Class A vs AB vs D amplifiers

[SSS]

I am familiar with those HP models as well. When I was a tech specializing in mechatronics I worked part time at a metrology lab that also bought, refurbished and calibrated test equipment for resale. The owner would go to large corporations' auctions in the USA and buy used operational top name brand test gear and after he got it calibrated and ready for sale he was averaging about 500%+ markup. Very lucrative operation. The HPs scopes that you have use a fine trace so the resolution can be pretty detailed as compared to a fat bright blurry trace found on inferior scopes. Those HP scopes are fine pieces of gear.

Unfortunately the 1740A got a vacuum leak CRT. Since I have other scopes it is not worth to repair it. I take it for spare parts if my other hp measuring instruments may need a new knob.

 

[Blenderguy]

The frequency range of what you might hear of let's say 20Hz to 20kHz (A fantasy number but it doesn't matter here for my purpose.) That frequency range is very low frequency stuff and meters can easily meter that signal. You are trying to make excuses for this and that and your ideas simply do not fit reality.

I take issue with this statement. I know this is my first post, but I have been reading this forum for several years now.
Back in the 80's I designed and build my own amplifiers. My history with audio goes back to the 60 when i build the Popular electronics Brute 70 amp.
Anyways, I always had a signal generator and speakers back then that had responses way past 20kHz. University Sound supertweeeter.
So I was curious how high i could hear. My conclusion was that the high frequency perception is really good when you are young. When I was 18 I could perceive up to 22 kHz, my brother 5 years younger could perceive 24kHz. I took part in a science hearing test where they plotted your hearing response to the generally accepted Fletcher Munsen curves for hearing sensitivity. As this is based on an average of people that they tested in the 30s, it does not represent everyone. There are always outliers. I happen to be one of them, and at that time my threshold of hearing was 10dB below that line at 16kHz. As you age this response keeps going down. Mine was reduced to 18kHz in my late 30's. When you reach 50's you are pretty much hearing disabled, so the statement you made has some merit to it. But it really should have some qualifications attached to it. Like I am over 60 and can't hear more than half the audio spectrum. Mine suckls too now.
Coming back to when I said that you can perceive it. It is hard to describe to people who can't hear that high. It is not a sound in the sense that people would describe a 1kHz tone. My perception of tones above 16kHz is more like ear piecing sensation and the higher it is above it, it becomes uncomfortable like a knife in your eardrum, most likely because the level has to be raised to very close the threshold of pain. It was not really comfortable to have such good hearing, because back in those days I could not enter areas that had a lot of TVs operating. Oh and "ultra-sonic" burglar alarm were a curse for me too. I worked part time for a company that installed them and I knew when it was switched on.
When I went to purchase speakers, it was pretty obvious to me which ones had huge treble rolloff. I would bring a few records that had a lot of cymbals and/or hi-hat sounds. Only a brief listening would eliminate many speakers. Back when my hearing was better, I could always identify a metal dome tweeter from a textile dome. Just harsh sounding. But as I realized, most people are relativly hearing impared. When it comes to vision, pretty much everyone knows how good or bad their vision is. It would be nice to see the hearing graph of people who make judgements on speakers or headphones.

 

[Doodski]

I take issue with this statement. I know this is my first post, but I have been reading this forum for several years now.
Back in the 80's I designed and build my own amplifiers. My history with audio goes back to the 60 when i build the Popular electronics Brute 70 amp.
Anyways, I always had a signal generator and speakers back then that had responses way past 20kHz. University Sound supertweeeter.
So I was curious how high i could hear. My conclusion was that the high frequency perception is really good when you are young. When I was 18 I could perceive up to 22 kHz, my brother 5 years younger could perceive 24kHz. I took part in a science hearing test where they plotted your hearing response to the generally accepted Fletcher Munsen curves for hearing sensitivity. As this is based on an average of people that they tested in the 30s, it does not represent everyone. There are always outliers. I happen to be one of them, and at that time my threshold of hearing was 10dB below that line at 16kHz. As you age this response keeps going down. Mine was reduced to 18kHz in my late 30's. When you reach 50's you are pretty much hearing disabled, so the statement you made has some merit to it. But it really should have some qualifications attached to it. Like I am over 60 and can't hear more than half the audio spectrum. Mine suckls too now.
Coming back to when I said that you can perceive it. It is hard to describe to people who can't hear that high. It is not a sound in the sense that people would describe a 1kHz tone. My perception of tones above 16kHz is more like ear piecing sensation and the higher it is above it, it becomes uncomfortable like a knife in your eardrum, most likely because the level has to be raised to very close the threshold of pain. It was not really comfortable to have such good hearing, because back in those days I could not enter areas that had a lot of TVs operating. Oh and "ultra-sonic" burglar alarm were a curse for me too. I worked part time for a company that installed them and I knew when it was switched on.
When I went to purchase speakers, it was pretty obvious to me which ones had huge treble rolloff. I would bring a few records that had a lot of cymbals and/or hi-hat sounds. Only a brief listening would eliminate many speakers. Back when my hearing was better, I could always identify a metal dome tweeter from a textile dome. Just harsh sounding. But as I realized, most people are relativly hearing impared. When it comes to vision, pretty much everyone knows how good or bad their vision is. It would be nice to see the hearing graph of people who make judgements on speakers or headphones.

