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The First Watt Model B1 Buffer Preamplifier
by Dick Olsher
Life at 55 MPH
First Watt’s latest DIY offering, the B1 buffer stage, is described by Nelson Pass as “a no-feedback JFET buffer that offers ultra low distortion and noise with ultra wide bandwidth.” Nelson’s article may be found here: www.firstwatt.com. If you are unfamiliar with First Watt’s product spectrum and with the underlying philosophy of its progenitor – Nelson Pass – I strongly suggest that you visit the First Watt website for an orientation. In a nutshell, Nelson believes that simple elegant designs are the most worthy of his time and your money.
The speed limit metaphor refers to the fact that the buffer has no voltage gain and thus the system’s overall gain is limited to the gain of the front-end source component plus that of the power amp. Well, that brings up the question of just how much gain is needed? Obviously, a CD player with a nominal 2V line signal presents no problems at all for the buffer preamp. Most power amps feature an input sensitivity between 1 and 2 V, which mean that a typical CD player needs no additional gain in order to redline most power amps. But take a look at the line inputs on most line stages and preamplifiers. The signal is forced to undergo 12 to 18 dB or more of amplification. That’s very likely a throwback to the days when line inputs were nominally 0.2 V (tuners and tape decks, for example), which require a gain of 1.5/0.2 (assuming a power amp sensitivity of 1.5 V) or a factor of 7.5. Now, that’s about 18 dB of gain. I am certain that no CD player, whatever its pedigree, would sound its best when fed into a high-gain line-level input. Imagine the sonic indignity of first throwing away most of the signal at the volume control and then forcing it through an active gain stage to build it up again – hardly an optimal situation.
Things may be less clear with respect to a phono front end, so let’s take a look at my current setup. My Grado Reference MM cartridge is specified at 5 mV nominal output. Again, resorting to a hypothetical power amp with a sensitivity of 1.5 V means that the phono stage requires a gain of 1,500/5 or 300 to drive the amp off the cliff. That’s equivalent to a gain of about 50 dB, not a problem for my Air Tight ATE-2 phono stage or most any other phono stage. Again, no gain boost is needed from a line stage. All of this should lead to the realization that the ideal line stage may well be a buffer stage with provisions for input selection and volume control. Nelson asks the following rhetorical question: “Do I feel like the pedal’s to the metal and I’m only doing 55?” He speaks for me as well when he responds with “No - I’m listening as loud as I want and I sleep soundly at night, knowing that I’m not throwing away signal with my volume control.”
A Few Technical Details
The so-called “passive preamp,” an attempt to achieve the ideal line stage without a buffer stage, has in my experience been a sonic failure. Lifeless and comatose are two descriptors that immediately come to mind. Simply inserting a volume control between the source component and power amp ignores two important interface issues. First, there’s the issue of impedance matching. Ideally, input impedance should be high and output impedance should be low. That’s difficult to achieve without the use of an active buffer or at least a transformer. My sample of the B1 was built by Nelson - as shown in the construction article schematic. The input impedance is a function of the setting of the 25 kOhm potentiometers and ranges up to a maximum of 25 kOhm. Nelson admits that the pots on the B1 are perfectly ordinary, but that they appear to benefit from the very high impedance of the active circuit. And while he has not perceived any sonic issues with them, he points out that you are perfectly free to use your favorite volume control in this application. I would have preferred, for example, a 50 kOhm pot, or even better for my birthday, a motorized remote-controlled attenuator. If you’re into stepped attenuators, note that his favorite for a long time has been the Elna with type RN55D resistors. The actual output impedance is dominated by a 1 kOhm resistor (R104 and R204 in the schematic). That’s fairly low, but Nelson says that this value can be arbitrarily lowered down to say 200 Ohm, though he cautions that could cause problems with wideband equipment. The second interface issue has to do with the ability of a stage to drive long and/or reactive interconnects. And that’s an area that an active buffer stage excels in, though I can’t say that I specifically challenged the B1 in this respect, having simply dropped it in to the an existing system which uses fairly short FMS Nexus interconnects.
