Everything shouldbe made as simple as possible, but no simpler." Simplicity is a commonelement of the best and most subtle designs. It is preferred for purelyaesthetic reasons, but also because fewer elements color the sound less, andlose less information. Many audiophiles, including myself, are willing tosacrifice other areas of performance to achieve the intimacy with the soundavailable through a simple circuit.

         爱因斯坦说：“一切都应该尽可能简单，越简单越好。”简单是所有好的设计的一个共同元素。这是纯粹的审美因素中的首选，因为最少的声音染色，我们可以获得最多的声音信息。很多发烧友，包括我自己，都愿意可以通过一个简单的电路来达到最亲人最入耳的亲密的声音，哪怕牺牲一些其他方面的性能。

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         An amplifier should be simple, but it also must be linear. Some measure of distortion in an amplifier is unavoidable and forgivable if it is of a less offensive type, but still it is important that the measured distortion performance be reasonably low. The advantage of a simple circuit is lost if the sound is overlaid with an excess of false coloration.
         放大器的设计应该简单到极致，当然要同时保证线性。但无论再怎样，失真是不可避免的，如果失真在一个合理低的范围内是可以被接收的，也是可以被原谅的，所以我们应该使我们的电路测量的失真尽量的低。那么我们可以说：对于那些被过多染色的声音来说，简单的电路的优点就是最少的染色，也是达到了最少的失真。

         Many complex topologies have been justified by high quality of measured performance. By objective criteria, this is a perfectly valid approach. There are many applications where the need for measured precision is important and subjective performance is unimportant. Any application where the performance is crucial to obtaining accurate numbers, such as in an MRI field amplifier, should be judged by objective means. But this is not rocket science; our objective is to make listeners enjoy sound. If we justify this approach by calling it art instead of science, that is perfectly fine, even preferable.
        那些许许多多的拥有复杂拓扑结构的放大器，也可以获得高品质的测量性能。当然通过客观的标准来衡量放大器的好坏，这是一个完全有效的方法，有许多应用中，确实需要测量的精度，主观的性能评测是不重要的，这这些特殊应用中客观测量的性能是至关重要的，以获得准确的数字，如在MRI领域放大器，应客观的判断，但恰恰不巧的是，我们不是在研究如何让火箭上天，我们的目标是让听众享受声音。如果我们认为音频放大器的设计更多的是为艺术而不是为科学，那就很好了，甚至更可取。

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         Resolving the apparent conflict between simplicity and objective performance is our goal. Commercially available power amplifiers have as many of 7 gain stages in series. The simplest I know of still has 3 stages. This succession of gain stages is essential to build up excess gain that can be used for negative feedback. The feedback is used to correct the performance of the gain stages. Paradoxically, the extra gain is used to correct the extra distortion of the additional gain stages.
        能够使放大器最简单同时也能使它的表现尽可能的客观是我们设计的原则和目标。市售功率放大器有设计多达7级放大的，我知道的最简单的放大器设计仍然有3级，这么多的级来放大是必不可少的，原因是他们必须建立超额放大，才可以设计负反馈来保证这么多级放大的性能。矛盾的是，额外的放大是用来纠正额外的放大所带来的额外失真，这这是一个悖论。

         How simple can we make a circuit and still have it perform well? Obviously an amplifier with a single gain stage will be about as simple as we can topologically create, and we ask the question, "How much performance can we get out of a single gain device?“
        那么到底我们可以设计的多简单，又同时可以保证它表现的还可以呢？显然，单端，也就是只有一级放大将是最简单的。那么好了，我们接下来要问的问题就是，“只有一级放大，它的表现到底怎样呢？”

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二、Single Ended Class A
       单端A类放大