Wowow. I have not had such a long detailed reply in some time.... You are very fortunate to have had and maybe still have superhuman hearing response. I used the 20Hz to 20kHz as a example only and not a line in the sand. I was able to hear using a oscillator for a source to ~17.5kHz. Now I can't hear well past ~14kHz. So I dream of super hearing but it's never happened for me.

 

[Blenderguy]

Well I can't hear past 8kHz now. I used to have electrostatic speakers which were a hybrid but reversed in that they used a tweeter that cut in at 7kHz. I bet if you disconnected it I would not be able to tell.
I found this discussion particular interesting, because after a 25 year hiatus from the money pit called Highend audio, I decided to put together a system before all my high frequency hearing is gone.
The things that high frequency hearing has nothing to do with super human. I believe if it was regularly tested like vision, you may find that kids say from 6 year old or so may probably hear well in excess of 20kHz.
This reminds me of an article i read about Fraunhofer development of he mp3 codec. I was surprised that only roughly 30 people took part in the closed development. Now I am an engineer and took several courses in statistics to get informed about 5 and 6 Sigma reliability.
Basically it states that 16 random samples out of a production line will predict the performance of 99.99% of the product and 32 samples will predict 99.999% on which will pass specifications. I was really amazed at how few things you have to test. So I assume that they used the same statistical analysis and said that if 99.999% of the people can't hear the difference, that's good enough for us. BUT seeing that there are billions of people on earth, it now is pretty obvious that if you multiply the percentage, you still will get millions that will be able to tell.
The part I liked was that they had a young kid on the team, that identified 100% of the time when it was an mp3. He only needed to listen for maybe 30 secs or so. He said all I need is to listen to the high frequencies like cymbals and then I know it all f** up. If you look at the codec you will see a sharp cutoff at 15kHz, and no channel separation from about 12kHz onward.

 

[Doodski]

Well I can't hear past 8kHz now. I used to have electrostatic speakers which were a hybrid but reversed in that they used a tweeter that cut in at 7kHz. I bet if you disconnected it I would not be able to tell.
I found this discussion particular interesting, because after a 25 year hiatus from the money pit called Highend audio, I decided to put together a system before all my high frequency hearing is gone.
The things that high frequency hearing has nothing to do with super human. I believe if it was regularly tested like vision, you may find that kids say from 6 year old or so may probably hear well in excess of 20kHz.
This reminds me of an article i read about Fraunhofer development of he mp3 codec. I was surprised that only roughly 30 people took part in the closed development. Now I am an engineer and took several courses in statistics to get informed about 5 and 6 Sigma reliability.
Basically it states that 16 random samples out of a production line will predict the performance of 99.99% of the product and 32 samples will predict 99.999% on which will pass specifications. I was really amazed at how few things you have to test. So I assume that they used the same statistical analysis and said that if 99.999% of the people can't hear the difference, that's good enough for us. BUT seeing that there are billions of people on earth, it now is pretty obvious that if you multiply the percentage, you still will get millions that will be able to tell.
The part I liked was that they had a young kid on the team, that identified 100% of the time when it was an mp3. He only needed to listen for maybe 30 secs or so. He said all I need is to listen to the high frequencies like cymbals and then I know it all f** up. If you look at the codec you will see a sharp cutoff at 15kHz, and no channel separation from about 12kHz onward.

Interesting... The statistical QC test is not something I expected and it's really good info to have.

The part I liked was that they had a young kid on the team, that identified 100% of the time when it was an mp3. He only needed to listen for maybe 30 secs or so. He said all I need is to listen to the high frequencies like cymbals and then I know it all f** up. If you look at the codec you will see a sharp cutoff at 15kHz, and no channel separation from about 12kHz onward.

Those are some fine ears for sure. I conducted a test of YouTube music streaming compared to flac files and I made sure that the levels where matched. I could not tell the difference with my ears. I tried and tried and after hours it was obvious that streaming codecs is good enough for my ears at this time. I wish it where otherwise but I'll take it as a hint to get active and lose some weight. LoL. In the past 7 years I have been sedentary and gained weight. My hearing is still very enjoyable and I listen to music about 4 hours to even 15 hours a day if I am having a busy active day.

I am interested in what gear you are considering for your new system.

