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Old 7th March 2008, 10:26 PM   #1
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Default Do all audio amplifiers really sound the same???

I was on another audio forum and was told that:

http://www.avsforum.com/avs-vb/showthread.php?t=985008

"The science behind hearing and amplifiers tells us that the person making the claim that he hears a difference between two (properly functioning) amplifiers does in fact believe this claim, but that there is in fact no audible difference. That's not a bad thing, the reasons are pretty well understood (at least among people who study psychoacoustics), they just have nothing to do with the amplifiers. IOW, if you think you can hear the difference between two normally functioning amplifiers then you deluding yourself, it's a common delusion, but a delusion none-the-less..."

"The basic theory is that two amps will sound alike unless:

1) One is playing louder than the other.

2) There are audible differences in frequency response (which can often be caused by impedance mismatches, particularly in the case of tube amps).

3) One is clipping.

So if you hear an amp as more forward or warmer (whatever that means to you), it has to be caused by one of the conditions above.

Now, here's the thing: Among modern solid-state amps driving typical home speakers, it is very rare for conditions 2 and 3 to hold. As for #1, that has nothing to do with the character of the amps, and everything to do with where you set the volume control. Tweak it a little, and both amps will sound the same.

So your next question is, OK, if that's all true, why do I and other audiophiles hear differences between amps? Three reasons:

1) You're comparing without matching output levels, which has to be done very precisely (i.e., your ears and/or a Radio Shack SPL meter aren't enough; you need a voltmeter measuring the signal at the speaker terminals).

2) You aren't comparing the two side by side, but are relying on your long-term memory of the sound of one of them. Our long-term memory of subtle sonic differences is really poor.

3) You are subject to what the psychologists call "bias," which simply means that your hearing perception is influenced by other factors--specifically, other things you think or know about the amps. If some salesman once told you that Brand X tends to be warm, that's liable to affect how you hear Brand X. Can't be helped, as you're only human. That's why scientific listening comparisons are always done blind."


I do not believe this to be true as I have owned over a dozen amplifiers and each one had a unique character to its sound.

What is your take on this subject?
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Old 7th March 2008, 10:46 PM   #2
RAndyB is offline RAndyB  United Kingdom
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It's quite late for me to be up so this may seem a little brusqe ....

Slew rate, settling time, frequency response, output impedance etc.

All amps are slightly different, if you listen to complex music and are able to follow the score, or can remember the music well enough - then the better amps will give better definition, more bass and all the rest.

"well designed", "properly functioning" are misleading, unscientific, and probably being used by people trying to persuade you to buy a poor piece of equipment for more money than it is worth.

I have built 4 amps over the last couple of years. Each one has given a significant improvement in the realism of the music. This is confirmed by trips to the concert hall and making comparisons.

"relying on your long term memory of sound" - implying that you have no hope - is nonsense. How does a good violinist consistently produce a good sound?

It would be nice not to go round this loop too frequently. What do the people who write these foolish assertions listen to?

Andy
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Old 7th March 2008, 10:53 PM   #3
SY is offline SY  United States
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4) Both are clipping but one has better overload recovery.
5) One has excessive distortion. Maybe both.
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Old 7th March 2008, 11:01 PM   #4
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Regardless of WHY i can definitely hear a difference between amps. My Classe has a much deeper and wider sound stage then my other amps, my Bryston has MUCH more bass but is harsher on the top, my Soundcraftsmen is the smoothest but sounds pretty close to my Conrad Johnson MFA-2200

The interaction between my speakers and the amps im sure has a large part to do with the differences. So how can anyone claim two different amplifiers really do sound the same, when there are clearly audible differences due to whatever factor???
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Old 7th March 2008, 11:01 PM   #5
bigwill is offline bigwill  United Kingdom
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The NAD 3020 is known for sounding warm

presumably this is despite having a nearly ruler flat frequency response, indicating that this warmth is created by other variables such as the structure of the distortion harmonics

Before knowing of the 3020's warm reputation I heard one and I distinctly remember noting to myself its warmth and if anything slightly rolled off nature, exactly as people describe this amp


Another similar thing happened when switching between a Radford STA-25 and Radford STA15, I could immediately hear that the STA15 sounded cleaner and sweeter. This was before knowing the STA15's reputation of being the better sounding of the two! I was even biased toward expecting the STA-25 to sound better due to more headroom, but my ears said otherwise and so do many people when comparing these two amps.
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Old 7th March 2008, 11:06 PM   #6
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A couple of responses.
(a) I think that a lot of information may well be concealled within the term "properly functioning" when applied to amplifiers. I personally, am sure that I hear differences but I understand that there are reasons for this at a technical level. It is just a matter of "asking the right questions to get the right answers". It's not 'black magic' but it is probably not as simple as equal THD, equal bandwidth and common SPL either.
(b) Secondly, as the Good Book says....."the heart is deceitful above all things and desparately wicked..."* and I have a great respect for the ear, brain, internalbiasnetwork, education, prejudice level, buget, WAF etc part of the brain to be less than truly objective. This is especially true if you or a friend built it, it is cheper than yours or you are too tired to bother building another one just yet......
(c) I also want to remain open to new discoveries in both hearing and electronics that will shed light on our subjective responses. I recently read a broad overview of science/tecnology for the last couple of millenium and it is a very sobering read to see how each sucessive generation was forced to review the accepted wisdom and "100% cast iron conclusions" on which they had functioned only to have to abandon them. I mean
as recently as the last 10 years the whole cosmological debate has been thrown into confusion by the appearance of 'dark energy' and an accelerating, expanding universe, co-discovered by some Australians BTW (if I have got that right).


* The prophet Jeremiah, I think.
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Old 7th March 2008, 11:13 PM   #7
jcx is offline jcx  United States
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one reason to consider the proposition -

The Carver Challenge:

http://www.diyaudio.com/forums/showt...392#post152392

just an ancedote, but worth considering as evidence that controlled listening tests seem to contradict what we all "know" by "just listening"

how many hobbyists actually build up 2 or 3 complete functioning (at the same time!) stereo amplifiers for blind testing of single change tweaks with the full controls psychoacoustics finds necessary to remove established audible differences cited above
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Old 7th March 2008, 11:19 PM   #8
teemuk is offline teemuk  Finland
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Let’s also add…

6) Both amplifiers are clipping but the transition characteristics to this condition are different (“soft” versus “hard” clipping)
7) Both are clipping but the overall “symmetry” of clipping is different in each amplifier

Maybe it's just easier to say that different ways of clipping create different harmonic patterns. Very often these also change when overdriving condition is extended (DC offsets vary and alter the symmetry etc.)
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Old 8th March 2008, 01:09 AM   #9
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Dr. Earl Geddes did some testing and came up with the "GedLee Metric" - a way of measuring differences based on criteria that are not the usual "distortion" figures.

I think his "metric" explains the reasons that amplifiers can and do sound different, and these diffs do not "track" with "distortion."

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Old 8th March 2008, 01:12 AM   #10
sidiy is offline sidiy  Canada
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Why not, if applicable to the design(s) in question let's add:

8) Positions of the zeroes notably the high pass at the input and ground leg of the NFB; likewise the position of the pole(s) , without even considering the dielectric type of caps, etc...

Easy to see on a chip amp...
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