Despite the Spartan appearance of my B1, it actually offers a capability lacking in much more expensive high-end preamp designs; namely, channel balance control. The dual volume controls allow for independent tweaking of each channel and to my mind this approach represents the preferred method of implementing a balance control. It’s surprising that so few modern preamps bother with such a control. In fact, the great J. Gordon Holt once opined that lack of a balance control is nothing short of a fatal design flaw. I find it extremely useful in compensating for inter-channel gain differences and for loudspeaker sensitivity deviations. For example, rarely are loudspeaker drivers matched to better than 1 to 2 dB, and with the B1, a simple tweak of either the left or right pot can re-center the soundstage.
My unit was outfitted with an Ault +18V (70W) Model MW116 switching power supply specified for medical applications. No complaints so far, but I’m very curious to substitute a linear DC power supply such as the B+K 1671A in the near future.
The Sound of One Hand Clapping
The B1 took its place in a reference system headed by the PrimaLuna Eight CD player and an analog system that included the Kuzma Reference turntable, outfitted with the Graham Engineering model 2.5 tonearm and Grado Reference MM cartridge. The associated phono stage was the all-tube Air Tight ATE-2. The rest of the system consisted of the TEAC Esoteric MG-20 loudspeakers driven by either the Vincent Audio SP-T800 monoblocks or Esoteric’s new A-100 tube amplifier.
For starters, the B1 displaced the Vincent Audio SA-T8 line preamplifier, which in concert with the SP-T800 monoblocks had already impressed me favorably in terms of detail resolution and rhythmic drive. Well, the B1 did even better in these respects. Lots of kinetic energy. But more than anything else, rising from below the threshold of conscious perception, a single word began to form: wow! A sensation of extreme clarity and transparency took hold of the soundstage. The sonic presentation was spectacularly open and spacious. It was as if my sonic window received the Windex treatment. Transients unfolded with speed and control. Image outlines were nicely focused. Massed voices were readily resolvable, thus enhancing the spatial impression of large choral works.
This darn gadget made familiar recordings sound more immediate and less electronic. Harmonic textures were squeaky clean, with commendable purity of timbre. And forget about listening fatigue. This is a low-distortion device, well-behaved over the entire audible bandwidth, and retains its textural suaveness from soft to loud levels. Bass lines were thunderous and well defined, as you would generally expect from well-designed solid-state gear.
It became clear fairly quickly that the B1 took its sonic cues from the associated gear. It didn’t impose a particular tonal character over the presentation but rather allowed each power amp to dictate matters. Tonal differences between the Esoteric and Vincent Audio amps were readily discernible. The A-100 evinced greater lower midrange weight, as it should, being a transformer-coupled tube amplifier. Differences in treble character and bandwidth were also evident. In my opinion, neutrality in a preamplifier is usually a good thing. But if, like me, you’re craving a touch of tube sweetness and 3-D image palpability then you’ll have to get your tube fix at the power amp. The key is to carefully select either a matching tube amp or a hybrid design such as the SP-T8000, which really clicked sonically with the B1.
At this point, I was really curious to find out just how competitive the B1 was with the best line preamplifier currently known to me – the Concert Fidelity CF-080. Note that the CF-080 does employ a tube based gain stage – a single 12AU7 per channel. And I do use the best sounding 12AU7 out there for this application – the Mullard CV4003 with box anode construction. Now, some of you may object to the notion of comparing a modest DIY design to an $18,000 ultra high-end design. It sounds crazy, but I needed to know. Well, there were differences. The CF-080 possessed more palpable image outlines and rendered harmonic textures a bit more richly. The B1, on the other hand, showed a tad more immediacy and better defined bass lines. In the end, I felt that most of these differences were simply explainable on the basis of tube versus transistor sound.
Conclusion
Don’t let its modest appearance fool you: this is one fantastically effective buffer stage. And it’s not about to leave my reference system any time soon. I’m still laughing out loud over this one – a DIY product that succeeds wildly in bringing the listener a significant step closer to the source. In hindsight, that should not be surprising as the B1 buffer stage eliminates unnecessary gain stages between the source and power amp. A powerful demonstration of the “simpler is better” principle, or more accurately, less gain – less sonic pain. My advice to preamplifier manufacturers is this: be sure to dedicate at least one line-level input and output to a buffer stage. It really is better to operate at the speed limit, especially in the context of CD players.