 

[Blenderguy]

As to the reason why I like the amp discussion, is that in the 80's I designed and build a Mosfet amplifier for my power hungry electrostatic speakers. The Dayton Wright speaker were very revealing, had distortion similar to the headphone tests i see on this forum, but the best part was the phase coherency. I tested them with a square wave, and it was the best I had seen, and not every speaker manufacturer publishes that unless it is exceptional. Anyways I made this design specific to driving a captive load with a amplifier that had a huge voltage swing and was able to supply current at the higher frequency without destroying the output stage. So it did quite well driving a square wave into a 3 ohm load with a 4.7uF cap in series. So in my experience I could listen to faults, make some circuit changes and hear what was different.
I know that misinformed people claim there is no difference between amps when:
1. It is a competent design.
2. It is not driven passed its design specs.
So Lets look at the corollary:
1. How do I know it is a competent design? I have looked at lot of schematics in my life, and not sure what is a competent design? When I designed mine, I am not sure I was competent back then. But now after reading the amplifier design book by Cordell, I feel pretty vindicated having designed in features which were not common at the time.
2. Someone who hooks up their "competently designed" amp to some unknown speaker, how does that person know the amp is not driven past it limits? They don't. I am sure that I drove my amp into clipping or near clipping levels almost every time i used it. So small circuit changes make it much more benign. One thing for sure, solid state amps that have protection circuitry that limit their current, always sounded completely nasty at high volume levels. Some of those circuits cut in fairly soon. I had a friend with exactly the same speakers and he asked me to remove the protection circuit on his amp, an SAE 200W/channel beast, I'd rather have a nice sounding amp and just replace the output transistor when they blow! LOL. Back in those days the TO-3 transistors were not that expensive because everyone used the same ones.
Another thing I should mention. When a phono cartridge misstracks, it produced larger amount of ultrasonic signals, I can't even hear, and stresses the amplifier. Has it been designed for that? Will it causes a lot of IM products in the audible band as you well know that the feedback diminished by 20db per decade, meaning distortion goes up 10 times.

My amp still works to day, but the on-off switch now is broken after I used it for a week, turning it on and off. I had used it before in my HT system and remotely turned it on with a relay.

 

[Doodski]

Dayton Wright speaker

I was at a staff meeting, we where drinking, my buddy took me home to sleep on the couch and I got to play with his Dayton Wright speakers for ~4 hours while they where sleeping. Wowow. Talk about accuracy to guitar notes and piano etc... Glorious sound. They where about 4 feet high and very wide and strangely thick for a electrostatic speaker as I remember them.

I know that misinformed people claim there is no difference between amps when:
1. It is a competent design.
2. It is not driven passed its design specs.

Before I returned to study electronics I was a sometimes subjective thinking audio gear salesman for 9 years. I worked 2 small mom and pop shops for 4 years and then went to a major retailer that had into then hundreds of models of speakers and hundreds of models of amps too. We had sound rooms up to 9 in one store that I worked at but 2 rooms was enough for my needs. So... I was comparing speakers and amps and in one room we had 40 amps and receivers and 40 pair of speakers too. That was a great environment all preconfigured for blind listening tests etc. We did not use a voltmeter as at the time we had no access to a oscillator or multimeter so we dialed in the volume very close to each other by comparison via switching in and out models using the switchbox. The end result was the Sony STK amps all obviously sounded bad. The Luxman, Pioneer, Yamaha (Most models.), Technics and NAD all sounded the same to our ears. The Harmon Kardon amps seemed to have some sort of softer bass sound but still thumped and sounded good and the ToP-ArT series from Yamaha sounded a tiny bit better than the others. From that I have been a proponent of encouraging people to put their budget into the speakers and get as much power as they need but I steer them towards Yamaha amps as I am very loyal to the company after working with Yamaha Canada for a bunch of years. Yamaha Canada was very good to me and the loyalty is deserved.

1. How do I know it is a competent design? I have looked at lot of schematics in my life, and not sure what is a competent design?

I look for adequate cooling of the overall device, good power BJT/FETs clamping, max power output, input to output linearity and power output linearity. Then if I want to be extra fussy I whip out a schematic if I can and look at the voltage and current amp sections of the topography (Class A/AB). I tend to like simpler designs as compared to using lots of transistors and caps etc. A side note, Harmon Kardon amps tend to use a lot of parts and maybe that is why they sounded different? This all brings about the questions about class D amps that some people have and the future of class D as a mainstream amp class. I would like to see a few schematics to see what exactly they are laying out on those PCBs so I can stop imagining class D stuff.

2. Someone who hooks up their "competently designed" amp to some unknown speaker, how does that person know the amp is not driven past it limits? They don't. I am sure that I drove my amp into clipping or near clipping levels almost every time i used it.

When clipping discreet design amps I can sense when the breakup/clipping starts occurring at the point where it could get danger zone for speaker drivers. The STK designs though it is a bit more difficult because the sound is distorted near all the time in the cheaper chip designs. There have been STK designs that pump out considerable power but it is very poor power linearity and 4 Ohms is a no no.

