Why do amplifiers sound different

Spectrum analyzers can see more of what's going on, with greater dynamic range than most people's hearing. With one big caveat: it can only measure a repetitive waveform that is nonvarying over "infinite time", something no musical waveform ever produces. Sure there's the fourier transform that can show that waveform accurately in the time domain that the scopes cannot, but it only allows for non-dynamic conditions.

Granularity of a signal, dithering of a signal, and random events all caused by an amp, and those do happen all the time, are "averaged away" by the precision spectrum anaylzer, because it only zeros in on the repetitive waveform, and tends to ignore the non-repetitive pieces of it. Even still, some harmonics and IMD signals are more damaging than other signals and we still are guessing how those varying combinations will make it sound.

There are sonic signatures of distortion from minor parts that measure almost perfect, and how can we possibly hear that, swamped out by immense other distortions? I once asked a similar question: how much of the chemical that ruins a fine bottle of wine by making it taste "corked" is required?

The answer: 5 parts per billion, or 0. Other chemicals have much less impact, even if you add some vinegar, or sulphuric acid, or worse. The only way to start examining the errors of the "perfect sound forever" CD was to have more than 16 bits and They are not perfectly equivalent.

The moral of this story: Seeing real time signals out of amps to the extent humans can hear requires a very high sample rate and measurement width bits resolution and watching over some time period from a source signal that is not a simple repetitive waveform.

But how to really compare the differences that do show up? How do you really interpret it? Still, there remains only one way - listen to the results in the context of the whole system. All audio designers that fail to do this are being oversimple and too trusting in their limited measurements and ignorant of the true nature of those measurements.

I've worked for a leading test and measurement company as a test engineer for 24 years now, and I think I know what I'm talking about on that subject. Kurt, thanks for your input.

A highly reputable Swiss manufacturer of audio amplifiers relies on the test bench results. According to this manufacturer a power amp should measure perfectly, until then it is flawed. When you do test bench measurements of this Swiss manufacturer's power amps, you will like to see excellent almost textbook perfect results. They measure the same? What did you measure? Kurt, I like your wine example. In amplifiers, it is TIM, IMD and high order odd harmonics that can make it sound "corked" even if the distortion levels are extremely small - would you agree?

Perhaps there are other "contaminants" that in extremely small doses can affect the sound audibly Dazzdax, That is still just one group of people's opinions. Transistor amps have always "measured better" than tube amps, as defined by standard bench tests devised by engineers. That is not sufficient to prove they are better, it's a belief that it proves it does. Now this swiss amp has heavy competition from amps that measure much worse than perfect, for the title of best amp.

How could that happen? Because it's still subjective. I used to be devoted to tube amps, but this is better in many ways for a moderate cost amp driving medium sensitive speakers. It's as modern a design as there is for amps, and measures well and sounds excellent. It has less personality than tube amps, yet more transparency than most transistor class A or AB amps and most tube amps as well. Since there is no perfect source and speakers, why should it be "correct" to own a perfect measuring SS amplifier?

What if it processes the signal a little that offers the illusion of richer instrument harmonics that got bleached out in the recording process? This could be considered better, not defective. Until source and speakers become perfect, I will never be pursuing the perfect "straight wire with gain" electronics to go with them.

I will search the best complementary electronics to go with them, within my budget. A lot of that comes from my custom built tube preamp where the parts and circuitry were all selected for overall sound quality, not bench measurement perfection. So where is the value in bench measurements for amps? Simple: factory quality control. An automated way to see if the completed product is within expected tolerances to ensure uniformity of them going out the door without the more expensive and impractical method of listening tests for all.

Shadorne, The levels of distortion that can ruin an amp can be so small that measurement is impractical, especially for a guy without very expensive modern test equipment.

And like I was trying to say, isolating the distortions in special cases are nearly impossible. In wine tasting, it's trivial to add 5 ppb of the diluted chemical that makes it taste corked. There are many chemicals to worry about in wine, and the levels that are needed to ruin the wine are all different. The chemicals can be isolated and added individually to find out this exact level needed to stay under to be safe. In audio, we don't have those numbers.

