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Double Blind tests *did* show amplifiers to sound different

DonH56

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Caveat: I have not really followed this thread.

My assertion is usually weasel-worded as "most SS amps operated within their linear region driving most typical speakers will sound the same". Lots of ambiguity because I have not listened to, let alone measured, a large sample of amps connected to a similarly large sample of speakers any time recently. Treat all that follows as opinion.

As an aside: I respect Kal's opinions, and he has certainly opined that he can hear differences among amplifiers. In some cases I have had no problem picking out amplifiers as well so am not hard over on the "all amps sound the same" camp. But it's complicated...

I suspect few of us would have a problem distinguishing a SS amp from a tube amp. The differences, measured and heard, are large enough to be clearly audible on most speakers. One time I designed an OTL tube amp with differential stages and all that jazz, including feedback to (try to) keep it from blowing up speakers if an output tube shorted, and managed to get halfway decent specs out of it. The result? "Too SS-like." I made one of the input stages single-ended again, restoring most of the tube-like distortion characteristics, and then folk agreed it sounded more like a tube amp should. The high output impedance of a typical tube amp, coupled with the fixed-tap output transformer, makes them pretty load-sensitive. One reason I have always felt on ESLs many (most?) tube amps offer gorgeous midrange, somewhat poor highs, and poor bass (where the load is usually pretty high, a mismatch for the transformer).

SS amps generally have low enough output impedance and sufficient frequency response (i.e. the feedback loop can be closed over the audio band) that they will drive most speakers with aplomb. Unfortunately there are a lot of speakers out there that present an "interesting" load impedance. Speakers with wild excursions in impedance magnitude and phase (I have seen <2 to >100 ohms, and with phase changes well over 90 degrees) can represent a very difficult load for an amplifier. ESLs tend to drop dramatically in impedance at high frequencies (the panel is one big capacitor, after all, and of course the transformer is in the picture as well), and that is where feedback falls off as well, so the amp's output impedance increases just when you want it lower. There are stability issues and such that can cause strange things to happen with some speakers.

The gain structure and noise floor of the amp is in play as well; one of things I (many people) found years ago was, in blind testing, an amp with a higher noise floor was readily distinguished from another amp. We did a test with two tape (yes, 1/2" tape at that time) loops playing the same music selections using a couple of big SS amps (have forgotten which, Krell, Threshold, and Levinson were in the store at that time, among others). The speakers I've forgotten but I think were either Magnepan MG-20's or B&W 801's ca. 1982'ish. We might have run with both speakers, too long for me to recall. We inserted a 2 s silence between the selections on one tape, and went straight from one selection to another on the other. The selections were a mix of music but did not have very quiet (silent) passages. Gain matched the channels, natch. With the 2 s gaps, people easily picked out the "noisier" amp, and commented how it "filled in" gaps between piano notes, drum strikes, and such. Without the gaps, nobody was able to tell the two amps apart. IIRC the noisier one was class A but had fairly low SNR, like 80 - 90 dB unweighted, whilst the other amp was something like 100+ dB.

To me the differences in amplifiers are really the difference in how the amp plays with a particular pair of speakers, and of course how close to exceeding the amp's linear range you are. Horn speakers generally require less power but their high sensitivity means more susceptibility to noise (hiss). Panels, ESL and planar-dynamic, tend to be lower impedance and lower sensitivity so push an amp closer to its linearity limits but noise floor (SNR) may be less an issue. And so forth.

FWIWFM - Don
 

Fitzcaraldo215

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Don, bravo. An excellent post.

Needless to say, I agree completely. I do not think all amps sound the same into real world speaker loads, even if the amps seem the same into "standard" loads for the purposes of measurement. I think it is a matching problem, although the differences are not necessarily sonically earth shaking, in terms of my own experience. Somehow, usually always, the music always emerges from the speakers.

If we could have access to a database of measurements of any and all amp-speaker conmbinations, that would indeed be wonderful. But, we don't.

If there were someting better that the highly imperfect practice of listening with our own imperfect ears, I would be all in favor. But, we don't.
 

Blumlein 88

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Don, bravo. An excellent post.

Needless to say, I agree completely. I do not think all amps sound the same into real world speaker loads, even if the amps seem the same into "standard" loads for the purposes of measurement. I think it is a matching problem, although the differences are not necessarily sonically earth shaking, in terms of my own experience. Somehow, usually always, the music always emerges from the speakers.

If we could have access to a database of measurements of any and all amp-speaker conmbinations, that would indeed be wonderful. But, we don't.

If there were someting better that the highly imperfect practice of listening with our own imperfect ears, I would be all in favor. But, we don't.