One thing for sure, solid state amps that have protection circuitry that limit their current, always sounded completely nasty at high volume levels. Some of those circuits cut in fairly soon. I had a friend with exactly the same speakers and he asked me to remove the protection circuit on his amp, an SAE 200W/channel beast, I'd rather have a nice sounding amp and just replace the output transistor when they blow!

I have seen a ton of protection circuit inclusive type amp designs. The circuitry is often not identified or it is very complex and so it might be current tripping and not voltage tripping. All the amps other than my Yamaha units had zero protection stuff. Yamaha is now in some models using the volume IC to limit the voltage output so as to protect the amp.

 

[Doodski]

When a phono cartridge misstracks, it produced larger amount of ultrasonic signals, I can't even hear, and stresses the amplifier. Has it been designed for that? Will it causes a lot of IM products in the audible band as you well know that the feedback diminished by 20db per decade, meaning distortion goes up 10 times.

I have not used a turntable since ~1986. I had Technics turntables. I started into the phono tech ideas and stuff and then pooF CD came out and I changed to CD and never really got absorbed into the turntable following.

My amp still works to day, but the on-off switch now is broken after I used it for a week, turning it on and off. I had used it before in my HT system and remotely turned it on with a relay.

Those power switches go bad often. So much that when I was repairing gear I kept a few in stock so I did not need to order parts or fish for a used one in junk units. Electronic suppliers most always have those various power switches listed in the catalogues because they are commonly bad.

 

[Blenderguy]

I still use a turntable because I bought a ton of exotic records back in the day. I think I have every Sheffield direct to disk they made, simply because back then they have the best and most realistic sound. Of course some of the vinyl was mediocre, and the other thing was i was not going to spend money on duplicate music on CD. Of course after 10 years after the introduction of CDs, I started buying them. Truth is, back when they were introduced, they sounded horrible. In the sense they were bright, non-musical and did not have the same musical engagement. As an engineer I never believed the marketing hype back then. Today we know what was wrong with the rocordings. The players did not have have real 16 bit D/A chips in them. Then they had timing issues lining up all the bits to convert to analog. Then the digital equipment in the studios sucked as this was all new to them. Anyways I bought a Linn Sondek when they came out and certainly was a revelation to what other options there were.
Now that I am back with a new setup, I have come to t he same conclusion. If I compare a CD made in the 80s, with a record from the same era, best case is that blind folded you want be able to tell the difference, worst case is that the CD sounds bright and grating. I have a nice Pioneer Elite player that I will keep, because mechanically it is first class. I bought an MRL DA converter that was in the top tier as tested on this site to listen to my CDs. Using a fiber link between D/A and the CD player. What surprises me is that my cartridge from 1988 still works beautifully.
I got myself a pair of what I consider entry level MartinLogan ESL speakers and I am not really disappointed. They seem a bit bright, but certainly have the resolving power I expect from an electrostatic. It's a hybrid and the bass integrates pretty well, but it sounds like a cone speaker. I do have an excellent motion feedback subwoofer for my HT, well actually two, but it can't really be used above 100Hz or so. And the transient response is excellent, and very low distortion in its operating range. Once you heard electrostatic bass it is hard to unhear it. A good description would be that there is bass but it does not sound like it is coming out of a speaker, it's just there. An example would be listening to a jazz quartet in real life. You don't think wow this has great bass, you just listen to the musical instruments and kick drums are kick drums and a double bass sounds like plucked strings.
On a side note, I found out after I bought the MartinLogan speakers, that the panels are made in Mississauga, Ontario, where I grew up.

 

[Doodski]

On a side note, I found out after I bought the MartinLogan speakers, that the panels are made in Mississauga, Ontario, where I grew up.

Good to hear. I have read and been instructed to expect from a re-paneling/membrane replacement job is that they are not rocket science. They can be disassembled and worked on. Know anything about this?

my cartridge from 1988 still works beautifully.

Airconditioned environment and low on UV light too?

 

[Blenderguy]

Good to hear. I have read and been instructed to expect from a re-paneling/membrane replacement job is that they are not rocket science. They can be disassembled and worked on. Know anything about this?

Here is a long post on how those panels are constructed. It's a ton of work, I took them apart and then life took over and I never repaired them.

Anatomy of a high efficiency high output electrostatic loadspeaker.

The issue is, if you read articles on the web, that Mylar or its derivative have a low energy bond, meaning in my understanding, that they repel liquids on their surface. So it appears that even if the spray and other stuff is easy to apply, it won't last. The trick is to modify the surface to...

www.martinloganowners.com

 

[Blenderguy]

Airconditioned environment and low on UV light too?

Yeah my turntable was always sitting on a table for 25 years. Way back in the 70s I had high compliance phono cartridges where after a year or so the suspension collapsed and the plastic guide was riding on the record. The one I have now is a high compliance moving coil. Fortunately there is enough interest in playing records that there are a few small companies that can replace the the diamond and cantilever. It does seem that the suspension is stiffer and is riding a tad higher than I remember, but that was decades ago, lol. Only verification to this fact is that I had to slightly lower the arm to get a different VTA, to make some distortion on female vocals go away. Was good that I could compare it to the CD.

