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First Watt F7 Amplifier

03-28-2017 | By John Hoffman | Issue 90

The First Watt series of amplifiers started as an exploration of uncommon circuit designs in a low wattage format, and has been an ongoing endeavor for two decades now. From Nelson Pass we have seen many an iconic audio product, such as the Threshold electronics, the Stasis circuit that Nakamichi commissioned, and of course the Pass Labs products. You must wonder how a designer can stay so creative over the years, and where does this diverse collection of circuits come from? Add to the equation that Nelson willingly gives of his time and knowledge to the DIY community, and it's no wonder that the audio world holds him in such high regards. The First Watt amplifiers are expansive in regards to the breadth of diverse circuit topology, yet all of them have the primary goal of being musically engaging rather than hitting a handful of specifications that should equate to "good sound". The First Watt family of amplifiers have the ability to integrate themselves into markedly different types of system configurations. Amplifiers such as the J2 can be considered a flexible choice and easily paired with a wide variety of gear. Other designs, such as the M2, have a tighter focus in terms of application, yet it shines brightly in the correct system. To paraphrase, I believe that Nelson has stated there is no perfect amplifier, but rather the best one for a speaker, or system, and ultimately a person. This is what makes the First Watt line so intriguing, that such an expansive collage of designs can still travel towards the end goal of a musically engaging listening experience.

First Watt F7 Amplifier

This brings us to our topic of the F7 amplifier, which is the latest release in the First Watt line. Technically speaking the F7 circuit is an evolution of the F5 design. The F5 previously held the title as the circuit with the lowest part count and direct signal path; until the unveiling of this amplifier. The F7 is a push-pull design that operates in Class A, with power output being 20 WPC into 8 ohms and 30 WPC into 4 ohms. This is a two stage gain circuit with a pair Jfets on the input stage, and a pair of Mosfets for output devices. The circuit topology employs a Common Source Mode design where a current feedback loop from the Mosfet output voltage is routed back to the source pins on the Jfet transistors. Other design goals for the F7 was to have wide bandwidth, low noise floor, heavily biased to Class A operation, and a direct signal path that is free from capacitors or transformers. The initial layout of the revised circuit showed promise, and yet Nelson felt there was a way to coax a higher level of performance from it. The dampening factor of the amplifier was a bit low, and so Mr. Pass made a startling move, akin to what chess Grandmasters have done in a tournament. In essence, the ability to see an elegant solution with a clarity that escapes the conventional linear line of reasoning. The solution was to roll in a couple of dB of positive current feedback into the circuit, which effectively lessens the effect of impedance variance created by the speaker load, yet does not adversely affect the output devices current flow. Nelson expands on this point, and his description helps clarify this issue.

NP: It's a little tricky to describe the role of the positive current feedback, as some of the terms such as "current feedback amplifier" are bad descriptions of what is going on. Since a CFA is not actually sensing output current—it simply has a low impedance negative input point, so the amplifier is best described as having low impedance voltage negative feedback and high impedance current voltage feedback."

The result of this balancing act of negative and positive feedback dramatically improves the dampening factor of the amplifier while maintaining the minimalist circuit design. The overall distortion number of the amplifier rises a bit, however the trade-off for performance gains in other parameters is worth making. The addition of one resistor became a game changing moment, and the final block was laid in the foundation of this amplifier.

First Watt F7 Amplifier

The First Watt amplifiers are all built from the same chassis, so externally they have a similar facade. The overall appearance is understated, and the fit and finish is impeccable. These days Pass Labs has taken over the assembly duties, as the demand for these amplifiers have been strong enough that a larger production facility became a necessity. These are not terribly heavy amplifiers, as they weigh 30 pounds, and are a full-sized component with dimensions measuring 17W x 15D x 5.5H. There are one set of RCA input jacks, and one pair of reasonably stout binding posts. Two blue LED lights adorn the face plate, along with an elegantly engraved First Watt logo. The MSRP of the F7 is $3000, and for that price there is not an ounce of audio bling that calls attention to itself. Yet looks can be deceptive, as this demure chassis holds an auditory gem that every hobbyist should get a chance to hear at one time or another.

In 2016 my wife and I undertook a move across the state, and this meant purchasing a different home. The new listening room was a fresh slate, and so I decided to acquire a pair of JBL 4365 speakers. The 4365 monitors are descendants from their highly regarded studio monitor series, and are the speakers that the F7 amplifier have been tasked to drive for this review. The preamplifier is a First Watt B1, which is a passive design with an active impedance buffering stage on the inputs.  Analog source components are a Galibier Serac turntable with Riggle Engineering String Theory arm and ZYX 4D cartridge. The phono stage is the Liberty B2B-1, which is a factory direct offering from PBN Audio. On the digital side an Audio Magic Kukama DAC is paired with a Macintosh Mini desktop music server running the Pure Sound player. Power conditioning is handled by a PS Audio P10 AC Regenerator. Cabling comes from the ZU Audio Mission line of wires. This all resides on a Salamander Audio Geneva equipment stand.

