Do amps have a sweet spot?


What I mean by this is do amps have an output range at which they sound better? The reason that I'm asking is that I'm now running some very small speakers (Minuet Supreme Plus) and they're probably the least demanding speakers I've had; but I've found that my setup sounds better when I have the volume turned up.

Out of curiosity, I took my Minuets to my local shop and hooked them up to an NAD C326BEE. I thought it sounded pretty darned good at "normal" listening levels. I almost bought it, but then I decided to start cranking it up to what I would call "rockin" levels and the amp started to clip. If it could have played louder, I would have bought it.

So...is it usual for an amp not to open up until you start pushing it?

My current amp is an Aragon 2004.
tonyangel
In most any practical sense, yes, it may be normal, especially for lower-priced gear, to have that portion of its volume range that seems to open up a bit better...although exactly which portion that may be could possibly be different in different systems. In one system the amp could sound better at 3/4 of its output and yet in another system sound better at 1/2. Usually when you start moving up the food chain and start buying better and better components, this sort of thing becomes less and less apparent and vol. and dynamics start to become more "linear" (as do power supplies). By the time you've done that, and/or have gone successfully enough down the power-conditioning road and perhaps have also looked into things like how much your vol. control is veiling the sound, being somewhat picky about interconnects for your own app and even about things like grounding issues, what you can end up with is an extraordinarily linear rig...although all that typically comes with the price tag as well, of course. But, if you did all that, the I believe the surprising part to me is that even your current gear would pass that kind of test with flying colors, giving absolutely ideal performance, no matter what the vol., right up to clipping. So the real answer is that, yes, you do have any given amp's tendency to sound better at whatever point it will, but, that characteristic is in no way inherent to the amp itself, and, in the long run at any rate, there are those things I mention that you can look into to improve the situation. All this that I'm talking about here is apart from the ins and outs of matching your amp to the right speakers and so forth, which could at least influence things. Hope this helps.
The simple answer to your question is yes. Its very possible that your amp will sound better when you push it. I differ a bit with Ivan, though, in that you can have the same issue with very expensive components. It all comes down to system matching. Also, with newer components, its not the issue it once was. Your Aragon is a pretty old unit. Newer designs, are less prone to have this problem. If you liked the NAD, try the next model up. It sounds like you need just a little more power than the model you heard.
Let me add that some speakers sound better at higher volume as well.
Thanks guys. At least, I now know that I may not be crazy.

I really can't explain the love affair that I'm having with this Aragon. I do know that it's really OLD and out dated. I suppose there's just something to a two channel 100 wpc amp weighing 40lbs.

Still, I did like what I was hearing out of that newer NAD model. My dilemma (isn't there always one of these?) is that NAD's top of the line classic unit is $1500. I really don't need a pre amp. Mine is a NAD C162 and is pretty nice. My dilemma is what sort of amp to go with. I've been very interested in the Class D offerings. I also have to decide how much power it is that I really need.

Anyway, thanks a lot for the comments.
Not alone so much, but in practice along with the rest needed to make music, yes.

The "sweet spot" regarding human hearing is overlooked. We hear better ie our ears have a flatter frequency response at louder volumes. That's probably the biggest and most common factor. Next would be specific amp/speaker matching and room acoustics, which varies more case by case.
A particular amp with a particular speaker in a particular room with known ambient noise level for a particular individual, yes.

The question is how do you know the amp was clipping and not the speakers breaking up?

Did the amp shut itself down?
The guy at the shop said that it was the amp soft clipping. I don't know much about that because I've never had an NAD amp with that feature before.

I know it wasn't the speakers. They sounded very in control and clear, right up to the point where the signal started going in and out. Besides, I've had the speakers up to higher levels in my den, which is larger than the listening room at the shop.
If he said the NAD was soft clipping it's because he had the clipping switch on the back on, which limits the amp at full output. Can't blame him because a salesman wants to protect his gear. What I'm surprised about is that you would want to crank those little 3 inch woofers so much!

Oddly enough I've got both the Nad c162 and C326BEE. Pretty good stuff for the price but if you want more than the 50 wpc C326BEE can give you, remember that 100wpc will only get you an additional 3 decibels of volume over the 50 wpc. I found that the newer NAD sounds a little more open than the C162.
Well, sometimes I like to play it loud and I needed to make sure that what I was considering could do what I wanted it to do. As for cranking those little 3" woofers, as I said, the speakers were showing no signs of stress.

I understand that doubling the rated power of the amp is only supposed to get me an additional 3 db, which is why I didn't even bother to try the two other upper models that they had.

