Why Audio Amplifiers Can Sound Different

[TLS Guy]

I'm certain amps sound different. The question is, do we measure the right things? I have maintained for years not nearly enough attention is paid to low signal behavior, only at power. How much THD at 200 watts? Much more we should answer what is the performance at a fraction of a watt. Not important you say? Well I can tell you the ear is far more sensitive to trouble at very low signal levels, that at full bore.

Those tests really sort it out. The reason I believe is that we are very sensitive to ambient tails. If you think about it there is huge evolutionary advantage to that.

We get back to the pop classical divide. Pop music is highly produced with purposely built in distortion and very little in the way of natural ambient information.

Low bit rate streams really show this up, as they wreak havoc on the ambient tails. The wisdom is it is not important.

I really don't like bit rates lower than 320 kbs, and even then it is problematic 640 is better and no loss in a codec better still.

Quite honestly I don't like listening to class A/B amps, I don't think they sound right and I can and have picked them out. I think class A designs do sound better, and is probably the reason for the tube persisting.

I use Quad current dumping amps. I think they do best any standard A/B and to me they give far more relaxed and detailed listening. I admit part of this is that all my speakers are designed and voiced with these amps. However I have tested other speakers with these amps. I can tell you that I think the top end B &W speakers sound significantly better powered by Quad than MAC.

 

[Seth=L]

@TLS Guy

I know you have probably covered this topic before, but what is it about Quad that makes them unique from most if not all other amplifier manufacturers?

 

[TLS Guy]

They are a unique topology. In the early 70s Peter Walker and Williamson published a paper showing that you could design an amp , that was feed forward and not just negative feedback and keep it stable. The concept, was to have the output transistors give gobs of power and be biased to operate in their efficient range and not produce a ton of heat and premature failure. A very high quality class A amp then provided a feed forward error signal to correct the "dumper" output stage. To prove his point the dumpers were originally biased class C. He showed by math and by results that the performance was set by the class A amp and not the dumpers.

The first was the 405. There were significant teething troubles with those. The 405 II were much better, the later versions better. However the whole 405 series was a work in progress which just fascinated Peter. There are a lot of iterations of the 405 and 405 IIs. You can only tell which iteration by the number on the circuit board.

The last two iterations of the 405 II are superb amps.

Here is a 250 watt into 4 ohm amp board in a 909.

However it was not until the Quad 606 that I think this design was truly mature. The 909 is a really superb amp. The new QSP that replaced it is controversial, produced under the ownership of the new Chinese masters.

In any event these amps do perform and measure as class A. The output transistors operate in a range where they are nice and cool, but heavily biased to class B. They are biased A/B though.

The circuit is elegant with a very low part count. I know of no other powerful amps were the boards are so small and with so few components. Because of the self correcting nature of the design, few if any high tolerance components are required, and the power transistors do not even have to be matched! Components can age and wander up to 30% from spec in most cases without affecting performance.

All these factors make for a design which sounds excellent, runs cool and long life can be expected.

All I know is that since the 909 was replaced by the QSP, the value of the 909 has skyrocketed, especially the older ones made in Huntingdon. I understand some of the Chinese ones have had ground plane issues. Most of mine are UK built, I do have at least one of Chinese manufacture and have not had a problem with it.
These amps are dead quiet. Now I have gone to LED bulbs and replaced all the dimmers with the latest Lutron Maestro LED dimmers, there is zero audible sound from the speaker, even right up close.

Nelson Pass did produce an amp that is feed forward like this and the controversy continues about whether this was a patent infringement.

However only Quad and Nelson Pass have taken this approach.

Although the circuit at first glance looks simple, it is anything but, and looks as if it should not work, but oscillate like fury.

I think this issue of how to handle the feed forward issue and maintain stability scares most designers off. That is a pity. I have not experienced stability issues since the very first versions of the 405. In those days I had a lot of trouble getting the amps stable after a need to service. When all ease failed Peter would just send me an amp board that he knew worked, free of charge!

