amplitude portions of the audio signal while the second side uses an NPN). But this imperfect balance is still doubtless an improvement over the conventional asymmetric configuration. And pragmatically this balance probably works pretty well to a first approximation, since within each half the two dissimilar devices in their series ladder probably effectively share the rails voltage in proportion to their voltage gain, so that their proportional contribution to the final output signal differs for the two push-pull halves, in such a way as to achieve good overall symmetrical balance for the two push-pull halves. Remember of course that this ingenious innovation takes effect only when all four output devices are called into action, which is when the audio signal demands power between 50 and 200 watts, i.e. when the class C upper devices are brought into action. Which is why, uniquely in this amplifier, class G can sound so good, even sounding better rather than worse at loud levels when the class C devices are brought into play.
A second innovative feature of the FAA 1000.5 centers around and derives from the unique way that the output MOSFET devices are connected. According to Fosgate Audionics' technical literature, they connect the source of the MOSFET to the high voltage rail, which offers about ten times the power gain of the voltage follower connection conventionally used for output MOSFETs. The intended advantage of having much higher gain than usual in the output stage is that all earlier stages of the power amplifier can be made much simpler, and that these earlier stages do not have to work as hard to drive the inputs of the output MOSFET devices. This can improve the amplifier's overall sonic fidelity, firstly because simpler circuitry can be inherently more transparent, and secondly because better sounding devices with less drive capability can be employed in the earlier stages of this amplifier (whereas such devices would not have enough drive capability to be employed in a conventional MOSFET power amplifier topology). This Trans-Ana design concept does indeed seem to pay off sonically. The FAA 1000.5 uses JFETs instead of the usual bipolar transistors for the input differential amplifier stage, and the musical signature of these high quality low level JFETs shines through the whole sound of the amplifier, just as intended by the Trans-Ana topology. Indeed, heard at its best, the sound of this Fosgate Audionics power amplifier is reminiscent of some of the finest high end JFET preamplifiers of yore, such as the Infinity FET and the Spatial preamplifiers.
The driver stage of this power amplifier employs bipolar transistors, but because they do not have to work hard to drive the output MOSFETs, they do not impose the typical bipolar sound of sterility, strain, or glare on the audio signal, again when the FAA 1000.5 is configured to sound its best.
The output MOSFETs themselves are the latest vertical MOSFET types, which are a vast improvement over the lateral MOSFET output devices which were the only choice for early MOSFET power amplifiers in years past. These vertical MOSFETs are also said to have much lower resistance than earlier lateral MOSFETs, which means they dissipate less heat internally under high power loads, which in turn means that the heat sink requirements are minimized for such a high power amplifier, with the consequent benefits discussed above.
Our only question about the Trans-Ana's uniquely different source-on-rail connection of the output MOSFETs concerns output source impedance. Early MOSFET power amplifiers had somewhat high output source impedance, and this was probably at least partly responsible for the soggy quality of their low bass, in contrast to the tight bass control and solid impact of competing amplifiers with bipolar transistor output devices, which can have a very low output source impedance. The low bass of the 1000.5 still retains this soggy quality, in spite of the lower series resistance of the new vertical MOSFETs employed, so we wonder if the source-on-rail connection mode gives away some of the beneficial low source impedance that could otherwise be realized from vertical MOSFETs as output devices.
A third innovative feature of the Fosgate Audionics FAA 1000.5 revolves around its power supply. Unlike conventional power supplies in most power amplifiers, the power supply in this amplifier is a switching type of power supply. A switching power supply charges the DC reservoir capacitors many, many times each second, instead of merely 120 times per second. The Fosgate Audionics literature states that their implementation of a switching power supply in this amplifier actually charges the reservoir capacitors at a staggering rate of 100,000 times per second.
This much higher recharge rate has a number of advantages for you. The first set of advantages pertains again to cost, size, and weight of the product. The power transformer for a switching power supply can legitimately be made much smaller, lighter, and less expensive than the massive power transformer conventionally required for a power amplifier putting out 5 times 200 watts, or a total of 1000 watts. Likewise, the bank of reservoir capacitors can be made much smaller, lighter, and less expensive. They don't have to store as much energy for nearly as long, because they are refreshed with new energy 100,000 times per second instead of merely 120 times per second.
The second set of advantages pertains to sonic quality. With the reservoir capacitors being refreshed much more frequently, there is less sag in all the power supply voltages fed to all the various amplifier stages, especially under the high power demands of loud audio signals. This means that all stages see more constant voltages. Thus they remain closer to their ideal operating points (for better linearity). Also, you can get cleaner sound because there is less modulation distortion. With conventional power supplies, the draining demands of say a loud bass note in the audio signal can modulate the power supply voltages for various stages, which in turn can modulate the simultaneous treble information also contained within the audio signal, thus producing a garbled kind of modulation distortion for this treble information. But with this switching power supply, the voltages can stay more constant, even in the face of heavy draining demands by loud bass notes, so the simultaneous treble information stays cleaner, without suffering the degrading sonic effects of modulation distortion via the power supply.
