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Reviewer: Srajan Ebaen
Source: Zanden Audio Model 2000P/5000S; Ancient Audio Lektor Prime; AMR CD-77 [on review]
Preamp/Integrated: Supratek Cabernet Dual; Wyetech Labs Jade; ModWright SWL 9.0SE; Bel Canto PRe3; Melody HiFi I2A3; ModWright LS 36.5 [on review]; Almarro A318B [on review]
Amp: 2 x Audiosector Patek SE; First Watt F3; Yamamoto A-08S; Fi 2A3 monos w. JJ 2A3-40s
Speakers: Zu Audio Definition Pro with Gallo Ref 3 SA bass amp/crossover/EQ; Mark & Daniel Ruby with OmniHarmonizer; WLM Diva Monitor with Duo 12 passive subwoofer, Alto bass amp, Pre/Passive and Bass Controls; Gallo Acoustics Ref 3.1; DeVore Fidelity Nines [on review]; Mark & Daniel Maximus Monitor [on review]
Cables: Crystal Cable Ultra loom; Zanden Audio proprietary I²S cable; Crystal Cable Reference power cords; double cryo'd Acrolink with Furutech UK plug between wall and transformer
Stands: 2 x Grand Prix Audio Monaco Modular 4-tier
Powerline conditioning: 2 x Walker Audio Velocitor S fed from custom AudioSector 1.5KV Plitron step-down transformer with balanced power output option
Sundry accessories: GPA Formula Carbon/Kevlar shelf for transport; GPA Apex footers underneath stand, DAC and amp; Walker Audio Extreme SST on all connections; Walker Audio Vivid CD cleaner; Walker Audio Reference HDLs; Furutech RD-2 CD demagnetizer; Nanotech Nespa Pro
Room size: 16' w x 21' d x 9' h in short-wall setup, with openly adjoining 15' x 35' living room
Review Component Retail: $2,500
|The X Factor. In today's game, that's what we call gain. What comes in goes out, simply amplified or enlarged X times. If you strap together an active preamp and an amplifier -- the pervasive combo -- you put together two of those factors for X-squared multiplication. Therein lies the rub. Most people most of the time face seriously redundant gain with this scheme. That's why they need to throw most of it away again to not blow themselves and their neighbors out of the weeds. Throwing away gain is called attenuation. Not only is excessive amplification with subsequent deep attenuation silly and wasteful, it often creates noise especially with highly sensitive speakers. The X Factor doesn't just multiply signal. It simultaneously multiplies noise. The majority of audiophiles find themselves battling redundant amplification with severe attenuation. This raises the noise floor and throws out micro resolution. That much is well known though nowhere near as equally well practiced.
The in-series gain blocks of multi-stage amplification circuits and the paralleling of output devices necessary to achieve high X factors additionally tend to sacrifice subtlety and refinement. In other words, less gain can make for simpler circuits which can sound better. Hence the appeal of micro-power triode amps which suffer their very own limitations and restrictions. Because of that and jive on the salesfloor, it is barely appreciated just how much -- or rather, little -- gain is really required with regular sources and normal speakers. It's this question which Nelson Pass, America's preeminent designer of transistor amps, invites us to consider with his newest FirstWatt power amplifier. The F4 is that rare amp whose X factor is zero. It's minus 0.5dB in fact. Hence it doesn't really amplify. But it most certainly conditions the signal.
|That conditioning action makes the F4 a power buffer or Class A impedance converting amplifier - no voltage gain, no feedback. Its input impedance is 48/96Kohm single-ended/balanced-mono respectively, its output impedance about 0.2 ohms. The responsibility to swing voltage and create the desired SPLs remains|
|with your preamp. A standard active preamp should be perfectly sufficient to fill the usual digs with high sound pressures over standard 90dB speakers. Alas, your preamp still couldn't strap to your speakers directly even with a custom cable. Despite being equipped with perfectly adequate X factor to generate all the desired loudness, high output impedance and insufficient current delivery conspire against actually driving the speakers with a preamp. Enter the F4 follower amp with current -- not voltage -- gain.|
|"I've run into this before but occasionally you have to be hit over the head more than once. In this case, similarities of an SE tube with feedback and an SE Mosfet without but with the same THD figures brought it home clearly. I have to conclude that 1% or so THD at 1 watt is just not an acceptable figure, 2nd harmonic or not, feedback or not. Anyway, the 35-watt unit arrived and sounds much better in this regard. It's spec'd at 0.1% although I haven't had the chance to measure it. I'm looking forward to spending more time with it, particularly as I've been on a vinyl spending spree the last few months, and I have a lot of stuff to wade through.
