心仪的前级之一：The First Watt B1 Buffer Preamplifier
The First Watt B1 Buffer PreamplifierArticle By Nelson Pass Of First Watthttp://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm
Side A
http://www.enjoythemusic.com/diy/0708/pass/inside.jpg
The First Watt B1 Buffer Preamplifier Article By NelsonPass Of First WattSo here we are in the New Millennium, and thanks to TomHolman and THX we've got lots of gain in our electronics. More gain than someof us need or want. At least 10dB more. Think of it this way: If you arerunning your volume control down around 9 o'clock, you are actually throwingaway signal level so that a subsequent gain stage can make it back up.Routinely DIYers opt to make themselves a "passive preamp" ? just aninput selector and a volume control. What could be better? Hardly any noise ordistortion added by these simple passive parts. No feedback, no worrying aboutwhat type of capacitors - just musical perfection. And yet there are guys outthere who don't care for the result. "It sucks the life out of themusic", is a commonly heard refrain (really - I'm being serious here!).Maybe they are reacting psychologically to the need to turn the volume controlup compared to an active preamp.
I suppose if I had to floor the accelerator to drive55 mph, maybe I'd think the life was being sucked out of my driving. Thenagain, maybe I like 55. Nice and safe, good gas mileage... Is impedancematching an issue? Passive volume controls do have to make a trade-off betweeninput impedance and output impedance. If the input impedance is high, makingthe input to the volume control easy for the source to drive, then the outputimpedance is also high, possibly creating difficulty with the input impedanceof the power amplifier. And vice versa: If your amplifier prefers low sourceimpedance, then your signal source might have to look at low impedance in thevolume control. This suggests the possibility of using a high quality buffer inconjunction with a volume control. A buffer is still an active circuit usingtubes or transistors, but it has no voltage gain - it only interposes itself tomake a low impedance into a high impedance, or vice versa.
If you put a buffer in front of a volume control, thecontrol's low impedance looks like high impedance. If you put a buffer after avolume control, it makes the output impedance much lower. You can put buffersbefore and after a volume control if you want. The thing here is to try to makea buffer that is very neutral. Given the simple task, it's pretty easy toconstruct simple buffers with very low distortion and noise and very widebandwidth, all without negative feedback. There are lots of differentpossibilities for buffers, but we are going to pick my favorite:
Side B
http://www.enjoythemusic.com/diy/0708/pass/buffer_pre1_thumb.gif
Figure 1 above shows the full schematic of the B1 bufferedpassive preamp. You can see a full-sized PDF by clicking here. There are twochannels shown with a common power supply. Supply parts in common are numberedfrom 1 to 99. Parts in the right channel are 100 to 199, and the left channelis 200 to 299. With the exception of R1, all the resistors are 0.25 watt ? Iused RN55D types, but you can use whatever you like. C1 and C2 are big electrolytictypes, with a nominal rating of 15000 uF at 25 Volts. C100, 200, 101 and 201are high quality film capacitors. You can use these values or substitute inyour favorites. For C1 and C2 I used Digikey P6890-ND. The value is notcritical, and you can use as low as 1,000 uF at 25V. C3, C100 AND C200 are 1uFmetallized polypropylene film capacitors (Digikey BC2076-ND) C101 and C201are 10 uF polyester film capacitors (I used Axon 10 uFmetallized polypropylenefrom Orca Design). Feel free to use any comparable types.
http://www.enjoythemusic.com/diy/0708/pass/aeon_capacitor.jpg
D1 is a generic 1N914 type diode, and D2 is a generic LED forindicating power the board. All of the transistors are N channel JFETs. Thestock parts are 2SK170's, LSK170's or 2SK370's, and you can use substituteshaving Idss between than 5 and 10 milli-Amps and transconductance numbers from5 to 30 milli-Siemens. The potentiometers are linear taper at 25 Kohm, butagain you can easily use higher or lower values as you like. The buffer uses anexternal power supply from 18 to 24 Volts DC. You can power it with batteries,but most convenient is an external regulated supply running off the wall. Thepreamp typically draws fewer that 0.02 Amps, so current is not much of anissue. A regulated supply is better, but the circuit is pretty good at ignoringnoise on the supply and minor fluctuations. The design uses RCA input andoutput connectors, and a DPDT switch for selecting one of two inputs. You are,of course, free to use a switch with many more inputs.
http://www.enjoythemusic.com/diy/0708/pass/rear_panel.jpg
For a fact this circuit can be easily constructed withperf-board and point-to-point wiring. I know, however, that many people won'tstart a project like this without a circuit board. The Gerber artwork is postedat www.passdiy.com and I have arranged to have finished PC boards available atcost around the time you read this.