This desirable power supply constancy is further helped in the FAA 1000.5 by the incorporation of regulation for the switching power supply. This regulation actually consists of a separate feedback-controlled amplifier in the power supply. It senses when the power supply voltage has strayed from its optimum, and quickly acts to correct it. Since the power supply is a fast switching type power supply, this correction can be actually implemented very quickly, perhaps within the next burst of energy to the reservoir capacitors, coming just 1/100,000 of a second later.
The switching power supply design in the FAA holds forth the promise of yet another set of advantages, which pertain to immunity from fluctuations in your powerline, ranging from slowly varying voltage levels to high frequency trash. In effect, this amplifier's power supply acts as a powerline conditioner for the amplifier's circuitry. And, because the power supply contains its own feedback-controlled amplifier, it can correct for and provide immunity from such powerline variations, be they low or high in frequency.
Furthermore, because this power supply design senses what should be the correct output voltage from the power supply, and can correct for it so fast and so often, at a 100,000 Hz rate (which comfortably exceeds the 20,000 Hz audio bandwidth), it should also in theory provide excellent immunity from the source inductance of your powerline (including the power cord). With conventional power supplies, this powerline and power cord source inductance can impede the amplifier's ability to refresh its reservoir capacitors quickly enough to keep up with audio's highest frequencies, and thus it can audibly soften and blur audio's higher frequencies (strong treble demands can drain the power supply capacitors at a rate of up to 20,000 times per second, while a conventional power supply can only refresh the capacitors at a much slower rate of 120 times per second). But the power supply of this Fosgate Audionics amplifier can sense and correct for energy deficiencies at a 100,000 times per second rate, far faster than the fastest rate (20,000 times per second) that even the highest frequency treble demands can drain it. So any inductance in the powerline or power cord source should be easily compensated for and corrected over the five cycles of 100,000 Hz refill bursts that are available before the next 20,000 Hz demand comes along. However, in our testing we found in practice that this Fosgate Audionics amplifier was just as sonically sensitive to various power cords as other high quality power amplifiers are (more discussion below).
A switching type of power supply does have one potential drawback. It generates high frequency garbage from its internal switching (in this case, at 100,000 Hz and at harmonics beyond that). This high frequency garbage could interfere with other audio (and perhaps video) circuits in your system. It could cause high frequency strain, overload, or intermodulation distortion in very wide bandwidth circuits elsewhere in your system, and it could also cause interference, noise, and intermodulation distortion in other circuits (especially digital circuits) that also do high frequency switching. This unwanted interference could travel to other circuits in your system through the powerline, or through the air. This Fosgate Audionics amplifier contains input filtering, including series inductors, to prevent noise of its own switching power supply from feeding back into the powerline, from where it could enter and interfere with other circuits in your other audio and video components. This input filtering also attenuates any high frequency hash that might already be in your powerline, to prevent it from interfering with the desired operation of the sensing and correcting circuits within the switching power supply of the FAA 1000.5.
As to the possibility of radiated high frequency interference escaping the chassis of this Fosgate Audionics amplifier and traveling through the air, we did not have the opportunity to specifically test how well shielded the switching power supply is in this amplifier, but we did not run into any problems with the associated equipment we tried it with. It is conceivable that there is some audio or video component out there that would not kindly tolerate being placed right next to this Fosgate Audionics amplifier. But we don't expect that you would experience any problems. In any case, it is always wise to place power amplifiers of any kind at a reasonable distance from sensitive components handling low signal levels, if only because of radiated heat and radiated magnetic fields that emanate from all power amplifiers, so it would be prudent to continue this wise practice with this Fosgate Audionics amplifier.
There are other technical features of the Fosgate Audionics FAA 1000.5 also worthy of your attention, and you can read about them in the Technical References section of the owner's manual, available on the web at www.fosgateaudionics.com.
The Sound, Chapter 1
Fair warning: this is going to be a long odyssey, with very unexpected twists and turns. So let's start easy.
The Fosgate Audionics FAA 1000.5 sounds markedly different in different configurations (to be explained later). So we'll start by describing its sound in the configuration that we think sounds best overall. This configuration uses the factory supplied generic power cord, and sets a little switch on the rear panel to 6 (don't ask, yet).
This Fosgate Audionics amplifier features what we would call the classic JFET sound. It's very musical, very enjoyable, very relaxing to listen to. This sound is similar to tube sound, and the early high end JFET preamplifiers of past years, including the Infinity JFET and the Spatial preamplifiers, even boasted of how well they had captured the genie of tube sound in a solid state bottle. But there are subtle sonic differences between JFET sound and tube sound, so the JFET sound of this Fosgate Audionics amplifier does not completely mimic tube sound.
Starting at the upper end of the audio spectrum, the mid and upper trebles are soft and relaxed. This has some pleasantly euphonic consequences, such as strings sounding silvery sweet. But it also has some less desirable consequences, such as treble details in this region sounding defocused, blurred, or smeared together, without enough articulation or individuation. We would judge this amplifier's sonics in this spectral region to be adequate, and perhaps even desirably euphonic, for film soundtracks, but marginal if you also use this amplifier in a music system and want to hear mid and upper treble detail with the best possible articulation and clarity.