 

[Blenderguy]

Coming back to amplifier blind testing. I was a doing a quick of the cuff power calculation using a medium efficient loudspeaker, typical of high end speakers. Take 86 dB SPL for 1W at 1m. Every time you double the distance you loose 3dB. So lets sit back at 12 ft, not an unreasonable distance from a speaker in a dedicated sound room. Put in lots of sound absorbing material to get rid of a lot of room bounce, carper is mandatory. So now we are down to 80 dB SPL with 1Watt. Lets play loud because the music is good. Grab some recordings from before the compression and maximum bass wars. A recording that has a real life balance. I want an 86dB average level. Many recordings I have have up to 15dB peaks. BTW there is a site that rates a huge number of recordings for dynamic range. The landscape look pretty disappointing from real music perspective. Basically the digital recording and processing has destroyed high fidelity. That is probably why I have not purchased any music for decades.

Album list - Dynamic Range DB

Back to the calculation. So to get 86dB average level at your chair. you need 6 Watt of power now. Add the 15db for peaks and we are at 40 times 6 watt = 240W. Now this is 8 Ohm power, if you have a speaker like a B&W high end version as an example, it may dip to 4 or even 3 ohms. So now the amp has to deliver the equivalent current of a 4 Ohm load. We are at 480W for the peaks. It is not really that bad because you got two speakers, so we need 480W from the two channels.
I believe that blind amplifier testing from what I read, are rigged to guarantee the outcome that testers want. Either use a speaker with a benign load impedance like Magnepans, or play the music so amp does not clip or pick music that the listeners are not familiar with.

 

[Jim Taylor]

I believe that blind amplifier testing from what I read, are rigged to guarantee the outcome that testers want. Either use a speaker with a benign load impedance like Magnepans, or play the music so amp does not clip or pick music that the listeners are not familiar with.

I suppose you've already viewed Amir's video on blind testing here.

A few thoughts:

Depending on who we are discussing, many so-called "blind" tests are nothing but shams. So you are correct; many are rigged. But if you follow the procedures laid down on this site, and follow them rigorously, you will have the control that you need to make the test valid.

When testing amplifiers, my personal opinion is to test them with the speakers that you will be using. Yes, that means that you may have to deal with clipping or thermal instability or whatever, but part of the point of testing amps is to see whether one gives better results than the other FOR YOU. If you switch to Maggies for the test and then return to the box speakers that you intend to use, that doesn't make for a valid comparison.

I know that misinformed people claim there is no difference between amps when:
1. It is a competent design.
2. It is not driven passed its design specs.

These people are not misinformed. Anecdotal evidence is not scientifically valid ... scientifically controlled tests are. Your memories are based on bias (here), where, for example, you said ...

... certainly have the resolving power I expect from an electrostatic.

An expectation (expectation bias) can completely skew your results. Not only that, but "resolving power" is a subjective fallacy. Electronics either provide you with a signal that has distortion characteristics below the threshold of human hearing, or it doesn't. In the first case, there is no audible imperfection, and in the second case there is.

Whether or not amplifiers are "competent" is a matter of tests and measurements. Many tests do not show the whole range of tests that can be administered, mostly because of all the time and hard work that goes into doing it, and the fact that such extensive tests are interesting to only a small percentage of the public. But tests can be run that show the performance of amps under stressful loads, and there are definitely differences that show up.
This is also a method for showing what the "design specs" are. I think we all know that there are companies that are engaged in vicious price-cutting competition with their adversaries in this business, and corners can definitely be cut.
But tests and measurements accurately show both of these qualities, and allow the consumer to gauge with greater accuracy whether the product they are considering is right for them or not. I think that's great!

Jim

 

[Doodski]

I believe that blind amplifier testing from what I read, are rigged to guarantee the outcome that testers want. Either use a speaker with a benign load impedance like Magnepans, or play the music so amp does not clip or pick music that the listeners are not familiar with.

When I have blind tested gear of those 40 speakers we where not using anything like a Magnepan, Apogee or a conventional speaker design like the Kappa 9. We had up to about $2500 dollar speakers in MB Quart, B&W, KEF, RFT, JBL, Definitive Technology, Celestion, Infinity, Mission and Polk Audio.