 

[Seth=L]

Thank you for that informative post. I'll re-read it again and do some more research. I've always been slightly interested in their stuff.

What can you tell me about this Niles SI-275 I've been using? From what I understand it uses a triple darlington output stage configuration and is dual mono. I've read a few people say that it's dark and lifeless and not really worthy of high fidelity use. Niles advertises it as being stable down to 2.66 ohms although it doesn't give a wattage rating for that figure.

• 2 X 75 Watts RMS/Channel Into 8 Ohms, .05% THD (Both Channels Driven)
• 2 X 120 Watts RMS/Channel Into 4 Ohms, .08% THD (Both Channels Driven)
• Stable Into Low-Impedance Loads (2.66 Ohms)

I'll add a picture if it helps.

 

[TLS Guy]

Thank you for that informative post. I'll re-read it again and do some more research. I've always been slightly interested in their stuff.

What can you tell me about this Niles SI-275 I've been using? From what I understand it uses a triple darlington output stage configuration and is dual mono. I've read a few people say that it's dark and lifeless and not really worthy of high fidelity use. Niles advertises it as being stable down to 2.66 ohms although it doesn't give a wattage rating for that figure.



I'll add a picture if it helps.

I don't know that amp. So much comes down to implementation.

What little I do know about triple Darlington output stages, is that current requirements are low, and they are good for low impedance loads.

Their Achilles heel is frequency dependent phase shifts, especially with rising frequency. This might occur in the Niles amps and could easily account for their reputation. Again this is not something that would show in usual amp test procedures..

 

[highfigh]

I'm certain amps sound different. The question is, do we measure the right things? I have maintained for years not nearly enough attention is paid to low signal behavior, only at power. How much THD at 200 watts? Much more we should answer what is the performance at a fraction of a watt. Not important you say? Well I can tell you the ear is far more sensitive to trouble at very low signal levels, that at full bore.

Those tests really sort it out. The reason I believe is that we are very sensitive to ambient tails. If you think about it there is huge evolutionary advantage to that.

We get back to the pop classical divide. Pop music is highly produced with purposely built in distortion and very little in the way of natural ambient information.

Low bit rate streams really show this up, as they wreak havoc on the ambient tails. The wisdom is it is not important.

I really don't like bit rates lower than 320 kbs, and even then it is problematic 640 is better and no loss in a codec better still.

Quite honestly I don't like listening to class A/B amps, I don't think they sound right and I can and have picked them out. I think class A designs do sound better, and is probably the reason for the tube persisting.

I use Quad current dumping amps. I think they do best any standard A/B and to me they give far more relaxed and detailed listening. I admit part of this is that all my speakers are designed and voiced with these amps. However I have tested other speakers with these amps. I can tell you that I think the top end B &W speakers sound significantly better powered by Quad than MAC.

With a full surround system being a minimum of 5 speakers, how much power is being dissipated when someone is achieving 105dB, anyway? A few Watts/channel, is my guess. Max output is for the sales/marketing departments, unless the installation actually requires a specific output and even then, they'll be choosing amplifiers based on stated output and headroom.

The standard IM distortion tests are good, but I think it would be difficult to measure or analyze the signal's distortion at extremely low levels when the complexity of music is used as the source. I don't know is anyone is expanding the time /division as a way to see this when they design or test amplifiers.

 

[Bruce M Chassy]

I have no technical expertise in electronics but I enjoyed this discussion. I do believe that amps with the same specs sound different and it's good to know at least one test that reveals differences. Following up on square waves on a scope, I wonder if you could reconcile the difference in sound with what we hear coming out of a speaker--and which if you look at the speaker output doesn't look like a square wave at all. It's frequency dependent and speaker dependent i know, but many speakers mutilate square waves yet what we hear comes from speakers not scopes. There are all sorts of beliefs around certain speakers pairing well with certain amps. Is it possible that the kinds of overshoots and undershoots you are talking about minimize or add to the alterations imposed by the speaker? This might even explain why an inferior amp could sound better with a particular speaker than an expensive one. i don't know if I have asked this correctly but could you comment on how perfect square waves get mangled by less than perfect transducers and how that fits in to your observations.

