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In Reply to: RE: This amp is a no-brainer for me posted by N.B.C. on February 06, 2025 at 21:35:54
I've owned several including a D90 DAC in my main stereo system.With the caveat that many such products are Chinese, it ought to be dawning on audiophiles that great performance is available at prices that are relatively much less than was possible even a decade ago.
The mystic of super-high-end gear is fading fast.
As for the B200 we may note that it's class
A/BB (?) not class D; this amp seems to demonstrate that that "class distinction" is neither here nor there in terms of performance.
Dmitri Shostakovich
Edits: 02/07/25 02/08/25Follow Ups:
Based on the B100 being class B. I'm assuming the 'B' means something.
Topping isn't the first to make class B amps that challenge what we think we know about class A or AB.
ElectroVoice made some very interesting class B amps in the mid to late 1950s. They solved the magnetic spike problem that tube amps usually have when the magnetic field in the output transformer collapes by using a Circlotron variation known as the Wiggins Circlotron.
Topping in this case of course isn't using tubes. But they have a lot of loop gain combined with a very high Gain Bandwidth Product in this circuit so are able to apply a lot of feedback hence the low distortion.
My concern is a class B amp needs a beefy supply to be successful, much the same as a class D amp. Time will tell if they addressed this, but so far Topping has been batting well above their price points.
and likely most expensive as well. The value is unknown. If one likes it enough whatever they charge can be justified if not, $200 is too much .
Edits: 02/08/25
How do U define a class B amp. Every amp has some bias and therefore at least a tiny amount of class A.
Plus just a comment on power supplies. As far as I'm concerned the better the power supply the better the amp. Great amps have better power supplies. Topology is usually not as important as power supply. The power supply is the amp. The amp circuit is basically a variable valve that opens and closes the power supply that directly feeds the speakers.
"Class B amplifiers are those in which the output transistors only conduct during half (180 degrees) of the signal waveform. To amplify the entire signal, two transistors are used: one conducting for positive output signals and the other conducting for negative outputs."
So, one transistor completely shuts off before handing off to the other one. That is Class B.
This will ALWAYS cause a zero crossing distortion because of the non-linearity in transistors turn on and shut off. This cannot be eliminated through the use of negative feedback and no matter how small it will always produce unpleasant distortion. It is particularly damaging at low volumes where the relative contribution to the signal is larger.
I don't care how low the distortion of this amp is, the inherent sonic issues with Class B will still be there at some level and will be audible.
This will ALWAYS cause a zero crossing distortion because of the non-linearity in transistors turn on and shut off. This cannot be eliminated through the use of negative feedback and no matter how small it will always produce unpleasant distortion.
This statement is false. I have an example on a shelf here at the shop- the Electro Voice A-20C. Its class B and exhibits no crossover artifact at all- just as the Topping amp of this thread. I refurbished this EV amp because I was curious about this issue. It has no measurable or audible zero crossing artifact at any power level.
A lot of class B tube amps did have a zero crossing artifact. When the magnetic field in the output transformer collapsed when the power tubes were in cutoff, a spike was generated. The EV gets around that by using a Circlotron output circuit.
Solid state class B amps simply have to have the bias close enough that the crossing is seamless. They don't have the spike problem because no output transformer. They don't have to have an A region bias to pull this off- just good design.
It's inherent in how transistors are non-linear in turn on and shutoff. Here are many examples of even so-called Class AB that have zero-crossing distortion. If you don't put enough bias then it is guaranteed to be there.
https://www.stereophile.com/content/jmf-hqs-7001-monoblock-power-amplifier-measurements
https://www.stereophile.com/content/plinius-reference-150-power-amplifier-measurements
The Class AB mode for this amp has zero crossing distortion and the Class A mode does not.
https://www.stereophile.com/content/naim-classic-200-series-nap-250-power-amplifier-measurements
https://www.stereophile.com/content/infigo-method-3-monoblock-power-amplifier-measurements
https://www.stereophile.com/content/karan-acoustics-master-collection-powera-mono-power-amplifier-measurements
https://www.stereophile.com/content/dan-dagostino-master-audio-systems-progression-m550-monoblock-power-amplifier-measurements
https://www.stereophile.com/content/sae-2hp-d-power-amplifier-measurements
https://www.stereophile.com/content/audio-alchemy-dpa-1m-monoblock-power-amplifier-measurements
https://www.stereophile.com/content/plinius-audio-sa-103-power-amplifier-measurements
Again, AB has zero crossing distortion and Class A doesn't.
https://www.stereophile.com/content/class233-ca-3200-three-channel-power-amplifier-measurements
As you can see, many modern amps suffer this problem even ones called Class AB. Probably only the Naim would claim to be Class B.