Then, in the lower treble, classic JFET sound, and this amplifier's sound as well, goes in the opposite direction, and indeed slightly overcompensates. The lower treble is slightly overemphasized in quantity, is slightly hard in quality, and is very articulate. If you are just listening casually, it might seem that this prominent and highly articulate lower treble compensates and makes up for the subdued soft defocus of the mid and upper treble, giving a pleasant overall sound to the treble regions. But if you listen attentively, you might find that the trebles are slightly skewed within themselves, with the lower treble being a little too prominent in quantity and a little too hard in quality, whereas the mid and upper trebles are the opposite, a little too subdued and soft. This skewing is more apparent on some program material, e.g. trumpets and vocal sibilants. These colorations are really only slight in degree, but of course the slight coloration in one treble region is made more obvious by the fact that the very next, adjacent spectral region has the opposite coloration, so one stands out like a sore thumb relative to the other.
The midranges of the FAA 1000.5 have a very musical, beautifully liquid quality to them, much like tube sound. This is the most striking sonic feature of classic JFET sound, and of this amplifier's sound. You hear it instantly, and you continue to hear it on all kinds of music, and all kinds of film soundtrack material. It is immensely enjoyable, and worth its weight in gold. It is the most valuable tubelike aspect of this amplifier's sound. If midrange liquidity means a lot to you, and you value this tubelike midrange quality above all else but want the convenience of a solid state amplifier, then this alone might be enough to make this Fosgate Audionics FAA 1000.5 the power amplifier of choice for you. If on the other hand you do enjoy midrange liquidity but also want other sonic virtues, then you should still personally audition this amplifier, listen for all the sonic pros and cons we're describing here, and balance the pros and cons based on your personal preferences and priorities, to arrive at a purchasing decision.
We've just discussed the liquid quality of the midranges. But what about the quantity of the midranges? In other words, what is this amplifier's tonal balance through the midranges? Again, this amplifier follows the pattern of classic JFET sound. The upper midrange region is very subdued, dark, and recessed. And it seems all the more so because the immediately adjacent spectral region of the lower treble is slightly overemphasized. The underemphasized quantity of the upper midrange is of course a tonal coloration, and is has several consequences, some euphonic and charming, others somewhat deleterious.
First, some euphonic consequences of this upper midrange tonal balance recession. It puts music or stage action at more of an apparent distance, which can make it more relaxing to listen to, and can also compensate for typically too closely miked recordings and soundtracks, thus putting the sonic events at a more natural sounding distance. It can also compensate for some loudspeaker brands that have too much energy in the midrange (you know who you are), or for loudspeaker drivers that often exhibit nasty and bright sounding cone breakup in the upper midrange. And it can compensate for electronic ills earlier in the chain, such as the upper midrange glare often added by the IC chips in the recording chain for film soundtracks, or by the IC chips in your CD or DVD player. This upper midrange recession also enhances the apparent blackness or silence of the background, and improves apparent intertransient silence, letting you more easily hear the music in other spectral regions.
Having the sound at a greater apparent distance enhances the apparent depth of the stereo or surround image, between you and the music, but conversely it decreases the apparent depth of the stage and ambient space within the ensemble and behind the ensemble (that's in part because hall wall reflections and reverberation, vital to hearing directional ambience and depth cues, contain lots of information in the midrange and upper midrange, where our human hearing is most sensitive, so subduing these spectral regions will also subdue this information).
One of the deleterious effects of this upper midrange recession might (depending on your taste and preferences) be the fact that music and soundtrack effects lose some of their dynamic, up front immediacy and natural brilliance. There's also a loss of apparent transparency, because you simply don't hear as much of the abundant information in the upper midrange when it is so tonally subdued. The native true transparency of this Fosgate Audionics amplifier is quite good (though not quite as revealing of music and soundtrack information as some competing amplifiers, e.g. the McCormack DNA-HT5), but the Fosgate Audionics' apparent transparency in the upper midrange suffers even more in comparison with competing amplifiers, because these other amplifiers are more tonally neutral and less recessed in the upper midrange, so they naturally reveal information more prominently in this spectral region.
As we proceed lower in frequency, from the lower midrange down through the upper bass, the tonal balance of this Fosgate Audionics amplifier gets progressively richer. We find this richness to be very musical and euphonic, down through the warmth region. It gives musical instruments and human voices wonderful body and weight. The wooden sounding boards and large cavities of pianos, double basses, guitars, etc. acquire a very natural prominence, which is very enjoyable and natural contrast to the typical solid state bipolar transistor sound, wherein these lower frequencies are too lean, making the overall sound too sterile and bright. This rich quantity of lower frequencies also combines wonderfully with the natural sounding liquid quality that this Fosgate Audionics amplifier bestows upon the midranges. Again, all this is typical of classic JFET sound.
However, in our judgment, this progressively increasing richness of the tonal balance, at
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