progressively lower frequencies, finally gets excessive in the upper bass. We find the upper bass of this Fosgate Audionics amplifier to be too prominent and heavy in quantity. Moreover, its quality is disappointing. Upper bass transients sound soggy and poorly defined, without enough attack impact, and with too much overhang after the transient is over.
Moving next to the lower bass, matters get even worse, but in the opposite way. There simply isn't nearly enough low bass. Low bass demands the most power and muscle from a power amplifier. Yet, in spite of the high 200 watt-per-channel muscle of this amplifier, and in spite of its advanced power supply design, it didn't come close to providing that frightening or kick-in-the-stomach low bass impact that most other amplifiers can provide, to varying degrees (for example, the Fosgate Audionics was clearly bettered in low bass impact by the McCormack HT5, rated at merely 125 watts per channel, which in turn is bested by more expensive power amplifiers, such as McCormack's own larger amplifiers or the Plinius Odeon). Remember though that a power amplifier's bass capabilities are of no concern to you if you are using powered subwoofers, so in this case the Fosgate Audionics FAA 1000.5 would re-emerge as a very strong candidate and an excellent value for you.
We verified that the Fosgate Audionics FAA 1000.5 can indeed play very loud, and put out a lot of power, from the upper bass region upwards in frequency. So its 200 watt-per-channel rating, and the muscle provided by its quick acting power supply design, is clearly vindicated. Just don't expect that high power, muscle, and loudness to extend down into the low bass.
We were curious why the upper bass should be overly heavy and soggy, while the lower bass is weak. This type of bass sound was typical of early MOSFET power amplifiers, employing lateral MOSFETs, and was one strong reason why many people preferred power amplifiers with bipolar transistors as output devices. At that time, it was hypothesized that the higher output source impedance of MOSFETs, compared to bipolar transistors, was at least partly responsible for these bass anomalies. But nowadays, with amplifiers such as this Fosgate Audionics employing the more modern vertical MOSFETs, the bass quality should be better. We can only guess that perhaps the unique source-on-rail output MOSFET connection, used in this Fosgate Audionics amplifier to achieve other praiseworthy goals, has once again raised the output source impedance, perhaps just dynamically, or by lowering effective feedback - or that it has in some other similar way compromised the bass.
In other sonic aspects, this Fosgate Audionics amplifier fares very well, when set up in its optimum configuration. For example, stereo and surround imaging is very good, with very good width extending beyond the loudspeaker locations, and quite good ambience and depth (subject only to the apparent diminutions due to that upper midrange recession, as discussed above). The sound is admirably clean and pure, and in a musically natural way (as opposed to the clinically sterile cleanliness one hears from some solid state amplifiers).
So long as you have a powered subwoofer, the Fosgate Audionics FAA 1000.5 is an excellent sonic choice that will continue to please, with all the musical virtues of its classic JFET sound. It is an outstanding bargain for a 200 watt-per-channel multichannel amplifier, since many other quality home theater power amplifiers out there cost more, yet offer you only about half the power. The many technical innovations in the FAA 1000.5 really do pay off, giving you more power and better, more musical sound for less money, in a convenient and easy to handle package.
The Sound, Chapter 2: That Little Switch
You could easily miss it entirely. It's so small, and it's so hidden in a corner of the rear panel, that you might never notice it. More importantly, no other amplifier has such a switch, so you would never expect it or think to look for it. And, unless you're one of those rare OCD types who carefully studies an owner's manual from cover to cover, you would never get a clue that such a switch even existed. After all, who needs to study an owner's manual to set up a solid state power amplifier? You simply plug in all the connections, turn on the power switch, and listen, right? In this case, wrong.
That little innocuous switch, so unexpected and so well hidden, turns out to be crucial to the sound quality of this amplifier.
That little switch has three positions, labeled simply 4, 6, or 8 ohms. The owner's manual tells you briefly about this switch, and instructs you to simply set it to the number that corresponds to the impedance of the loudspeaker(s) you are connecting to each channel. You should read the owner's manual, as we did, to learn about this switch. And then you should ignore the owner's manual. Do what we tell you to do instead.