Manufacturer
比胆机更有胆味：评Pass Labs XP-10前级发布: 2008-9-10 10:36 来源： 影音中国
■文/陈国荣 美国柏思Pass Labs从1997年推出第一部内带译码器的D-1前级后，陆续在1997年推出X-2前级（2002年停产）、1998年推出X-0前级（2001年停产）、1999年推出X-1前级与电源分体的唱头放大器X-Xono、2001年推出三分体的旗舰X-0.2与一体式的X-2.5、2002年推出电子分音器XVR1、2003年推出一体式前级X-2.2（2008年停产）、产品依价格高低有很清楚的界线，想当然的越高型号各种表现会越好。但其中的X-1却历久弥新连续多年在世界各地获奖，可以说是Pass Labs前级的代表作。通常基本型号X-2.2多数用来搭配X-150.5（输出功率150瓦）或X-250.5（输出功率250瓦）后级﹔更高一级的X-2.5前级建议搭配X-350.5（输出功率350瓦）或X-600.5（单声道输出600瓦）等功放。至于X-1或X-0.2前级，足以和其它Hi-End名器一较长短，搭配性更广。在Pass Labs为功放改换系列之后，厂方推出了新的XP系列前级与之匹配，目前有一体式的XP-10与电源分体式的XP-20二个型号。 令人讶异的胆味
首先来说说这部新前级令人讶异的地方。试听时我们使用Vimak DT-900T CD机，Pass Labs XP-10前级连接同厂的XA-30.5纯甲类后级，搭配丹麦DALI达尼新的HELICON 400 MKII音箱（这是DALI为25周年纪念而推出的产品，具体改良在于单元的磁路进一步加强，分音电路上采用更高级的组件）。参考的功放是Muse Audio的MA-C2前级+MA-FU29 II后级，单声道后级采用独特的FU29强放管，驱动力与控制力都非常强，分析力、动态起伏、低音的规模感都有一流表现，特别是飞快的速度与极高的通透感，让这对中型落地箱在《新音响》的听音室发出了无比壮阔的音响效果。原本要把XP-10替换电子管前级，没想到后级的保险丝突然烧掉一边，只好整套Pass Labs上阵。
我们欣赏了国内录音《雅鲁藏布》、日本JVC发行的一张《展览会之画》管弦乐DG发行的电影《夜宴》原声带，几段音乐过去后，在场的人面面相歔满是疑惑与不解。Pass XA-30.5后级的功率有限大家心理明白，所以无法在爆棚乐段取得惊天动地的音压也能接受，但我们一致的看法却是﹕把眼睛闭起来，Pass Labs的声音居然比Muse Audiio胆机更具有胆味！或许不应该以“胆味”这样有争议性的形容词来说明Pass Labs，传统意义上“胆味”似乎与速度慢、音色略带晕黄、动态起伏比较温和、中音浓稠高音甜美低音松软有弹性、音质圆润形体感比较大、冲击力比较平和……等可以画上等号。其实资深发烧友可以明白，最好的胆机是没有上述“胆味”的，譬如不用输出变压器的OTL胆机，那种灵敏的瞬态反应、一览无遗的通透感，还有广阔的频响、非常纯净清爽的质感，都与第一流的Hi-End晶体机没有二样。
笔者说Pass Labs XP-10前级+XA-30.5后级有“胆味”，这是一种比较值，因为Muse Audio的速度太凌厉了、动态对比太强悍了、源源不绝的能量太可怕了，相比之下Pass Labs显得斯文儒雅，像个小姑娘似的。乍听之下Pass Labs的组合好象规模缩小了，动态限制了，音场的宽深与型体感都减少了。