How Much Difference Does a More Powerful Amp Make?

"The other downside of powerful amps is that they feature many output devices (by "output device", I mean output transistors in the case of solid-state amps and output tubes in the case of tube amps). All of those devices muck up the sound in systems that are otherwise high resolution because, among other reasons, it is very difficult to match output device pairs, every device adds noise, and they make the circuit more complex."

Great sounding Coda Technologies S5, 50W/8ohm class A (no global feedback) has 60 output devices. As for noise it is exceptionally quiet with S/N=120dB.

State of the art Atmasphere MA-3 (also no global feedback) amplifier uses even more output devices (about 40 tubes per channel).

In both cases a lot of output devices doesn't "muck up the sound" but makes it better (at the expense of complexity).

Like someone stated earlier they make a difference for inefficient speakers with low impedence drops, they also make a difference with many multi driver speakers with complex xovers as the xovers are known to eat up as much as half the power before ever reaching the drivers

Metman - that's true, but I would rather have lower power amp that can perfectly drive very low complex loads. 50W/8ohm Coda S5, I mentioned, can output 200W at 2 ohm and according to Stereophile test can even drive 0.47ohm.

Half of the power loss in crossover, that you mentioned, is only 22% of loudness loss.

06-22-11: Raquel
......
First, it is very difficult to control a high-powered circuit without global feedback and virtually every high-powered amplifier therefore uses it. .....

Raquel, I believe that this is *not* a true statement. I think that you are confusing power amplifier gain with power amplifier (output) wattage. They are different. You need global negative feedback when you have many cascaded gain stages (wherein the power amp has a lot of output to input voltage gain) so that you can keep the entire design stable (oscillation free), lower in distortion & lower in overall noise.
To design a high wattage power amp you need to design in the correct transformer size, the correct number of output devices to handle the output current, the correct size & quantity of power supply caps to handle the charge being delivered to the load. This can be done using minimal number of power amplifier gain stages (for example, Pass does this often with just 2 gain stages hence he can avoid global negative feedback & still deliver to the market a X600 beast of an amplifier).

Also, you use the term "high-powered circuit". what, according to you, is a "high-powered circuit"?? you probably mean 'high wattage circuit'? Might be better to use the correct terminology to avoid ambiguity esp. if you are sharing some of your technical views on a subject. Just FYI.

Bombaywalla:

I was trying to keep it simple to make a point. Most amps, powerful or not, have anywhere from three to five gain stages (very few have two), and we all know that using global feedback with such designs makes the amp builder's job a lot easier. I do not agree that feedback ultimately lowers distortion - it changes the types of distortions to those that are different from the harmonics of live instruments (which is why it screws things up so much). Nelson Pass wrote the following:

"We have seen that nonlinear distortion becomes larger and more complex depending on the nonlinear characteristic of the stages, the number of cascaded stages, and the number of spectral elements in the music.

Negative feedback can reduce the total quantity of distortion, but it adds new components on its own, and tempts the designer to use more cascaded gain stages in search of better numbers, accompanied by greater feedback frequency stability issues. The resulting complexity creates distortion which is unlike the simple harmonics associated with musical instruments, and we see that these complex waves can gather to create the occasional tsunami of distortion, peaking at values far above those imagined by the distortion specifications."

Source: www.passdiy.com/pdf/distortion_feedback.pdf

PS - Pass makes a no-global-feedback amp that is even more powerful than the X600 monos: the X-1000, which also has only two gain stages.

Kijanski:

I really respect Ralph Karsten's (Atma-Sphere's) designs, and I have no doubt that his amp with 40 tubes is really good for what it is, but this is precisely the type of amp that will be noisy ("mucky"!) compared to an amp having, say, 4 tubes. 40 tubes?! Or 40 transistors? Have you ever heard an amp with that many tubes or transistors in a really resolving system? More importantly, have you heard an amp with only a small handful of tubes or transistors in a really resolving system? Come on.