I know that my Aragon does what I need it to do with these speakers in the volume department. I suppose it's another example of the fact that not all watts are created equally.

I suppose I need to find an amplifier that sounds equally good at both low and higher volumes in my system.
Good point, indeed all watts are not created equally. I've got a small pair of Tannoy Revolutions, the DC4 model. They also have a small driver as well but are designed to handle much less power. I've had them for 2 years, but only when I replaced a cheap Onkyo receiver with the Nad C 326BEE did I get really impressed with the Tannoys.

It sounds like your speakers do indeed excel with more power.
remember that 100wpc will only get you an additional 3 decibels of volume over the 50 wpc
Runnin, just wanted to point out that 100WPC is 3dB more power (& not volume) over 50WPC.
How much more volume/SPL you will get with a 100WPC is really dependent on the 100WPC amp design - really it's power supply design & current handling capacity of its transformer.

IMHO the issue you are facing is the classic amplifier-speaker interface issue. You are having to turn up the volume to overcome the marginal amp-speaker interface by sheer grunt power from the amp.
We discussed this in quite a bit of details back in early May 2013. Lots of good info in that thread by some very knowledgable members. here is the link to that thread -
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1367644336&&&/Current-amp-vs-Voltage-amp

i know it's a lot to read but do take the time to read & digest the info.
I have upwards of 25 amps and they all sound best when they're 'cookin'. Does that not make sense from an engineer's point of view? Or from the one buying the amp for that matter.
Bombaywalla,

I'm going to read that thread, for sure. Thanks for the heads up.

Runnin,

Yeah, the Minuets are small, but they can eat some power. As mentioned above, I'm running an old Aragon 2004. It's a bit of a beast for what it is. It's rated at 100wpc at 8 ohms and 200 wpc at 4 ohms; and weighs right at 40lbs. My only problem with it is that I don't get that satisfying feeling from the music until I turn it up a bit until everything comes together.

My feeling was that maybe if I got into a smaller amp, I could get that satisfying sound at a lower volume. The NAD for me sounded good, but it didn't quite get it for me. It also didn't go quite loud enough for when I do want it loud.

I could have gone for one of the more powerful models, but at those prices, I'd have several options in terms of getting an amp.

Right now, for some reason, I really have a bug to get into a class D amp just to try it out, but that's a subject for another thread, which I'm gonna start right now.
http://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves
just wanted to point out that 100WPC is 3dB more power (& not volume) over 50WPC. How much more volume/SPL you will get with a 100WPC is really dependent on the 100WPC amp design - really it's power supply design & current handling capacity of its transformer.

I must be either reading this wrong or missing something.

I thought increasing the voltage across a speaker's input will increase its output in SPL based on the speaker's sensitivity. I don't see how that's related to the voltage source (the amp) in any way.

The increase in SPL by increasing the voltage by 3 dB will always be less than 3 dB due to the speaker not being 100% efficient (it has losses).

What am I missing?
The increase in SPL by increasing the voltage by 3 dB will always be less than 3 dB due to the speaker not being 100% efficient (it has losses).
If the speaker is being operated at volume levels that are not high enough to cause it to behave in a significantly non-linear manner (e.g., for "thermal compression" to become significant), then 3 db more in will result in very close to 3 db more out, as the % efficiency will be the same at both power levels.

On the other hand, see this post by Duke of Audiokinesis, about thermal compression.

Regarding Bombaywalla's comment about 50W vs. 100W, I believe he is simply referring to the fact that different 100W amps may differ from each other, both subjectively and objectively, in terms of their maximum volume capability with a given speaker load. Same goes for two different 50W amps. Obviously there are many possible reasons for that, including the ones he mentioned as well as the distortion characteristics of the particular amps at various power levels, differences in dynamic headroom, etc.

As far as the OP's question is concerned, yes amplifiers can have "sweet spots," but as others have mentioned there are a lot of other variables that may be involved, including the behavior of the speakers at different volume levels, the Fletcher-Munson effect, amplifier-speaker interactions, and acoustical differences between your listening room and the shop at which you listened to the speakers. Or perhaps the problem is simply that capacitors in the Aragon have degraded over time, and need to be replaced. I don't see a path forward at this point that wouldn't be somewhat hit or miss.

Regards,
-- Al
I must be either reading this wrong or missing something.

I thought increasing the voltage across a speaker's input will increase its output in SPL based on the speaker's sensitivity. I don't see how that's related to the voltage source (the amp) in any way.

The increase in SPL by increasing the voltage by 3 dB will always be less than 3 dB due to the speaker not being 100% efficient (it has losses).