         Only one approach is available for linear performance from such a simple circuit: Single-Ended Class A. It was the topology in the earliest use of gain devices (tubes, of course), but has not been widely employed in the output stages of solid state power amplifiers due to its
Push-pull circuits have higher efficiency, and they also have an advantage in being able to source current in excess of the idle, or bias, current, by dropping into a lower class of operation. A Push-Pull Class A amplifier idling at a 1 amp bias current can deliver 2 amp peaks before leaving Class A, and can deliver still higher currents considered as a Class AB amplifier, where one half of the amplifier experiences cutoff, and does not carry the signal for a portion of the waveform. By contrast, Single-Ended Class A amplifiers cannot linearly deliver current beyond their bias point, and they generally must dissipate at idle more than 4 times their rated output. Typical efficiency is about 20% maximum.
      只有一种方法是既可以获得线性性能又是最简单的电路：单端A类放大.它是电路设计最早使用的放大电路，但单端A类放大没有被广泛采用，因为相对于单端的方法推挽电路具有更高的效率。推挽式的设计有他们的优点，就是效率高，推挽式放大可设计成AB类放大器。与此相反，单端A类放大器效率低，有空闲电流流掉，其典型效率只有约20%。

This tremendous inefficiency alone explains why Single-Ended Class A has received limited attention, although careful consideration of possible circuits reveals that efficiencies approaching 50% are possible. In addition, there are ways in which a Single-Ended Class A amplifier can be operated as a push-pull device beyond its bias point, the assumption being that push-pull performance is preferable to clipping. Pass Labs has received one patent and has an application for another reflecting new developments in this area.
      这种巨大的效率低下解释了为什么单端A类获得的关注很有限，虽然仔细考虑可能的电路，效率接近50%是可能的。此外，我们研究了一种新方法，将一个单端A类放大的设计在一个推挽电路中，作为它的一部分，我们的实验室已获得一个专利，并有另一个更新的应用设计在这方面有新的发展。

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           Figure 1 shows a simple example of a Single-Ended ClassA circuit. In this case the gain device is a FET, although the concept appliesequally well for a tube for bipolar transistor. The input signal is applied atthe gate, and the transistor provides current and voltage gain which appears atthe drain. The gain stage is biased by some form of impedance which sources thebias current to the transistor.

          图1显示了单端A类电路的简单例子。在这种情况下，放大器件是场效应管，虽然概念同样适用于晶体管或电子管。输入信号施加在栅极上，在放大管的漏极处获得放大的电流和电压增益。这种放大状态需要对放大管实施某种形式的偏置。

          This impedance might be a resistor, or it might be aconstant current source, or it might be some other load, such as a loudspeaker.Because this element carries the DC bias current, it is unlikely that we wouldwant to use a loudspeaker for this, and typically we would want to attach theloudspeaker in parallel with the bias element, in series with a blockingcapacitor.

          因为这个放大电路中的三极管携带有直流偏置电流，所以我们需要把扬声器与偏置三极管并联，而不能串联，并且我们需要在两者之间串联一个隔直电容器，以保证喇叭只接受到交流信号。

          If the bias element is a resistor, we see a typicalefficiency of about 4%. This means we idle the circuit at 100 watts and have amaximum output energy inefficiency. Single-Ended Class A operation has receivedincreased attention lately, primarily from tube enthusiasts, and recently anumber of companies have introduced tube SingleEnded Class A amplifiers. They are characterized by limitedpower, high cost, and multiple gain stages.

          如果我们用一个电阻来偏置，这个电路的典型效率约4%。这意味着我们有100瓦空转，输出能量效率低下。单端A类最近收到了越来越多的关注，主要是电子爱好者，最近很多公司都推出了管单端甲类放大器。它们的特点是功率有限，成本高，多个放大级。

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         I published a 20 watt bipolar Single-Ended Class A design in 1977 in Audio Magazine, and it had four gain stages. Pass Labs has been manufacturing the Aleph series of Single-Ended Class A amplifiers since 1992, and they have three gain stages. I am unaware of other solid state offerings in the US, although I expect that my hegemony will be shortlived, with the imminent appearance other single-ended transistor amplifiers.
        我在音频杂志上发表了一个20瓦单端A类设计，它有四级放大。通过实验室制造了单端放大器1992以来的ALEPH系列，他们有三个放大级。我不知道在美国其他产品，虽然我认为我的领先将是短暂的，其他单端晶体管放大器即将亮相。

         Simplicity is not the only reason for the use of the single-ended topology. The characteristic of a single-ended gain stage is the most musically natural. Its asymmetry is similar to the compression / rarefaction characteristic of air, where for a given displacement slightly higher pressure is observed on a positive (compression) than on a negative (rarefaction). Air itself is observed to be a single-ended medium, where the pressure can become very high, but never go below 0. The harmonic distortion of such a medium is second harmonic, the least offensive variety.
        简单并不是我们考虑的唯一原因，更重要的是单端放大的特点是音乐上最自然。它的不对称性类似于将空气压缩和释放的特性，空气本身被观察到是一个单端介质，其中的压力可以变得非常高，但从来没有低于0（这类似于空气介质本身也是被加了偏置气压的，也工作在甲类状态）。空气介质的谐波失真是二次谐波。