Side C
Let's talk about what some of these parts do. Theinput switch selects one of the two input signals, routing it to the top(clockwise position) of potentiometers P100 or P200. A divided input signalappears on the wiper. This signal goes to the Gates of Q100 and Q200 through aresistor R102, R202 and capacitor C100, C200. As a practical matter, the inputimpedance of this preamp is determined by this volume control potentiometer. A25 K Ohm pot gives 25 K Ohm input impedance.
R102 and R202 are there to prevent parasiticoscillation with the very wide bandwidth JFETs. C100 and C200 are there becausethe Gate of the JFETs needs to be set at half the DC voltage of the powersupply - a voltage delivered to the buffer inputs by R2, R3, and C2 throughR103 or R203.
D1 performs the service of drawing down this DCvoltage with the power supply when the power is turned off, otherwise C2 mayhold a charge for a long enough time to give you a turn-on thump when poweredback on. By the way, the time constant of R2, R3, and C2 are long enough thatit takes a minute or two for the circuit to reach normal operating values, sodon't get excited if there's no sound for a few seconds when you turn it on.
R1 and C1 filter noise coming from the externalsupply.
Q100 and Q200 are JFETs operated as followertransistors. The Source pins of these transistors follow the voltage at theGates. The input impedance of the Gate is exceedingly high - many millions ofohms, and the output impedance at the Source pin is about 50 ohms.
Q101 and Q201 are constant current sources formed bysimply attaching the Gate pins of the JFETs to the Drain pins. They providewithout loading them down or creating significant distortion.
The best performance generally comes from matching theIdss of Q100 and Q101, and also Q200 and Q201. The Idss is simply the currentthat flows through the JFET when the Gate and Source are grounded and +10 voltsor so is applied to the Drain. Often when you buy JFETs you can get them inIdss grades. I use GR or BL grades for this project.
The Source DC voltage of the JFETs Q100 and Q200 isabout the same as the Gate DC voltage (1/2 the supply voltage), and the outputfrom the Source needs to have the DC voltage removed by C101 or C201, leavingthe AC output signal, which passes through another safety resistor R104 orR204.
Resistors R100, R200, R105, R205 are there to preventthe various potential thumps from switching inputs and turn-on transients.
Side D
The circuit of Figure 1 has quite good performancespecifications. Upon measuring, I noted that distortion at 1kHz was extremelylow and flat at all frequencies. Below a volt, the distortion comes in at about.0007%, and about the time your amp is clipping, it measures about .003%
Figure 3 above shows the .0007% distortion waveform at1 Volt and 1 kHz. Careful measurements show me that the distortion versusfrequency is extremely low and does not alter over the audio band. Figure 5below shows a 100 kHz square wave at 1 volt at the output. The bandwidth of thepreamp is -3dB at about 700 kHz. On the bottom end, the low frequency roll-offis about 1.5 Hz into a 10 Kohm load and about 0.3 Hz into 47 Kohm.
Side E
http://www.enjoythemusic.com/diy/0708/pass/front_panel.jpg
The First Watt B1 Buffer Preamplifier Article By NelsonPass Of First Watt So how does it sound? Well, no suckage here. I've noticedthat simple no-feedback circuits have tremendous clarity if the circuit haswide bandwidth and really low distortion. At the moment I'm driving a pair ofLowther DX55's with some passive baffle-step correction (6 dB loss there) andan F3 amp with only 12.5 dB voltage gain. The preamp is fed by anXono phonostage with a low output cartridge (Grado Statement). The sound is extremelyneutral without being clinical - just about what you were looking for when youwere thinking about a passive preamp. A teensy bit of second harmonic and nonoise at all.