-then its bias isn't properly set up- its actually class B until the bias is set up properly. Or there's a design bug- this sort of thing was solved in the 1970s or earlier!!
You'll note I said 'doesn't have to' in my prior post. That isn't the same as 'all'...
When I was putting myself through engineering school in the 1970s I worked at Allied Radio Shack's service department. I ran into amps and receivers with this problem quite often. Its easy to fix- increase the bias until the crossover notch is gone. Its easy to do by ear or 'scope. Looking at the specs of the equipment which we had on hand since I worked at the service department for 5 state region, when I had the equipment set up right, the bias current was nominally within spec. So this says one way Radio Shack was able to undercut the competition is they didn't spend as much time setting up the equipment prior to shipment. Found a similar issue with FM tuner alignment. Radio Shack often sold equipment that was the same inside as Kenwood or Pioneer but for less money. It didn't perform as well either, unless you spent the time setting it up.
The Topping B100 is a class B design and doesn't have this zero crossing problem, same for my EV amp I mentioned earlier. Please don't try to gaslight me on this...
This all goes to what I stated earlier:
They don't have to have an A region bias to pull this off- just good design .
Sorry, you said Class B amps don't have to have zero crossing distortion and I just showed you many examples of so called Class AB amps that have crossover distortion. This would imply that basically all Class B amps have this because that is simply how transistors behave.
I don't know what Class the Topping amp is and I don't think you know for sure either. I also don't know if it has zero crossing distortion. Have you seen independent measurements for it?
You showed me problems that some AB amps have. Its not all AB amps that have that problem. The assumption that all AB amps have a zero crossing because some do is not logical.
I admitted that a lot of class B amps are problematic. But I mentioned two that are not. I measured one of them myself after it was refurbished.
Therefore we know that even class B amps can be made without a zero crossing problem.
The other I amp I mentioned I found out about (and is the little brother to the amp that is the topic of this thread) thru an independent review. The link is below.
Sorry, you are trying to twist things. I never said all AB amps. I said even a lot of AB amps have zero crossing distortion, so reduce that bias current further to get Class B and they will always have zero crossing distortion.
I'm not twisting anything. I have been told many times I take things too literally.
Sorry, you said Class B amps don't have to have zero crossing distortion and I just showed you many examples of so called Class AB amps that have crossover distortion.This would imply that basically all Class B amps have this because that is simply how transistors behave.
The conclusion in the above statement isn't supported by its opening sentence. In addition to that I see you are qualifying it now by this comment:
I never said all AB amps.
That is true, where your argument falls apart is this conclusion:
I said even a lot of AB amps have zero crossing distortion, so reduce that bias current further to get Class B and they will always have zero crossing distortion.
Your comment here takes the form of a logical 'If then' statement; 'so' being the 'if' and 'and' being the 'then'.
The logical failure is the assumption that somehow because some AB amps have this problem (which I pointed out earlier is either a setup or design flaw and isn't inherent to class AB) then all class B amps will have a zero crossing problem, despite the fact I showed two that do not.
What you are not taking into account is that a designer of a class B amp might have a solution to prevent crossover distortion. Your assumption seems to be that such solutions don't exist, despite examples that belie your position.
You never demonstrated anything of the sort. You simply stated that some old Class B amp you knew of didn't have zero crossing distortion.
Last time I checked, your statements are not factual proof of anything.
Show the measurements of the amp in question. Demonstrate how it is possible for a Class B amp to not have zero crossing distortion when it is clear that the transistors are going into cutoff and it is highly non-linear. The disjointedness of the handoff between transistors in Class B, where one is going into cutoff and is non-linear and the other is also non-linear (but with a different transfer function in that region) upon turn on is inherent in the devices and the Class B bias.
The amps that are Class AB and showing zero crossing distortion are ones where the bias has been set too low and they are not completely eliminating the zero crossing distortion as the transistors are now in a quite non-linear region of their transfer function. You can call this poor design if you want but it shows clearly what happens when the bias is set too low...exactly what you get in Class B.
