Pro or hi-fi amp, which one would you choose?

I have very limited experience with negative feedback, but I'll share it anyway. On my VAC 70/70, there is an adjustable negative feedback (either 0 or an assortment negative feedback, I think 6, 7, 8, 9 or something like that).

Anyway, the zero setting sounds WAY better. Negative feedback sounds dry and constricted, even after the volume is adjusted to compensate. The zero NFB has so much more life, is richer, fuller, so much more enjoyable. I would never use the NFB, and wonder why there is even a switch on the amp to increase it.

Dennis: It is possible that a circuit can become "overly dynamic" sounding due to non-linearities in gain characteristics. In other words, very small differences in input drive levels can be amplified at a much greater rate than levels just barely below that. This has to do with how linear the gain curve of the circuit is to begin with. Since most all circuits will have some type of "knee" in the curve, there is a point where more drive equals more output ( sometimes drastically so ) and then you start to hit the point of diminishing returns ( compression ).

To top off the potential for exaggerated dynamics, this can take place at various rates across the frequency band. Bass might REALLY tend to jump out as drive is increased whereas treble might not be amplified at the same rate. As such, it can change the entire presentation of a recording and a system.

Bare in mind that there are different ways to impliment negative feedback and not all are created equally. I would tend to agree that it should be used extremely sparingly though, if at all. Most all amps do have some type of feedback or "error correction" circuitry built into them though. This is even more true for professional designs as they tend to face harsher environments in terms of the load presented to them, the volume required and drive conditions.

Like i said, the "average" commercial / pro sound amp is a very different beast from the "average" hi-end amp. And for good reason. Sean
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Sean, How is it possible to have measureable distortion at 2-3khz if the amp's response can go up to 20khz? You know that we hardly ever hear 16khz. I understand that a musical program around 1-3khz will have harmonics in the upper-frequency. Having odd harmonics in the upper-frequency is not a good because it can sound harsh, lifeless, and colored. In contrast, even harmonics is what makes the presentation more musical and life-like. An oscilloscope is not really use for distortion but it can be use to analyze the wave form. If you want to find the THD, SID, or TIM, you need a RTA and a Distortion Analyzer. Of course, your ears are your main priority. BTW, I'm not against you or any thing, I just disagree with some of your answers so don't take it personal.

Sean, have you heard some type of a transformer placed between high output impedance amp and speaker. Audio Asylum had a thread on this maybe 2 weeks ago. Looked like a good way to improve damping factor. Any thoughts?
I will try to find the thread but it may not be easy.
Also, I tried and tried to find your comments about line arrays but couldn't. You had mentioned some inherent problems with the design - don't know if it was imaging, comb filtering, etc. but could you describe again. Thanks!

Highend64: An amplifier that is bandwidth limited to just above 20 KHz will show "rounding" of the leading edge of a square wave at appr 2 KHz. That is a distortion as far as i'm concerned as it is not replicating the input signal. Passing a sine wave can be "gravy" but square waves are much faster, require greater linearity and are closer to the dynamic impulses that we call "music".

Cdc: Line arrays are like any other speaker i.e. they have some advantages and some disadvantages. If done correctly, they can have some very strong advantages such as increased power handling, lower distortion due to reduced excursion, high spl capacity, sustained spl levels at greater distances, etc... Obviously, this design works best if not sitting right on top of the speakers.

If i can ever get my act together, i've got a very large line array that i'm working on for a friend's system. He is brutal on audio equipment to say the least, so after thinking about it, i decided on a line array for the above reasons. The mains ( this is a combo 2 channel / HT system ) will consist of thirty six tweeters, eighteen 4" mid-woofers and eight 12" woofers per side. This is a "budget" project in terms of the drivers selected, but i'm trying to do the best i can for him and his specific system needs and give him something that sounds pretty decent, will hold up to the chronic abuse that he dishes out and can literally shake the house on demand.

As such, i've had to do some studying on the subject and am learning more as i go along. One thing is for sure though, crossovers need to be done actively OR passively at a very sharp slope rate if you want to avoid comb filter based problems. I've been able to learn quite a bit about this subject courtesy of the "speaker nuts" on Madisound and their own personal websites that they have provided links to.

If i'm lucky, i may be able to get these speakers done in a few months. As you might guess, it is going to be VERY labor intensive in terms of just cutting all of the holes let alone installing and wiring all of the drivers. To top it off, i've got to do a center and two surrounds for him too. Needless to say, the other speakers will NOT be anywhere near as big as the mains but they will all make use of identical multiple drivers in order to maintain consisting "voicing" within the system.

As far as using a transformer between an amp and speakers, i don't like the idea unless it is a necessity. I personally prefer active multi-amping as this allows one to bypass passive components between the amp and individual speaker drivers. It has been my experience that "direct drive" sounds far more natural and dynamic than what you can get out of even the very best passive crossovers. Sean
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