There's just enough gain. If you were using any otherpower amp, you'd get 8 to 18 dB more gain, and would be able to break yourlease or the speaker, or both. Do I feel like the pedal's to the metal and I'monly doing 55? No, as I'm listening as loud as I want and sleep soundly atnight, knowing that I'm not throwing away signal with my volume control.
Side F
Have you noticed that they're putting out some LP'swith not just 2, not just 4, but with 6 sides holding the content of a CD? It'ssweeeet. Two cuts to a side, and when you look at the grooves you can see theland area between them. Right now I'm listening to High Fidelity Lounge, vol 4,Side F.
NOTE: You can see Dick Olsher's review of this unit byclicking here.
Manufacturer
First Watt (assembled unit) or Pass DIY (kit version)
Phone (530) 367-3690
Website: www.passdiy.com
[ 本帖最后由 davidxtb 于 2012-8-3 12:20 编辑 ] The First Watt Model B1 Buffer Preamplifier
Operating at the speed limit!
Review By Dick Olsher
http://www.enjoythemusic.com/diy/0708/first_watt_b1_preamplifier.htm
First Watt's latest DIY offering, the B1 buffer stage,is described by Nelson Pass as "a no-feedback JFET buffer that offersultra low distortion and noise with ultra wide bandwidth." If you areunfamiliar with First Watt's product spectrum and with the underlyingphilosophy of its progenitor, Nelson Pass, I strongly suggest that you visitthe First Watt website for an orientation. In a nutshell, Nelson believes thatsimple elegant designs are the most worthy of his time and your money.
The speed limit metaphor refers to the fact that thebuffer has no voltage gain and thus the system's overall gain is limited to thegain of the front-end source component plus that of the power amp. Well, thatbrings up the question of just how much gain is needed? Obviously, a CD playerwith a nominal 2V line signal presents no problems at all for the bufferpreamp. Most power amps feature an input sensitivity between 1 and 2 V, whichmean that a typical CD player needs no additional gain in order to redline mostpower amps. But take a look at the line inputs on most line stages andpreamplifiers. The signal is forced to undergo 12 to 18 dB or more ofamplification. That's very likely a throwback to the days when line inputs werenominally 0.2 V (tuners and tape decks, for example), which require a gain of1.5/0.2 (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 itspedigree, 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 thevolume control and then forcing it through an active gain stage to build it upagain ? hardly an optimal situation.
Things may be less clear with respect to a phono frontend, so let's take a look at my current setup. My Grado Reference MM cartridgeis specified at 5 mV nominal output. Again, resorting to a hypothetical poweramp with a sensitivity of 1.5 V means that the phono stage requires a gain of1,500/5 or 300 to drive the amp off the cliff. That's equivalent to a gain ofabout 50 dB, not a problem for my Air Tight ATE-2 phono stage or most any otherphono stage. Again, no gain boost is needed from a line stage. All of thisshould lead to the realization that the ideal line stage may well be a bufferstage with provisions for input selection and volume control. Nelson asks thefollowing rhetorical question: "Do I feel like the pedal's to the metaland 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, knowingthat I'm not throwing away signal with my volume control."
A Few Technical Details
First Watt Model B1 Buffer PreamplifierThe so-called"passive preamp," an attempt to achieve the ideal line stage withouta buffer stage, has in my experience been a sonic failure. Lifeless andcomatose are two descriptors that immediately come to mind. Simply inserting avolume control between the source component and power amp ignores two importantinterface issues. First, there's the issue of impedance matching. Ideally,input impedance should be high and output impedance should be low. That'sdifficult to achieve without the use of an active buffer or at least atransformer. My sample of the B1 was built by Nelson - as shown in theconstruction article schematic. The input impedance is a function of thesetting 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 theyappear to benefit from the very high impedance of the active circuit. And whilehe has not perceived any sonic issues with them, he points out that you areperfectly free to use your favorite volume control in this application. I wouldhave preferred, for example, a 50 kOhm pot, or even better for my birthday, amotorized remote-controlled attenuator. If you're into stepped attenuators,note that his favorite for a long time has been the Elna with type RN55Dresistors. The actual output impedance is dominated by a 1 kOhm resistor (R104and R204 in the schematic). That's fairly low, but Nelson says that this valuecan be arbitrarily lowered down to say 200 Ohm, though he cautions that couldcause problems with wideband equipment. The second interface issue has to dowith the ability of a stage to drive long and/or reactive interconnects. Andthat's an area that an active buffer stage excels in, though I can't say that Ispecifically challenged the B1 in this respect, having simply dropped it in tothe an existing system which uses fairly short FMS Nexus interconnects.
