Determinants of amplifier performance

[Sawyer]

Question : What then should decide the purchase of an amplifier?

Answer: Your EARS only.

Agreed. How do you ensure the only part though?
Your sense of what you have heard is a brain process. This process takes inputs from the ears, the eyes, and the skin. And from resident knowledge in the brain, that results in things like expectation bias, all of which go into the experience known as hearing.

 

[Sawyer]

That all modern day solid state amplifiers working within their design limits will not have a sonic signature is quite natural. It is the outcome of a lot of years of effort of many designers working towards the objective of making their device hew to one classic definition of an amplifier - straight wire with gain. The problems relating to achieving this to the degree required to meet this objective to the extent human hearing can hear have been solved a long time ago.

It also makes commercial sense to make these kind of amplifiers, because they can then be sold to a larger market. Leave a sonic signature in place and you restrict the market to people who like that particular signature. Far more profitable to build in tone controls, which allow customers to tweak the sound to the kind they like to hear once the speaker is at home, interacting with room acoustics to deliver the final product. And almost all modern day amplifiers come with well implemented tone controls to allow just that.

 

[Sawyer]

Re: Amplifier tech specs

The simplest way I've found is to try the amp with your speakers.

Yes, that is one way. Wire in the amp, see how it sounds, like it, buy it. Job done.
Easy.
Where it gets difficult is when one has to choose between more than one - either when upgrading or when having to choose between two new ones. What then?

 

[kanwar]

The main thing which co-relates with the 'Sounding' of the amplifier into Bright, Warm, Dry is the Inter-Modulation Distortion which is not much published.

Harmonic distribution 3D spectrograph obtained from 19k+20K & 6.5k +10khz signals can reveal alot but ,unfortunately very rarely done.

 

[kanwar]

Ok, here we go.
Layman question: My amp is 140 wpc, and also has peak current supply of 11 amps a channel. Don't the two go together - will there be another 140wpc amp, that does not supply the same current level if needed to? Assuming both amps are honestly specced.

Its not the peak current only which is needed to drive the reactive energy system comprised of Lossy Passive XO + drivers , what we call as speakers. The impedance is not resistive in nature its reactive means the peak current demand is not linear with voltage, rather it has phase angle at which it is being drawn from the amplifier, it could be 30degree or 45 degrees.

Under those conditions the amplifier will have zero crossing at voltage at output but the current flowing through it can be as high as 10 amperes. Which can put great stress on the output devices and considerable heat generation occurs in linear class-A/AB amplifiers. Class-D amplifiers are immune to this, they recycle the reactive energy back to power supply hence are fun to play with.

So 2 different amplifiers with same rated wattage cannot be same unless designed on similar lines by taking consideration of reactive current.


See the pic, current and voltage waveforms are not following each other, they are PHASE SHIFTED due to presense of reactive elements[capacitors & Inductors] in the path of current.

 

[jai1611]

Re: Amplifier tech specs

If some one likes to hear distorted tube sound as a preference, that is one thing. The word distortion doesn't by definition mean unpleasant. Some people also like the distortion caused by low powered amplifiers - clipping mildly this may be a very rational subjective preference. Question is - are they being as true to the recorded signal as another amp, say a modern solid state amp from almost any reputed global brand?

Unfortunately its not as simple as that. Going by specs (THD, SNR), the Marantz PM7001 should be more resolving than the tube amp I currently use. Unfortunately it wasn't. So I guess it wasnt as true to source.

As to the Harbeth/Dynaudio difference - my view is that it is just a matter of one needing a lot more power than another to perform as designed. This is not any reflection of how they sound, or which one sounds better. The only difference is that the power hungry speaker will need a more powerful, and therefore more expensive amp to work well. I can't imagine that over two adequately powerful amps, the Dynaudio will be picky in terms of preferring one over the other. If I am wrong, I would love to hear a scientific reason for this.

I have heard a very high powered, well reviewed and extremely well specified Nuforce amp with Dynaudios and it sounded like rubbish. I also heard a very high powered and well specified amp that Kanwar made with Dynaudios and it sounded excellent.

