Which amp specs really matter?

[filmis]

Practically speaking, which of the advertised amp specs do you look at when buying, or, in your experience, make the most impact on your listening experience? I understand they may each contribute to different elements of the sound...

The ones that make sense to me:
- frequency response range
- S/N ratio
- damping factor
- total harmonic distortion

And I can barely make head nor tail of the others.

 

[E-Stat]

Practically speaking, which of the advertised amp specs do you look at when buying, or, in your experience, make the most impact on your listening experience?

None as most are useless to convey valuable information.

With some, I find an inverse relationship. If the THD has three decimal places, you know the designer used lots of corrective feedback which has a deleterious effect to music playback in my experience.

I use my ears when evaluating audio gear.

 

[filmis]

None as most are useless to convey valuable information.

With some, I find an inverse relationship. If the THD has three decimal places, you know the designer used lots of corrective feedback which has a deleterious effect to music playback in my experience.

I use my ears when evaluating audio gear.

Sure, ears. But you can't possibly audition every single amp, so you have to start by narrowing it down somewhere. This is why I'm asking about specs.

 

[shelly_d]

You have the top three. Use the RMS continuous, both channels driven to get a feel for the output power. The rest, taken in total and together (no one being more important then the others) will give you a really clear idea of how well the device will sound. My first amp was an Eico kit bought on specs. Very modest power (15 watts RMS into 8 ohms) but excellent specs for noise, frequency response and distortion. It performed beautifully. Sounded great. This has been borne out in many subsequent experiences that I and others have had. This presupposes that what you desire from an amp is that it's output is as faithful to it's input as possible, before the use of equalizers and tone controls. If on the other hand, you want your amp to make the music sound more musical (sorry I don't know what that means but others on this forum seem to), then the specs you use (as well as I) would probably cause some to call the amp sterile. As far as damping factor is concerned, anything past an 8 or 9 is probably not very important due to the presence of the DC resistance of the speaker's own voice coil.

Hope this helps.

Shelly_D

 

[E-Stat]

This is why I'm asking about specs.

You won't find the answer there.

So, what speakers do you use? Budget?

 

[E-Stat]

Input sensitivity and input impedance are the first ones I try to find.

Those are helpful for matching purposes, but neither is a qualitative measure.

 

[bhunter]

Practically speaking, which of the advertised amp specs do you look at when buying, or, in your experience, make the most impact on your listening experience? I understand they may each contribute to different elements of the sound...

The ones that make sense to me:
- frequency response range
- S/N ratio
- damping factor
- total harmonic distortion

And I can barely make head nor tail of the others.

It depends on what you're trying to achieve. For instance, if you're looking for an amp for a quality home audiophile system, then E-Stat is correct, in that, the only sure way is to listen to the amp in that system. Obviously, the amp must have some minimal amount of power to properly drive your preferred speakers. OTOH, if you're designing a system for, say, a stadium, then power would be most important. Aside from audiophile systems, there is really not that much difference between quality professional amplifiers, thus, reliabilty and serviceability becomes paramount. The four specifications above are irrelevant past a certain threshold IMHO.

 

[shelly_d]

I disagree with with both E-Stat and bhunter. If you are after an amp that has an output that is accurate to its input (the original meaning of high fidelity) the specs are a very clear indicator of what you will get. I will not claim that it is the sole criterion. Some speakers will present a difficult load for an amp and individual amps will react in different ways. This however tends to be a rare as most speakers do not present difficult loads. The specs can indeed tell you a great deal about the performance of an amp.

Shelly_D

 

[onwardjames]

Slew rate.

I've heard that makes quite a difference.

 

[62caddy]

A better question would be: How bad can specs be before their negative effects are audible?

Almost any spec is important - if it's bad enough.

 

[Mojo Warrior]

None.

What does matter is what sounds best to you.

There are plenty of posts about amp and speaker matching. This is not reflected in any specs. There is the room where you listen to music, which influences the sound more than any spec. Finally, there is the actual music you listen to, which may be quite different than a reviewers tastes.

Specs are like a recipe for pudding. It's all about the the taste.

 

[sqlsavior]

Well, the old FTC standard of "X watts per channel (continuous RMS, both channels driven), at Y% THD, into Z ohms" gives you a good idea of output power into the stated load. S/N ratio is usually meaningful. Frequency response may provide a clue, or be boilerplate. But there is so much more to sound quality than is characterized by these standard specifications.

When I bought my latest amplifier, I considered just about everything except specifications. Luckily, I have a reviewer whose eyes and ears I trust. Besides the build quality and reputation, my main concern was reliability. The multitude of protection features and the adaptive auto-bias with support for multiple tube types won me over. Not a spec in sight, frankly.

 

[62caddy]

None.

What does matter is what sounds best to you.

There are plenty of posts about amp and speaker matching. This is not reflected in any specs. There is the room where you listen to music, which influences the sound more than any spec. Finally, there is the actual music you listen to, which may be quite different than a reviewers tastes.

