Amplifiers and power: the more I learn, the less I know.

[lunchmoney]

The ONE thing I thought I understood about amplifiers is that more power is a good thing...

For example, within the realm of more-or-less trustworthy AVR brands (Yamaha, Onkyo, Denon, etc), I believed that the heavier amp with the higher power rating would be better, that more power meant cleaner sound, and not just at ear-splitting volumes. Many many people believe this, and I've read many posts from VERY knowledgeable people, who have explained in detail, why this is one of the few solid truths in audio.

But it seems that, as with ALL things in this hobby, the answer is "not so fast". Some recent posts by equally knowledgeable folk on this forum suggest that it's a lot more complicated than that... lots of talk about "cheap watts", power supplies that aren't up to the task, number of amp sections, and of course specs that can't be trusted.

And multi-thousand dollar amps delivering only 50 watts per channel, that maybe aren't snake oil. This one really boggles my mind.

I've started a new thread here because I want to read a really focused on discussion on:

AMPLIFIERS: Is more power a good thing? Why or why not? What are the caveats? How can you know if the new higher-powered amp you're about to buy is going to make an improvement? Is ANYTHING sacred in this hobby?!

[lunchmoney]

Re: Amplifiers and power: the more I learn, the less I know.

Allow me to kick it off with a recent discussion between myself and Deward Hastings

If an amp is generating significantly more power than another (measured and verified), doesn't that represent a meaningful advantage?

Doesn't the one with more power A. exhibit less distortion at any given volume, since it's not working as hard, and B. handle dramatic transients a lot better? I assume this is why my new receiver sounds so much better (or does it?:rolleyes.

Maybe, no and no. It doesn't work that way. All an amplifier with a higher power rating gives you is . . . more power . . . which brings no benefit if you don't need it (efficient drivers, lower listening levels). Distortion (except for noise) is measured (and heard) as a percentage of the applied signal . . . when measuring distortion at one Watt the power capability of the amplifier makes no difference. And if at your "normal" listening level 0dBfs from the source produces 20 watts at the amp output then a 50 Watt amp and a 500 Watt amp will handle "dynamic transients" the same. If you "turn it up", or get less efficient speakers, that might change . . . and that "50 Watt" power supply might not hold up under sustained load, but that's a different issue. As with cars, where a "big block" V8 has obvious advantage towing a boat trailer but gains you nothing driving to the store for half a gallon of milk.

There are other considerations that might favor a "bigger" amplifier . . . paralleled output stages tend to lower crossover distortion, for example, and the often larger design budget allows for better front ends too. But "bigger" is no guarantee of "better" . . . and there comes a point at which there is no such thing anyway . . . there are plenty of amps that do "sound alike", having reached the level where further "improvement" produces no better sound. A LM3886 is not going to be sufficient to drive a big subwoofer or a 2 ohm load, but any amp that sounds different from a 3886 at 20 Watts peak into 8 ohms is defective, either broken or a bad design regardless what it costs. Similarly if you need more power or to drive low impedance get an old Adcom gfa565 . . . nothing sounds better (although several of the $5,000 amps sound just as good, as do some of the newer, and less expensive, class D amps).

There are plenty of "good" amps out there, amps which if properly matched to the load sound indistinguishable (one of the many advantages of active crossovers is that they make "proper load matching" easy). There are also some dogs, which in an otherwise clean system will readily show their flaws to a critical ear. "Amplifiers all sound alike" is simply wrong, as is "amplifiers all sound different". Some do . . . some don't.

Regarding A/B testing (which yes, I have done) . . . it's not always enough. I have, on occasion, been unable to distinguish between two amps in a simple A/B which when compared over time showed their differences clearly. There are "distortions" which we can easily ignore (or not hear at all) in short snips which become annoying or fatiguing over time. A/B testing is great for quickly identifying flaws or big differences, but it's not the end-all that some would have it be.

[mzisserson]

Re: Amplifiers and power: the more I learn, the less I know.

The ONE thing I thought I understood about amplifiers is that more power is a good thing...

For example, within the realm of more-or-less trustworthy AVR brands (Yamaha, Onkyo, Denon, etc), I believed that the heavier amp with the higher power rating would be better, that more power meant cleaner sound, and not just at ear-splitting volumes. Many many people believe this, and I've read many posts from VERY knowledgeable people, who have explained in detail, why this is one of the few solid truths in audio.

But it seems that, as with ALL things in this hobby, the answer is "not so fast". Some recent posts by equally knowledgeable folk on this forum suggest that it's a lot more complicated than that... lots of talk about "cheap watts", power supplies that aren't up to the task, number of amp sections, and of course specs that can't be trusted.

And multi-thousand dollar amps delivering only 50 watts per channel, that maybe aren't snake oil. This one really boggles my mind.

I've started a new thread here because I want to read a really focused on discussion on:

AMPLIFIERS: Is more power a good thing? Why or why not? What are the caveats? How can you know if the new higher-powered amp you're about to buy is going to make an improvement? Is ANYTHING sacred in this hobby?!