 

[ATLAudio]

Does this mean I'll finally stop getting flamed every time I post on here about stuff sounding different but measuring the same, given the limited set of traditional measurements?

Can you provide any evidence to support this statement? Are you saying that there's no way to possibly measure some sounds which our ears can hear???

 

[TLS Guy]

With a full surround system being a minimum of 5 speakers, how much power is being dissipated when someone is achieving 105dB, anyway? A few Watts/channel, is my guess. Max output is for the sales/marketing departments, unless the installation actually requires a specific output and even then, they'll be choosing amplifiers based on stated output and headroom.

The standard IM distortion tests are good, but I think it would be difficult to measure or analyze the signal's distortion at extremely low levels when the complexity of music is used as the source. I don't know is anyone is expanding the time /division as a way to see this when they design or test amplifiers.

You are right this is a difficult problem. Peter Walker did study this. Unfortunately he was not good at publishing so much of is hard work. But he did tell me the poor performance of A/B amps was the really big push to find an alternative.

All his solid amps were current dumpers except his first which was the 303. It uses tripples in the output stage but only outputs 45 watts per channel. The amp was severely derated to keep it out of high swings to class Bias. It is a long lived very stable amp and sounds good. It is one of the very few amps that can be parallel bridged. However he was in constant search of something better.

 

[TLS Guy]

I have no technical expertise in electronics but I enjoyed this discussion. I do believe that amps with the same specs sound different and it's good to know at least one test that reveals differences. Following up on square waves on a scope, I wonder if you could reconcile the difference in sound with what we hear coming out of a speaker--and which if you look at the speaker output doesn't look like a square wave at all. It's frequency dependent and speaker dependent i know, but many speakers mutilate square waves yet what we hear comes from speakers not scopes. There are all sorts of beliefs around certain speakers pairing well with certain amps. Is it possible that the kinds of overshoots and undershoots you are talking about minimize or add to the alterations imposed by the speaker? This might even explain why an inferior amp could sound better with a particular speaker than an expensive one. i don't know if I have asked this correctly but could you comment on how perfect square waves get mangled by less than perfect transducers and how that fits in to your observations.

The only speaker I know of that produces a half respectable square wave are Peter Walker's ESLs

Crossovers just play fast and loose with time and phase. We are just so used to what is really the dreadful performance of the vast majority of speakers, it covers the other ills.

Most say these terrible trespasses speaker play with time and phase don't matter.

As E.J. Jordan has pointed out, most speakers totally disconnect the fundamental frequencies from their associated harmonics. Unfortunately at this state of the art creating these types of issues is to an extent inevitable.

I do work hard to minimize these problems. I don't play fast and loose with phase and time, not at all.

I have quite a number of these 4" full range drivers, and properly loaded listening to them in many ways is a total revelation.

I think the day is not far away when active speakers with digital time and phase coherent crossovers will highlight the problem. However the need to space drivers will not allow total elimination of the problem. However I do believe that very wide band drivers operating over most of the audio range, certainly the crucial speech discrimination band could be produced. The fact there has not been movement on this is actually nothing short of scandalous.

The speaker as we know could be improved drastically at this time, and without the end result requiring a mortgage. The vast majority of speakers available today are very sorry affairs indeed. So much so, amp issues pale in comparison.

 

[Shike]

First, I will say that amplifiers that measure roughly equivalent will sound the same. This means that they need to be stable into equally low loads. If a speaker is dipping into two ohms impedance and one copes better with the load then there's a chance of audible difference. That's simply a fact.

How do you know if an amplifier is linear? Know the load the speaker is presenting, and know the load the amplifier can run stable with. Buying an unknown amplifier of questionable quality or expecting an entry level AVR to run ribbons is silly. Tons of review sites like Audioholics perform various degrees of testing that can give lots of information. Some speaker manufactures even list minimum impedance their speakers hit.