I have in plenty of my comments on the matter indicated amps and speakers still need matching, and there are real though usually small differences. Same of microphones and mic pre-amps. In between I think we have transparency all the way for any competent gear. Not all gear is competent nor is all gear designed to be transparent. You can't sell a 'house' sound unless you have one that isn't transparency. Something I have in mind, but never gotten around to is something I think modern reviewers of amps/speakers should do in all reviews. Have a circuit to connect at the speaker terminals, reduce voltage in a transparent way, and feed an ADC. Then make those test listening tracks available for download.

Yes your own speaker/system colorations would be on top of those of the review system, but I think it would let you hear how amp/speaker combos differ in most instances.

Sonic Sense has done something similar for studio monitors. They record with a good quality omni condenser mike at about 1 meter various studio speakers. This is in a well treated fairly large studio that is on the dead side. Seemed like plenty of gotchas that would ruin such a simple minded idea. We record speakers so you can hear what they sound like remotely. I wished they used different, better and more music. Yet as goofy as it is this I have found lets you get a really good handle on the balance of response differences between various monitors. Recording speaker output at the speaker terminals would be several steps up from that in validity for remote comparisons.

Here is one example if you would like to try it.
 

DonH56

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Don, bravo. An excellent post.

Needless to say, I agree completely. I do not think all amps sound the same into real world speaker loads, even if the amps seem the same into "standard" loads for the purposes of measurement. I think it is a matching problem, although the differences are not necessarily sonically earth shaking, in terms of my own experience. Somehow, usually always, the music always emerges from the speakers.

If we could have access to a database of measurements of any and all amp-speaker conmbinations, that would indeed be wonderful. But, we don't.

If there were someting better that the highly imperfect practice of listening with our own imperfect ears, I would be all in favor. But, we don't.

Thanks Fitz. To your last point, if more people tested with more complex loads, we'd be able to better see the variation among amplifiers. There's the cube test that stresses magnitude and phase, and any number of more realistic test loads, that might show very measurable differences among amplifiers in a THD or even better an IMD test. Something like load pull tests routinely performed on RF amplifiers. Square wave testing, preferably into those loads, would be a good stability test. And so forth. Probably too much work for too few people who would understand the results.

My Maggies are a fairly benign if low-impedance load. Most amps handle them fine, provided they can handle a 3-4 ohm load and have enough power given their low sensitivity. I'm interested to see how the Salon2's perform with the same electronics.
 

bravomail

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the methodology they used and the number of people listening - makes it as unscientific as it could. while I would agree that all amps should sound the same, my short experience with DAC/Amps shows that every one of them have a distinct sound. I don't have that many.
Schiit Modi3/Magni2 - best so far, clean, transparent, powerful
Yamaha AVR 683 - more musical, but less details
Schiit Modi3 to Yamaha 683 - improves things, much easier to pick dialog details in the movies.
Galaxy S7 edge phone - very good and detailed
Hifime Sabre 9018 - good, "sweet" sound, I suspect some harmonic distortion
FX-Audio X6 - good, strong, "dark" sound, pleasant, but less details
Sabaj Da2 (SMSL Idea) - harsh sound
SMSL M3 headphone out - harsh sound, less details than Modi3/Magni2
Speaka USB dongle (XtremPro) - harsh, boomy and muddy sound

For the life of me, I don't know where that harshness comes from. Certainly, Amir measurements don't show it. But it makes listening for longer time absolutely impossible. I tried 2 headphones with each "device" - AKG K7xx and Audiotechnica M40x. Not very demanding.
 

Xulonn

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the methodology they used and the number of people listening - makes it as unscientific as it could.

Please describe the robust scientific methods - including double blind techniques - that you used used to achieve your results.

Or do you just have horrible hardware incompatibility problems that are causing severe distortion?
 

jamtinge

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Indeed my belief is that the difference in amplifier sounds occurs at the limits of their output. It is then that each amp acts very differently than others.
@amirm Sorry for bringing this old thread back to life. please take it as i am doing my homework.
You are the most knowledgeable/experienced person i can think of to ask this question.

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?
 
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ex audiophile

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I've had the pleasure of owning two powerful amplifiers, both with meters showing their output in watts (McIntosh MC312 and Anthem STR). Even when listening at high volume levels (85-90 db) the meters never showed an output greater than 30-40 watts and often much lower. This output is of course way below their max output of 300-400 watts/channel). Can I therefore assume that these amps were never at the point of clipping and would likely be indistinguishable from each other with all other factors equal? I've often wondered why the need for 100s of watts when real world listening typically requires very few watts (i.e. the first watt scenario).
 