Education. I think you need to educate yourself on the types of amplifiers and how they work to understand what exactly is going on. Do not foget about headroom too. Understand what it is from a technical perspective before buying into anyone's religon.

Research these amp types and how they work.

Class A, A/B, B, D, T (somtimes called H)

For tube: Ultralinear, Triode... There are others, but these two represent 99% of what is out there.

The powersupply dictates how much current the rails will be supplied with before they sag, also, a good power supply will be extremely low noise because let's face it, if the raw power being used to amplify the signal is noisy... Guess where that noise is going to go?

That's just the high gain section! What about the signal handling when it gets to the amp?

Oy-veh. There are so many other conciderations as well. Just like designing a loudspeaker, there are MANY factors in an amp and it can actually be far more complex than a loudspeaker. A little information can be dangerous... Things are not always as they appear, and usually the textbook calculations suck.

There are extremely educated people who have made it their life's work to study, design, and create new amplifiers that preserve the MUSIC as intended and after years it is still a WIP. Just....Like.... Loudspeakers.

That is why I think a shoot out at one watt between several amps is a great idea. I have done it, the difference is never subtle. On paper, they should all sound the same, but they never do.

[djg]

Re: Amplifiers and power: the more I learn, the less I know.

I have this Class D Audio amp which should have 500 Watts per channel. It has an Antek toroid transformer, a power supply and amp circuit boards of about 4" x 5". A small aluminum bar stock heat sink. doesn't seem right to me. And an old Yamaha M-80 amp with 225 watts per. It is very heavy.

[Servicetech]

Re: Amplifiers and power: the more I learn, the less I know.

The quickest way to catch a lie is look at the input rating on the amplifier. Continuous output can NEVER exceed input power. Most AVR's are about 50% efficient, look at watts rating on the UL plate and divide by 1/2 to get true power output. Car amps can be calculated by taking the fuse amperage x 14.4 then dividing by 1/2. Of course class D amps are more efficient, 80% is more typical.

Also keep in mind no 120V plug-in appliance can draw more than 1500W and get a UL rating tag. Any amp claiming to have a higher output power better be running on 240V or have double 120V plugs. There are a few amps over at outlaw audio that have 2 power plugs because one wasn't enough !!

[PWR RYD]

Re: Amplifiers and power: the more I learn, the less I know.

I have this Class D Audio amp which should have 500 Watts per channel. It has an Antek toroid transformer, a power supply and amp circuit boards of about 4" x 5". A small aluminum bar stock heat sink. doesn't seem right to me. And an old Yamaha M-80 amp with 225 watts per. It is very heavy.

Good one ;)

[mzisserson]

Re: Amplifiers and power: the more I learn, the less I know.

Allow me to kick it off with a recent discussion between myself and Deward Hastings

Deward is correct in much of what he said. On paper it looks great. However, it ignores losses, reactive loading, and current capability of the powersupply/output combo. It also ignores the signal handeling when the raw input from the component comes into the amp, phase issues, ect. If it was as easy as Deward explained, there would be five amps in existance, and everyone would be happy with one of them.

The problem is with the V8 analogy is this: The corner store is really on a corner 20 miles away, and there are hills with 30% grades, and long straight away's with high speed limits, followed by stop and go's, then steep grades again, did I mention the traffic and the weather?

It is like saying that any speaker with a flat frequency responce sounds the same.

Also, music can have 20+ dB of dynamic range, even at 1Wrms, that still is asking for A LOT of power to properly reproduce transients.

[lunchmoney]

Re: Amplifiers and power: the more I learn, the less I know.

Can we hypothetically assume, for the sake of discussion, that the amps in question have factual specs?

I think we all know that specs lie...

[Pete Schumacher]

Re: Amplifiers and power: the more I learn, the less I know.

I have this Class D Audio amp which should have 500 Watts per channel. It has an Antek toroid transformer, a power supply and amp circuit boards of about 4" x 5". A small aluminum bar stock heat sink. doesn't seem right to me. And an old Yamaha M-80 amp with 225 watts per. It is very heavy.

Class AB amps, like the Yamaha, waste at least 30% of the power they consume, as heat, and with music, a much higher percentage than that. Hence the need for big heat sinks, and a power supply capable of producing at least 50% more power than the amp can possibly deliver to the speakers.

Class D is 90%+ efficient, even under music conditions. Thus the aluminum block heatsink, and smaller, lighter power supply.

Lunch, if you like to turn it up, then a big amp is always better than a smaller one if you want to avoid any kind of clipping. If you never crank it, then why waste the money on the big one?

[MGrant1957]

Re: Amplifiers and power: the more I learn, the less I know.