Despite the Spartan appearance of my B1, it actuallyoffers a capability lacking in much more expensive high-end preamp designs;namely, channel balance control. The dual volume controls allow for independenttweaking of each channel and to my mind this approach represents the preferredmethod of implementing a balance control. It's surprising that so few modernpreamps bother with such a control. In fact, the great J. Gordon Holt onceopined 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 differencesand for loudspeaker sensitivity deviations. For example, rarely are loudspeakerdrivers matched to better than 1 to 2 dB, and with the B1, a simple tweak ofeither the left or right pot can re-center the soundstage.
My unit was outfitted with an Ault +18V (70W) ModelMW116 switching power supply specified for medical applications. No complaintsso far, but I'm very curious to substitute a linear DC power supply such as theB+K 1671A in the near future.
Receiving The Windex Treatment
The B1 took its place in a reference system headed bythe PrimaLuna Eight CD player and an analog system that included the KuzmaReference turntable, outfitted with the Graham Engineering model 2.5 tonearmand Grado Reference MM cartridge. The associated phono stage was the all-tubeAir Tight ATE-2. The rest of the system consisted of the TEAC Esoteric MG-20 loudspeakersdriven by either the Vincent Audio SP-T800 monoblocks or Esoteric's new A-100tube amplifier.
For starters, the B1 displaced the Vincent Audio SA-T8line preamplifier, which in concert with the SP-T800 monoblocks had alreadyimpressed 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 thananything else, rising from below the threshold of conscious perception, asingle word began to form: wow! A sensation of extreme clarity and transparencytook hold of the soundstage. The sonic presentation was spectacularly open andspacious. 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 oflarge choral works.
This darn gadget made familiar recordings sound moreimmediate and less electronic. Harmonic textures were squeaky clean, withcommendable purity of timbre. And forget about listening fatigue. This is alow-distortion device, well-behaved over the entire audible bandwidth, andretains its textural suaveness from soft to loud levels. Bass lines werethunderous and well defined, as you would generally expect from well-designedsolid-state gear.
It became clear fairly quickly that the B1 took itssonic cues from the associated gear. It didn't impose a particular tonalcharacter over the presentation but rather allowed each power amp to dictate matters.Tonal differences between the Esoteric and Vincent Audio amps were readilydiscernible. The A-100 evinced greater lower midrange weight, as it should,being a transformer-coupled tube amplifier. Differences in treble character andbandwidth were also evident. In my opinion, neutrality in a preamplifier isusually a good thing. But if, like me, you're craving a touch of tube sweetnessand 3-D image palpability then you'll have to get your tube fix at the poweramp. The key is to carefully select either a matching tube amp or a hybriddesign such as the SP-T8000, which really clicked sonically with the B1.
At this point, I was really curious to find out justhow competitive the B1 was with the best line preamplifier currently known tome ? the Concert Fidelity CF-080. Note that the CF-080 does employ a tube basedgain stage. Specifically, a single 12AU7 per channel. And I do use the bestsounding 12AU7 out there for this application ? the Mullard CV4003 with boxanode construction. Now, some of you may object to the notion of comparing amodest DIY design to an $18,000 ultra high-end design. It sounds crazy, but Ineeded to know. Well, there were differences. The CF-080 possessed morepalpable image outlines and rendered harmonic textures a bit more richly. TheB1, on the other hand, showed a tad more immediacy and better defined basslines. In the end, I felt that most of these differences were simplyexplainable on the basis of tube versus transistor sound.
