What is the advantage of ultra bandwidth?

Bingo! Greg and Sean have said it all. Cheers,

Ummm... I have a different viewpoint.............................

Anyhow, rise time does not mean that the amp in question will have more or less ringing than another amp with slower rise time. It is perfectly possible to have fabulous rise time and be horribly under damped with lots of very fast ringing - in fact I see this all the time on some scary fast opamps, which is one reason that they often sound like dog poop when used in audio gear.

Rise time and slew rate tend to be closely coupled.

Along with that both are then related to bandwidth.

Wide bandwidth amps like the Spectrals can have benefits. However they also can have deficits. One of the biggest deficits is that they will amplify within the AM broadcast band (550kHz - 1700kHz.). This means that there is the *potential* to send significant out of band signal through the amp/preamp combo and have it amplified substantially. In essence this is almost like having a parasitic present in the amplifier - it could potentially effect the way things sound rather dramatically.

Secondly, wide bandwidth amps can become a bit unstable when hit with the "wrong" load and the "wrong" frequency input to excite them. (I'm not saying that this happens with the Spectrals, just that it is a consideration in wide bandwidth designs)

There is some question as to the benefit of a 1 Mhz. bandwidth in terms of the signal within the nominal audio range, especially given the RFI issue. My product, the Symphony No.1 amplifier is spec'd to about 250kHz. at about 75V/us. I think this is more than sufficient, and avoids getting significant gain in the broadcast band.

One of the potential advantages of wide bandwidth is the potential to do "justice" to a square wave. But, this is a false goal, since *nothing* that we have today as a signal source does much better than a ratty square wave! In practice, regardless of the bandwidth I have found that the damping (not damping factor) of the amp design is far more important to the resulting sound than is anything else!

In fact, I can "tailor" the sound of most amps using this criterion alone. Conversely, it is pretty accurate to predict the sound of an amp based upon a look at the square wave response on a bench! (especially into a reactive load)

So, the ultimate determinant of what you hear from a Spectral or other amp PROBABLY has more to do with factors other than bandwidth, frequency response, slew rate or rise time than you might imagine. Indeed, I'm pretty confident that I can mod a Spectral without changing those specs very much at all and give you a *completely* different subjective sound, and probably without any significant topology change!

So, what I'm saying is that a very large component to any given amps sound is the *implementation* details, not the raw specs. (Of course there are some amps that are not going to sound good no matter what you do, but that's a different topic)

_-_-bear

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Thanks for your responses! I was out of town and just got back. Any thoughts on high frequency interference or distortion distorting audible frequency signals?

Robert, i think that Bear touched base on that subject. Going "mega-bandwidth" CAN open up a whole new can of worms if your not careful.

On the other hand, one of the gentleman that was first responsible for "super-fast, wide-bandwidth" designs ( Dave Spiegel ) stated that his findings show that slower designs of limited bandwidth are more susceptible to RFI based problems. As to who is "right" is up to whom you want to believe.

Other than that, I basically agree with what Bear has to say. I will also add that what one considers to be "wide bandwidth" is obviously a subjective thing. To my way of thinking, anything that can reproduce 100+ KHz while remaining linear is "wide bandwidth". I say this because most components DON'T make it out this far or do it "gracefully". I will also say that i think that active components "should" be able to make it out past 200+ KHz for best results. The slew rate that Bear quotes of 75 V/uS is quite reasonable with most EE's and audio engineers thinking that 50 V/uS is sufficient. My personal "preference" is that it should be as fast as possible.

As to his comments about fast rise / fall times NOT equating to "good performance" due to severe ringing and lack of damping, i don't doubt his findings in the least. As one might assume, there are always "oddballs" that tend to break certain "rules" while basically conforming to others. My comments were only meant to be a "generalization" at best and i hope that they were taken as such.

Speaking of integrated circuits, Stereophile had an article a while back pertaining to the differences in IC's ( Integrated Circuits ) from manufacturer to manufacturer. Even though they were supposed to be built to the same spec and carried the same part number, there were differences of appr 70 dB's from one brand to another in terms of noise floor !!!

Obviously, some parts / components are WAY better regardless of published specs. As such, one could see how substituting just a few raw parts could drastically alter the "sonic flavor" of a component. The fact that i've experienced such changes first hand leads me to agree with such a logical deduction and Bear's statements. After all, if changing passive parts can make such a difference, why shouldn't changing active parts do even more ??? Sean
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