First Watt F7 Amplifier

Since the early 2000s I have used Single Ended Triode tube amplifiers in my systems, and have consistently assembled nice sounding music rigs. The JBL 4365 speakers required me to change course, and re-evaluate my options. Even though the JBL are 93dB efficient, they require more current and a higher dampening factor from an amplifier than a typical 300B based SET amp can provide. So, I knew either a solid state or push-pull tube amplifier was needed. What I could not sacrifice was the beautiful tone, dense harmonic texture, or the immediate presence I had become accustomed to in my systems. This led me to exploring the latest offering in the First Watt line-up. I have listened to previous models, and knew that there was a touch of magic in these deceptively simple amplifiers. Yet I have been a tube guy since I bought my first Dynaco Stereo 70. Could I really find contentment with a solid-state amplifier? The answer is yes, as the core attribute of the F7 is the ability to infuse a breath of life that provides an elusive spark which makes music worth listening to. As hobbyists, we allocate a great deal of time and money to our audio systems, and the payoff should be an experience that brings the essence of an artist to our music room. That is what this hobby is bout isn't it? "Little White Candles" by The Gypsy Moths [The Gypsy Moths; White Rose Media WRM-002] is a long-time reference recording for me, and it gets played on every piece of gear that comes across my path. This is a minimalist recording that is an honest representation of what these ladies style and talent are. I have heard the Gypsy Moths perform several times at local folk festivals, so I have a firmly grounded memory to compare this listening experience against. This is one reason why this album is a valuable reference tool for me. The F7 amplifier is remarkable in how it presents the vocals on this song, as Raina and Meredith's voices have an authentic tone that is free from any artificial warmth or enhancement that might be alluring, but is an alteration of the recording. The picked guitar line on this song is light and delicate, with an easy flow that highlights a complex interplay between the two performers. The First Watt amplifier steps out of the way and lets the essence of their wonderful guitar playing just flow from the speakers. Every facet of the instrument, from the picked stings, to the fingers sliding down strings, to light hand strikes to the body of the guitar, it just sounds authentic. Yes, it is a recording with some inherent limitations, but it has a natural feel to the sound that brings the experience of a musical performance alive. As a listener, you can forget the technical numbers, the configuration of the parts contained in the chassis, the weight of the amplifier, or any other empirical yardstick you use to evaluate a component. Just sit down and listen for a bit, and it is likely that you will find that the F7 helps create music in a meaningful way, and that the experience of enjoying your favorite artists is all the justification you need to own this amplifier.

Large format JBL speakers excel at presenting the scale and weight of a band. These are studio grade monitors, and they are uncompromising in revealing anomalies in components. The F7 amplifier is designed to have wide bandwidth, and I was curious to know if this piece could maintain control these large format woofers during complex musical passages. For it was painfully obvious that my 300B tube based amplifier could not accomplish this. "Satesboro Blues" by Taj Mahal [The Real Blues; Sony Special Projects  A28418] is a fine example of how the First Watt amplifier can power through a high-energy song, and keep the drive and pace of the track without sacrificing the scale of the music. The bass guitar line has unrelenting drive, dense tone, and sharp snap to the sting plucks. The drum kit stays transparent and dynamic, as the snare drums a distinctive resonance to each strike, and the kick drum has a solid pop. The tone to Johnsons guitar is pure, and is articulate to each bend and sustain worked into it by this skilled guitarist. The overall scale of the performance is realistic, with the overall sound being large and expands into my living room. The music just growls, and once again has that live feel of a jumping blues band.

Then there is there is the subject of bass extension. Let us talk about that for a minute, as it is point worth discussing. The F7 may have a refined and genteel character, but when required to conjure up some serious subterranean notes, it belies what on the surface appears to be a modest power rating. On "Friends" by the ska band Skadanks [Give Thanks; Elektra 61586-1] there are some wickedly low bass notes. Yes, they are synthesized, however these are notes that move past the threshold of hearing and are felt more than heard. The 15 inch woofers of the JBL 4365 are rated to 35Hz, although informal room measurements show them to get to the mid 20s in my room. Now the F7 amplifier can provide the power and current to make this happen. A judicious twist of the volume knob on the B1 preamplifier is rewarded with deep and extended bass, and the 93dB efficiency of the JBL allows for some enthusiastic volume levels to be achieved. While these may not be the volume levels your favorite club DJ hits, it does come close, and with a sound quality that is appreciably superior.

The F7 amplifier presents space in a manner that is both expansive and believable. The scale and location of instruments within a soundstage, and in relation to each other is properly balanced. On Dvorak's #9 Symphony New Philharmonia Orchestra; EMI 1C06302802Q] each section of the orchestra is tightly defined, with woodwinds, strings, brass, and percussion neatly placed within the confines of the soundstage. Equally important, each section of the orchestra is properly sized, with no unusual aberrations to the overall scale. Now this is certainly a function of a properly balanced full range speaker system, yet the amplifier plays its part with an even tonal balance. I have experienced romantically voiced amplifiers make an utter mess out of an orchestra, so it is a challenging task to get correct. On the other side of the coin, amplifiers with extra energy in the upper registers can present a hyper realistic portrayal of this kind of music, but almost always at the cost of emphasizing specific instruments and affecting the cohesiveness of the recording. The F7 amplifier gets the spatial relationships inside the music right, and this is one aspect of many that contributes to an authentic and genuine presentation of the music.