Instead of looking for theory, try this experiment: take 2 50w amps - say a Naim 5i and a Marantz 6xxx. Play them back to back with a familiar pair of speakers and see if they sound different.

You missed the point about output impedance - that is speaker dependent and is not just linked to power (as measured by wattage) but output impedance. A lot of amps don't even come with that specification, let along things like slew rate.

 

[Sawyer]

Re: Amplifier tech specs

Instead of looking for theory, try this experiment: take 2 50w amps - say a Naim 5i and a Marantz 6xxx. Play them back to back with a familiar pair of speakers and see if they sound different.

I have. Many times with amps I have owned over the last 15 years. Unison S6, Unison Unico, Conrad Johnson 2500, Quad 909, Nad c350, Rotel Ra2, a Marantz whose model name I don't recall, it was one with Class A and AB operation selector.
No difference in the heard sound. Provided sound level matching was done with some care.
PS: the same results once with a monster Plinius power amp that had finger cutting heat sink fins if one tried to lift it up - I think it was a Class A thing. But that was just a 2 hour session, it did not make any sense to me to buy it.

 

[jai1611]

Re: Amplifier tech specs

I have. Many times with amps I have owned over the last 15 years. Unison S6, Unison Unico, Conrad Johnson 2500, Quad 909, Nad c350, Rotel Ra2, a Marantz whose model name I don't recall, it was one with Class A and AB operation selector.
No difference in the heard sound. Provided sound level matching was done with some care.

To each their own. Unfortunately, I do hear a difference so have to pay attention to amps

 

[Sawyer]

The main thing which co-relates with the 'Sounding' of the amplifier into Bright, Warm, Dry is the Inter-Modulation Distortion which is not much published.

Harmonic distribution 3D spectrograph obtained from 19k+20K & 6.5k +10khz signals can reveal alot but ,unfortunately very rarely done.

But the above can be measured and seen on instruments if one chooses to do so, right?
Taking what you say further then, an example of say Marantz and Rotel. I am not sure about the adjectives used, but Marantz is said to sound more musical while the Rotel is more punchy and analytical. Whatever that means.
The IMD you refer to, if measured for these amps should show different readings?
Assuming that to be the case, a follow up question:
Is this IMD difference something that the respective designers would have built into the amps, or is it something that happens by accident or oversight?

 

[kanwar]

But the above can be measured and seen on instruments if one chooses to do so, right?

Yes, they are easily measurable, provided one has the test equipment to do so.

Taking what you say further then, an example of say Marantz and Rotel. I am not sure about the adjectives used, but Marantz is said to sound more musical while the Rotel is more punchy and analytical. Whatever that means.
The IMD you refer to, if measured for these amps should show different readings?

Yes

Assuming that to be the case, a follow up question:
Is this IMD difference something that the respective designers would have built into the amps, or is it something that happens by accident or oversight?

IMD difference depends on lot of things, choice of components, circuit design, implementation and so on, its not by accident, its the measure of inter modulation distortion components produced by the amplifier itself.

 

[Sawyer]

IMD difference depends on lot of things, choice of components, circuit design, implementation and so on, its not by accident, its the measure of inter modulation distortion components produced by the amplifier itself.

Excellent. I read this to mean that IMD is introduced in the amplifier by design, to give it an audible sonic signature and different levels of IMD will result in different sonic signatures.
Before going further, let me say that all I am trying to do is understand why is it that among the many amps I have owned, of various makes, I was unable to perceive any difference once I had done an approximate sound level matching, which is all one can do at home. This isn't just frivolous theorising, so bear with me for a while.
Coming back to the IMD point, the next logical assertion based on what I have understood you to have said about IMD is that Marantz and Rotel, just to continue with the same names, have different levels of IMD built into them by design to provide them with a desired sonic signature, although they can choose not to do so, and have the means to both measure and bring down the IMD to levels where any sonic signature disappears to below human hearing thresholds. They may not publish IMD data, but it is reasonable to assume that they have the instrumentation to measure it. It is also reasonable to assume that the technology to get any sonic signature down to below the hearing threshold is now commonly known.
Which means, that by design and by intent, both are choosing to depart from the technical objective of hifi, which is to be as true to the source signal as possible, keeping in mind cost constraints to meet price point needs.
Is there any thing wrong in what I have said till now?

