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"Amps all sound the same" (more or less)

I recently built the well known hitachi mosfet amplifier, the basis of many a popular amplifier, it sounds good, detailed good bass......yada yada yada but after a few hours I want to go back to the current dumping amplifier. I can happily listen to class A, current dumping and dynamic bias but there is something about a class AB amplifier that is not quite right even though they measure well. I have a suspicion that in AB it’s because the distortion occurs round about the lowest point of the signal where the ear is most sensitive. I designed the circuit boards for the hitachi, so they follow a similar layout topology to my own designs and the power supplies are close in transformer size and amount of smoothing.
 
I recently built the well known hitachi mosfet amplifier, the basis of many a popular amplifier, it sounds good, detailed good bass......yada yada yada but after a few hours I want to go back to the current dumping amplifier. I can happily listen to class A, current dumping and dynamic bias but there is something about a class AB amplifier that is not quite right even though they measure well. I have a suspicion that in AB it’s because the distortion occurs round about the lowest point of the signal where the ear is most sensitive. I designed the circuit boards for the hitachi, so they follow a similar layout topology to my own designs and the power supplies are close in transformer size and amount of smoothing.


What is dynamic bias? I mean I don't what an electronic explanation, I wouldn't understand it, I just want to know if there are commercial amps which implement it like there are commercial current dumping amps.

Re your thoughts about A vs AB, it makes me wonder how few watts of Class A you think you can get away with before switching to class B. 1W?
 
I think the way the first statement is hedged does give some wriggle-room. Jez (Arkless) post up thread seems to suggest that a significant proportion of amps are not competently designed. Perhaps one might also say that an otherwise competent design might be compromised by cost cutting to fit it to a market sector. The more you charge, the fewer compromises you have to make.

I'm not for one moment suggesting that the differences are due to competence of design.... although that does vary considerably as well!
Unfortunately the reasons for the differences are completely and utterly unknown to science. We can speculate and speculate but just when we think we have hit the nail on the head we can often find a unit that breaks most of the "rules" we think are important and yet sounds great...
Once those areas that are readily measurable have been adequately dealt with such as the unit can be described as technically "blameless", ie THD 0.1% or below, frequency response <20Hz - >20Khz, damping factor at least 15 - 20 then I'm afraid we are still in a "here be dragons" world! There are many techniques used by designers such as myself which we've found from experience tend to give a better subjective result than other technically equally applicable methods and different designers will have their favourite "go to" circuit techniques/topologies.

The vast majority of amplifiers, at least ones at "real world money" tend to (loosely!) be of the same generic type ie solid state, direct coupled, class A/B (but almost class B) and high negative feedback. They are the offspring of "the Lin topology" (yes one N and nothing to do with Linn. Goes back to late 50's). If it's not valved and not class A or class D then it's probably this type. They tend to share the same limitations in sound quality. Why is such a generic topology so popular? Because it is the cheapest way to make high power amplifiers, that don't get that hot, measure well, don't require special quality components or hand selected components, are relatively insensitive to power supply quality, will be the same each time and have a long service life without anything really needing adjustment.
Most of the techniques which I could pretty much guarantee would make for a much better amplifier will also make it MUCH more expensive... Such is life.
 
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I think the way the first statement is hedged does give some wriggle-room. Jez (Arkless) post up thread seems to suggest that a significant proportion of amps are not competently designed. Perhaps one might also say that an otherwise competent design might be compromised by cost cutting to fit it to a market sector. The more you charge, the fewer compromises you have to make.

And you also have that ‘within their operational limits’ angle. It may be that an amplifier built to a tight budget operates in a narrower window of those limits, than an amp with more budget brought to bear.

At the budget end, e.g. the cheapest AVR receivers, aggressively building down to a price will likely prevent the amplifiers from being audibly neutral (identifying blind sense) due to their having almost no effectively linear region of operation. Move further up the range and this will likely improve substantially. The absence of an audio press serving the interests of consumers means where this tends to occur is far from easy to determine for consumers.

At the expensive end though things are different. Boutique audiophile amplifiers often do not seek to maximise technical performance but other properties that may be valued by some audiophiles. Expensive valve SET amplifiers for example are meant to audibly distort in an attractive way (or at least I think they are given it can be difficult to translate into measurable reality the reasons given by enthusiasts for the high value to them). At the expensive end price is a less reliable indicator of whether an amplifier will be audibly neutral (identify blind sense) in use or whether that is what the consumer is looking for in an amplifier.