The reality is the speakers need to match the amplifier or vice-versa unless you want to create a potential upgrade path for something more demanding.

For example let's take speakers that are super easy to drive. Anyone remember the original NHT SuperZero? Basically never dips below 8 ohms and is of average sensitivity. In a nearfield setup, what are the odds you would hear a difference between an entry AVR and a multi-thousand dollar amplifier when level matched? This speaker is so dead simple to drive, it would be near impossible to drive an established modern AVR out of stability. I drive some in an ambiophonic setup using an E200.

In comparison, a pair of Magnepan MMG I used to own might drive it into protection at the right distance/level - likely with the sound degrading quite a bit leading up to that point.

If you stack the deck by using a load the amplifier was likely never intended to face in reality then the problem isn't really the amplifier, but instead the misuse of it. A budget AVR is made for the traditional HTIB, not a pair of vintage Apogee ribbons.

On another note the idea that a different topology and a slight difference in distortion and output impedance (on solid state designs) is going to be responsible for differences is being grossly optimistic. How many people here believe cables make a difference? If you have a silver cable vs. a copper cable, are you prone to tell the difference? No, because we realize the material change in this case is hardly important to the end result. Surely the capacitance, resistance, and shielding will measure different but it's not seen as significant in most cases. You could build something so bad, so awful that it sounds different, or have ones that under extreme cases may do something like pick-up noise where one with better shielding wouldn't, but for all intents and purposes most argue there really is no difference in most cases.

Gene notes they've done blind tests, but not which products and how the testing was performed. Was the full input sensitivity utilized, were they voltage matched at output, was channel balance completely confirmed, were the amps ran within their linear range, and were enough trials ran to be considered statistically significant beyond guessing? If not, saying they heard a difference could just as likely be blamed on the testing methodology itself.

In tests where these have all been addressed no one has found a difference under controlled conditions yet.

 

[&dre]

I was hoping you'd cover vacuum tubes. I've had so many audiophiles laud the merits of vacuum tubes, but I've yet to see some science behind it. I'll admit that they look cool.

 

[Speedskater]

Well the papers were interesting, but the YouTube was a total pain! At one point they would say that 'A' is true, later they would say that 'A' is false. Oh they also added a few straw-men along the way. Now I don't think that they planed to do either of those things, but YouTube's lack the discipline of writing a paper.

 

[Seth=L]

Their Achilles heel is frequency dependent phase shifts, especially with rising frequency. This might occur in the Niles amps and could easily account for their reputation.

How is that precisely? I'm not as well versed as you. How would you explain this to the layman?

 

[Buckeyefan 1]

Class A 30 watt amplifier for me, please. A little tube distortion never killed anyone.

 

[highfigh]

I was hoping you'd cover vacuum tubes. I've had so many audiophiles laud the merits of vacuum tubes, but I've yet to see some science behind it. I'll admit that they look cool.

One main difference between tubes and solid state is in how each distorts and what the product(s) of the distortion are. Tubes create 2nd harmonics, which blend with the fundamental in a musical way and I'm not getting all care bear when I use the term 'musical'. I mean it's a musically harmonic frequency that's considered to be consonant, not dissonant. Dissonant tones clash with the fundamental and make the sound harsh, edgy or whatever someone wants to call it. The 2nd harmonic is the first octave above the fundamental. Also, solid state amps don't stop there, they continue to add the 3rd, 4th, 5th, 6, and worst of all (according to many), the 7th harmonic. According to John Curl, who is a noted amp designer, the old AT&T tube manual shows that any amount of the 7th harmonic is a very bad thing for the sound. The others don't work well, either.

There are many other differences between tunes and solid state including how the amp couples with the load, how the amp's load affects the output section WRT the way the load is reflected back and how the various sections of the amp work.

There's a lot of info on tube circuits, in print, online and in videos on many websites including YouTube. I was just watching a video with Nelson Pass and if you're familiar with Threshold amplifiers or the DIY Audio website, that's him. Very informative and he touches on how tubes compare with some of the solid state devices he's working with.