There is no doubt that the Fist Watt F7 is a refined, articulate, and expressive amplifier. The next question is can it be fun? After all, we listen to music to bring us enjoyment, and an audio system should be capable of being able to relate that attribute of music to us. It would be a shame if the F7 was so revelatory in nature that only the finest of recordings could be enjoyed on it. So, I pulled out my copy of Elephant by White Stripes on the Acoustic Sounds label, and cued up "Seven Nation Army" [Elephant; Acoustic Sounds ATMR 535433]. Now this is a song that gets played on every season of those vocal talent shows because it just flat out rocks. No, it is not challenging music, and yes, this album is a decent recording. The verdict is that the F7 does indeed have a fun side to its personality, and does not render music like this unlistenable. This song is all about the groove, and the F7 and JBL's are well suited to laying down that distinctive bass line that makes this song so compelling. Jack White's vocals are immediate and raw, and the kick drum has a physical punch to it. As the song builds in scale, the amplifier never loses its composure. In my opinion the F7 would be equally comfortable driving large format speakers like the JBL, Altec Lansing, VMPS, as well as smaller monitors such as Usher, Spendor, or KEF. This is a versatile amplifier that adeptly balances resolution and listenability, and never strays too far to either end of the spectrum.

Music reproduction is an unusual hobby, as it is a convergence of both science and art. The design and construction of audio gear is firmly planted in the discipline of electrical engineering. Yet the music we play on our systems, and its subjective evaluation and grading is more akin to art and the appreciation of it. This creates a lot of friction in this hobby, as those at the extremes of either school of thought cannot see the merits of those on the other side of the pond. Compound this situation with the notion that people like to categorize and analyze situations to provide order and understanding to the world, and this is especially true in this hobby. So, we get truisms or stereotypes, that offer at best a limited understanding of how things can play out. So how does a hobbyist navigate this landscape and make sure they get honest value for the money they spend? That is a difficult question to answer, and my best response is to look to a designer or company that values and understands not only engineering principals, but also the amorphous concept of the beauty in music reproduction. There is a small contingent of audio designers that work in this manner, and Nelson Pass is certainly one that comes to mind. A quote from Nelson in a 2011 interview with Steven Stone brings this point into sharp relief.

First Watt F7 Amplifier

NP: "There is progress to be made, and the necessary tools are already on the table. From a strictly objective standpoint we are largely finished—adding more zeros to the usual distortion numbers isn't going to improve the sound very much. What remains is the need for clearer insight into subjective effects. Our brains are very much different from test equipment and are easily fooled by some phenomena and very sharp at discriminating others.  Reading the literature in cognitive psychology, it's clear that we don't know very much about musical perception. As a practical result, we have to emphasize critical listening with potential designs. The necessary tools for this are experienced ears and perseverance."

With the First Watt F7 amplifier you get a component that is grounded in solid engineering principals. There is no magic fairy dust tucked in the innards, no reinvention of the laws of physics, or new age treatments meant to move ordinary parts into a new realm of metaphysical consciousness. Yet what we do have is Mr. Pass's nimble and imaginative mind, which is capable of finding fresh applications of known principals to the acknowledged limitations of amplifier design. Couple this with the willingness to listen with a critical ear, and put in the work to continue the refinement process of the product. Nelson could have rested with the final iteration of the F5 circuit, and had a successful and well regarded product in the market place. Yet he chose to continue to push the envelope with the circuit, looking for the tools to tease higher levels of sound quality and increased compatibility with a wider range of speakers. This was accomplished by simplifying the circuit, paying close attention to the selection of parts used in the design, closely guarded assembly techniques, and the final twist of balancing the opposing forces of negative and positive current feedback in the circuit. The result is a 20/30 WPC stereo amplifier that measures respectably well, but can reproduce music in a natural manner, with a degree of authenticity that eludes so many audio components. This amplifier is not the most powerful design in its price bracket, its specifications are not head and shoulders above its competitors, the circuit is not an elegantly complex tour de force, and it is not a weighty beast that is a testament to an overbuilt chassis and power supply. If that is the kind of amplifier you desire, there is no shortage of products out there built in that manner. With the First Watt F7, as with all FW amplifiers, you get a component whose first and only purpose is to bring recorded music alive in a meaningful way for its owner. If you love the essence of music, I would urge you to find one of Nelson's creations and give it an in-depth evaluation. I think you will find the beauty and magic that has infused in these remarkable amplifiers, and everyone should experience the best that Nelson Pass has given to the audio community.

F7 Amplifier

Retail: $3000

First Watt

www.firstwatt.com

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