I have always wanted to make my own amp that was compareable to a macintosh amp for a fraction of the price but what exactly makes it better?
Ultimately I think amplifier quality is in most cases just another case of marketing triumphing over engineering. But there are lots of engineering factors which affect quality.
1. How much was it derated for operating at its worst case output power? This impacts reliability and operating life. Commercial designs tend to be much better than consumer designs in this respect which is expected.
2. Is it a simple or complex class-AB design? At high frequencies the former might produce 0.1% THD while the later produces 0.001% or better. I am always struck by how simple class-AB designs literally duplicate the simplified schematic for an early 3 stage operational amplifier.
3. How does it perform (or fail) under adverse operating conditions like a 2 ohms load or output short?
4. How well does it recover from clipping? Tube amplifiers have a natural advantage here do to their softer saturation characteristics but some solid state designs are truly horrible in this regard for reasons having nothing to do with saturation.
5. Does it protect the speakers against amplifier failure?
Bob Cordell's book Designing Audio Power Amplifiers gives a great overview of simple versus complex designs and the attention to detail necessary for a high quality design.
The thing which puzzles me is why poor designs are produced when most of the cost is in the output transistors and power supply that could be the same in a low or high quality design. This might simply be do to diminishing returns, poor source material, and low customer expectations.
First of all, there are no legal standards against which audio amps are measured.
In the US there has been since 1974:
https://www.ftc.gov/enforcement/rules/rulemaking-regulatory-reform-proceedings/amplifier-ruleNowadays they make Class-D amplifiers with a single chip (digial input) 100+W output and <0.01% THD+N. I dont even understand why there are amplifiers anymore. Seems so pointless. I believe that good quality active speakers are the way to go.
That level of distortion is typical for a good but simple class-AB design.
Yep. Class D has come on in leaps and bounds over the last decade. All the old class A and AB stuff is pretty much obsolete.
Modern MOSFETs mean class D amps can be amazingly efficient. Tiny sub-$10 chips can power big powerful systems with almost zero THD.
eg. http://www.ti.com/product/TPA3255/datasheet
So yeah, amplifier problem is solved. Look at speakers and room acoustics instead.
I notice that TI leaves intermodulation out of their datasheet and how does it respond to clipping? The other specifications do not strike me as particularly outstanding compared to a complex class-AB design. The efficiency is nice of course.
I agree that the amplifier problem is solved but only in the sense that the speaker problem is solved. In both cases most consumer examples are mediocre but with the
loudness wars, that is good enough.
It is exactly on this principle (massive bass boom) that loudspeakers type bass reflex are based.
They are tuned to the resonance frequency to boost these bass and recover them to add to the sound from the front of the speaker membrane.
If they are tuned properly, then the result is not "massive bass boom" but extended low frequency response, a second order low frequency roll off, and lower impedance at resonance. The last is important because minimizing the cone movement minimizes intermodulation distortion which otherwise makes deep base sound boomy and indistinct. Some people of course like that sound but I place them into the same class of people who like the loud hiss from harmonic distortion, indistinct vocals, and excessive compression from the loudness wars.
In a practical setting, the lower intermodulation distortion means being able to turn the volume up to shake the room and contents without sounding loud.
They're also usually made of chipboard/mdf instead of fancy wood.
It's not the manufacturers being cheapskates, those "woods" resonate less than the real thing.
But they are rarely heavy enough. On the other hand, most consumers would prefer speakers they can lift easily. I am somewhat amused when I find old bookshelf speakers which weight more than modern but cheap floor speakers.