Conclusion
Don't let its modest appearance fool you: this is onefantastically effective buffer stage. And it's not about to leave my referencesystem any time soon. I'm still laughing out loud over this one ? a DIY productthat succeeds wildly in bringing the listener a significant step closer to thesource. In hindsight, that should not be surprising as the B1 buffer stageeliminates unnecessary gain stages between the source and power amp. A powerfuldemonstration of the "simpler is better" principle, or moreaccurately, less gain - less sonic pain. My advice to preamplifiermanufacturers is this: be sure to dedicate at least one line-level input andoutput to a buffer stage. It really is better to operate at the speed limit,especially in the context of CD players.
NOTE: You can see Nelson Pass' DIY article of thisunit by clicking here.
Specifications
Type: Stereo preamplifier DIY Kit or Assembled
Inputs: Two stereo inputs via gold-plated RCA jacks
Output: One stereo pair via gold-plated RCA jacks
Price: $1000 assembled, price not available for kitversion
Company Information
First Watt
PO Box 7607
Reno, NV 89510
[ 本帖最后由 davidxtb 于 2012-8-3 12:24 编辑 ]
Nelson Pass老家人自己的文
B1 Buffer PreampSo here we are in the New Millennium, and thanks to Tom Holman and THX we’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
http://www.firstwatt.com/graphics/b1.jpg
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.
I suppose if I had to floor the accelerator to drive 55 mph, maybe I’d think the life was being sucked out of my driving. Then again, maybe I like 55. Nice and safe, good gas mileage…
Is impedance matching an issue? Passive volume controls do have to make a trade-off between input impedance and output impedance. If the input impedance is high, making the input to the volume control easy for the source to drive, then the output impedance is also high, possibly creating difficulty with the input impedance of the power amplifier. And vice versa: If your amplifier prefers low source impedance, then your signal source might have to look at low impedance in the volume control.
This suggests the possibility of using a high quality buffer in conjunction with a volume control. A buffer is still an active circuit using tubes or transistors, but it has no voltage gain – it only interposes itself to make a low impedance into a high impedance, or vice versa.