 

[3db]

What this thread is pointing out that amps do sound different but that's because some aspect has been measured to cause the audible difference. There is no doubt in my mind that amps that measure the same in all aspects (measured in detail beyond what the audio rags report) WILL sound the same well within their operational limits despite class. I'm also of the school that everything we hear is measurable and our hearing sensitivity is far less capable in discerning nuances than test equipment and a well thought out test plan. I don't believe in "golden ear super hearing capabilities" either. Trained listening yes.. but even that ability changes with age.

 

[ATLAudio]

One main difference between tubes and solid state is in how each distorts and what the product(s) of the distortion are. Tubes create 2nd harmonics, which blend with the fundamental in a musical way and I'm not getting all care bear when I use the term 'musical'. I mean it's a musically harmonic frequency that's considered to be consonant, not dissonant. Dissonant tones clash with the fundamental and make the sound harsh, edgy or whatever someone wants to call it. The 2nd harmonic is the first octave above the fundamental. Also, solid state amps don't stop there, they continue to add the 3rd, 4th, 5th, 6, and worst of all (according to many), the 7th harmonic. According to John Curl, who is a noted amp designer, the old AT&T tube manual shows that any amount of the 7th harmonic is a very bad thing for the sound. The others don't work well, either.

There are many other differences between tunes and solid state including how the amp couples with the load, how the amp's load affects the output section WRT the way the load is reflected back and how the various sections of the amp work.

There's a lot of info on tube circuits, in print, online and in videos on many websites including YouTube. I was just watching a video with Nelson Pass and if you're familiar with Threshold amplifiers or the DIY Audio website, that's him. Very informative and he touches on how tubes compare with some of the solid state devices he's working with.

I think a lot of the desire in tubes comes from the fact that tube amps are desirable for production of music, like a tube guitar amp. However for reproduction I want music as unchanged as possible. I do not want more distortion, I want the amount of distortion that the artist added- no more. A quality solid state will do this.

That said, most quality tube amps don't add that much distortion, if at all, and also look really, really cool. I honestly think imho that it's more of an appeal to Luddite that draws many folks to tubes. My only real reservation with a tube amp is limited output, but with sensitive speakers this won't be an issue.

 

[ATLAudio]

What this thread is pointing out that amps do sound different but that's because some aspect has been measured to cause the audible difference. There is no doubt in my mind that amps that measure the same in all aspects (measured in detail beyond what the audio rags report) WILL sound the same well within their operational limits despite class. I'm also of the school that everything we hear is measurable and our hearing sensitivity is far less capable in discerning nuances than test equipment and a well thought out test plan. I don't believe in "golden ear super hearing capabilities" either. Trained listening yes.. but even that ability changes with age.

Agreed. Building an amp isn't random guess work, like turning a kaleidoscope until you suddenly get the right sound. It's deliberately changing the right components with the intent to change specific, measured, sonic characteristics.

 

[AcuDefTechGuy]

What this thread is pointing out that amps do sound different but that's because some aspect has been measured to cause the audible difference. There is no doubt in my mind that amps that measure the same in all aspects (measured in detail beyond what the audio rags report) WILL sound the same well within their operational limits despite class. I'm also of the school that everything we hear is measurable and our hearing sensitivity is far less capable in discerning nuances than test equipment and a well thought out test plan. I don't believe in "golden ear super hearing capabilities" either. Trained listening yes.. but even that ability changes with age.

Yeah, I agree. I've owned and heard plenty of different amps. There has never been a single instance that has made me believe amps sound significantly different.

Maybe I could hear a significant difference if I use my STETHOSCOPE. But I don't want to use a "stethoscope" while I am enjoying the music.

I just like to sit back, relax, and enjoy the heck out of the music and sound.

Audio religion is what this is.

I couldn't care less whether the amp is class A or A/B, etc. If the music sounds awesome, then it is awesome.