What design trick could be made to eliminate the zero crossing when biasing an amp Class B? Oh wait! I know, bias it in Class AB or Class A! If done correctly it will eliminate or mostly eliminate the issue. If there was a better way to do it then I think you would see most amp makers doing that because you can of course get away with a smaller power supply because of the very low power consumption on idle. So, please spare me your "what if the designer has a way around the issue"...that way around the issue is to build a bigger power supply and bias the transistors with a lot higher quiescent current. Negative feedback is not the solution to this particular (or any really) problem with amp design.
BTW., one of the amp measurements I showed was a Naim amp. Not surprisingly, it has zero crossing distortion because...it's Class B!
Show the measurements of the amp in question. Demonstrate how it is possible for a Class B amp to not have zero crossing distortion when it is clear that the transistors are going into cutoff and it is highly non-linear. The disjointedness of the handoff between transistors in Class B, where one is going into cutoff and is non-linear and the other is also non-linear (but with a different transfer function in that region) upon turn on is inherent in the devices and the Class B bias.
A power amp is considered class B if the output transistors go into cutoff at the zero point. So how could such an amp have no zero crossing artifact?
The answer is the driver transistors drive the speaker at very low levels. They don't go into cutoff like the outputs do. At higher levels the outputs are doing the work so the driver section doesn't get hot although heatsinks on driver transistors are common.
Any technician that has seen emitter resistors open up in the output section knows to expect shorted outputs, but you might be surprised to find that if the drivers are OK, an amp damaged in that way might play just fine at a low volume. The driver transistors are the bit you're not thinking about.
In a class B amp if you want it to be musical you'd simply be careful about how the driver section is designed. I've pointed this out several times but not this specifically. I hope this helps your understanding.
"The answer is the driver transistors drive the speaker at very low levels. They don't go into cutoff like the outputs do."
At that point (for the duration of that low level operation) the amp is not a Class B amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Or the simpler explanation is you simply have no clue of what you are talking about. Occam's Razor suggests since that is the simplest explanation, its likely true.So once again, below is a link to measurements (which I posted before) of a class B amp, the Topping B100, which is a smaller version of the amp that is the topic of this thread.
Go and look at it this time! Or you can refuse to learn- that's up to you.
Would you like a photo sine wave response of the class B EV amp I have in the shop? It makes 20 Watts at full power. What power level would you like to see such that you are convinced??
Edits: 02/18/25
From a DIY poster:
"4A is not much current, especially for inefficient 4 ohm speakers (i.e. Maggies). That being said, I listen at background music levels.
The B100 is a class AB bridged chip amplifier with a lot of feedback. It also has a microcontroller that prevents it from blowing up. 😉
Ed"
Some DIY guy or:
https://stereonet.com/reviews/topping-b100-amplifier-review
https://www.audiosciencereview.com/forum/index.php?threads/topping-b100-amplifier-review.57036/
So where do you suppose the reviewers got their information?
Reviewers believe any old s&$T.
"FWIW - My little boxes went into protection during 'normal' use several times. They should not be allowed to advertise these as 100W amplifiers, IMO. I won't be trying out the B200 based on my experience with the B100. Topping kind of let me down with these. I had high hopes. I cannot recommend them, because I am now of the opinion that they certainly do not "work as advertised" like I thought.
Cute little buggers... and they do sound nice ... but...
Overall two things (so far):
1 - Goes into protection at what I'd even consider moderate listening levels with less sensitive speakers. What I'm curious about is why they both go into protection almost at the exact (or exact) same time. I can't imagine the signal to both channels is perfectly 'stereo' with most of my music, but ... bass may be what's stressing the little guys out... and that's typically even between both channels. Thoughts appreciated.
2 - Sure they're cute, but when a fairly typical pair of speaker cables drags them off the rack... it's annoying. Anyone using spades will likely be quite irritated.
I can take some time after the holidays maybe to do some fairly basic measurements. I feel like it may be worthwhile to see if mine perform similarly to the measurements posted previously.
I admit that I'm a bit cynical in the fact that it would seem that Topping is using ASRs measurements as their specs. That is only at first glance. I did not do a line for line comparison. The format looks remarkably similar though. If that is the case, then both ASR and Topping have lost a lot of credibility with me."
Another DIY guy who doubts the claims.