You see, the owner's manual failed to tell us exactly what this switch does in the amplifier circuit, and exactly why we should set it to different settings for different impedance loudspeakers. And that set off our alarm bells. After all, we know that tube amplifiers have different output transformer taps for optimum power transfer into different impedance loudspeakers, but who ever heard of selectable impedance taps or switches on a solid state amplifier without an output transformer? Moreover, solid state amplifiers naturally tend to enjoy higher power output capability into 4 ohm loads than into 8 ohm loads, so why would any switch adjustments need to be made? Our curiosity was aroused. We had to dig deep and investigate. As research scientists, we are by nature probers, investigators, analyzers. Unlike other reviewers, we don't simply accept surface appearances or surface sonics at face value. We are constantly digging beneath the surface, trying to discover why things sound the way they do, and then we explain our findings to you.
In our investigation here, we learned things about this little switch and about this amplifier that the manufacturer himself didn't even know. And now we'll share this special inside knowledge with you.
It turns out that different settings of this little switch have other side effects, because of what this switch does in the amplifier circuit. The most important side effect is the sound quality. This amplifier in fact sounds profoundly different at different switch settings, regardless of loudspeaker load, and even at quiet or moderate sound levels. That's a huge finding, for a switch that you might easily overlook because it's so small and hidden, and because you'd never even be expecting it to exist on a solid state amplifier. And that's a huge investigative finding, since the owner's manual does not warn you that this switch has any side effects, such as sound quality. In most cases, you will want to choose a switch setting that gives you the type of sound you prefer from this amplifier, at all volume levels, and thus you'll want to ignore the advice in the owner's manual about picking the switch setting that matches your loudspeaker impedance. Only in rare cases will the advice in the owner's manual be more pertinent (we'll discuss this below).
So, it's time now to address the first key question: how does this amplifier's sound change at different switch settings? Then we'll address the second key question: why does the sound change at different switch settings, and why does one setting sound the best?
When this little switch is set to 6, the amplifier's sound is as described above. If, however, you set it to 8, this amplifier changes its sound markedly. It becomes brighter, especially in the upper midrange, and all the upper spectral frequencies acquire a sharper delineation and articulation. That might all seem to be for the good, since (as discussed above) the upper midrange is tonally quite recessed (perhaps too much so), and the mid and upper trebles are somewhat defocused, when this little switch set to 6. However, other things go sonically wrong, when this little switch is set to 8. This amplifier loses its wonderfully natural liquidity in the midranges, and its upper frequencies acquire an artificial hard glare, similar to that in other solid state (especially bipolar) amplifiers. In sum, this Fosgate Audionics amplifier loses its special musical magic, and sounds like other conventional solid state bipolar amplifiers, when the little switch is set to 8. That's too high a price to pay, in our listening judgment (obviously, it's very easy for you to experiment with this little switch and decide for yourself which type of sound you prefer on your system).
When this little switch is set to 4, this amplifier again markedly changes its sonic personality, but this time in the opposite direction. The sound gets duller, the imaging width collapses (becomes literally narrower), and everything sounds closed in. When you listen to this amplifier playing with the switch set to our recommended 6 position, you hear the musicians arrayed on a wide open stage, with a wide open sense of airy space around them, and the music sounds alive and natural. Then, if you change the switch to the 4 position on the same piece of music, the same musicians suddenly sound as though they were playing in a confined closet instead of a wide open stage, and they also sound as if they were playing underneath a blanket instead of out in the open air. Another way of describing this would be to say that the musicians suddenly sound as though they were playing underwater, or better yet under a dark, heavy syrup. Obviously, we recommend that you don't even bother with the 4 position of this switch, except perhaps out of curiosity.