         It is occasionally misunderstood that single-ended amplifiers intentionally distort the signal with second harmonic in order to achieve a falsely euphonious character. This is not true. Low distortion is still an important goal, and it is my observation that deliberate injection of second harmonic into a musical signal does not improve the quality of sound.
        这里有一个误解，说单端放大器故意歪曲信号，使二次谐波为它的特点。这不是真的，低失真仍然是一个重要的目标，这是我的想法，故意注入到音乐信号的二次谐波并不能提高声音的质量。

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         Single-ended amplification is distinct from push-pull designs in that there is only one gain device for each gain stage, and it carries the full signal alone. Linear singleended designs operate only in Class A. In contrast, push-pull designs share the signal between two opposing devices, one concentrating on the positive half, the other the negative half. This positive/negative half of an audio signal is an artifice imposed by the desire to efficiently handle an AC only signal, with no DC component. Most Push-pull Class A designs offer energy efficiency of twice that of most single-ended designs, and they also offer a measure of distortion cancellation.
        单端放大不同于推挽设计，它只有一个器件做为放大级，并进行全波的放大。推挽式设计是用两个设备分别放大正负一半。这种设计是一个诡异的设计思路，它确实能有效地处理一个交流信号，也没有直流分量。大多数推挽式放大是单端A类效率的两倍，同时他们还采用了失真消除的措施。

         A well matched push-pull pair of gain devices will have lower measured distortion due to cancellation, and will concentrate the harmonic content into third harmonic and other "odd" harmonics, reflecting the symmetry between the plus and minus halves of the waveform. Operation is possible in Class A, Class AB, and Class B modes. The most linear of these is Class A, in which the circuit will dissipate at idle more than twice its rated output of 4 watts. We can dramatically improve the efficiency if we separate bias current from signal current, so that the bias source handles purely DC, and of course our blocking capacitor insures that the speaker sees only the AC portion of the signal.
        一个良好匹配的推挽放大器将有较低的测量失真，它所含的谐波分量为三次谐波和其他“奇数”谐波，在A类、AB类和B类模式中，A类是其中最线性的。我们可以提高这个电路的效率，如果我们分离偏置电流和信号电流，使偏置源为纯粹的直流，当然我们的隔直电容确保流经扬声器的只有交流部分的信号。

烧到三八度

应该还有吧，等下文

CreaNSR

PASS老头那些古灵精怪的想法还是很值得玩味的。记得有一版ZEN用一颗低压开关电源用大电流JFET推IR MOS，说是利用了JFET类似于电子管的工作曲线，听上去很吸引人。但是这个JFET在国内几乎不能买到，当时我联系过国内代理，告知最少一次要拿5K的量，然后货在香港付款后再报关进来---太苛刻只能放弃，后来干脆厂家都销声匿迹彻底无缘了。

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          We can achieve this by biasing the circuit with a constant current source and the efficiency climbs to about 20%, or about 5 times better. The constant current source provides only DC current which does not vary with the signal. In addition to the improvement in efficiency, the constant current sources removes power supply noise from the bias and provides an absolutely constant load for the power supply. As a result of this absolutely constant power supply draw, it becomes relatively unimportant what resistance is seen in the power source circuit, and two channels can draw off of one supply without modulating each other's signal.  Clearly the use of a constant current source for the bias is justified by the performance over the use of a resistor, although not every singleended designer agrees.
         我们可以实现这一点，就是采用一个恒定的电流源作为偏置电路，它可以使效率提升至约20%。恒流源只提供直流电流，并且这个电流不随信号变化。除了效率的提高，恒流源可以消除电源噪声，并为电源提供了一个绝对恒定的负载。由于采用了这种绝对恒定的电源供应，在电源中的内阻变得相对不那么重要了，并且两个通道信号可以不互相调制彼此。显然，一个偏置恒流源的使用来代替偏置电阻是有道理的，虽然不是每一个单端设计师都同意。
   