 

[Blenderguy]

@Jim Taylor
I agree with you.
Amp tests not done with the speakers you use are not really useful to you. Also let's face it, the only reason class G amps exist is to produce output power cheaply. In some cases the designs are driven by portable equipment where quality is secondary. Back when the average HiFi equipment was not made in China, the price relative to income was fairly high. And because of this adding a dollar or two to include better components was not a big deal. Also because of the cost, many people had their equipment repaired. It seems all this is behind us plus the general attitude of companies that do not want the end user to repair the equipment. The discussion on how reliable class G amps are is pretty simple. Count up the number of components, have a reliability coefficient attached to each. And even if you don't know that, statistically the more components it has the more unreliable it will be, all thing being equal. But that not all, Now we have to worry about substandard capacitors that explode, bad soldering, or cold solder joints, maybe running the semiconductors at the ragged edge of the specs, none of this obvious to the buyer.
Even if you follow all the rules as Amir laid out in his video, I can still claim that you can get an outcome that is determined by the tester such as this case.
Lets take a blind test in comparing two cars. In this case double blind is not possible. Subconsciously the planner thinks all cars are much the same. So he rents an oval track, get a higher end BMW3 series and a Honda Accord. He put the people blindfolded in each. The driver drives around the track at sedate speeds, typical of what they are in a city, accelerates slowly and brakes slowly. I'd say that almost no one will be able to tell the difference. The big difference comes when each is driven to the limit. If we rule out engine noise as a factor to relinquish the two.
Does this make sense?

 

[Jim Taylor]

Even if you follow all the rules as Amir laid out in his video, I can still claim that you can get an outcome that is determined by the tester such as this case.

My advice is to actually go through the blind test. I know that it's a lot of trouble, but suppositions are not enlightening.

Jim

 

[Blenderguy]

This response is really two topics.
I had some time to think about this topic. So based on what I read recently and in this thread, all articles that published the result of blind testing, are irrelevant to me. If this testing is supposed to be scientific, the rule is that to make the result valid, anyone should be able to repeat. The problem I see is 1. You need to have the same amplifiers, the same speakers, the same speaker cables, the preamp and the same source hardware. Not to mention the same music.
Frankly I just don't get it, why I need to know if people can or cannot hear the difference between a certain model of a brand of amplifiers to another? That is is like telling you I have a rosebush that has wilting roses? Is that relevant to you? Almost never do i see the gearing test chart of the people listening. What if they are half deaf and can't hear half the arbitrarily defined spectrum?
On another hand why exactly do I need to do that at my house with my equipment? If I don't have different equipment to test that may or not sound different, why exactly do I want to do this? Now I have to buy even more equipment. This is my workbench. Let's just put this out there. I am retired RF engineer that has developed and design broadband RF amplifiers for CATV system amplifiers that hang on the pole, for almost 30 years. Never did I or any other engineer do any blind (no pun intended) to discern the difference between equipment. All faults that you see on your TV have measurable causes. I have designed audio amplifiers on the late 80's. Every one is still working today because I did not use crappy components. For me it is easy to determine if an audio amplifier is a crappy design.
Also I not only use frequency domain measures that Amir mostly uses, I also prefer to use time domain measurements. And a digital scope and decent signal generator cost a fraction of what Amir paid for his distortion analyzer. One thing I always test and amp for is a square wave to look for high frequency oscillation when I use a slightly capacities load. A 100 MHz scope is a good thing to have. In the picture I have a nice classic 100MHz HP scope, and the little lunchbox beside it is the latest Siglent 14bit 100MHz oscilloscope. Frankly ergonomics on the new digital stuff is complete crap. To do simple things you need to push so many buttons and some stuff is nested too many button pushes down. It does have an auto measurement button, but that is only good for the first time as it resets everything. Sorry for the rant. What the digital stuff is good for is to measure parameters that are preprogrammed. For an amplifier it is good to see the phase response over the 20-20K bandwidth. This gives you an idea on what kind of speaker load will it give it some trouble. With the signal generator and scope, it can be done in a few minutes.I also like to test an amp at full power at 20kHz to see how hot it gets after a few minutes and if it goes into current limiting or shutdown. Back when the first high power solid state amplifiers came out, the output stage would blow, because the transistors were too slow and as one turned on the other did not shut off so you had mutual conduction and the transistors went into avalanche destruction as you exceeded the safe operating area. Of course the manufacturers claimed it was not how the amplifier was going to be used, but I just call it a crappy design and cost cutting. Don't claim it can produce full power 20-20kHz. The class G amps switch at high frequencies. The output transistors are stressed as they have a finite bandwidth and much less margin than a transistor being used at audio frequencies. If you look at the specs of power Mosfets from the early devices made by Toshiba and the more recent ones developed for switching, the difference is not that same ration as 1MHz to 20kHz. All class G amps have to put in a dead zone where both transistors are cut off so the space charge can dissipate. So when one turns on the other is guaranteed to be off. I would worry that over a decade or longer that the timing circuit may get unstable and when both conduct, its game over.
When I buy audio equipment I try to to get a schematic either before or after. This way I can fix it if there is a problem. Some of the newer audio equipment is disposable, so it does not really earn my respects if it is not repairable.
I think this mostly covers what I wanted to say in this post.

 

[DonH56]

I am not sure where this is coming from, so just responding to the post itself. Been a busy week, sorry if irrelevant.