What am I missing?
Bob_reynolds
Firstly, thanks Almarg for jumping in & clarifying for me. :-)

Yes, Bob_reynolds you are missing something. it's called "current".
If there's voltage across the speaker terminals, then current must flow from one speaker terminal to the other. Where does this current come from? From the power amp. THAT'S how it is related to the voltage source (amp) in every way. ;-)
You must remember that voltage & current are duals - if there is one, the other must be present. Ohms's Law.
What if the voltage source/amp is incapable of supplying the current (transformer does not have the current capacity, power supply not robust enough)? Will we able to sustain that voltage across the speaker terminals? No!
The criteria that I cited & those that Almarg added (thanks!) all come into play when you put the 100W (or any amp) into the signal chain. Simply buying any 100W & swapping out your 50W/ch amp & expecting an increase in SPL proportional to your increase in the volume knob on your preamp will be a roll of the dice if you have not thought it thru - particularly if you have a hard-to-drive speaker.
The amp-speaker interface is important. Hence the link to that thread. Almarg along with other members have taken the time to write some lucid notes to explain the matter. Do take the time to read.
Thanks.
Thanks Al. You said what I had originally thought. But, for some reason I started doubting that when I began thinking about what is meant when we say something is linear. Anyway, my post is pretty screwed, so thanks for the fix.

-- Bob
Bombaywalla, your post was a bit confusing and thus, my "HUH?" post in response. What I missed from your post was that you were considering practical limitations of an amp that could come into play with some speakers. It sounded like you were, in general, refuting that a 3 dB increase in power yields a 3 dB increase in SPL from a speaker.

I was thinking theoretical behavior of a speaker and so your post was confusing. In your scenario, you are never able to increase the power by 3 dB, so there will not be a corresponding 3 dB increase in SPL.
To change the subject, do you think different amp technologies, or circuits, have a sweet spot in terms of rated output? To make clear what I mean, I was reading a review by Ken Kessler, of the Audio Research Ref 75 amp, which he and I too, think sounds wonderful. He suggested that the push /pull configuration Audio Research use, was such that an output level around 75 watts, seems particularly magical. He referred, if I remember to the old ARC D60 amp, as a memorable example from the past. He also felt the 75 sounded better, in suitably sensitive speakers, to it's bigger brother the ARC ref 150.

I am not sure if this is fanciful or not, any thoughts guys?
06-15-13: David12
To change the subject, do you think different amp technologies, or circuits, have a sweet spot in terms of rated output?
I'd be hesitant to generalize, David, at least without having a very large empirical database, that would most likely be impractical to compile. There are simply too many variables involved in the performance of different designs to allow meaningful generalizations to be inferred from a limited set of experiences, IMO. And if any general tendencies were identified, there would undoubtedly be many exceptions to the rule.

Best regards,
-- Al
I think solid state amps, such as yours, do have better TDH+noise specs at something like 80% of the power rating.
You might want to dig out some old AUDIO magazine when they still published test results, and you will see how the TDH+Noise varies with output power (as do other factors, I suppose).

One big reason Tubes sound better, is they simply test better for TDH+noise at very low power levels.
One big reason Tubes sound better, is they simply test better for TDH+noise at very low power levels.

You mean like this?

Simaudio Moon Evolution 880M http://www.stereophile.com/content/simaudio-moon-evolution-880m-monoblock-power-amplifier-measurements

Audio Research Reference 75 http://www.stereophile.com/content/audio-research-reference-75-power-amplifier-measurements

A trend that does appear to be true is that solid state amps have a "U" shape curve whereas tube amps have a line shape with a fairly steep slope.
While curves like those can provide some insight into the characteristics of a particular amplifier that is being reviewed, I'm not sure that they help to answer David's question.

As I interpreted it he was asking if optimal power RATINGS could be defined for different basic categories of amplifier design. Things like tube vs. solid state, the type and quantity of output tube in the case of tube amplifiers, push-pull vs. single-ended, class of operation (A, AB, D), balanced vs. unbalanced, amount of feedback, and other differences in circuit topology.

The first problem is that curves depicting distortion or distortion + noise as a function of power level are not much help in trying to choose an optimal power RATING for a given application. Unless the user listens almost exclusively to very over-compressed recordings, the amplifier will be operating at points pretty much all over those curves, as a function of the music.

And in comparing performance at different power levels, a given increase or decrease in THD or THD+N may be subjectively either better or worse, depending on how the THD is distributed among different harmonics, on the relative amounts of THD vs. noise, and on the spectral characteristics of the noise.