If you put a buffer in front of a volume control, the control’s low impedance looks like high impedance. If you put a buffer after a volume control, it makes the output impedance much lower. You can put buffers before and after a volume control if you want.
The thing here is to try to make a buffer that is very neutral. Given the simple task, it’s pretty easy to construct simple buffers with very low distortion and noise and very wide bandwidth, all without negative feedback.
And here we are...
http://www.firstwatt.com/graphics/b1_int.jpg
Download the B1 Manual
[ 本帖最后由 davidxtb 于 2012-8-3 11:20 编辑 ] FIRST WATT B1前级
见文一：http://bbs.hifidiy.net/attachments/month_0810/20081026_5c7fba5f73bfa46c692bU0BL6hRMPt4x.jpgFirst Watt B1是一台无源前级，巧妙地采用了一个高输入阻抗的JFET电晶体作信号缓冲，对于线路它是没有提供任何的增益。这台 "缓冲前置放大器 "以极其简洁的线路和极高等级的元件、线路组成一台高质量的前级。
http://bbs.hifidiy.net/attachments/month_0810/20081026_be44184babfe8bc65cd9gGSfreTYuSSG.jpg
http://www.enjoythemusic.com/diy/0708/pass/buffer_pre1_thumb.gif
http://www.enjoythemusic.com/diy/0708/pass/front_panel.jpg
见文二：牙尖嘴利音響頻道
玉作搔頭金步搖，高張苦調響連宵。欲知寫盡相思夢，渡水尋雲不用橋。
2009年1月3日星期六
新年新希望：First Watt B1 Buffer Preamp
http://bbs.headphoneclub.com/attachments/month_1208/20120803_75c4d70aab1859885cfdGCHws6r6v7fJ.jpg
2008 年夏天，Nelson Pass 在他旗下的 First Watt 網站上，發表了一個極簡的晶體前級線路：First Watt B1 Buffer Preamp。
這個線路非常簡單，一言以蔽就是以一級 JFET 做源極隨耦器 (source follower)，並以另一顆 JFET 做恆流源（constant current source），前後各一顆交連電容，如此而已。
這個電路不但簡單，其實還很基本，之前塞爾維亞的 DIY 名人 Rogic Pedja 就曾在網站上提出類似的架構。也因此 Pedja 發表聲明，指責 Pass 剽竊他的設計。
不論如何，Nelson Pass 總之是寫了一篇清楚明瞭的好文章，詳細地告訴你 B1 的工作原理、測試數據、零件的選擇、製作要點。照著 Pass 的解說來做，從選料、搭棚、裝機，都會非常愉快順利。
奇怪的是，曾有一段時間，國內的 DIYer 很熱衷 clone Pass 的機器。這次在幾個主要的國內 DIY 網站上，卻都沒有看到相關的討論。連用 Google 去搜尋 "Pass B1 Buffer” 都只有一篇繁體中文的結果，還是香港的。不知是國內的 DIY 資訊落後，還是 DIY 風氣冷清。
http://bbs.headphoneclub.com/attachments/month_1208/20120803_d6b6bc16cd26467ce0cbPxazFGXSyt9n.jpg
自從 Gainclone 和 TDA1541A DAC 漸漸穩定，又購入了 CEC TL51X 轉盤，我的興趣漸漸移到了前級上。本來已經有一件 Audio Note Japan M7 Line Stage 的半成品，但一直找不到適當的機殼，所以遲遲沒有完成。這次卻被 Pass 的 B1 Buffer 所吸引，因為他強調現在的前級，其實不太需要多餘的增益，用 single end JFET 作簡單的電流放大即可得到自然中性的聲音。Pass 對於 DIY 有很多貢獻，他推崇的極簡線路，single end 放大，也都與我的偏好不謀而合。但之前一直沒有興趣製作他的線路，因為他的後級總是非常難搞，即使號稱小功率、極簡，也需要笨重的變壓器和龐大的散熱片，累煞人也。相比之下，前級簡單多了，線路極簡，製作起來就真的不會太麻煩。所以今年看到這個線路，就立刻開始準備製作這台前級。
可能太久沒有製作新機器，我花了很多時間才把心情沉澱，並把相關的零件和機箱準備好。結果拖到了年底，這才一切就緒，於是趁著新年假期把第一版試作機裝了起來。
製作筆記：
1. B1 Buffer 每聲道要兩顆 2SK170-BL，而且要配對，Pass 更強調這是好聲的關鍵所在。我手邊剛好有將近 20 顆 2SK170-BL，用洞洞板搭了一個簡單的線路，2SK170 的 source 和 gate 接地，以 9V 電池，透過 1k 電阻送給 drain。最後選了四顆 Idss 在 9.01 - 9.03 mA 之間的晶體。