What the blazes is going on here? We had a lengthy, probing discussion with the engineers at Fosgate Audionics. They were not aware that the different settings of this switch changed this amplifier's sonic personality, so we were teaching them something new, something that we had discovered in our probing investigative analysis of this amplifier's sound. It turns out that this little switch does not in fact have much to do with somehow tailoring the amplifier to sound optimally best with different loudspeaker load impedances. So you can safely ignore the owner's manual instructions to set this little switch to match the impedance of your chosen loudspeaker load. You won't get better sound by obeying the owner's manual instruction to set this switch to match your loudspeaker. Instead, you should think of this switch as being a personality switch, that profoundly changes the amplifier's sonic personality, regardless of the loudspeaker impedance load you put on it. If you agree with our sonic assessment and follow our recommendations, you'll find that this Fosgate Audionics amplifier sounds its best when this little personality switch is set at 6. Only in rare special circumstances (discussed below) would you want to consider another setting of this switch.
So what then does this little switch actually do? What this little switch actually does is change the rails voltage on the output MOSFET devices. That is all it does. It does not in any way tailor the amplifier to somehow more optimally drive different impedance loads.
Why then does this little switch change the amplifier's sonic personality so profoundly? Here is our educated hypothesis, as we also explained it to the Fosgate Audionics engineers. We already know that, in every solid state power amplifier, setting the bias too low (for a leaner class AB) yields a more artificial solid state sound, with ugly artifacts like upper frequency glare. This is just what we heard in the 8 position of that little switch, which, as it turns out, supplies the highest rails voltage to the output devices. And we already know that, in every solid state amplifier, turning up the bias to a higher (richer) level cures these solid state artificialities, and makes the sound of all these amplifiers more musically natural. From all this observational data, we inferred the following logical hypothesis. What seems to count most, in setting class AB bias to a rich enough level to achieve natural musicality and avoid solid state artificiality and ugly glare, is the ratio of bias to rails voltage. Now, what does this ratio hypothesis mean for this Fosgate Audionics amplifier? In this amplifier, that little switch changes only the rails voltage, but leaves the class AB bias the same. This in turn would mean that, in this Fosgate Audionics amplifier, setting the rails voltage too high (as in the 8 position) for the given constant bias level would produce a ratio of bias to rails voltage which is too low, which is equivalent to setting the bias level too low (lean), thereby producing the artificiality and glare we in fact heard when that little switch was set to 8.
Another way of saying the same thing is that output devices, including any transistor or tube, have optimum linear operating points, where their characteristic amplifying curves are most linear, and where their sound is therefore the most musically natural and free from artificialities. Setting the bias too low (lean) for a given rails voltage makes the device deviate from its optimum operating point, and creates the ugly artificialities, probably by driving that device into nonlinear areas where it produces (in the case of solid state devices) expansive odd order distortion byproducts, which tend to sound artificially hard, with an ugly glare that also blocks or clogs natural, true musical information. And, likewise, setting the rails voltage too high for a given bias level does the same thing, changing the operating points away from the optimum ratio of bias level to rails voltage, and thus forcing the device into that same nonlinear region of its operating characteristic where it produces those ugly sounding artificialities.
What about the converse scenario? If the rails voltage is set too low, as it evidently is in the 4 position of that little switch, then the output devices are also forced to operating points that deviate from their most linear optimum, but this time in the other direction. The sonic result is that dull, closed in sound we heard, as though the musicians were suddenly playing under dark, heavy syrup. Setting the rails voltage too low, for a given bias level, makes that critical ratio of bias level to rails voltage too high, which according to our hypothesis would also not be good for the best sonics, since it forces the output devices away from their most linear operating points.
