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

magicbox4me

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。

magicbox4me

          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。
   

magicbox4me

四. The Circuit.
     电路

magicbox4me

（注：此图为自己画的，不在原文里）

magicbox4me

IRFP140  参数：


  
（注：此图为自己画的，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

         Figure 2 reveals the complete circuit of the amplifier. Q1 is the gain stage, biased by the constant current source of Q2.
         图2显示了完整的放大电路。Q1是放大级，偏置由Q2的恒流源完成。

    Dealing first with the current source, we note the circuitry associated with Q2. Q3 is used to regulated the gate drive for Q2. It is fed current (biased) by R6/R7, with C5 used to filter out power supply ripple. As current passes through Q2, it develops a voltage drop across R1, and when this voltage drop reaches about .66 volts (2 amps through Q2/R1), it turns on the junction of Q3, and Q3 then limits the voltage appearing at the gate of Q2 to about 4 volts. This little loop operates to keep the current through Q2 at a constant 2 amps. R3 and R4 are there to add stability to the loop and prevent parasitic oscillation of the Mosfet Q2.
        首先来看电流源部分，就是与Q2相关的电路。Q3用于调节Q2的栅极驱动器。这是美联储当前（偏）R6 / R7，C5用于滤除电源纹波。由于电流通过Q2，它开发了R1电压下降，当这个电压降达到约0.66伏特（2安培通过Q2 / R1），它打开的交界处的第三季度，第三季度，然后限制电压出现在第二季度的大门约为4伏特。这个小循环，以保持电流通过Q2在一个恒定的2安培。R3和R4有增加稳定的循环和防止MOSFET Q2的寄生振荡。

magicbox4me

（注：此图为自己所画，不在原文里）

magicbox4me

         This constant 2 amp current is fed to Q1. Resistor R8 and potentiometer P1 form a DC feedback loop which operates the gate of Q1 at about 4 volts and places the Drain potential of Q2 at the midway point of the power supply, or about 17 volts. Input signal passes through C6 and R5 to the gate of Q1, and output signal passes through C3 and C4 in parallel to the loudspeaker. R9 and R2 are there to bleed off DC, but are not particularly essential. Z1 is essential to insure that an input transient cannot exceed the 20 V gate rating of the Mosfet.
         这种恒定的2安培电流被馈到Q1。电阻R8和电位器P1组成直流反馈回路由Q1的栅极在4伏的电源和地的中间点，Q2的漏极电位，或约17伏特。输入信号通过C6和R5到Q1的栅极，输出信号通过并联的C3和C4的扬声器。R9和R2有直流，但不是特别重要。Z1是确保MOSFET的栅极输入瞬态不能超过20 V ，这至关重要。
   

zhainm

多谢奉献！！
多谢分享！！
.........

magicbox4me

多年前就买好了的，巨大型的散热片，买了两个，这次终于用到了，

话说，没有焊过纯甲类的人生，是不完整的人生啊......

magicbox4me

全局图

magicbox4me

magicbox4me

magicbox4me

关于制作：
                 1.  零件都是在网上买的，都比较好买，不算电源部分，大约2000元左右。变压器和滤波电容就用以前3886后级的稍微改一下就行；

【最重要的是听感：】
                  
                 1.  一点接地，背景噪音基本听不到；

                 2.  试听下来最大的感受就是：太太太费电了！！！  散热片太太太热了！！！纯甲类后级试听几天，电表唰唰唰往下走，适合那些用电不交钱的用户，纯甲后级使用成本电费很高！！！

                 3.  听感：声音的总体感觉是一种“酥酥”的声音，就是那种老BBC广播的温暖而酥酥声音，但也不是特别的强烈。这应该就是单晶体管二次谐波的听感吧；
                                 声音有几个不完美的地方：高音并没有璀璨的华丽感；声音虽然酥，但并不润，稍微有些干，干酥干酥的；另外可能是由于高音的问题，总体声音并不是特别的细腻；这些都是有些遗憾的地方；
                                 也许，只试听一周左右，还不能煲透机器，那是后话了。