Amplifiers bench tests results-should we care or not, regardless of audibility, are those thresholds such as -100, -80, -40 dB THD+N, IMD etc.useful?

[lovinthehd]

Whether the repair shipping is Free or not.

You are really hung up on that one While roundtrip is nice, it's not exactly a standard either. Always good to check out sales as well as warranty terms for yourself IMO....

 

[highfigh]

The problem is a focus on THD. Peter Walker showed with listening panels that THD below 2% was not easily identified by blinded listening panels.

However small amounts of crossover distortion, which is the curse of AB amps, was easily identified in small quantities. This is what led to his development of the curent dumping amp, which have zero crossover distortion. I do believe that is why these amps are so easy on the ear and listenable.

I do not know its prevalence in class D amps, but I suspect it is also non existent. I abandoned class AB amps a long time ago.

If those amps cause no crossover distortion, how do they eliminate it, are they biased higher than ClassB?

No, the point is that crossover distortion does show up as THD. The point is that not all THD is created equal. Crossover distortion occurs as the wave crosses the zero axis, and is highly objectionable.

This cartoon exaggerates, but shows what I mean.

The more an amp is biased to class B and away from A then the crossover distortion increases. For some reason the ear is much more sensitive to this type of distortion compared to the distortion at the peak of the wave. Tube amps do not suffer from this distortion and neither do any class A amps.
I do not know how class D amp rate here, but I would suspect they are free of it.

And yet, Peter Walker is said to have developed ClassAB before others. Hmmm


Always strive for better.

 

[highfigh]

Excellent point.

Let’s say we have all kinds of different distortions including XO-THD.

If TOTAL distortion (all distortions combined) + Noise is 0.003%, then logic tells us that XO-THD is even less than 0.003%.

Even more than that, if the speakers have a TOTAL DISTORTION of 0.1% from 20Hz-20kHz, then logic also tells us that the TOTAL SYSTEM (AVP + Amp + Speakers) DISTORTION will more than 0.1% THD. And that’s not even including the NOISE from the room.

Other than active speakers, where have you ever seen S/N specs for speakers? I get that they distort, but they don't add noise as that word is typically used in electronics. And where have you seen speakers that are rated at .1% THD 20-20KHz? If you have an example, I would like to see it.

Noise from the room generally masks most, if not all, electronics distortion so, at some point, trying to achieve .00000% is pointless. Add the listener's hearing losses and it's totally futile.

 

[AcuDefTechGuy]

Other than active speakers, where have you ever seen S/N specs for speakers? I get that they distort, but they don't add noise as that word is typically used in electronics. And where have you seen speakers that are rated at .1% THD 20-20KHz? If you have an example, I would like to see it.

Noise from the room generally masks most, if not all, electronics distortion so, at some point, trying to achieve .00000% is pointless. Add the listener's hearing losses and it's totally futile.

1. I mean speaker THD, not SNR.

2. I’ve seen online articles stating that speakers THD range from 0.1% to 10%.

3. My point is, why do people measure and talk about electronics THD, but they hardly ever talk about speaker THD?

 

[highfigh]

1. I mean speaker THD, not SNR.

2. I’ve seen online articles stating that speakers THD range from 0.1% to 10%.

3. My point is, why do people measure and talk about electronics THD, but they hardly ever talk about speaker THD?

To answer #3, it's because speakers have been known to be one of the highest sources of distortion in a playback system- broadcast radio, tape, vinyl and speakers are the four worst but at least the user has the ability to decrease tape distortion by not trying to make the VU needle bend when it hits the post on peaks. For the rest, all we can do is live with it and do what we can to choose equipment that doesn't distort very much.

Materials aren't absolutely rigid and in the case of a speaker cone being driven near the center, the area near the surround is resisting the in/outward movement via inertia and compliance and then, there's the physical distortion of the cone between the nodes that occur because of the frequency.

This video deals with pistonic speakers-

 

[lovinthehd]

Well just from a marketing viewpoint for speaker manufacturers, I can see why discussion of distortion doesn't come up much in specific terms just based on the very term "distortion"

 

[highfigh]

Well just from a marketing viewpoint for speaker manufacturers, I can see why discussion of distortion doesn't come up much in specific terms just based on the very term "distortion"

The THD from our speakers is half of the competition's speakers"- not saying much when the competition's speakers are introducing 5%. Passive crossovers cause phase shift and that's bad enough but when the cone's distortion is added, it can be pretty awful. I would have thought cone tweeters would be a thing of the past, but they're still being produced.

 

[lovinthehd]

The THD from our speakers is half of the competition's speakers"- not saying much when the competition's speakers are introducing 5%. Passive crossovers cause phase shift and that's bad enough but when the cone's distortion is added, it can be pretty awful. I would have thought cone tweeters would be a thing of the past, but they're still being produced.

It 's not something that's particularly marketable is all I'm saying....easier to talk about silly wattage ratings....

