Double Blind tests *did* show amplifiers to sound different

[Wes]

Two Questions:

1. What about "soft clipping" circuits, as used by NAD?

2. What about crossover distortion (A to B)? Benchmark went to considerable trouble to license the THX feed-forward circuit design in it's SINAD-winner amp.

 

[FeddyLost]

have a denon 3600 with Emotiva

Your fronts T2 have some dips in impedance around 100 hz and your denon's power amp section don't have any 4 ohm load power specified, but 70 db is just milliwatts so all must be ok in theory.
Cheapest way to check if you'll have any profit from separate power amp is to set up bi-amping your fronts and try to find any difference at max volume that you'll ever use. If you will notice stable difference in sound between normal and bi-amp, you can consider upgrading power amp section.

 

[jamtinge]

I initially didn't state what speakers i had because i wanted to ask @amirm if he thinks or has tested if two different amps
(internal denon amp vs external power amp in my case) could make different sound under normal operations condition (before clipping) as i never listen to anything at reference level.

I think most of the reply is based on the assumption that implies "no" to my question.
what is interesting is though.. ATI enginner thinks otherwise.. ( and i have heard really good things about ATI.. like monolith amp, outlaw high end amp.. ati 4000/6000 series along with 52x nc series )

i honestly don't know why this is so confusing.. but this question costs about $2~3k for myself as i am about to buy my first power amp, and its going to be either cheap one for rear height speaker or 2~3k range amp for my fronts or base layer speakers.

 

[MakeMineVinyl]

what is interesting is though.. ATI enginner thinks otherwise.. ( and i have heard really good things about ATI.. like monolith amp, outlaw high end amp.. ati 4000/6000 series along with 52x nc series )

I think there's always room for improvement in the state of the art, even in cases where those changes could be inaudible. There are other motivations too, like improved reliability etc.

 

[FeddyLost]

if two different amps
(internal denon amp vs external power amp in my case) could make different sound under normal operations condition

Personally I prefer to think that normal operation is the condition clearly mentioned in specifications/user manual for amp.
So, using 4 ohm speakers is NOT normal for amp without power rating into 4 ohm at all. Not even considering that 4 ohm rated speaker is absolutely not a resistor.
Maybe it's too conservative opinion, but without testing we can't be sure if that ok.
Amir's tests say that you can get around 160w into 4 Ohm in stereo so I'd expect not much difference with separate power amp in your scenario, especially if you cut off all below 80 and route it to sub.
Big problem for power amps is back EMF from paralleled woofers in modern speakers, but in your case they are barely working hard...

 

[jamtinge]

Personally I prefer to think that normal operation is the condition clearly mentioned in specifications/user manual for amp.
So, using 4 ohm speakers is NOT normal for amp without power rating into 4 ohm at all. Not even considering that 4 ohm rated speaker is absolutely not a resistor.
Maybe it's too conservative opinion, but without testing we can't be sure if that ok.
Amir's tests say that you can get around 160w into 4 Ohm in stereo so I'd expect not much difference with separate power amp in your scenario, especially if you cut off all below 80 and route it to sub.
Big problem for power amps is back EMF from paralleled woofers in modern speakers, but in your case they are barely working hard...

First of all.. thank you very much for your input. i really appreciate it.
You must be on the side that the all amps sound the same unless it isn't clipping.
I have been trying to find an answer to my question for a long time and can't find any conclusive comment on this subject.

One side says watt is watt and there is no audible difference unless it's clipping. (which makes perfect science sense)

On the other hand, people say they do observe the sound difference regardless of volume, hear things they hadn't before, voice has higher clarity, bass is stronger even at the same volume. I have been looking at the listings on Audiogon.com and see some amps going for >$10k used
so there must be some kind of justification for it.

I am fairly new to this hobby, but has seen wonderful reviews Amir has done here, and really would like to know what science says about my question.

 

[MakeMineVinyl]

I have been trying to find an answer to my question for a long time and can't find any conclusive comment on this subject.

I don't believe you're going to find a "conclusive" answer as long as people are different, have different experiences, different goals, different types of systems (mine uses extremely sensitive/efficient horns) and different musical tastes. This is no different than in any other human endeavor such as wines, cigars or you-name-it.

You take what's important to you, get the best information you can and run with it. As far as power amplifiers go, I don't think you're going to find a truly awful one made by any good manufacturer.

 

[SIY]

First of all.. thank you very much for your input. i really appreciate it.
You must be on the side that the all amps sound the same unless it isn't clipping.
I have been trying to find an answer to my question for a long time and can't find any conclusive comment on this subject.