I don't know much about the new (to Me) class D and class T amps, but the best sounding amp I ever heard was a little beasty called the Robertson Audio Forty Ten, and was rated at 60w/ch. I did a side by side comparison with it against a Soundcraftsman amp that was rated at 500w/ch. We drove both amps to the point of clipping. The Soundcraftsman clipped at 86w, while the Robertson Audio didn't clip until we were pushing 960w/ch!. That equates to 12db of headroom. The difference in the two amps was mostly in the power supply. That little Robertson weighed in at somewhere around 60lb. When we opened it up to take a look inside, there were 2 very large transformers, 6 very large caps, and 4 power transistors, not MOSFETS. That arrangement allowed the Robertson to drive a very complex low impedance, high capacitance, highly reactive load to very high currents with out having the voltage droop of a lesser power supply. Some of the high $$ amp companies will put in a moderate power supply and try to back it up with lots of capacitance to handle the transients, and it works... up to a point. If the transients last more than 50 or 100 milliseconds the caps get drained and the voltage drops, causing clipping. (very audible) Some put in a better power supply, but don't put in enough capacitance to give the amp any headroom, these amps will put out their rated power all day, but through a fast transient at them and they simply can not drive the load for more than 10ms. Both of these situations are part of the design decisions made by the company. some to cut costs, ( really big capacitors are expensive ) others are to keep the weight down to something you can actually carry. Take a look at one of the larger Krell amplifiers, and you will find military grade fiberglass printed circuit boards with gold traces on them along with 0.1% resistors throughout. These matched components are costly to use, but the results speak for themselves. There is a reason the Krell costs so much. There are just too many variables in designing an amp, that you can't just say 'the heavier, the better', but it is a good starting place.

[ligs]

Re: Amplifiers and power: the more I learn, the less I know.

Class AB amps, like the Yamaha, waste at least 30% of the power they consume, as heat, and with music, a much higher percentage than that. Hence the need for big heat sinks, and a power supply capable of producing at least 50% more power than the amp can possibly deliver to the speakers.

Class D is 90%+ efficient, even under music conditions. Thus the aluminum block heatsink, and smaller, lighter power supply.

Lunch, if you like to turn it up, then a big amp is always better than a smaller one if you want to avoid any kind of clipping. If you never crank it, then why waste the money on the big one?

Can you describe how does amplifier clipping sound like? I don't usually listen at high volume so I may be missing something?

[Sydney]

Re: Amplifiers and power: the more I learn, the less I know.

Can we hypothetically assume, for the sake of discussion, that the amps in question have factual specs?

I think we all know that specs lie...

One of ( perhaps the most important ) issue is developing a standardized set of test criteria that reflects the wide variations of real world loads and operating conditions.
Amps are tested with pure resistive loads NOT dynamic reactive loads.
Unscrupulous manufacturers going for big wattage numbers know how to set up the test conditions to get higher numbers.

[fbov]

Re: Amplifiers and power: the more I learn, the less I know.

Since we all recognize it's not that simple, let's also be aware of some of the why's. Audioholics does a nice job. Here's their amp section,

http://www.audioholics.com/education/amplifier-technology/

an article on power ratings

http://www.audioholics.com/education/amplifier-technology/amplifier-power-ratings

and one on what mfrs. will do to pass UL/CSA, and why we care.

http://www.audioholics.com/education/amplifier-technology/impedance-selector-switch-1

I like their mid-article summary: "the whole process is unadulterated horse-feathers."

Have fun,
Frank

[Sydney]

Re: Amplifiers and power: the more I learn, the less I know.

Can you describe how does amplifier clipping sound like? I don't usually listen at high volume so I may be missing something?

A signal can be clipped at any level ( esp. in a situation with multiple gain stages ). It can be a matter of exceeding the design capacity of a circuit.

[neildavis]

Re: Amplifiers and power: the more I learn, the less I know.

I have this Class D Audio amp which should have 500 Watts per channel. It has an Antek toroid transformer, a power supply and amp circuit boards of about 4" x 5". A small aluminum bar stock heat sink. doesn't seem right to me. And an old Yamaha M-80 amp with 225 watts per. It is very heavy.

Look at the input power vs power delivered curves for a class AB vs class D amplifier, and you will understand why that Yamaha amp has to be big and why that class D amp can be small. A representative curve for a class AB amp is from the LM3886 data sheet, on page 14 (Power Dissipation vs Power Output): http://www.national.com/ds/LM/LM3886.pdf.

Although the theoretical efficiency of a class AB amp is around 75% (which is only achieved at full volume), the amp is usually running at efficiencies closer to 40%, with more power dissipated than delivered. So you need that big transformer in the Yamaha to heat up the big heatsink :eek:.

Compare that to the efficiency curve for a class D amplifier, which is around 90% for 8 ohm loads at moderate power levels. (see figure 4 in http://focus.ti.com/lit/ds/symlink/tas5630.pdf). Much easier to keep the class D amp cool, and the transformer can be smaller.

Unfortunately, the audio quality of class D amps may not be as good as well designed class AB amps. I doubt that people can hear the difference between properly designed class AB amps of comparable power levels. However, I know for a fact that there are clearly audible differences between some of other older class D amps (Tripath vs Apogee/ST), and I have a test fixture that can prove it. I don't know if the newer class D amps have reached the level of the best class AB or class A amps yet--that would be a worthwhile test.