sergeauckland

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I've had the pleasure of owning two powerful amplifiers, both with meters showing their output in watts (McIntosh MC312 and Anthem STR). Even when listening at high volume levels (85-90 db) the meters never showed an output greater than 30-40 watts and often much lower. This output is of course way below their max output of 300-400 watts/channel). Can I therefore assume that these amps were never at the point of clipping and would likely be indistinguishable from each other with all other factors equal? I've often wondered why the need for 100s of watts when real world listening typically requires very few watts (i.e. the first watt scenario).
One problem with meters on amplifiers is that they are hardly ever PPMs, and probably never true-peak PPMs, but generally are some sort of VU(ish) average reading meter. As such they are far too slow to show true peaks, which can be 20dB or more higher than the peak indicated by an average-reading meter. Your 30-40 watts indicated can be 20dB higher, or 100x, i.e. easily be 3000-4000 watts real peaks, so could well be clipping the amp. This isn't so much of an issue with a clean clip and fast recovery, but as Amir showed at the beginning of this thread, amps don't all clip clean and recover fast. They do all sorts of nasty things which can be audible. Once clipping goes on, what you're hearing isn't any difference between amplifiers, but the difference in their overload behaviour, which isn't (or shouldn't be) normal operating conditions.

I have not seen any evidence that two decently measuring amplifiers when used within their design parameters, i.e. no clipping and with permitted loads, will sound different.

Edited:- 20dB is 10x voltage but 100x power!!!!!!

S.
 
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Jimbob54

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@amirm Sorry for bringing this old thread back to life. please take it as i am doing my homework.
You are the most knowledgeable/experienced person i can think of to ask this question.

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?

See the replies below your post. The rest of the thread would indicate "no" to your question, but the question really is "but do you know if it actually isnt clipping ?"

You dont mention your speakers so its impossible for anyone to even begin to calculate whether your listening level could possibly cause the Denon to clip.
 

jamtinge

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See the replies below your post. The rest of the thread would indicate "no" to your question, but the question really is "but do you know if it actually isnt clipping ?"

You dont mention your speakers so its impossible for anyone to even begin to calculate whether your listening level could possibly cause the Denon to clip.
I have a denon 3600 with Emotiva T2, C2, E2, and 2 pairs of B1 ( 9 speakers + 1 active subwoofer ), sit about 12ft away from TV and listen around 65~70db on average. The speakers have crossover set at 80. I am fairly new to this hobby (Mostly movie) , but i thought i could notice if the sound was indeed clipping. Is it hard to tell?
 

ex audiophile

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One problem with meters on amplifiers is that they are hardly ever PPMs, and probably never true-peak PPMs, but generally are some sort of VU(ish) average reading meter. As such they are far too slow to show true peaks, which can be 20dB or more higher than the peak indicated by an average-reading meter. Your 30-40 watts indicated can easily be 300-400 watts real peaks, so could well be clipping the amp. This isn't so much of an issue with a clean clip and fast recovery, but as Amir showed at the beginning of this thread, amps don't all clip clean and recover fast. They do all sorts of nasty things which can be audible. Once clipping goes on, what you're hearing isn't any difference between amplifiers, but the difference in their overload behaviour, which isn't (or shouldn't be) normal operating conditions.

I have not seen any evidence that two decently measuring amplifiers when used within their design parameters, i.e. no clipping and with permitted loads, will sound different.

S.
Many thanks, that helps. I'm still looking up PPM but I'm sure it's not parts per million or Peter, Paul and Mary o_O
 

ex audiophile

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One problem with meters on amplifiers is that they are hardly ever PPMs, and probably never true-peak PPMs, but generally are some sort of VU(ish) average reading meter. As such they are far too slow to show true peaks, which can be 20dB or more higher than the peak indicated by an average-reading meter. Your 30-40 watts indicated can easily be 300-400 watts real peaks, so could well be clipping the amp. This isn't so much of an issue with a clean clip and fast recovery, but as Amir showed at the beginning of this thread, amps don't all clip clean and recover fast. They do all sorts of nasty things which can be audible. Once clipping goes on, what you're hearing isn't any difference between amplifiers, but the difference in their overload behaviour, which isn't (or shouldn't be) normal operating conditions.

I have not seen any evidence that two decently measuring amplifiers when used within their design parameters, i.e. no clipping and with permitted loads, will sound different.

S.
Peak Performance Meter!
 

sergeauckland

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Many thanks, that helps. I'm still looking up PPM but I'm sure it's not parts per million or Peter, Paul and Mary o_O
Peak Programme Meter.

They have a fast rise time and slow decay, and show the peak level reached. However, even the electronic ones (traditionally they were mechanical) have a fixed integration time, so won't indicate very fast peaks, typically of 2mS or shorter.

True-peak PPMs as their name suggest, measure the actual peak, however short, so would indicate even the shortest peak, limited only by the sampling rate of the ADC, which will be microseconds, so some 1000x faster than a normal PPM.