One side says watt is watt and there is no audible difference unless it's clipping. (which makes perfect science sense)

On the other hand, people say they do observe the sound difference regardless of volume, hear things they hadn't before, voice has higher clarity, bass is stronger even at the same volume. I have been looking at the listings on Audiogon.com and see some amps going for >$10k used
so there must be some kind of justification for it.

I am fairly new to this hobby, but has seen wonderful reviews Amir has done here, and really would like to know what science says about my question.

When they back up their claims with ears-only, no peeking listening tests, then you can take them seriously.

 

[RayDunzl]

Assuming an average user & equipment. do you think or could it be scientifically proven that amp can make sound improvement/difference under normal operation(=before clipping) ?
In other words, i have a denon 3600 and only listen around at 65~70db. Do you think i will notice any sound improvement by adding an external power amplifier (rated higher than avr power.. say 500wpc 4ohm) although i don't notice any clipping right now?

At low volume, maybe not.

"Power" consumed by the speakers increases rather dramatically as the level increases.

An average of 70dB SPL implies peaks of 90dB. - 100x more power drawn than the average

A crude example of how power requirement increases with small changes in volume. a 3dB change is "a little", 10dB is generally considered as "twice as loud".

My little JBL LSR 308 with their internal 50W amps run out of steam pretty quickly when turned up some.

The mains with 700W available don't, at least, I haven't noticed it.

I use the JBLs daily for listening to TV and radio, but switch when it's time for paying attention to some music or watching a special movie.

 

[b1daly]

I initially didn't state what speakers i had because i wanted to ask @amirm if he thinks or has tested if two different amps
(internal denon amp vs external power amp in my case) could make different sound under normal operations condition (before clipping) as i never listen to anything at reference level.

I think most of the reply is based on the assumption that implies "no" to my question.
what is interesting is though.. ATI enginner thinks otherwise.. ( and i have heard really good things about ATI.. like monolith amp, outlaw high end amp.. ati 4000/6000 series along with 52x nc series )

i honestly don't know why this is so confusing.. but this question costs about $2~3k for myself as i am about to buy my first power amp, and its going to be either cheap one for rear height speaker or 2~3k range amp for my fronts or base layer speakers.

I think the chance of you getting a perceptible improvement in sound from fancy external amps is close to zero. Unless there is something broken in the Denon.

The thing to realize is that even if there is a difference in sound between two amps (playing below clipping) it will be very small and likely just a slight difference in frequency response. But this difference will be dwarfed by factors like your speakers, placement, room treatment, good stands.

To do any fair comparison between amps requires very close level matching at least to .1db. Otherwise the amps will be easy to distinguish.

In the ‘real world’ scenario of unplugging and plugging gear to compare, it’s hopeless because our ‘audio memory’ is short and the chance of getting a level match is zero.

If amps have different gain structures or controls to adjust gain this can radically bias perception.

For example, if your external amps have less gain than the onboard amps in the Denon, they will be quieter at the same volume level on the knob, likely making them sound weaker, or at the least confounding attempts to compare.

My personal experience is that amps do sound ‘different’ in my day to day use, but there are many things that affect this perception beyond actual sound quality, so I discount these particular perceptions heavily.

One issue that is striking is the ‘taper’ or shape of the volume knob function.

On AVRs you often have to rotate the knob many times to cover the full range. Compared to an old school amp with a potentiometer which covers the entire range in less than 360 degrees, I feel like the AVR amps are ‘weak.’

I think of this as ‘interface biasing’ and it’s a profound effect. Another area it plays out with the resolution of the knobs is with EQ. There can be quite a bit of difference in how much, let’s say, a degree of turn on a tone knob actually boosts or cuts the signal. There is an impulse I feel where there is kind of a ‘sweet spot’ on how much I’m inclined to rotate a control. I want to turn it ‘a bit’ so how well this intuition about using the control correlates with the actual audio effect is an area of differentiation for audio gear.

 

[Vasr]

First of all.. thank you very much for your input. i really appreciate it.
You must be on the side that the all amps sound the same unless it isn't clipping.
I have been trying to find an answer to my question for a long time and can't find any conclusive comment on this subject.

One side says watt is watt and there is no audible difference unless it's clipping. (which makes perfect science sense)

On the other hand, people say they do observe the sound difference regardless of volume, hear things they hadn't before, voice has higher clarity, bass is stronger even at the same volume. I have been looking at the listings on Audiogon.com and see some amps going for >$10k used
so there must be some kind of justification for it.

I am fairly new to this hobby, but has seen wonderful reviews Amir has done here, and really would like to know what science says about my question.