并不是说XA-30.5后级的力道不够，根据Nelson Pass所写的一篇文章，XA-30.5后级的纯甲类输出功率正常时为30瓦，瞬间最大输出却可达到纯甲类57瓦，甚至比X350.5的纯甲类30瓦还要高（X-1000.5单声道后级瞬间纯甲类输出有118瓦，其余都是甲乙类输出，而XA-200.5单声道后级瞬间纯甲类输出高达409瓦）。但请别忘了，Nelson Pass更注重的是“最甜美的第一瓦”，所以他并不强调供放的驱动力有多强，而是功放的音质有多美！Nelson Pass在文章中说到，如果他的音响系统中没有纯甲类线路，他会担心得晚上睡不着，因为不只是声音上的差异，从各种测试参数中就能发现纯甲类才是最完美的放大方式。
高偏压A类线路
一体式的XP-10前级设计详情尚未公布，厂方只说这部全新的遥控前级在线路上使用最少的组件，内部为高偏压A类的线路（high bias Class A topology circuits），其表现与温度紧紧相关，在正常的运作下热机较为缓慢，约开机24小时以后表现才会稳定，随着时间越来越好。没错，XP-10与早前的X-2.2或X-2.5前级相比，最大的差异在于纯甲类放大，所以XP-10前级干脆不设电源开关，插上电后它就随时保持工作状态。厂方请大家别担心耗电问题，由于线路非常简洁，XP-10前级的耗电量只有10瓦左右，算是绿色环保的，用家请不要关机。XP-10不像X2.2前级面板上用按键来操控音量，而是在右边装设了一个转动起来会有哒-哒声的大型旋钮，操控质感非常好，看似传统的模拟音控。实际上这仍是由Wayne Colburn设计的数字音控，可在70dB的范围内做每级1dB的调整，声音讯号不经过IC，线路板上装置了许多精密电阻才是真正的音量控制区域，讯号只经过一只电阻而已。数码操控线路与模拟放大线路的电源是独立的，放大线路仍然采用Pass Labs专利的Super-Symmetric超对称甲类线路。
电源分体式的XP-20前级，电源箱除了供电给前级外，还能提供唱头放大器的需求。目前原厂尚未公布XP-20的详细资料。 还有一个重点是全平衡设计，而且是从输入部份就开始采平衡架构，Nelson Pass独创的MOSFET晶体单端A类放大方式工作，几乎没有负反馈，因此也没有相位飘移的问题。建议使用时用平衡线连接，要注意的是家中的电源最好要确实接地。我们知道非平衡连接两端的地线上都有电流，由于接地点不同会产生电位差，所以必须采以较高的阻抗减少电流降低电位差。平衡式连接的电流发生在信号正负线，地线是真正的参考点，各点将会相同，确实地执行接地对于噪声的抗干扰能力才能完全发挥。如果买了XP-10前级却不用平衡连接真有点可惜，即使以RCA讯号线连接XP-10，也要经过一道差动转换手续进入平衡线路。用平衡线连接时XP-10的音压并不会变大，但听感上动态与能量感却增加了，音像变结实了、中低频的厚实感提升了。
醇美的质感
XP-10前级的增益可选择0dB或10dB二段调整，如果使用的讯源输出够大（例如CD机的平衡输出电平达到4V），那么最好放在0dB增益，也就是XP-10只起到被动前级的功用，负责衰减音量而已，这时声音最直接无损失，质感最纯净无染。要是觉得动态不够大，力道不够强，可以把增益设定在10dB，在声音规模感变庞大的同时，也会使声音的细腻精致感受到一点影响，笔者以为差异还是明显的，这时XP-10像是一个壮硕的青年，而不再是含蓄的小姑娘。从参数上来看，XP-10前级的输出电平与增益比X-2.2、X-2.5前级都要高，失真率却比二者更低，但频宽也从100kHz降为60kHz，输出与输入阻抗提高了，噪音水平也有所不及。这是很有意思的情况，新型号的噪音背景与频率响应反而不如旧产品，Pass Labs究竟在想甚么？