We can't isolate the contaminants without changing something else with it. All distortion claims are scientifically invalid as a result. Then in the 's it was stated that it better be under 0. The difference was the different content of the average amp's harmonic spectra, between the 's tube amps and the 's transistor amps.

And that was just the tip of the iceberg. I can hear the difference in resistors in an amp. What are the distortion levels caused by resistors? Almost nil, unmeasureable except to the best equipment available, like down dB. That's about 0. But its a different kind of distortion. A lot of it is some HF ringing from spirally wound inductive or possibly capacitive laser trimmed resistors, some also from magnetic nickel or steel construction in it with hysteresis distortion.

Capacitors have more impact, especially coupling caps. The greatest distortion generator in tube amps are the magnetics of interstage and output transformers. The main one being the large saturation and hysteresis distortion. Then there's the imperfections down in the microscopic level at the magnetic domains. Some domains don't respond well to small signals and low level detail might be obscured at low volume levels.

Nickel is better than silicon steel for the low signals and should be used for anything before the output transformer. Those kinds of distortions often don't really show up well in repetitive waveform measurements.

And if they do, they just ride on top of a bigger and more recognized distortion, or it looks like it's all from one known source. Again, isolating the audible small distortions that ruin the sound is a near impossibility. But some distortions are small and very annoying in limiting performance, one of the worst offenders being the distortions of different capacitor dielectric material. Yet for high level distortions that are seemingly more benign are the magnetic transformer distortions.

In transistor amps, the worst offenders are the transistors themselves IMO. Lots of high order distortion that need plenty of NFB to try to get rid of. And the typical vertical MOSFET has huge modulating input capacitance loading, which has shown to be a big negative to the sound. Luckily we now have lateral MOSFETs that go a long way to solving that problem, somewhat more expensive and hard to find, but are featured heavily in Ayre amps.

And now to the most controversial topic: wire and connectors. Does it have a distortion? If so, can I prove it? The answer is yes. The cell phone companies found the problem for the first time and measured it for the first time with the most expensive test setups. One channel might be transmitting watts out while the adjacent channel is receiving only 10 microwatts on the same cable. So they set out to measure the distortion of the cables since it appeared it was not good enough.

They were right. The distortion measurement is called Third Order Intercept, where the third order harmonic would reach the fundamental at a theoretical output. To fix it, they re-designed the connectors by silver plating them. Then the distortion of the cabling systems went down to an acceptable level. You can buy silver plated RF connectors now for this problem.

Anyway, it seems some people can hear connector and cabling distortions well. And there's some evidence to back up their claims. Although alluded to before, it seems that the amount of negative feedback is a big issue. The one without will likely sound more relaxed, since it lacks the global feedback which enhances odd-ordered harmonics which in turn behave as loudness cues.

We are not talking a lot, like Kurt says- hundredths of a percent is all it takes to make the difference. A further complication is the idea of 'constant voltage' output, which is the same as doubling the output power as the load impedance is cut in half. Other amplifiers are designed with the idea of "constant power" in mind- that is that power does not change regardless of the load tube amps are good examples of this.

Such amplifiers, sometimes referred to as 'current source' amplifiers, have a higher output impedance and an entirely different class of speakers exist to accommodate them Sound Labs and horns for example. Normally one paradigm will take over in a field of endeavor but that did not happen in audio because the 'prior art' tubes did not go away like they were supposed to- too many people like them.

Another interesting thread with great contributions by everyone. Is someone able to explain the difference between "current paradigm" and "voltage paradigm" amplifiers? Usually this refers to a tube amplifier, but not universally. What do you think about that? And what is up with that picture hahaha , is it some sort of a tin-foil hat?

Thank you!!! Can't believe i missed this feature , you guys surely created such a helpful tool. And when you mentioned a lack of power , do you mean as in the capability of the amplifier f.