 

[TLS Guy]

1. I mean speaker THD, not SNR.

2. I’ve seen online articles stating that speakers THD range from 0.1% to 10%.

3. My point is, why do people measure and talk about electronics THD, but they hardly ever talk about speaker THD?

People do talk about speaker THD, and its not pretty, but it is a significant problem. It is very much a factor of power and cone excursion. This is where multiple drivers help.

 

[TLS Guy]

If those amps cause no crossover distortion, how do they eliminate it, are they biased higher than ClassB?


And yet, Peter Walker is said to have developed ClassAB before others. Hmmm


Always strive for better.

That is absolutely not true. Toby and Dinsdale proceeded Peter on this by a wide margin. The problem is that those early designs blow up on a really regular basis.

Peter's achievement was to design and build the first really reliable solid state amp, the Quad 303 in 1969. These amps are incredibly reliable and seldom fail. The BBC replaced all their line amps with 303s. I bought my first 303 in 1970. I used it for years. I have not used it in a while, but as far as I know it still works. I have two of them.

Quad 303 domestic version.

Quad 303 pro version.

Those amps are so stable that you can parallel the inputs and outputs to bridge them. I know of no other power amp you can do that to. The rest blow up instantly.

They still fetch good money. If people want a really reliable amp, then they look for a Quad 303 still. They were class AB and I think the only class AB amp he produced. Then went on to produce the 405, 405-2, 606, and 909. He also made pro versions of all of them I think, for the BBC and studios. He also designed the amps for the legendary BBC transmission line monitors at Maida vale. They were an active design, in which Peter, Raymond Cooke of KEF, and Jim Rogers all cooperated. All had their own companies.

While we are mentioning these, four of the amp boards from those legendary speakers came up for sale, and I could not resist buying them. I have installed them in two 405-2 amp cases, as they are basically a special version of the Quad 405-2. I could not resist adding them to my museum. They are a special part of audio history.

In the 405 and 405-2 the output transistors are biased class C! There is feed forward error correction from a small class A amp. Performance is class A. The 606 and 909s output transistors are biased class B, again with feed forward error correction from a class A amp.

Nelson Pass did infringe on Peter's patents, but Peter never mentioned it himself or made a fuss. He was always conflicted about patents, and basically was of the view that good ideas should be freely distributed.

I have finally found a picture illustrative of the sort of cabinetry with high WAF seen in the 1960s

 

[PENG]

If those amps cause no crossover distortion, how do they eliminate it, are they biased higher than ClassB?

There you go again?

Well designed class AB amps should of course be biased higher than class B amps at any output levels, many are even biased to run in class A territory at lower levels from a couple watts to 20 watts or higher and to class AB at higher levels. I know you mentioned class AB amps that were biased for class A at low output and class B at higher output. Personally, I will not use such amps, and I don't think there are too many of such designs anyway, never know of one of such design, may be they are more on the "pro" side.

 

[AcuDefTechGuy]

People do talk about speaker THD, and its not pretty, but it is a significant problem. It is very much a factor of power and cone excursion. This is where multiple drivers help.

Good point. I do love multiple drivers and big drivers and good efficiency.

 

[AcuDefTechGuy]

The THD from our speakers is half of the competition's speakers"- not saying much when the competition's speakers are introducing 5%. Passive crossovers cause phase shift and that's bad enough but when the cone's distortion is added, it can be pretty awful. I would have thought cone tweeters would be a thing of the past, but they're still being produced.

Do you get the feeling that speaker distortion is more like 1%-10%, not 0.1% to 10%?

If the average speaker distortion is in the neighborhood of 5%, it’s no wonder nobody wants to talk about it.

Oh yeah, my Amp has distortion of 0.00002%, but my speakers have distortion of 5%.

And we don’t want to hijack this thread, so this talk about speakers THD leads back to the question and poll of this thread - how good do measurements for amps/AVR/AVP need to be?

It Is interesting to have party discussions of why the new AVR doesn’t measure as AWESOME as the old AVR (THD+N 0.001% vs. 0.004%) because they used a different DAC on the new AVR. It’s cool to talk. At least we know the reason why it went from 0.001% to 0.004%.

But after all the interesting talk, at the end of the party, how significant is this SINAD measurement compared to all the other factors like features, warranty/service, brands, aesthetics, etc.?

 

[highfigh]

It 's not something that's particularly marketable is all I'm saying....easier to talk about silly wattage ratings....

I agree- people like bigger numbers, but only when they're presented as "more is better". Since distortion of any kind has a stink, nobody is going to see more as better, although I wouldn't be surprised if someone with a 'high end, audiopile' gadget that removes this particular type.

Let's recap everything!

 

[highfigh]

That is absolutely not true. Toby and Dinsdale proceeded Peter on this by a wide margin. The problem is that those early designs blow up on a really regular basis.

Don't take it personally. I didn't search for long, but I read comments about Walker being one of the first in ClassAB, so maybe someone can tell the writer of the article that they're wrong.