笔者思考良久，大胆猜测Pass Labs的工程师们觉得音响器材的性能其实已经到不容易突破的阶段，那些参数对声音并没有太多实质助益，很多发烧友认为新产品过于冷静缺少感情，反而是老器材有丰富的韵味。于是在推出XP系列前级时，Pass Labs一反常规，推出规格参数没有明显进步，但声音更趋向人性化，更温暖容易讨好耳朵的器材。我们还是回到“胆味”的问题，国外并没有相对应的名词，从XP-10前级所听到的声音却让我联想起Audio Research与Conrad-Johnson二个胆机品牌。虽然我们用了《麦景图女声示范碟》来进行人声试听，但XP-10不像麦景图那样的丰满，它在圆润光泽满溢，甜美气息不断的旋律中，还有非常好的阴柔透视感，极高频泛音丰富完整，高频的明亮度适中，所有尖锐菱角都被磨平打光，眼前的音乐舞台看起来既清晰又没有压力。
这部前级不一昧的强调速度（虽然它的瞬态反应非常好）与动态（大小音量之间的对比仍然鲜明），它呈现的人声身材结实匀称没有多余的赘肉，乐器线条清楚比例合宜，中音带着很好的肉感，低音正确不夸张，整体的味道比过去要浓郁黏稠许多。而其中最难得的可能是纯度很高的背景，带着烘烘暖意的音色，还有醇厚甜美的质感，这些都是过去Pass Labs前级所少见的。拿一部现代胆机与XP-10前级比胆味，鹿死谁手还不一定呢！
文‧郭漢丞 圖‧郭振榮
在美國Hi End音響圈當中，Nelson Pass可說是活傳奇之一，而且這位「先輩」的長相活似「回到未來」電影裡面的怪博士，灰白的爆炸頭和他的言論一樣勁爆，我在CES曾經與他有一面之緣，聽他聊天起來倒是率直，是不折不扣的技術人。不過看起來粗獷的Nelson Pass，設計出來的擴大機卻是如此細膩。新系列的XP-10與XP-20前級之前曾經在代理商安排下，搭配全套Pass器材與Piega喇叭試聽，印象深刻，這次借回來仔細試聽，只覺Nelson Pass不僅寶刀未老，對音樂重播的深思熟慮，卻是更上層樓了，而這不僅是Nelson Pass一人的功勞，還加上整個設計團隊的努力。
「少就是多」的信奉者
深思熟慮？這話會不會講得離題？先不講聲音，XP-10就比起前一代X系列前級多了一些想法，Pass一直是「少就是多」（less is more）哲學的信奉者，XP-10確實越來越精簡了。哪裡精簡？把錄音輸出端子直接拔掉，也沒有連動控制的RS232，XP-10真的是不折不扣的高電平放大前級，除此之外就沒有了。拔掉這些功能有哪些影響？省去錄音輸出端子，線路自然更精簡一些，深思熟慮在哪裡？以前很多人需要CD轉錄在錄音帶上，現在連錄音帶都幾乎買不到了，何必畫蛇添足。至於省去RS232連控，代表Pass是「純音響派」，不想跟著自動控制系統的潮流起舞，Custom Installation在美國非常流行，身為美國音響廠商，Pass這麼做可能會失去一些市場，但卻是真正為好聲做設計。所以我說XP-10是深思熟慮之後的新產品，他們念茲在茲都是為了好聲著想。
「永不關機」
「少即是多」的設計觀念在XP-10上面處處可見，不單是拔掉錄音輸出與連控端子，XP-10也沒有電源開關，插上電源線直接就開機。沒電源開關怎麼關機？Pass就是不希望用家沒事開開關關，隨時讓前級保持在最佳工作狀態，這樣會影響機器的壽命嗎？以前級來說問題不大，因為前級耗電量不多，工作溫度也沒那麼高，加上Hi End廠商用料嚴謹，「永不關機」應該沒問題，我自家使用的晶體前級和DAC幾乎都不關機，也從來不傷風感冒。在XP-10面板上，就只有簡單的4個按鍵，一個是靜音（mute），旁邊是模式選擇（mode），接下來兩個是輸入檔位切換開關，真是夠簡單了。