2. Pass 本來採用外部的 switching power 作為 18V 的輸入。這樣當然非常簡單省事，而且 Pass 說這個線路對電源並不敏感，所以用 switching power 就很不錯了。但我一直覺得好的 switching power 很難找，如果隨便用上一個不熟悉的電源，將來在試聽和調音時會增加不確的因素。所以我還是搭了一個簡單的 18V 線性供電。用 Schottky Diode 11DQ06 整流，LT317A 作簡單的穩壓。電容有 Panasonic FM、Elna Silmic、BCC 013、UCC SPP 等，是從庫存裡湊出來的。
3. 主放大電路，Pass 用了兩顆 15000uf 電容供電，我手邊沒有那麼大的電容，也不喜歡那麼大的電容，加上 Pass 說幾千到幾萬 uf 都可以，所以我改用 Panasonic FM 2200uf 代替。
4. 每聲道有兩顆交連電容，輸入交連是 1uf，輸出交連是 10uf。Pass 建議用 metalized film 電容，但我不喜歡 metalized film 電容的聲音。然而，我手邊雖有 1uf 的 MultiCap RTX，非常好聽，但體積實在太大，裝在這個小小電路板上未免費事。現在既然只是試做機，我一律用 Black Gate N 代替，這已經是非常好的交連電容了，我覺得 Black Gate N 甚至勝過許多 film 電容，體積又小。
5. 本來電路上有訊源切換的設計，但我的訊源只有 DAC，所以直接捨棄，訊號進來就直入 VR。
6. VR 採用手邊東京光音很便宜的一款產品（價位在800塊上下），這款 VR 聲音偏軟，清爽甜美。
7. 我把電路板鎖在一大片一公分厚的 MDF 上，再置入唐竹賣的厚鋁黑色機箱，搭配銀色霧面旋鈕，非常美觀穩重。
8. 所有的電阻都是 Philips MPR-24 0.1%，除了連接 LED 指示燈的改用便宜的 MRS-25。
一開機就很順利，電源的電壓、輸出直流等測試都一切正常。接上我的系統試聽，背景很乾淨，聽不到噪訊。一開始就發出非常生活有朝氣的聲音，與原本的被動式前級比起來，B1 雄渾有力。但聲也有一點衝，有一點硬，不如被動式前級柔軟純淨。Break-in 半天之後，B1 試作機聲音柔順許多，但還是有一股「晶體味」，但還算耐聽，至少我聽了一天下來，覺得相當愉快。目前試過古典樂、Jazz、人聲，音色的確如 Pass 所言，非常中性，頻帶很寬。加上 B1 之後，我的系統聲底變得陽剛許多，不像之前那麼陰柔。
First Watt B1 Buffer Preamp 的確是簡單好玩的機器，試作機只是開始，可以調的東西很多，例如電源、零件、layout 等等。我對晶體線路沒什麼經驗，還有很多很多地方要實驗和了解，接下來 2009 年可以好好的改機調音了。
線路圖和 Nelson Pass 的解說，可以在 First Watt/PassDIY 網站上下載到 PDF 格式的檔案。
http://bbs.headphoneclub.com/attachments/month_1208/20120803_3af29b609377f31d69f9Xmf2pNX3WQ5G.gif
[ 本帖最后由 davidxtb 于 2012-8-3 12:26 编辑 ] 国外相关的讨论帖子
http://www.diyaudio.com/forums/pass-labs/124889-b1-buffer-preamp.html?perpage=25&pagenumber=1 又要上了啊 请问LZ目的是什么？ 目的待明，上次有朋友说要上 熊大去搞一个?搭配FIRST WATT J2应该不错 上次买F1J的时候，问了代理效果如何，对方评价倒是很高，而且和FIRST WATT F1之类的非常搭配。
都已经付了款了，后来还是因为米不够而放弃了。
:$ :$ :$ 原帖由 davidxtb 于 2012-8-3 11:41 发表 http://bbs.headphoneclub.com/images/common/back.gif
上次买F1J的时候，问了代理效果如何，对方评价倒是很高，而且和FIRST WATT F1之类的非常搭配。
都已经付了款了，后来还是因为米不够而放弃了。
:$ :$ :$
不知道和NAGRA PLL比较如何?看设计,估计声音密度,动态会弱些 性价比高的前级，难找啊，呵呵 不错的DIY项目 原帖由 headfan 于 2012-8-3 12:03 发表 http://bbs.headphoneclub.com/images/common/back.gif
不错的DIY项目
有做的更为复杂的：
http://i46.servimg.com/u/f46/14/16/74/88/totale11.jpg
http://i46.servimg.com/u/f46/14/16/74/88/sopra17.jpg
http://i46.servimg.com/u/f46/14/16/74/88/b111.jpg
http://i46.servimg.com/u/f46/14/16/74/88/fronte14.jpg
或者更复杂的搞法：
http://invisiblemoose.com/images/amp/1.jpg
http://invisiblemoose.com/images/amp/2.jpg
http://invisiblemoose.com/images/amp/3.jpg
http://invisiblemoose.com/images/amp/4.jpg
http://invisiblemoose.com/images/amp/5.jpg
http://invisiblemoose.com/images/amp/6.jpg
http://invisiblemoose.com/images/amp/7.jpg 内部真够简洁啊！
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