This is first hand user experience, not hearsay...at least try to understand what is being shared.
-
This is first hand user experience, not hearsay...at least try to understand what is being shared.
But you didn't so its not first hand.
We don't know what the comments really are. We don't know who posted them and so on. So its hearsay.
If it is a quote from that person saying they tested it then it is not hearsay...learn the English language Ralph. You can question whether they really did the test or not, that would be a fair challenge but stop misusing the English language by calling it hearsay.
-
According to this advertising, it is Class AB
"Topping's latest ultra-high pure full-time class AB mono power amplifier with Tang-ku-la technology. The amplifier is capable of up to 100W @ 4 Ohms or 70W @ 8 Ohms, with an outstanding dynamic range, extremely low noise and minimal distortion."
That throw's cold water your "Class B doesn't have to have zero crossing distortion"... the amp is not really Class B that you have chosen as an example.
Also, this thread on DIY audio throws a lot of doubt about it's class of operation:
https://www.diyaudio.com/community/threads/topping-b100.417717/page-3
A simple google search reveals the source of the advertising and the DIYAudio quote you linked are the same thing:
https://www.muzix.eu/us/spd/MG-TPPNG-B100-BLACK/TOPPING-B100-High-End-Desktop-Mono-Amplifier-Unit
Your claim is based on a logical fallacy called a 'false authority'.
You'd want more than a single source wouldn't you??
Look at this a different way. The DIYer's say the heatsinks are small and that is verified by photos of the interior. A class AB amp of this sort of power would have larger heatsinks because it will make some heat even at idle! You may not have much experience with solid state so you may not know.
A class B amp wouldn't need large heatsinks since it will run cool most of the time. People who push this amplifier report that it can get quite warm. That is consistent with class B operation. This is of course simply evidence not proof.
The bottom line is if you want to get to the bottom of this you need to do more research. I noticed Topping is very careful to not mention the class of operation on their website. Doesn't that strike you as a bit odd, since class B has such a bad reputation?? They don't hesitate to mention their class D amps are class D...
Pure speculation from your part...
-
only speculation.
And another thing, you can't ignore me on this forum but you have put me on ignore on WBF and yet you spill over conversations from here onto WBF where I can't challenge your statements. I am sure you like wearing the mantle of expert that can't be challenged (yet you still manage to get plenty of people riled up), but there are a number of erroneous things you post that you spill over there (like this Class B amp nonsense you spew).
What are you afraid of Ralph? I have never personally attacked you...just your ideas.
You've done that several times now.
You are saying I'm afraid; that isn't attacking a post, its attacking me.
The reason I put you on ignore on What's Best is quite often your posts about technical issues on that site are incorrect, and you repeat them like propaganda. Is is a Sisyphean task to try to get you to read up?I just didn't feel like it over there, where there's far less technical education on display.
The irony is Ralph is that you, as the amp designer, make a lot of wrong statements, especially about psychoacoustics.
What name did I call you Ralph?
WRT pshychoacoustics; when you change the subject like that and do it in the form of an attack as you did just now, that is a classic verbal abuse tactic. If that was not your intention you might want to make a note of it.
'Amateurish'
'snowflake' off the top of my head.
FWIW the issue here is class B and what I've been saying about it isn't 'nonsense'. Its clear from your responses you've not delved into the topic and the idea that such an amp can be free of artifact is foreign to your way of thinking. Let's start with the link below, which is a patent document about the Wiggins Circlotron, which is the kind of amp EV used to make.
Do a search on 'class B' and you'll see
Still another object of the invention is to provide an
improved amplifier not subject to switching transients
when operated either as class AB or class B.lack of switching artifact
I explained earlier what he's talking about here. Guessing you didn't read it.
There is no measurement in the patent to substantiate this claim. Therefore, it is just a claim and not a fact. Just circuit diagrams, which are interesting and maybe result in a good sounding amp.
The question then is: if this amp was low distortion/no zero crossing and low consumption, why then didn't you build such an amp? This patent was clearly expired when you started building amps?
Why did you make high bias amps, if it was possible to make them as good with low bias?
it makes you look a bit foolish. Its not a whole lot different from attacking the UL patent... Google is your friend; take a look at the link and you'll see it stating clearly its a class B amp; and a comment about 'switching transients eliminated'... sheesh.
why then didn't you build such an amp?