這麼簡單的前級，大多數人買回家只要接好訊號線，電源一插，XP-10就可以快樂唱歌了。但如果你是多聲道與兩聲道「共治」，要怎麼辦？放心，Pass瞭解這項功能不該省，可以把一組RCA輸入切換為bypass，整合在多聲道系統當中。可是為了精簡，XP-10的面板就那麼4個按鍵，沒辦法設定，得要從遙控器操作。
至於面講到Pass設計團隊，在他們家的產品當中，後級擴大機設計多出自Nelson Pass之手，至於高電平放大與唱頭放大，大都是副總裁Wayne Colburn負責，在機板上面也可以看到他的大名。至於XP系列新的外觀，則是現任總裁Desmond Harrington規劃，這位先生過去曾在Krell服務，簡單地在面板上增加了一道凹槽，就讓XP-10的外觀增添了現代感，同時也維持了Pass既有的產品風格。
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「全平衡」連接
XP-10如此簡單的設計，真的是簡單接好線就能聽，不過偏好全平衡的Pass，建議最好能採「全平衡」連接，最能發揮XP-10的好聲，這全平衡包括從CD到前級、後級都要平衡。我很少這樣建議如此使用，因為理論上全平衡並不保證好聲，而是保證噪訊較低（保證的前提是認真做的線路），但我把North Star Design USB DAC32的平衡端子和RCA端子都連接到XP-10上面，交互切換比對，不難聽出音質細部的差異，全平衡不僅噪訊更低，質地、厚度、細節都比RCA要好上一籌，可見Pass處理「全平衡」確實有一套。大部分的前級XLR和RCA也都或有差異，但差距不大，XP-10在這兩者之間的差異則比較明顯。數位訊源平衡了，搭配的後級也一併平衡，聆聽時搭配Mark Levinson No.532H後級，驅動JK Audio PM-10號角喇叭。
音符更為圓潤
XP-10的聲音魅力來自音樂的純度，早年X系列的前級我也聽過不少，但總覺得Pass的後級要來得比前級高明，但XP系列則讓人改觀。與前一代X系列印象相比較，XP-10更顯溫潤、更顯醇厚，如果套句音響迷喜歡用的形容詞，就是聲音變得更甜了，印象中的X系列音質一樣純，但質地冷冽許多，聲音厚度沒有XP-10要好，相較之下，XP-10的聲音個性很容易一聽就討喜，而且這種厚聲並沒有犧牲中性的聲底，XP-10雖然更溫更醇，但卻不是增添音染來討喜，而是讓音符更為圓潤，就好像精心打磨過一般，多了一些溫暖的音樂光澤。或者這麼說更直接，以往的X系列前級偏向理性，而XP則增添了感性，真實之外添加了美感。
細膩、圓潤、厚實的聲底
這麼說很抽象，舉例來說吧，用XP-10播放小提琴，弓弦摩擦的細節很豐富，共鳴也很飽滿，印象中X系列前級的小提琴就沒有XP-10這麼地飽滿厚實，播放一些激烈的小提琴音樂，XP-10更顯游刃有餘，像是Astoria樂團演奏的「Astor Piazzolla: Adios Nonino」，收錄探戈大師皮耶佐拉的曲子，用弦樂與打擊樂熱鬧演出，第一軌「Michaelangelo 70」小提琴快速由低而高的滑音，衝勁十足，如果音響系統細瘦薄弱，小提琴肯定尖銳火辣，馬上就聽不下去了，但XP-10細膩、圓潤、厚實的聲底，讓小提琴如熱刀切奶油一般，一下子滑開，乾淨快速，散發明亮璀璨的光澤，但卻一點也不刺激刮耳，緊跟著進來手風琴、弦樂群和打擊樂熱鬧地合奏，交織出熱力十足的探戈場面，音樂雖然火辣辣，但XP-10輕鬆地鋪陳出條理分明的旋律線條，小提琴激昂地和手風琴、打擊樂對話，大提琴與中提琴則襯底呼應，XP-10則把內中的感情表現得精彩，這樣的探戈有著健康的活力，熱鬧卻不吵鬧。