They really nailed the cosmetics of that Quad equipment- so much AV equipment looks terrible and it's all 'set it on a shelf, connect the speakers and use it' but in the past, people who used this kind of gear were hobbyists in a true sense, buying the pieces, making cabinets, installing it in an existing table or other furniture- such a practical thing to do.....

Are the components that may need replacement in those models easy enough to source that buying one isn't as risky as some of the new stuff, which manufacturers stop supporting after only 3-5 years?

 

[highfigh]

There you go again?

Well designed class AB amps should of course be biased higher than class B amps at any output levels, many are even biased to run in class A territory at lower levels from a couple watts to 20 watts or higher and to class AB at higher levels. I know you mentioned class AB amps that were biased for class A at low output and class B at higher output. Personally, I will not use such amps, and I don't think there are too many of such designs anyway, never know of one of such design, may be they are more on the "pro" side.

What do you mean by "There you go again?"?

ClassAB always operate in ClassA at lower power levels and use B at higher levels with some brands operating in ClassA until ~5W? Are you saying that you only use ClassA or ClassD amplifiers? Perhaps ClassG/H, with additional sets of output transistors that are only used at the higher power levels?

 

[Trell]

Oh yeah, my Amp has distortion of 0.00002%, but my speakers have distortion of 5%.

So which amp of yours is that has a THD of 0.00002%, that is, -134 dB?

 

[PENG]

What do you mean by "There you go again?"?

ClassAB always operate in ClassA at lower power levels and use B at higher levels with some brands operating in ClassA until ~5W? Are you saying that you only use ClassA or ClassD amplifiers? Perhaps ClassG/H, with additional sets of output transistors that are only used at the higher power levels?

Because you stated the same before. That is not quite correct, or at least misleading.
Yes, class AB and class B amps have the same kind of push pull configuration, but with class AB, there is always some bias current to ensure both output transistor in the simplest form of push pull would conduct for more than 180 degrees, thereby minimizing crossover distortion.

There are plenty of articles to read, below is just one example:

Classes of Power Amplifiers (Class A, B, AB, C, D Amplifiers Explained) (circuitdigest.com)

 

[highfigh]

Do you get the feeling that speaker distortion is more like 1%-10%, not 0.1% to 10%?

If the average speaker distortion is in the neighborhood of 5%, it’s no wonder nobody wants to talk about it.

Oh yeah, my Amp has distortion of 0.00002%, but my speakers have distortion of 5%.

And we don’t want to hijack this thread, so this talk about speakers THD leads back to the question and poll of this thread - how good do measurements for amps/AVR/AVP need to be?

It Is interesting to have party discussions of why the new AVR doesn’t measure as AWESOME as the old AVR (THD+N 0.001% vs. 0.004%) because they used a different DAC on the new AVR. It’s cool to talk. At least we know the reason why it went from 0.001% to 0.004%.

But after all the interesting talk, at the end of the party, how significant is this SINAD measurement compared to all the other factors like features, warranty/service, brands, aesthetics, etc.?

I don't remember seeing .1% THD stated for a speaker- someone may have developed one but after seeing so many laser interferometry photos and videos over the decades and new designs still haven't eliminated it, I'm not too optimistic the speakers will reach that low level. OTOH, our ears aren't as able to detect some distortions ad many make them out to be and the type of distortion matters WRT how easily we hear it. IM can cause some nasty components that are definitely audible, but it's harder to notice if the music is 'busy' and the waveforms are complex. THD is more audible when the harmonics are odd order, rather than even order and that's one of the arguments many make for using tubes but those aren't the most accurate, either.

The point of decreasing the distortions in the electronics between the source and speakers is just to minimize it where possible because many sources just won't produce sound without some distortion. I don't have a problem if an amp produces .1%, as long as it sounds good.

WRT serviceability, one of my customers recently called to tell me that they lost two TVs at some point over the Summer (they were gone most of the time) and I found that both were totally inoperable- D-E-D, ded. I know a store that services just about anything and asked if he wanted me to take it there for an estimate. Well, I got the estimate- a 3 year old TV and parts aren't available. What a bite in the rump.

Waiting to get an answer from the parts place provided by Vizio- I'm sure the servicing dealer has called, but I just want to dot my Ts and cross my Is.

 

[highfigh]

Because you stated the same before. That is not quite correct, or at least misleading.
Yes, class AB and class B amps have the same kind of push pull configuration, but with class AB, there is always some bias current to ensure both output transistor in the simplest form of push pull would conduct for more than 180 degrees, thereby minimizing crossover distortion.

There are plenty of articles to read, below is just one example:

Classes of Power Amplifiers (Class A, B, AB, C, D Amplifiers Explained) (circuitdigest.com)

View attachment 59393

If you're going to claim that someone posted something which is wrong, please re-post it, so we don't need to guess at what you're referring to. "There you go again" doesn't mean anything without the context.