It is a bit more nuanced than can or cannot hear a difference and not as definitive one way or the other.

There are two major aspects that can differentiate amps - distortion products and tonal balance. Taking extremes of these is audibly different to anybody but the deaf. So, the question is when do those differences become hard to detect. There are some minor factors like damping factors, slew rate, etc., whose effects are harder to measure and predict the effect of.

If distortion products are measured with the kind of measurements Amir is doing and two amps are both well below hearing thresholds, then it would be reasonable to conclude that anything you hear from them will not be different for distortion product reasons. But this comes with a strong caveat which is that the distortion products will not vary too much from the measured values when a real-life load of a speaker is introduced. AFAIK, the jury is still out on whether that caveat is a given. But there are strong opinions on it. Also, a clean amp in that fashion does not necessarily imply one will subjectively like the sound it produces.

If the distortion products differ in their dispersion and get higher than the absolutely inaudible range (and there is a large grey area there especially combined with the caveat above), then the case for saying they are not audibly different becomes less convincing. Some amps suppress high order harmonics but let the second and third get high. Some keep the second and third harmonic not get too big but have a lot of higher order harmonics. Yes, all of these will get counted in the distortion numbers but distortion numbers is not correlated necessarily with SQ. Two amps with the same distortion numbers may have different distortion characteristics that are audibly different and hence differentiable. It could happen that subjective preferences prefer one over the other within such differences.

Tonal balances also work the same way. A single frequency sweep across the audible bandwidth and beyond can establish the behavior across frequencies and IMD tests allow limited inferences when multiple tones exist. Even in this case, if two amps show performance without any effects that are in the audible range, then it supports the likelihood that they are indistinguishable again with caveat above on how well this models real music on real speaker loads.

Some of the amps through history did not aim for complete and clean transparency. They made decisions for getting a certain "sound" either via their approach in shaping the distortion dispersion or affecting the tonal balance. Will these measure very well in these tests, most likely not. But will people like what they hear and pay a lot of money for some of them sure. Eventually, the world is divided into two camps.

Those that like to hear the sound the way they enjoy it viscerally and those that cannot enjoy the sound unless it measures clean.

This gets into debates somewhat like the Bogleheads groups on active vs passive investing. There are Bogleheads who believe an active fund just cannot beat an index if the test for performances and portfolios were "properly designed". But any such test would, in practice, constrain the active manager to buy exactly from the set of stocks that the index fund has and so would not show any consistent out-performance.

Purists here will not accept any claims of difference unless it is done under conditions that are in practice very difficult to set up and do. So, it maintains the divide with no resolution.

 

[FeddyLost]

You must be on the side that the all amps sound the same unless it isn't clipping.

I'm even more cautious in such opinions.
I'd say all the amps sound the same if they work with all possible and measurable distortions in "non-audible" range.
Clipping is not the only one reason to get some distortion.
For example, Matti Otala, founder of Electrocompaniet, "discovered" some TIM distortion and eliminated it his products.
Some russian company also claimed they have eliminated some weird kind of distortion (their know-how) and they are making some studio amps (CSA, CSB and CSM models). Our local sound engineers found their amps as great bang for buck at least.
On other side there are lot of amplifiers without feedback and they are also successfully being sold for crazy money, and even some sophisticated amps like CH Precision M1 with regulated amount ot global negative feedback which changes their sound and distortion profile...

We can go on for long time, but my main concern is that we never listen for sine tones (or even static multitones) into resistor and all these measurements can help us to distinguish crooked crap from well-engineered amp but they are barely usable when we try to find better one well-engineered amp of two.
There are lot of situations where difference must be not audible, but it's obvious and force people to buy one or another expensive unit.

really would like to know what science says about my question

As an some kind of engineer, I'd say that only properly done experiment will prove a lot of statements in sufficiently complicated system.
So I'd recommend you to try multi-amping (because in your case only impedance dips may cause some troubles) or get some power amp with moneyback option.
Some other solutions in 2-3 K$ range may exist if you are not satisfied with your setup. Like exchange of your mains to some big bookshelves of better class because you don't need anything below 80 anyway.

If you want my opinion about apm measurements, I'd say we can't really predict amp performance beyound basic requirements unless we know what was a technical requirement for design team.
Maybe they managed 0,002% of HD at 1 Khz into 8 Ohm resistor and didn't even try to use this amp at any real-world speaker (which is very realistic scenario for small hi-fi systems with bookshelf speakers included). I've tried few small cd receivers in big shop on some B&W 70x small floorstanders. It was total disaster even at reasonable SPL, I'd say.