This response is really two topics.
I had some time to think about this topic. So based on what I read recently and in this thread, all articles that published the result of blind testing, are irrelevant to me. If this testing is supposed to be scientific, the rule is that to make the result valid, anyone should be able to repeat. The problem I see is 1. You need to have the same amplifiers, the same speakers, the same speaker cables, the preamp and the same source hardware. Not to mention the same music.

No, you can do multiple trials during one test cycle to obtain a statistically significant sample. If you repeat the test later, since what you are listening for are differences, then it does not really matter if everything changed except the thing you are testing. One caveat is that amplifiers interact with speakers, so changing speakers may change the test results, though they will be valid for those speakers. One reason it is important to list and understand all the components in the test. And why the best test for a given person is using his own system.

Frankly I just don't get it, why I need to know if people can or cannot hear the difference between a certain model of a brand of amplifiers to another? That is is like telling you I have a rosebush that has wilting roses? Is that relevant to you? Almost never do i see the gearing test chart of the people listening. What if they are half deaf and can't hear half the arbitrarily defined spectrum?

Listener hearing acuity is frequently mentioned and can affect test outcomes. Most of the significant content is in the midrange so HF hearing loss is not necessarily a disqualification. And using multiple users tends to expose outliers. Again, multiple tests using multiple listeners is best.

On another hand why exactly do I need to do that at my house with my equipment? If I don't have different equipment to test that may or not sound different, why exactly do I want to do this? Now I have to buy even more equipment. This is my workbench. Let's just put this out there. I am retired RF engineer that has developed and design broadband RF amplifiers for CATV system amplifiers that hang on the pole, for almost 30 years. Never did I or any other engineer do any blind (no pun intended) to discern the difference between equipment. All faults that you see on your TV have measurable causes. I have designed audio amplifiers on the late 80's. Every one is still working today because I did not use crappy components. For me it is easy to determine if an audio amplifier is a crappy design.

Presumably there is no human bias for how CATV amplifiers sound. All faults in audio equipment are also measurable, but some people deny that, and some people like to know what they are and/or if they can really tell a difference.

Also I not only use frequency domain measures that Amir mostly uses, I also prefer to use time domain measurements.

Frequency and time domain are related, see Fourier. (Yes, I know you know that, yanking your chain.) Many of us like to perform both frequency and time domain measurements as they highlight different things. Step response is a lot easier to see on a 'scope than from an FFT, but it is often not obvious how flat the audio band is from looking at the step response.

And a digital scope and decent signal generator cost a fraction of what Amir paid for his distortion analyzer.

But getting -100 dB THD, SNR, SINAD and so forth is difficult to impossible from a typical 'scope and inexpensive signal generator. On a 'scope, about the best I can do is maybe 6 bits or so by eye, maybe 8 bits if I can overlie a perfect sine wave on the measured one.

One thing I always test and amp for is a square wave to look for high frequency oscillation when I use a slightly capacities load. A 100 MHz scope is a good thing to have. In the picture I have a nice classic 100MHz HP scope, and the little lunchbox beside it is the latest Siglent 14bit 100MHz oscilloscope.

Perfect example of why many of us use a 'scope. I need to get one myself now that I have retired and no longer have access to multimillion dollar test lab (for GHz stuff, though, so the 'scopes worked OK but the spectrum and network analyzers often didn;t go all the way down to the audio band).

Frankly ergonomics on the new digital stuff is complete crap. To do simple things you need to push so many buttons and some stuff is nested too many button pushes down. It does have an auto measurement button, but that is only good for the first time as it resets everything. Sorry for the rant.

No worries, I suspect most of use agree. Some is better than others, but a lot of stuff is unintuitive. I still like knobs, easier to reach up and turn a knob than wade through menus. Tek did better than HP/Agilent/Keysight but they go back and forth.

What the digital stuff is good for is to measure parameters that are preprogrammed. For an amplifier it is good to see the phase response over the 20-20K bandwidth. This gives you an idea on what kind of speaker load will it give it some trouble. With the signal generator and scope, it can be done in a few minutes.

Easier if you can get inside the amp to measure the loop response. Otherwise a programmable load really helps.

I also like to test an amp at full power at 20kHz to see how hot it gets after a few minutes and if it goes into current limiting or shutdown. Back when the first high power solid state amplifiers came out, the output stage would blow, because the transistors were too slow and as one turned on the other did not shut off so you had mutual conduction and the transistors went into avalanche destruction as you exceeded the safe operating area. Of course the manufacturers claimed it was not how the amplifier was going to be used, but I just call it a crappy design and cost cutting. Don't claim it can produce full power 20-20kHz.

A common complaint appreciated by many here. Fortunately we have much faster transistors these days and better circuit designs (as well as protection circuits). Not that every design is good, natch.