The 7-watt amp does well with no load to speak of and when I hooked it up driving the F4s, voilà! Lots of gain and that tubey sound that is so prized. Now I've got them on a pair of PM6As (with Ticonal), biamping to Audax PR380 woofers in big TLs. And it's very good. So I've also got some other FirstWatt stuff cooking..."
|FirstWatt is obviously subsidized by Pass Labs. The latter affords Mr. Pass the leisure and economic freedom to run FirstWatt as a turnkey DIY venture rather than assembly-line operation. Creativity is king. Plus, Nelson is very hands-on through the Pass page at DIYAudio. A dedicated thread has been growing there ever since rumors of the F4's imminent release first surfaced. And unlike with earlier FirstWatt models, the full circuit schematic for the F4 has already been published. Folks try to roll their own and trip up on specific circuit junctures. The maestro -- or papa as some call him -- clearly delights in his Yoda role in that forum. He routinely doles out terse nuggets of wisdom to those whose demonstrate serious involvement and truly apply themselves. Anyone interested in F4 circuit specifics and possible variations thereof should log onto that particular thread. For the rest of us, Nelson hand-builds|
|a completed plug'n'play amp. All we really need to know is how it sounds - and whether our preamp will be up to driving our speakers with its own gain and voltage swing potential, the amp merely handling impedance conversion, current supply and buffering. Unless we insert a micro-power SET in-between. Which is where things could get really unconventional.|
In such a booster amp scenario, the F4's high input impedance won't load the driver amp which doesn't see the speakers but only the F4. This may require the insertion of load resistors: "It's my observation that transformer-coupled amps (or actually, any amplifier) has a 'sweet' load value at which they perform best. Usually it's at a higher value than the rated load but I have not encountered a case where it's no load at all. The 47K input impedance on the F4 would be considered no load for this purpose. In my testing here, I ended up with 22 ohms for the Nuera SET, which seemed the best compromise value for distortion and bandwidth. Of course it's dubious that buying a $700 SET and a $2500 follower makes better sense than buying a $3000 SET in the first place so I'm not really pushing that concept very heavily. More likely is that the real benefit with SET amps will come from bi-amping where an F4 is driving the bottom." In that case, the SET as tweeter/midrange amp is loaded by the speakers' upper terminals while tapping its signal in biwire fashion from the SET, the F4's unity gain means that no active crossover is required to level-balance between the speakers' upper and lower inputs. Additionally, it's likely that in such a scenario, much of a SET's sonic fingerprint transfers through the F4 to the speakers to minimize or eliminate the otherwise possible polarization between tubes on top, transistors on the bottom.
"By the way, when you are using the output of amplifiers to drive the input of an F4, it is important to establish what is ground on the source amplifier. On quite a few products the (-) output terminal is not ground. An ohm meter is particularly useful for establishing where the real ground is because this needs to attach to the RCA ground or XLR pin 1 on the F4 or else lots of current tends to flow needlessly." FirstWatt retailer Mark Sammut of Reno Hifi will assemble and sell the necessary spade-to-RCA custom cables for customers with booster or bi-amp applications. For conventional hookups from a preamp's outputs, the F4 of course needs no special interconnects at all and functions like any other amp - except for not being a FirstWatt but ZeroWatt amp. In case you didn't send Nelson happy birthday wishes through his forum, here's what you missed: "Thank you one and all. Your names will be placed on the Protected List and when my amplifiers take over, no harm will come to you."