But this raises a curious side question. If setting the rails voltage too low is indeed equivalent to making our ratio too high, which in turn is equivalent to making the class AB bias too rich, this would also mean that, in some other amplifier with fixed rails voltage but alterable bias level, raising the bias level to be too rich would be similarly sonically deleterious. But haven't we always been taught that, in class AB amplifiers, raising the bias to be richer should always be sonically better, bringing us closer to class A? Evidently this conventional wisdom is not true. And it makes sense that it should not be true, if it takes the devices away from their optimum operating points for the most linear portion of their transfer characteristic curves. Interestingly, Steve McCormack has done research with his amplifiers (employing bipolar output devices) which confirms exactly this. Steve reports that he, working with a fixed rails voltage that is set for the best power capability (of the devices and their associated circuitry), then tunes the bias level by ear, to get the best sound, the most transparency combined with natural musicality. And here's the kicker. Steve reports that, if he sets the bias too high (rich) on his class AB output stage, thus making the ratio of bias level to rails voltage too high, then the sound gets dark and syrupy. That's exactly what we heard from this Fosgate Audionics amplifier when the rails voltage was set too low in the 4 position of that little switch, which similarly made that ratio too high. This kind of corroboration, from an independent researcher working with totally different devices (bipolars instead of MOSFETs), suggests that our hypothesis is right on the money.
Now, changing the rails voltage in this Fosgate Audionics amplifier, by changing the setting of that little switch, does have some merit, but only for very limited special circumstances. When this switch is set to 8, the rails voltage is set to its highest level, so this amplifier will be able to put out the most power before encountering voltage clipping, into any loudspeaker load. Voltage clipping, as you know, makes the loudest peaks suddenly sound a bit raspy, and is a polite way that any amplifier tells you to turn down the volume. And, as with most other solid state power amplifiers, if the loudspeaker load you happen to put on this amplifier is less than 8 ohms, this amplifier will be able to put out even more than its rated 200 watts per channel, before it encounters voltage clipping. Indeed, you can often expect that a solid state power amplifier's power output capability will double (in this case to 400 watts per channel) if you put a 4 ohm loudspeaker on it instead of an 8 ohm loudspeaker. And sometimes, if the power supply and the circuit's high current capabilities are up to the task, you can even expect a further doubling of output power capability (to 800 watts per channel here) if the loudspeaker load were halved again to 2 ohms (Krell amplifiers are famous for having the brute strength to do just this).
However, there's a fly in the ointment. This higher power capability into lower impedance loudspeaker loads makes heavy current demands upon the power amplifier, including its power supply and its output devices, which in turn also implies higher internal temperatures within the output devices and more excess heat for the heat fins to dissipate. Either a current/power overload (even a brief one) or a high temperature could be unhealthy for various components in the amplifier circuit, including the output devices. All solid state power amplifiers must incorporate current sensing (or power sensing) and temperature sensing protection circuitry, to momentarily or temporarily turn off the amplifier if safe operating parameters are exceeded, which they easily could be if there is too much current demand from trying to feed a low impedance loudspeaker load at a very high volume and power level. When these protection circuits activate, there is sometimes a nasty sounding pop, or a sudden ramp that could blow your tweeter with high frequency energy at full power. This sounds much uglier, and is potentially more dangerous, than the relatively polite warning rasp of voltage clipping. So, if you intend to feed a low impedance loudspeaker at very loud, high power levels, it is wise to take steps to preclude these protective circuits being triggered and activated. It would be better if you could somehow set up the amplifier to encounter voltage clipping before the protection circuits are activated. Then, the less obnoxious and less dangerous sound of voltage clipping would warn you that you are playing the amplifier too loud, and would warn you to back off, before you ever encountered protection circuit activation.
In the case of this Fosgate Audionics amplifier, there is also further concern about long term heat build up. This amplifier's class G operation allows high thermal efficiency, which means that for normal applications the small heat sinks inside this amplifier will suffice just fine. And remember that it is this high thermal efficiency and these small internal heat sinks which allow Fosgate Audionics to give you such a high powered amplifier at such a low price in such a convenient package. But these small internal heat sinks also mean that this amplifier is less flexibly adaptable to high current applications, i.e. to applications where you might play very loud levels into low impedance loudspeaker loads, which might raise the power levels above the rated 200 watts per channel, and might thus also raise the temperatures and heat generation too high for those small heat sinks to handle.
(Continued on page 80)