It has been fairly straightforward to design and make audibly neutral (identify blind sense) amplifiers into reasonably behaved speaker loads for perhaps half a century. The larger established manufacturers of active studio monitors likely offer the highest technical performance for reasonable money and they have treated power amplifier modules pretty much as commodities for decades. Above the budget range, excluding boutique audiophile amplifiers, operating into a reasonable speaker load, with sufficient power across the audible frequency range not to clip on transients most home audio amplifiers are likely to be audibly neutral (identify blind sense). Without an audio press serving the interests of consumers it is very difficult for us to know which amplifiers that might be expected to be audibly neutral aren't and why. There are likely to be a few but I strongly doubt it is most under normal use in the home. Of course Jez's criteria for audibly neutral (or equivalent) may be different to the one above.
 
Jez, that’s really interesting, thanks. I’m curious that you can, on the one hand, say

Unfortunately the reasons for the differences are completely and utterly unknown to science. We can speculate and speculate but just when we think we have hit the nail on the head we can often find a unit that breaks most of the "rules" we think are important and yet sounds great.

yet you absolutely, out of hand, dismiss the notion that mains cables can make a difference. This does feel a bit inconsistent, a sort of ‘here be dragons, but over there, dragons are deffo mythical beasties’. I think that if you can’t offer an explanation for one category of difference (whether or not you can measure it), then perhaps a little more circumspection might be helpful for a different scenario where you also have no explanation?
 
Jez, that’s really interesting, thanks. I’m curious that you can, on the one hand, say



yet you absolutely, out of hand, dismiss the notion that mains cables can make a difference. This does feel a bit inconsistent, a sort of ‘here be dragons, but over there, dragons are deffo mythical beasties’. I think that if you can’t offer an explanation for one category of difference (whether or not you can measure it), then perhaps a little more circumspection might be helpful for a different scenario where you also have no explanation?

Absolutely not!!!! There is nothing on the subject of hi fi that I disagree with more strongly!! We can say with 100% guaranteed certainty that some things can never have any effect and mains cables are amongst them. It makes me very angry and every time I read someone saying that mains cables make a difference my only thoughts are "there's another complete and utter moron" I'm afraid. That's not an attempt to offend anyone but more me saying that if people had rather more understanding of how things work then they too would laugh at the very notion of mains cables making a difference. As I've said before, to anyone with electronics knowledge it is as patently stupid as the idea of square wheels for a car. And that is no exaggeration. Unfortunately to the non technical electricity is some "magic" that you can't see, hear, smell directly and to them it seems "anything is possible"

What you are saying is akin to "as we don't really understand where/how viruses originate we should keep an open mind over 5G being responsible"!!
 
Yes, Jez, I get that. But if you can't explain what measurements correlate to 'good' sound in an amp, that suggests we might not yet be measuring all that is important. That's the fundamentals of the subjectivist vs objectivist dichotomy. On that basis, while you may be confident in your own mind that you can't conceive of any factor being relevant that could be affected by a mains lead, you have no recourse to measurements (and associated arguments about why those measurements matter), to back it up. That's all I'm saying. By all means, argue that it can't matter, but for the sake of your blood pressure if nothing else, try not to get so arsey about it, hey?
 
At the budget end, e.g. the cheapest AVR receivers, aggressively building down to a price will likely prevent the amplifiers from being audibly neutral (identifying blind sense) due to their having almost no effectively linear region of operation. Move further up the range and this will likely improve substantially. The absence of an audio press serving the interests of consumers means where this tends to occur is far from easy to determine for consumers.

At the expensive end though things are different. Boutique audiophile amplifiers often do not seek to maximise technical performance but other properties that may be valued by some audiophiles. Expensive valve SET amplifiers for example are meant to audibly distort in an attractive way (or at least I think they are given it can be difficult to translate into measurable reality the reasons given by enthusiasts for the high value to them). At the expensive end price is a less reliable indicator of whether an amplifier will be audibly neutral (identify blind sense) in use or whether that is what the consumer is looking for in an amplifier.