Also, with many amplifiers, especially those using significant amounts of feedback, the THD numbers will be negligible even on the higher parts of the curve (well away from the bottom of the "U"). While TIM (transient intermodulation distortion), which is worsened by feedback and which is not normally specified or measured, may be a much more significant contributor to subjective sound quality (depending in part on how much propagation delay there is through the amplifier, that being another variable that is generally unknown).

So I don't see any reason to expect the amplifier to necessarily sound best when operated at the bottom part of the curve, and even if it does that would say little or nothing about what power RATING would be optimal.

Best regards,
-- Al
"So... is it usual for an amp not to open up until you start pushing it?"
As the quote I included in the post indicated, I wasn't addressing David's question, but presenting an exception to the generalization that 6550c made as to why tubes sound better.
I was addressing Al. Sorry for the confusion.
06-16-13: Csontos
"So... is it usual for an amp not to open up until you start pushing it?"
I don't know how "usual" it may be, Peter, but I certainly wouldn't be surprised if is an effect that is present to an audibly significant degree with many amplifiers. Albeit without a great deal of predictability.

For one thing, as Ralph (Atmasphere) has said in past threads certain odd order harmonics can, even in trace amounts, significantly affect our perception of loudness. Therefore variations of an amplifier's distortion characteristics that may occur as a function of signal level can significantly affect perceived dynamics.

For instance, if those particular odd harmonics are present to a greater degree, relative to signal level, on musical peaks than during soft passages, there will be a perceived increase in dynamics. And if the volume control is set lower the differences in distortion between musical peaks and soft passages may become smaller, resulting in a perception of lessened dynamics.

Also, of course, the operating temperatures of transistors and other circuit devices will be affected by the volume level, with all kinds of subtle sonic consequences being conceivable.

As I and others said earlier, though, in any given situation lots of factors unrelated to the amplifier could conceivably come into play, perhaps to a much greater degree, including the Fletcher-Munson effect and the behavior of the speakers .

Best regards,
-- Al
I wasn't taking you to task. Just pointing out the op's query. Seems it got lost. I knew you'd come through.
Every component has a sweet spot so to speak. This is where "synergy" comes into play. It's more than just the ideal operating point of a single component rather when all the components in a given system work together at their optimal levels to produce the best sound a system has to offer.
Lets say you have a perfect mate (okay, great match) between an amplifier and speakers. If the preamp is not a good fit to the amplifier (or amplifier speaker combination), you may blame the amp for the system's downfalls. Volume may get too loud prematurely or you may have to crank the volume to get the speakers to play at normal levels.
With an integrated amplifier that has been designed properly, this should not be an issue if matted with the proper speakers.
The general behavior of all my amps is the same whether it's a 45 wpch amp or 800 wpch amp. I don't start hearing prominent inner mid-range detail until the amp is 'cookin'. Does this not stand to reason? Why would I design an amp not to perform it's best at rated output? Nothing is perfect. The whole technology is rife with compromise.
I don't start hearing prominent inner mid-range detail until the amp is 'cookin'.

If by "cookin'" you mean higher SPL, then most likely, as I think has been stated in this thread, it's not an amp thing, it's a human hearing thing depending on the individual, the speaker and the room.
No. SPL's have nothing to do with it. Like I said, they all exhibit the same behavior regardless of power rating. Obviously, SPL's are going to change accordingly. But just because it's louder doesn't mean the same things aren't going to happen. Characteristically, they are the same.
Csontos, I didn't understand what you just said.

Why does your listening level change when the power rating of the amp changes?

I assume that you listen at a certain level that suits you. My point was that, regardless of the amp, you hear things once the SPL is at a certain "cookin'" level.

Why would I design an amp not to perform it's best at rated output?

From a strictly measurement perspective no amp performs its best at its rated power. Distortion rises with power. Solid state amps typically reach their rated power around 1%; tube amps around 3%.
My pre amp brings a typical ss amp to rated output at about 6-7 on the dial. SPLs are obviously going to vary among different amps with different power ratings. Measured distortion is not necessarily an indicator of performance as Al pointed out.
OK, I'm done. Almost...

Measured distortion is not necessarily an indicator of performance as Al pointed out.

That's not what Al said. Measured distortion (THD + Noise) is certainly an indicator of performance. What's not clear is at what level (and what harmonic) will it become an issue for any one individual.

Why would I design an amp not to perform it's best at rated output?

I assure you that no amp sounds it's best near clipping, which is near its rated power.
I stand corrected, I suppose. I also stand by my initial statement. What I meant by 'cookin', is nominally what an amp can stand without driving it into clipping which will vary depending on the dynamic range of the recording.