S.
 

raindance

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I recall a demo of some Vandersteen 1's with a Mac amp with VU meters. Vandersteen speakers are fairly inefficient. This salesman was trying to get a realistic volume level out of them in a medium sized room. The meters were almost hitting the stops and the woofers were clearly hitting their limits, making plopping and farting sounds, and his comment was: "I don't recall these little guys having so much bass!". Yeah, no sale.
 

ex audiophile

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Peak Programme Meter.

They have a fast rise time and slow decay, and show the peak level reached. However, even the electronic ones (traditionally they were mechanical) have a fixed integration time, so won't indicate very fast peaks, typically of 2mS or shorter.

True-peak PPMs as their name suggest, measure the actual peak, however short, so would indicate even the shortest peak, limited only by the sampling rate of the ADC, which will be microseconds, so some 1000x faster than a normal PPM.

S.
Thanks, much appreciated.
 

MakeMineVinyl

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Generally meters on amps are just voltmeters. We went a bit farther with the recent SAE HP-2 in that the meters are "virtual" and have two pointers, one for peak and one for average. There's a physical switch which selects calibration of the meter for 8 or 4 ohms. Of course, the meters are still basically voltmeters, but they are a better representation of what is going on than a mechanical meter. Some of our pro amps use clipping protection where the input signal is limited near clipping; I designed one of these circuits where the amp is actually analyzing distortion products, not simply detecting voltage.

I believe that amps have the potential to "sound different" at clipping, but also at low levels where bias current becomes critical.
 

jamtinge

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Generally meters on amps are just voltmeters. We went a bit farther with the recent SAE HP-2 in that the meters are "virtual" and have two pointers, one for peak and one for average. There's a physical switch which selects calibration of the meter for 8 or 4 ohms. Of course, the meters are still basically voltmeters, but they are a better representation of what is going on than a mechanical meter. Some of our pro amps use clipping protection where the input signal is limited near clipping; I designed one of these circuits where the amp is actually analyzing distortion products, not simply detecting voltage.

I believe that amps have the potential to "sound different" at clipping, but also at low levels where bias current becomes critical.

Thank you very much for the comment. Could you please elaborate more on this bold sentence?
I think this is what i would like to know in real life experience as i don't listen to anything at reference level, but would like to know if i could benefit from adding an external power amplifier.
 

DonH56

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You can get a rough idea of how much power you are using from an online SPL calculator like this: Peak SPL Calculator They have issues, though, like not knowing the impedance and sensitivity over frequency, simplified assumptions about room reflections and such, etc.

Severe clipping is pretty easy to hear as a harsh/raspy sound. Clipping just on peaks may be unnoticeable (how much clipping would it take to change the sound of a gunshot or explosion?) but could also lead to fatigue over time (clipping peaks on drum strikes and such so clean signals become "hashed").

Low bias and low feedback can increase (very) low-level ("crossover", not the same as the crossover in your speaker) distortion. That is rarely an issue for modern SS amps but some have postulated in may be higher due to the desire to run very low bias currents in multichannel AVRs and amplifiers to keep them cooler and more "green". I do not know.

Comparing SS (solid-state) amp to SS amp it is pretty hard to tell the difference IME unless they are very different (e.g. noise level, output impedance) and the speakers very hard to drive. Most folk (again IME) greatly overestimate their average power usage but underestimate the peaks, which can be 20 dB (100x the power) higher than the average level. I suspect most people who buy a power amp would not notice if you removed it in a blind test but there are enough exceptions, and enough poor AVRs, that there is no general rule (for me anyway).

FWIWFM - Don
 
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MakeMineVinyl

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Thank you very much for the comment. Could you please elaborate more on this bold sentence?
I think this is what i would like to know in real life experience as i don't listen to anything at reference level, but would like to know if i could benefit from adding an external power amplifier.
In a typical class A/B amplifier, bias is usually set at a level which is somewhat "conservative", meaning that consideration is given to effects of component aging, temperature variations in the real world and other factors so that under no circumstances can bias drift cause the amplifier to enter thermal runaway. Under some circumstances, crossover distortion can become a factor, and I have found it can be audible, especially with very efficient speakers where the amplifier is running through the region where operation transitions out of pure class "A". Some amplifiers avoid the problem by running very "rich" in bias, and subsequently run hot and tend to be lower power; some amplifiers run pure class "A" all the time, but these run even hotter and have lower power. There are other methods to handle this situation.

In an upcoming series of our amplifiers, we tightly regulate the bias current based on several real-time factors within the output stage. Therefore, we can run bias current far higher than usual into the optimum range without risk, while also offering high power . The bias is held at optimum levels all the time, under all circumstances.
 
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