It has been fairly straightforward to design and make audibly neutral (identify blind sense) amplifiers into reasonably behaved speaker loads for perhaps half a century. The larger established manufacturers of active studio monitors likely offer the highest technical performance for reasonable money and they have treated power amplifier modules pretty much as commodities for decades. Above the budget range, excluding boutique audiophile amplifiers, operating into a reasonable speaker load, with sufficient power across the audible frequency range not to clip on transients most home audio amplifiers are likely to be audibly neutral (identify blind sense). Without an audio press serving the interests of consumers it is very difficult for us to know which amplifiers that might be expected to be audibly neutral aren't and why. There are likely to be a few but I strongly doubt it is most under normal use in the home. Of course Jez's criteria for audibly neutral (or equivalent) may be different to the one above.

I guess so. To make an amp which is neutral in terms of no obvious colourations of the excess/insufficient bass or treble or mid etc is dead easy and has indeed been easy for decades.
The areas where IMHO the majority of SS high feedback class A/B amps tend to fail are rather more difficult to describe but all too easy to hear! To risk getting all "6 moons" and "pseuds corner", most commonly a lack of depth perspective, limited soundstaging ability, a "forced" quality to everything, a "greyness" with the inability to fully render timbre and "texture" and a kind of "lifelessness" which any attempt to ameliorate it by turning up the volume just results in more of a "wall of sound" "in yer face" effect. Loud sounds tend to mask quieter ones and upon listening to an amp that fulfils my rather nebulous criteria one will become really aware that eg that banjo picking doesn't end when the intro ends and all the other instruments come in but rather continues very clearly, if quietly, for the entire track... and in fact sounds like it's 10' back and to the left of the other instruments.
 
I guess so. To make an amp which is neutral in terms of no obvious colourations of the excess/insufficient bass or treble or mid etc is dead easy and has indeed been easy for decades.
The areas where IMHO the majority of SS high feedback class A/B amps tend to fail are rather more difficult to describe but all too easy to hear! To risk getting all "6 moons" and "pseuds corner", most commonly a lack of depth perspective, limited soundstaging ability, a "forced" quality to everything, a "greyness" with the inability to fully render timbre and "texture" and a kind of "lifelessness" which any attempt to ameliorate it by turning up the volume just results in more of a "wall of sound" "in yer face" effect. Loud sounds tend to mask quieter ones and upon listening to an amp that fulfils my rather nebulous criteria one will become really aware that eg that banjo picking doesn't end when the intro ends and all the other instruments come in but rather continues very clearly, if quietly, for the entire track... and in fact sounds like it's 10' back and to the left of the other instruments.
To be clear, Jez, what you're describing here is everything I feel about what a good amp and a bad amp do (or don't do) so we're obviously very much on the same page. I'd add to this a facility with timing, so you can appreciate the difference between a 'competent' musician, or a 'good' or a 'great' one as a fair bit of that comes down to how exquisitely they can measure out both timing, and texture.

The really wierd thing is that I've heard all these attributes improved by attention to mains cabling, too. You do have to start with an amp that gets the basics right enough, though. Fail to do that, and you're going nowhere.

For the sake of this thread, and our respective blood pressures, shall we agree to disagree, and respect each others' positions on this particular matter. Then we need never speak of it again! ;)
 
. Expensive valve SET amplifiers for example are meant to audibly distort in an attractive way (or at least I think they are given it can be difficult to translate into measurable reality the reasons given by enthusiasts for the high value to them). At the expensive end price is a less reliable indicator of whether an amplifier will be audibly neutral (identify blind sense) in use or whether that is what the consumer is looking for in an amplifier.

It has been fairly straightforward to design and make audibly neutral .
Excuse me picking out parts of your post, but I could not stop myself from commenting.
The valve set distortion is a common and understandable reaction to why a well made set amp may sound good compare to a 'neutral' class a or a/b solid state job,
I build both valve and solid state single ended amps, and in my view, both can sound a real step up from all of my push pull solid state amps it's not distortion that's making the difference its less cancellation of the audio signal. Push pull operation, simple power supplies poorly matched transistors and valves all come into play to cancel the original signal.
Most amplifiers fall apart when the simple test tones, that most amps are measured with are replaced by a far more taxing music signal.
I'm not pro valve or solid state, I just like what i think sounds the best.
For me it single ended operation.
Slightly more second harmonic but much less of all the other issues that make some of these so called neutral amplifiers
 
Yes, Jez, I get that. But if you can't explain what measurements correlate to 'good' sound in an amp, that suggests we might not yet be measuring all that is important. That's the fundamentals of the subjectivist vs objectivist dichotomy. On that basis, while you may be confident in your own mind that you can't conceive of any factor being relevant that could be affected by a mains lead, you have no recourse to measurements (and associated arguments about why those measurements matter), to back it up. That's all I'm saying. By all means, argue that it can't matter, but for the sake of your blood pressure if nothing else, try not to get so arsey about it, hey?