Specs are like a recipe for pudding. It's all about the the taste.

I understand the spirit of your comments but they are overly simplistic. Knowing output power, at a given impedance is absolutely critical in matching equipment to speakers. A small receiver isn't exactly going to bring the best out of a pair of inefficient pair of 4 ohm speakers.

 

[E-Stat]

If you are after an amp that has an output that is accurate to its input (the original meaning of high fidelity) the specs are a very clear indicator of what you will get.

I learned the contrary back in the 70s. Compare the specs of the Crown D150 with that of the Audio Research D-76. Which looks better to you?

The Crown had a horribly hard sound (the IC-150 preamp was even worse) although it definitely looked *better* on paper than the ARC unit. I kept mine for under a year. But then I was a clueless teenager at the time. Reason? The Crown used crappy Fairchild op amps using copious amounts of negative feedback to *fix* the distortion while the Audio Research sounded like music.

Arguably, some of the very best solid state amps today are designed by Nelson Pass. Similarly, the specs don't look terribly impressive. 1% distortion? Then listen to one!

 

[shelly_d]

I have listened to the Crown D 150. It was a long time ago so I really don't trust my memory on what they sounded like. There is such a thing called euphonic distortion. It can be defined as:

"Euphonic distortion is a phrase coined to cover the distortions found in some non-linear processes that sound 'pleasant' or 'musically useful' to some human ears.

The example normally quoted is the third harmonic distortion that is produced by valve (tube) amplifiers.

There is a difference of opinion between Hi-Fi enthusiasts, who broadly accept euphonic distortion, and audio engineers, who generally interpret 'high fidelity' as meaning minimal distortion of any kind. This is well illustrated by this article from Walt Crawford."

(The above definition taken from this site: https://sites.google.com/site/sssglossary/Home/E/euphonic-distortion)

Seeing your reference to Nelson Pass and the description about how the DC 150 sounded "hard" I come to the conclusion that you prefer to hear some euphonic distortion. As I stated in my remarks, if you want the faithful reproduction of the original source, the specs do matter and will tell you how well the amp will perform. If you like "musical" sounding amps, then an amp like the DC 150 will sound (my words) sterile or (your words) hard.

I am of the camp that likes my amps to reproduce the input as closely as possible. I did found nothing objectionable in the Crown, as I recall, and would probably be happy with it's performance today (I would not trade my McIntosh for it as I like the looks and performance of that piece). I will not presume to say that those who enjoy the presence of such euphonic distortion are wrong, but I do emphatically state that if you want (as I do) an output as closely matched to the input as possible, specs are very telling. I find that performance the most enjoyable.

Shelly_D

 

[sqlsavior]

You can lead a horse to water, but you can't make him drink.

 

[shelly_d]

You can lead a horse to water, but you can't make him drink.

It is a matter of taste. I don't want distortion, euphonic or otherwise. I suspect that EStat does. Do you? Do you acknowledge that taste is important? There are many that, like me, don't want the amp to alter the music.

Shelly_D

 

[E-Stat]

The example normally quoted is the third harmonic distortion that is produced by valve (tube) amplifiers.

Actually, that would be second order. Which our perception is relatively blind to even in relatively high amounts. It is the odd harmonics that are the devil's brew. The Crown's sin lies with its spectrum in the 5th, 7th, 9th, etc. The challenge is that measurements based upon sine waves bear little resemblance to that when playing dynamic music. Unless of course, you are a test tone fancier.

Seeing your reference to Nelson Pass and the description about how the DC 150 sounded "hard" I come to the conclusion that you prefer to hear some euphonic distortion.

I prefer the sound of live, unamplified music. Perhaps that experience is foreign to you. I enjoy it regularly when wifey plays the baby grand in the living room and when we attend the symphony.

I did found nothing objectionable in the Crown, as I recall, and would probably be happy with it's performance today

"Nothing objectionable?" The sound of nails scratching across the chalkboard and a narrowed soundstage must not bother you.

We have very different points of reference!

 

[Gibsonian]

I sure look at specs but the main things I look at are:

-circuit design/type
-power into different impedances
-weight
-reputation or feedback from users (with heavy filtering)
-damping factor on bass amps (active crossover system)

After that it's kinda a crap shoot. Some of the best speced units I've had didn't stay long. I do look at build quality /layout but that can be quite misleading as well.

 

[stereofanboy]

My favorite speakers are difficult to drive, so it matters to me whether an amp can survive driving a low ohm load. Anything that can't is out of the running regardless of its other qualities.

I can't help but suspect that those most dogmatic about listening for yourself either live in or at least regularly visit a city that has one or more stereo shops. As someone who would have to drive several hours one direction to visit the nearest stereo shop, and several hours in a different direction to visit the next nearest, I can sympathize with your reasonable desire to narrow the field first.