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三、Mosfets
       场效应管

         We have to consider what type of gain device is suitable for this application. Actually the choice is simple: Bipolar devices have too low an input impedance to be useable, and tubes have too little gain to be used in a single stage power amplifier. The only usable device is the power Mosfet, which is a transconductance device like the tube, and has a high input impedance, but operates with enough gain at high enough currents to be driven directly by line-level signal.
       那么关于元器件的选择，我们必须考虑什么类型的放大设备适合这种情况。其实选择很简单：晶体三极管的输入阻抗太低，同时单管的放大增益也太小，可用于在一个单级功率放大器，唯一可选的器件是功率型场效应管，这是一个跨导器件，有点类似电子管，它具有足够高的输入阻抗，同时具有足够的单管增益，当我们采用较高的电流驱动时。

         As a coincidence, the Mosfet happens to be my gain device of choice in general. Even in more complex circuits Bipolar transistors do not have the transconductance characteristic I find desirable, and tubes require a coupling transformer, with its attendant degradation.
        作为一个巧合，场效应管碰巧是我对放大器件的一般选择，即使在更复杂的电路中。晶体三极管没有跨导特性，而电子管需要一个耦合变压器，显然他们已经太落伍了。

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        The use of transformers as a load for a single-ended circuit is very problematic, since the DC current passing through the transformer tends to saturate the core. The solution that has been employed is to use a core with an air gap, wish' the result that the primary and secondary coils become only loosely coupled, with performance suffering even more.
        变压器作为负载的单端电路的设计是非常有问题的，因为通过变压器的直流电可以使变压器趋于磁饱和。大多数采用的解决方案是使用一个空芯的变压器，但是这样会使初级和次级线圈变得松散耦合，带来的性能损失更让人痛苦。

        Mosfets have not been adequately appreciated for their characteristics in high end audio. I believe this is due to the relatively lackluster sound associated with the commercial offerings to date. This is not the fault of Mosfets, however. Examination of the amplifiers on the market reveal two serious flaws in how Mosfets are being used for amplification. First, nearly all designers simply dropped Mosfets into the same (complex) topologies that were developed for bipolar devices without regard for their special characteristics. This unimaginative use of a new gain device results in a sound that is marginally different than the original bipolar circuit, and not much of an improvement.
        场效应管在高端音频中的特性并没有得到充分的重视。我相信这是由于一些人错误的应用获得了平淡的声音与产品的商业周期有关。这不是场效应管自身的原因。看遍在市场上的放大器中，揭示了两个严重的使用场效应管的问题：首先，几乎所有的设计者都简单地在电路中将场效应管代替晶体三极管，而不考虑它们的特殊特性。这种缺乏想象力的设计应用，即便使用了一个新型的放大元件，但是所产生的声音比原来的晶体三极管电路略有不同，并没有多大的改善。
   

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         The Mosfet designs on the market are also Class AB designs. The transfer curve of Mosfets reveals serious nonlinearities at low bias currents, resulting in crossover nonlinearity in push-pull designs. This design flaw makes for a sonic signature that many have referred to as "Mosfet mist", where a loss of detail is apparent. To fully realize the  benefits of Mosfet transistors, they must be operated in Class A. So it is not surprising that Mosfets have not found the favor among audiophiles that the devices deserve. I expect this to change in the near future, particularly as Mosfets find their way into single-ended Class A amplifiers.
        场效应管的设计市场上也有AB类设计之分。场效应管的放大曲线揭示了它在低偏置电流时存在严重的非线性，这种特性导致了大多数人都采用非线性的推挽设计。这种设计缺陷使得场效应管获得一个“绰号”，许多人称之为“场效应管有雾气”，其中损失的细节是明显的。为了充分认识到场效应管的好处，我们必须使它工作在A类状态。所以，场效应管并没有被发烧友广泛认可就不足为奇了。我预计这将在不久的将来改变，特别是场效应管会找到他们的方式进入单端A类放大器。

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四. The Circuit.
     电路

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（注：此图为自己画的，不在原文里）

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IRFP140  参数：


  
（注：此图为自己画的，不在原文里）

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（注：此图为自己所画，不在原文里）

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（注：此图为自己所画，不在原文里）

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（注：此图为自己所画，不在原文里）