I'm sorry if this question sounds a bit dumb haha , but i'm not fully sure if i understood you correctly. Joined Jan 22, Messages Likes In a word, bollocks!

It's true that some of the carbon composition resistors used in the s have changed value by enough to affect performance, but these haven't been used since the early s. Electrolytic capacitors can change in value, but even those usually last at least 20 years, and I have several amplifiers over 40 years old and still working to spec with original capacitors.

Pretty much all other components hardly age at all, although of course can fail. Joined Jan 24, Messages 24 Likes The point about people applying tube-amp degradation and characteristics to ss amps and even digital signals is very true.

The only thing you have to do is make sure the amp is powerful enough to properly drive the load and is made from at least decent components. A lot of people confuse the fact that a suitably powered amp sounds good due to a million other reasons aside from that basic point.

They start with a decent W amp into 4 ohm speakers at 83db sensitivity but drive it to clipping or distortion trying to reach the volume they like. Usually this amp now supplies wpc in the same speakers and what do you know?

It sounds great! Use the right tool for the right job and ignore the psychopaths that can literally convince themselves of anything, we're smarter than that. Buy decent equipment suitable for your application and you will happy for the rest of your life. Ignore the siren song to buy equipment 10x the price due to what idiots say and then try to convince yourself you made the right choice because you can't admit to yourself you wasted an exorbitant amount of money.

Well said Milk , thank you for replying to the thread. These terms - although describing a listener's experience - have no direct meaning in electrical terms. I don't have any real idea as to how we can directly link these to the common terms used by reviewers and listeners. Some writers have claimed that all amplifiers actually sound the same, and to some extent comparing apples with apples this is "proven" in double-blind listening tests.

Several years ago, noted reviewer Tom Nosaine conducted a study for Stereo Review magazine in which he attempted to compare the sound of two systems to a listening group through blind A-B testing. One system was made up of the very latest SOTA components and connectors. An acoustically-transparent but visually-opaque drape was drawn in front of the systems and the room lights were dimmed to assure no visual distraction.

Nosaine was well known for his adherence to the scientific process and his rabid attention to detail, so the scenario was well executed. His results showed that as long as neither system was pushed into distortion there was no statistically-significant preference shown for either system by the group, using a very extensive and varied selection of program material. It made no difference. Whether novice or golden ear, no listener or group of listeners scored any better at identifying which system was which.

Told ya so. So, in the end, his test settled nothing. There are some differences that cannot be readily explained. An amp that is deemed "identical" to another in a test situation, may sound completely different in a normal listening environment. It is these differences that are the hardest to deal with, since we do not always measure some of the things that can have a big influence on the sound.

For example: It is rare that testing is done on an amplifier's clipping performance - how the amp recovers from a brief transient overload. I have stated that a hi-fi amplifier should never clip in normal usage - nice try, but it IS going to happen, and it is more common than we might think. Use a good clipping indicator on the amp, and this can be eliminated, but at what cost? It might be necessary to reduce the volume and SPL to a level that is much lower than you are used to, to eliminate a problem that you were unaware existed.

Different amplifiers react in different ways to these momentary overloads, where their overall performance is otherwise almost identical. I have tested IC power amps, and was dismayed by the overload recovery waveform. My faithful old 60W design measures about the same as the IC in some areas, a little better in some, a little worse in others as one would expect. Were these two amps compared in a double blind test avoiding clipping , it is probable that no one would be able to tell the difference.

Advance the level so that transients started clipping, and a fence post would be able to hear the difference between them. What terms would describe the sound? I have no idea. The sound might be "smeared" due to the loss of detail during the recovery time of the IC amp. Imaging might suffer as well, since much of the signal that provides directional cues would be lost for periods of time.

Highly-regarded equipment, operating well within its intended performance environment. For me, the real difference between the two amps is how they translate music into sound. It's akin to the difference between what a great chef can do with ingredients that the average person could never come close to matching. The "notes" may be the same, but flavors are a very different story.

With amps, the sound, as opposed to notes, is the first thing to go.