在一套hifi系统中，前级放大器的优劣，对声音的重现有着至关重要的影响。沐声潜心8年研究前级放大器，初心是自身作为发烧友的执著-找寻令自己满意的声音，而最终的成品就是这款代号为MH-SA001的晶体旗舰前级放大器。
这款具有全自主研制电路的前级，每个声道使用了12组工作在甲类状态的放大模块，并且根据放大模块各自在电路中功用的不同，设置了不同的电路参数，以达到最佳的工作状态。例如，有为输入信号缓冲设计的JFET输入模块，有为音量变换电路设计的电流型恒流驱动模块，有为信号输出设计的大电流输出模块。
有必要特别说明音量调节电路，这是任何一款前级放大器，始终绕不开的极为重要的电路部件。市场上有各种各样的音频音量电位器，例如比较常见且价廉的ALPS 16/27型碳膜电位器，中价位的比如AN或光音的薄膜电位器，高端的比如精密电阻分压型的电位器，再高端的比如高烧胆前级玩家较为熟悉的Elma、Seiden、Amco等品牌的电阻支架型电位器。总的来说，电位器对声音听感的影响及其巨大，究其原因，可以主要归咎于这些电阻分压型的电位器，具有高达数十千欧的阻抗。音频信号在经过高阻抗电位器后，再进入放大电路，导致放大电路因为输入信号的阻抗过高，不能工作在最佳状态，进而影响听感。
沐声在研制前级的过程中，尝试用过各种类型的电位器，比如曾用Seiden四联支架，88颗AN无感电阻，其中常用的几个音量档位用AN银电阻，这应该是我最为“高端”的一次尝试，也在一定程度上代表了传统机械电位器的“极致”。也尝试过电子音量芯片，比如NJRC的 MUSE72320系列。还用过多路继电器驱动的电阻网络电位器。上述的方案，各有优缺点。而最终使用的音量电位器方案，源于我们在解码器的多年开发中得到的启发。我们用特制的模块电路将输入的电压型音频信号转换为电流型信号，再经过恒定的低阻网络进行泄放式衰减，就得到了一直寻求的“理想”电位器。这种低阻抗电流型传输方式，完全避开了之前尝试过的机械型电位器和电子音量芯片因为高输入阻抗而引发的一些列问题，最终贡献出了我们想要的声音。而这种电路的实现过程是“艰难且痛苦的”。
除了“理想”电位器，我们格外注重电源设计。电源设计不佳导致的干扰和信号串扰，会导致声音纯净度下降，线条感变差，令人发狂。所以我们给左、右声道以及控制电路都用不同的电源牛供电，并且将数字控制电路和左右声道的音频模拟电路通过信号隔离器进行电隔离，最终做到了左右声道和控制电路完全独立、无公共地线的效果。这样可以说完全杜绝了左右声道音频信号的串扰，也杜绝了控制电路的数字电源噪声对模拟电路的串扰。所以这台前级虽然是单体机箱，但是内部可说是完全独立的三台机。
虽有了前面的这些电路设计作为基础，我们还特别注重电源退耦电容的选型。我们在搜寻来的几十款电容中进行长时间的聆听筛选，最终确认了合适的搭配，不同的电容组合也会明显的改变音色。这个过程需要你极具耐心，并且能以乐在其中为前提，否则基本是不可能完成的任务。
得益于上述追求极致的设计，这款前级放大器在听感的全频段都具有极为饱满密实的声音，真实，自然，高低频延伸毫无压缩感，能量感分布均衡，质感突出，线条感优异。而这种均衡的听感超过我曾经不惜工本做的胆前级，可能是胆前级用了高阻抗电位器的原因，胆前级的中高频段偏于纤薄，略微和低频段失衡，柔美透明。对我来说，我的胆前级的声音表现无法满足我听各种类型音乐的需求。而这款晶体前级无疑在非常多的声音特质方面超越了我的胆前级，满足了我的需求。
In a hifi system, the performance of the preamplifier has a crucial impact on the sound reproduction. We have been researching preamplifiers for 8 years to find the sound that satisfies us with our own passion as an audiophile, and the final product is this transistor flagship preamplifier, named MH-SA001.
This preamp with fully self-developed circuitry uses 12 groups of amplifier modules working in Class A state for each channel, and different circuit parameters are set according to the respective functions in the circuit to achieve the best working state. For example, there are matched JFET input modules designed for input signal buffering, constant-current driver modules designed for volume change circuits, and high-current output modules designed for signal output.
It is necessary to explain in particular the volume attenuation circuit, which is an extremely important part that can never be bypassed in a preamplifier. There are a variety of audio volume potentiometers on the market, such as the more common and inexpensive ALPS 16/27 type carbon film potentiometer, medium-priced, such as AN or TKD film potentiometer, high-grade, such as some precision resistor voltage divider type potentiometers, and then high-end, such as Elma, Seiden, Amco and other brands of Attenuator Switches. In general, potentiometers have a huge impact on the sound performance, the reason for this can be attributed mainly to its high impedances of up to tens of kilohms. First, the audio signal passes through the high impedance potentiometer, then into the amplifier circuit. Too high input impedance will affect the working state of the amplifier, then affect the sound.
We have tried to use various types of potentiometers, such as Seiden quadruple switches and 88 AN non-inductive resistors to form a resistive attenuation network, and we used AN silver resistors on the most commonly used gears. This should be our most "high-end" attempt, and can also be considered as some "ultimate" in traditional mechanical potentiometers. We also tried electronic volume chips, such as NJRC's MUSE7232x series. Multiplexed relay-driven resistor network potentiometers have also been used. The above-mentioned solutions, each with its own advantages and disadvantages. The volume potentiometer solution we finally used was inspired by our years experience of DAC development. We used a special modular circuit to convert the input voltage audio signal into a current type signal, and then attenuation the current signal through a constant low-resistance network. By this approach we obtained the "ideal" potentiometer we had been seeking, and we found the sound as we want. The process of implementing this circuit was "difficult and painful".
In addition to the "ideal" potentiometer, we paid extra attention to the power supply. Poor power supply design leads to interference and signal crosstalk, resulting in a loss of sound purity and clarity. So we use 3 power transformers for the left and right channels as well as the control circuit. At the same time, we use isolators to isolate the digital control circuit and the left and right channels, and finally achieve the effect of the left and right channels and control circuit completely independent, no common ground. This completely eliminates the crosstalk between channels, and also eliminates the crosstalk between the digital control circuit and the analog circuit. Although we use a single chassis for this preamp, but the internal is completely independent of the three parts.
We also paid special attention to the selection of power supply decoupling capacitors. We searched through dozens of capacitors for a long time listening, and finally confirmed the right match, different combinations of capacitors will also significantly change the sound. This process requires you to be very patient and to be able to enjoy the premise, otherwise it is basically impossible to complete the task.
Thanks to the above-mentioned pursuit of extreme design, this preamplifier has an extremely full and dense sound in the full range of listening, realistic, natural, high and low frequency extension without compression, balanced energy distribution, outstanding texture, and excellent sense of line. The balanced listening experience is better than my tube preamp which was made at any cost, probably because the tube preamp use a high impedance potentiometer, it is not very natural sound. For me, the sound performance of my tube preamp can not meet my requirements of listening to various types of music. And the new SA001 preamp definitely surpasses my tube pre in very many sound characteristics and meet my requirements.