 

[kanwar]

IMD is inherent as a byproduct not intentionally put in the design by the designer. Only some designers tweak the harmonic structure to get some particular sonic signature. I prefer transparent and neutral signature.

If you were unable to hear the difference, good for you, since i cannot comment on your listening prowess

 

[Sawyer]

IMD is inherent as a byproduct not intentionally put in the design by the designer. Only some designers tweak the harmonic structure to get some particular sonic signature. I prefer transparent and neutral signature.

Ahh...so it is not by design. A question then: would you agree that making an amp with a transparent and neutral signature - to the extent that can be audibly discerned - isn't rocket science anymore? Or, to put it differently, this is a problem that has been solved many years ago such that it can be solved to the extent required by mass manufactured solid state amplifiers, made from mass manufactured components, of the kind that the global audio majors use nowadays? Using the design expertise and manufacturing tech they have access to?

 

[Sawyer]

For anyone with the time and interest, the link below may be useful.

Post deleted, error in link.

 

[kanwar]

It depends on the designer's philosophy + manufacturer's motive + budget involved + target customer. Do not generalize it. Its highly variable. Not all amplifiers are transparent and not all amplifiers are colored heavily.

 

[Sawyer]

It depends on the designer's philosophy + manufacturer's motive + budget involved + target customer. Do not generalize it. Its highly variable. Not all amplifiers are transparent and not all amplifiers are colored heavily.

Hmm...perhaps some else here will chip in with a reply that is less ambiguous.

 

[mpw]

Hmm...perhaps some else here will chip in with a reply that is less ambiguous.

============================================

whats ambiguous here sawyer ? u want someone to measure for you and put up the results here ?

if you havent understood it - doesnt mean the reply is ambiguous.

or perhaps u want to see what u want to see and hear what u wanna hear ?? :lol:

mpw

 

[Sawyer]

if you havent understood it - doesnt mean the reply is ambiguous.

Perhaps. But post#33 is straight forward question that does not ask for any measurements or results.
I am quite happy to wait.

 

[Thad E Ginathom]

So, Sawyer, I would guess that 6 moons is not one your favourite sites? hyeah:

It depends on the designer's philosophy + manufacturer's motive + budget involved + target customer. Do not generalize it. Its highly variable. Not all amplifiers are transparent and not all amplifiers are colored heavily.

And not all magazine articles or reviews are rubbish, although I admit I'm extending Kanwar's statement onto much thinner ice here. Not only are some magazines quite good, they can even be good enough to admit getting it wrong sometimes. And they measure, if measurements float your boat.

I have to admit that (in so far as they mean anything to me) I'd rather look at, eg, Stereophile's measurements than any manufacturer's (outside pro audio) specifications. They may not lie, as such, but whatever they publish comes from the marketing department and not from the engineers, and presentation is all. People look at the graph; many don't look at the scale; perhaps the scale might be absent altogether. Perhaps this stuff might be more relevant to selling speakers, but I do think that it applies to all commercial domestic audio equipment. But then... I'm a cynic :lol:

I've hear it said that THD is one of least useful measurements, but people like to see it, and marketing departments want us to be able to show us number down there in the thousandths.

Isn't IMD a no-no nasty, enharmonic distortion, producing frequencies that don't musically relate to anything in the music content? (Just an off-topic question)

 

[Sawyer]

So, Sawyer, I would guess that 6 moons is not one your favourite sites? hyeah:

Is that where the guy - I think it is a he - with the unpronounceable and almost impossible to spell name writes?
Like most such places, it is free entertainment, often good for a laugh. And to expand my vocabulary of adjectives.