動的音樂條理分明，那表現靜的音樂呢？我想舉館野泉演奏的「西貝流士鋼琴作品集」，這是1971年的錄音，從CD的背景噪訊可以感受到原本是一張純類比錄音，很容易聽見母帶的嘶聲，但是XP-10卻能用深沈安靜的音樂背景，讓我們清楚地把母帶噪訊和音樂本體分離開來。是的，我們聽得到母帶噪訊，但音樂卻是浮在母帶噪訊之上，清楚地刻畫出來，那是XP-10漆黑安靜的背景，讓我們清楚地把類比母帶的底噪和音樂分離得清清楚楚。這張CD本身聽起來確實很有LP味，但用XP-10播放起來，LP的類比味道更濃了。一般愛樂者聽西貝流士，多半偏好他的管弦作品，像是「芬蘭頌」、「小提琴協奏曲」，音樂激昂中帶有民族風味，但西貝流士的鋼琴作品則流露出北國寧靜的意像，館野泉的演奏清清淡淡地，在XP-10上面聽來則多了一分人文味，鋼琴的顆粒感、重量感適中，音樂旋律線條簡單，流露出寧靜的氣氛，如果鋼琴的重量再重一點，音樂的寧靜感就會淡一點，如果音樂的重量感再多一點，那音樂就會比較凝重，如果硬要挑毛病，我會覺得XP-10的密度稍薄，收束比較鬆，不過這樣的均衡感可以讓音樂聽來更輕鬆一點，或許那是Pass調校XP-10的想法。
弦樂柔中帶剛
相較於X系列，XP-10確實是更沒有火氣，更為精純，而且音樂總是帶著很不錯的輕鬆感，遇到大場面一點都不會緊繃緊張。我想舉馬捷爾指揮維也納愛樂演出的「德弗札克第八號、第九號交響曲」，在第八號的第三樂章開始，弦樂漂亮地拉出充滿斯拉夫風情的旋律，音樂的線條感很重要，如果缺乏線條的力道，那濃郁的斯拉夫風情就會淡薄許多，XP-10很能掌握住張力的輕重，它不是張力很強很重的類型，卻是輕鬆中帶著韌性，弦樂的張力不錯，但當中還藏著柔軟的暗勁。又像是第九號交響曲的第四樂章，導奏一樣是弦樂開始，但卻是一段緊張接著緊張的開始，XP-10在表現一波又一波的弦樂，柔中帶剛，緊接著銅管鋪陳的第一主題，場面浩大，氣度恢弘，XP-10能賦予銅管漂亮的光澤，但卻不顯刺激緊繃。
更顯成熟韻味
從X系列到XP系列，Pass前級的改變很明顯，聲底更為乾淨，音樂更為輕鬆，或者說，前一代X系列是「剛中帶柔」，這一代XP系列則更像是「柔中帶剛」，換句話說，XP-10依然保有Pass中性、乾淨、通透、細節豐富的特質，但質地更溫、更醇、更厚，賦予音樂更柔、更媚、更甜的風貌，如果說Pass的前級本來就是麗質天生，XP-10則是更顯成熟韻味，增添了百媚千嬌的姿態，在中性之中，增添了音樂的美感。
Pass XP-10前級擴大機 器材規格
增益：0dB/10dB（可切換）
頻率響應：-3 dB @ 2 Hz,-3 dB at @ 60 kHz
失真：< .1 % THD typically, <.002% @ 2 volts @ 1KHZ
最大輸出：15 volts rms (平衡)、15 volts rms (非平衡)
輸出阻抗：150 ohms (非平衡)、300 ohms (平衡)
輸入阻抗：48 kOhm (非平衡)、96 kOhm (平衡)
CMRR typical：-60 dB（1KHz）
Crosstalk typical：-90 dB（1KHz）
訊噪比：< -110 dB, Ref 5V
電源消耗：10 watts
尺寸：431×101×304mm(W×H×D)
重量：14.5kg
參考售價：320,000元
進口總代理：進音坊
電話：(02) 2838-0729
網址：www.passlabs.com
[ 本帖最后由 davidxtb 于 2012-2-1 15:15 编辑 ] | 
发表于 2012-1-24 22:13:17
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