Sorry but no. Can we agree that suggesting square wheels for a car is patently stupid? And that most of us would regard someone suggesting such a thing (and yes they are serious) as a moron? If you had spent a lifetime studying electronics as I have then mains cables making a difference is equally as obviously and patently stupid as the square wheels! I don't know what part of that is so difficult for many to get their heads around...

You may as well waste your time trying to persuade an expert on virology that there is really something to the whole 5G masts thing just because lots of people with zero knowledge of virology believe there is... cos they read it on t' internet somewhere...

If folks want to discuss the kind of be all and end all mega importance stuff that IS HI FI that is being discussed above before mains cables came in as usual then fine but I shall bow out of any further cable discussion as to be honest it's too silly to take seriously! Pythonesque almost! To me this is rather like we're discussing cars, maybe the fuel injection system or high lift camshafts whilst (and nothing personal!:)) some others keep shouting up "what about the furry dice!? surely you can't deny that they improve acceleration?" Whilst another gives it "I don't know anything about fuel injection but I put go faster stripes on my car and it went 20mph faster! honest!"

It is this ignorance of the things that really matter and obsession with meaningless non functioning "accessories" that nearly gives me apoplexy on hi fi forums!:):rolleyes: "engines? gearboxes? blah blah measure-ist crap.. now lets get back to a 30 page car discussion on the important stuff we're all interested in... furry dice AGAIN!"
 
OK Jez, but you never explain why it can’t make a difference. At best, you say ‘the people who need the explanation wouldn’t understand it’, which doesn’t give us much to work with, if I’m honest. So it’s impossible to say whether your square wheels and furry dice analogy is valid, or a baseless exaggeration.
 
Sorry but no. Can we agree that suggesting square wheels for a car is patently stupid? And that most of us would regard someone suggesting such a thing (and yes they are serious) as a moron? If you had spent a lifetime studying electronics as I have then mains cables making a difference is equally as obviously and patently stupid as the square wheels! I don't know what part of that is so difficult for many to get their heads around...

You may as well waste your time trying to persuade an expert on virology that there is really something to the whole 5G masts thing just because lots of people with zero knowledge of virology believe there is... cos they read it on t' internet somewhere...

If folks want to discuss the kind of be all and end all mega importance stuff that IS HI FI that is being discussed above before mains cables came in as usual then fine but I shall bow out of any further cable discussion as to be honest it's too silly to take seriously! Pythonesque almost! To me this is rather like we're discussing cars, maybe the fuel injection system or high lift camshafts whilst (and nothing personal!:)) some others keep shouting up "what about the furry dice!? surely you can't deny that they improve acceleration?" Whilst another gives it "I don't know anything about fuel injection but I put go faster stripes on my car and it went 20mph faster! honest!"

It is this ignorance of the things that really matter and obsession with meaningless non functioning "accessories" that nearly gives me apoplexy on hi fi forums!:):rolleyes: "engines? gearboxes? blah blah measure-ist crap.. now lets get back to a 30 page car discussion on the important stuff we're all interested in... furry dice AGAIN!"

I can see a beautiful relationship blossoming here.
Brings a tear to my eye!
 
OK Jez, but you never explain why it can’t make a difference. At best, you say ‘the people who need the explanation wouldn’t understand it’, which doesn’t give us much to work with, if I’m honest. So it’s impossible to say whether your square wheels and furry dice analogy is valid, or a baseless exaggeration.

I've explained several times, sometimes in great detail, why it can't possibly make a difference and Martin Clark also provided an excellent technical explanation of precisely the same a few months back...
IIRC my most detailed explanation, with diagrams etc, was on AOS....
 
What is dynamic bias? I mean I don't what an electronic explanation, I wouldn't understand it, I just want to know if there are commercial amps which implement it like there are commercial current dumping amps.

Re your thoughts about A vs AB, it makes me wonder how few watts of Class A you think you can get away with before switching to class B. 1W?

Dynamic bias controls the bias voltage so the output transistors never switch off, I believe there were a few, Nelson Pass has a patent on one and Sansui and Toshiba produced amplifiers using the technique. If you do bias a 100 watt amplifier into class A for the first watt you will end up with a standing dissipation of around a hundred watts which will require a big heat sink and long life high temp capacitors and a severe attack of the vapours in the finance department.
 


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