For correct measurement I'd prefer to connect some voltage/current real-time registrator (like fluke norma) on real speakers and compare output waveforms with input ones.
Then we'll see real amp distortion numbers in real scenario, and I'm not sure that they will be much lower than those of good modern speakers.
But it's really expensive and troublesome to do and you'll have incredibly bad numbers for some audio review magazine, so I assume only some of best amp designers do something alike in-house during RD process and never show any results.

 

[Karbunkle]

Hi all, a newbie here, just discovered the site and already learning lots. Interesting points were made on relation of power and actual loudness, where an extra 3dB requires twice the power which really puts the discussion over differences between an 80 or 100 Watt amp in perspective.

Earlier on in the thread the point was made on how amps clip and/or what dynamic reserve there may be beyond rated power. Some manufacturers used Class G amps that allow an amplifier to achieve a high level of dynamic power, say an additional +6db over normal continuous rating into same impedance. If we listen to clipping that much with regular amplifiers, that could be an interesting proposition.
Also, from what I understand, Class D amps typically don't have much headroom over their power rating, so that may contribute to some of the negative views on Class D in general.
There's an interesting article on the issue of power & testing by John Atkinson in an article called "Must we test, yes we must!". The article is close to 30 years old, so the discussion is not new. Perhaps it is a good idea to test an amp's dynamic capabilities into different impedances and for more than a few nano-seconds, but more how long a true outburst/crescendo would last.

 

[Karbunkle]

On other side there are lot of amplifiers without feedback and they are also successfully being sold for crazy money, and even some sophisticated amps like CH Precision M1 with regulated amount ot global negative feedback which changes their sound and distortion profile...

Feedback is another delicious controversy. Bruno Putzeys (from uCD, nCore and now Purifi fame) states: "TIM isn’t caused by too much feedback. It’s caused by not enough feedback. That’s the exact reverse of what most people believe. If you see a lot of TIM it means you’ve tried, and failed to build an amplifier with a lot of feedback."
Below that article is a link to his PDF on the issue imaginatively titled "The F-word or, why there is no such thing as too much feedback". I've hearded several amps based on his designs and I like what I hear, so feedback can't be all bad.

 

[magicscreen]

I'm even more cautious in such opinions.
I'd say all the amps sound the same if they work with all possible and measurable distortions in "non-audible" range.

But if they work with all possible and measurable distortions in "audible" range can they sound different?
Interestingly, I cannot find successful blind test stories on the internet.

 

[SIY]

Feedback is another delicious controversy.

There's no controversy, unless you call "flat versus spherical Earth" or "Relativity can't be right!" a controversy- a hobby horse of a tiny but noisy fringe of people without any actual understanding of engineering and completely ignored by the vast majority of competent (and honest) practitioners.

This is one more pile of superstitious garbage that can be traced back to Jean Hiraga.

 

[JohnYang1997]

You always want to maximize loop gain. There's simply no room for discussion. Why care about distortion profile when you can achieve 1/1000th of the distortion altogether.

 

[FeddyLost]

Why care about distortion profile when you can achieve 1/1000th of the distortion altogether.

Which exactly distortion?
It's the main question. Distortion measured on some steady sine or good reproduction of incoming waveform of any shape and slew rate?

 

[JohnYang1997]

Which exactly distortion?
It's the main question. Distortion measured on some steady sine or good reproduction of incoming waveform of any shape and slew rate?

For audio, amplifiers are way too fast. I test using multitone.

 

[sergeauckland]

Which exactly distortion?
It's the main question. Distortion measured on some steady sine or good reproduction of incoming waveform of any shape and slew rate?

It doesn't matter.

ALL distortion is due to non-linearity. As the input voltage goes up and down a sinewave(or any musical waveform), the output MUST follow the input EXACTLY, scaled for gain. Any deviation from an exact match is distortion. It's due to the output NOT following the input exactly.

As ALL musical waveforms are a multiplicity of sine waves, of various frequencies and phases, and because of the Superposition principle, Non-Linearity using a single sine-wave is an EXACT measure of non-linearity, so the only benefit of multitone testing is to do on one test what requires several frequencies using a single tone. The results are EXACTLY the same.

As to Slew Rate, that's a total nonsense as the highest slew rate required for PERFECT reproduction is whatever the maximum voltage the amplifier is capable of, into its rated load, at 20kHz. get a low enough distortion figure for that, and Slew Rate MUST be adequate for no added distortion.

For a 100 watt amplifier into 8 ohms, the maximum slew rate required is 3.2V/uS, which is well within the capabilities of just about ANY amplifier worthy of the HiFi label.

S.