The class G amps switch at high frequencies. The output transistors are stressed as they have a finite bandwidth and much less margin than a transistor being used at audio frequencies. If you look at the specs of power Mosfets from the early devices made by Toshiba and the more recent ones developed for switching, the difference is not that same ration as 1MHz to 20kHz. All class G amps have to put in a dead zone where both transistors are cut off so the space charge can dissipate. So when one turns on the other is guaranteed to be off. I would worry that over a decade or longer that the timing circuit may get unstable and when both conduct, its game over.

I think you mean class D? The "dead zone" is usually designed into the circuit and will track the loop gain bandwidth and oscillation frequency over time and environmental (PVT) changes. I have designed class D circuits for military and space applications and that was actually fairly easy. The hard part was keeping overall performance high, especially after getting irradiated. Hard to meet distortion and noise specs when open-loop gain drops to almost nothing and thresholds shift all over the place.

When I buy audio equipment I try to to get a schematic either before or after. This way I can fix it if there is a problem. Some of the newer audio equipment is disposable, so it does not really earn my respects if it is not repairable.

Again, many folk here (myself included) miss the old days when a schematic was part of the owner's manual. Now, you often have to jump through all sorts of hoops and pay big to get one, if they'll even sell it to a consumer.

I think this mostly covers what I wanted to say in this post.

As you peruse ASR I think you'll find a lot in common with a lot of folk. Welcome aboard! (Now help bail.)

 

[Doodski]

This response is really two topics.
I had some time to think about this topic. So based on what I read recently and in this thread, all articles that published the result of blind testing, are irrelevant to me. If this testing is supposed to be scientific, the rule is that to make the result valid, anyone should be able to repeat. The problem I see is 1. You need to have the same amplifiers, the same speakers, the same speaker cables, the preamp and the same source hardware. Not to mention the same music.
Frankly I just don't get it, why I need to know if people can or cannot hear the difference between a certain model of a brand of amplifiers to another? That is is like telling you I have a rosebush that has wilting roses? Is that relevant to you? Almost never do i see the gearing test chart of the people listening. What if they are half deaf and can't hear half the arbitrarily defined spectrum?
On another hand why exactly do I need to do that at my house with my equipment? If I don't have different equipment to test that may or not sound different, why exactly do I want to do this? Now I have to buy even more equipment. This is my workbench. Let's just put this out there. I am retired RF engineer that has developed and design broadband RF amplifiers for CATV system amplifiers that hang on the pole, for almost 30 years. Never did I or any other engineer do any blind (no pun intended) to discern the difference between equipment. All faults that you see on your TV have measurable causes. I have designed audio amplifiers on the late 80's. Every one is still working today because I did not use crappy components. For me it is easy to determine if an audio amplifier is a crappy design.
Also I not only use frequency domain measures that Amir mostly uses, I also prefer to use time domain measurements. And a digital scope and decent signal generator cost a fraction of what Amir paid for his distortion analyzer. One thing I always test and amp for is a square wave to look for high frequency oscillation when I use a slightly capacities load. A 100 MHz scope is a good thing to have. In the picture I have a nice classic 100MHz HP scope, and the little lunchbox beside it is the latest Siglent 14bit 100MHz oscilloscope. Frankly ergonomics on the new digital stuff is complete crap. To do simple things you need to push so many buttons and some stuff is nested too many button pushes down. It does have an auto measurement button, but that is only good for the first time as it resets everything. Sorry for the rant. What the digital stuff is good for is to measure parameters that are preprogrammed. For an amplifier it is good to see the phase response over the 20-20K bandwidth. This gives you an idea on what kind of speaker load will it give it some trouble. With the signal generator and scope, it can be done in a few minutes.I also like to test an amp at full power at 20kHz to see how hot it gets after a few minutes and if it goes into current limiting or shutdown. Back when the first high power solid state amplifiers came out, the output stage would blow, because the transistors were too slow and as one turned on the other did not shut off so you had mutual conduction and the transistors went into avalanche destruction as you exceeded the safe operating area. Of course the manufacturers claimed it was not how the amplifier was going to be used, but I just call it a crappy design and cost cutting. Don't claim it can produce full power 20-20kHz. The class G amps switch at high frequencies. The output transistors are stressed as they have a finite bandwidth and much less margin than a transistor being used at audio frequencies. If you look at the specs of power Mosfets from the early devices made by Toshiba and the more recent ones developed for switching, the difference is not that same ration as 1MHz to 20kHz. All class G amps have to put in a dead zone where both transistors are cut off so the space charge can dissipate. So when one turns on the other is guaranteed to be off. I would worry that over a decade or longer that the timing circuit may get unstable and when both conduct, its game over.
When I buy audio equipment I try to to get a schematic either before or after. This way I can fix it if there is a problem. Some of the newer audio equipment is disposable, so it does not really earn my respects if it is not repairable.
I think this mostly covers what I wanted to say in this post.

I like your HP differential input rack mount scope. I had 2 of them and loved them very much. That HP 100 Mhz scope is no slouch either.