We have been looking into the use of the Wiggins Circlotron for some time. I have a prototype based on EL34s that's on my bench right now.
I simply pointed out the fact that the test data in the patent doesn't reveal whether or not zero crossing distortion is present or not. There is no plot of residual distortion in the patent, therefore, it has to be said that this particular patent claim is not supported by what's actually in the patent. As someone who is on three medical technology patents, I can tell you that such an unsubstantiated claims usually don't fly in a patent application. It is a rather old patent and probably they couldn't produce the correct measurements at that time to prove the claim.
You claim to be able to measure one, so do and publish the results.
There is no verbal abuse in changing the topic. Again, another attempt from you to play some kind of wrong victim. You yourself brought up WBF and my so-called "incorrect" statements. One of those topics of contention was your misunderstanding about what is said in various psychoacoustic publications...particularly about masking and your misunderstanding about how that works.
Just pointing out observed behavior from yourself...look closely at your posts and defensiveness and you will see it if you care to self-reflect.
'FWIW the issue here is class B and what I've been saying about it isn't 'nonsense'. Its clear from your responses you've not delved into the topic and the idea that such an amp can be free of artifact is foreign to your way of thinking. Let's start with the link below, which is a patent document about the Wiggins Circlotron, which is the kind of amp EV used to make.
Do a search on 'class B' and you'll see
Still another object of the invention is to provide an
improved amplifier not subject to switching transients
when operated either as class AB or class B.lack of switching artifact
I explained earlier what he's talking about here. Guessing you didn't read it."
Again, this is a tube amp and we were talking about the Topping TRANSISTOR amp. Tubes and transistors don't behave the same...maybe you even know that?
And again, even with your Class B circlotron tube amp, there is no measured proof that it has no zero crossing distortion. People state all kinds of things that later prove to be exaggeration or false.
There is no verbal abuse in changing the topic.
Any abuse victim understands what is going on when the topic changes as the prior topic was properly addressed.
This isn't about electronics; this is about you needing to be in control.
And again, even with your Class B circlotron tube amp, there is no measured proof that it has no zero crossing distortion.
100% BS. I have the amp in my shop. This is an excellent example of gaslighting. I though you were above this sort of thing. I'm not angry, just disappointed.
Your statements have no basis in reality, Ralph.
"Any abuse victim understands what is going on when the topic changes as the prior topic was properly addressed."
It was never properly addressed, no proof was ever given and now you want to further obfuscate your weak position by playing some sort of lame victim card. Pathetic...
"This isn't about electronics; this is about you needing to be in control."
No, it's about you proving something you claim. Of course you want to change the dialogue away from your lack of ability to demonstrate what you claim.
"100% BS. I have the amp in my shop. This is an excellent example of gaslighting. I though you were above this sort of thing. I'm not angry, just disappointed."
Great! Then it is very easy for you to post the proof. Again, you would rather rail against my challenge rather than just prove it and close the discussion...me thinks thou doth protest too much!
And another thing, you grasp of English and the meanings of words is poor. Go look up gaslighting and you will (if you were open minded) see that I my challenging you on this is not gaslighting. I am making a position statement that you are not able to debunk. Nevermind the fact that were were talking about SS amps and not tube amps in the original discussion. You then threw out a direction change with introducing a rare Class B tube amp that no one knows about and that has no real published measurements.
Your claims you have it on your bench is just that...a claim. Nothing more and nothing less. Show a picture of you with the amp and then the requested measurements...not that it changes my claim about Class B transistor amps.
I did debunk your specious claim that a solid state class B amp cannot operated without a zero crossing artifact. Link below.Your saying I didn't is false.
Great! Then it is very easy for you to post the proof.
Again, and for the 3rd time, what do you need to see as 'proof'? photos??
We both know what you will do when presented with that evidence.
Edits: 03/07/25
Doug Self lists the 8 types of distortion mechanisms when he is discussing his "blameless amplifier"
TABLE 1.
SOURCE ORDER SLOPE ORIGIN
1 Input stage (balanced) 3rd-order 18dB/oct Inherent
Input stage (unbalanced) 2nd-order 12dB/oct Inherent
2 Voltage Amplifier Stage 2nd-order 6dB/oct Inherent
3a Output stage LSN (4 Ohm) 3rd-order 6dB/oct Inherent
3b Output stage crossover Complex 6dB/oct Inherent
3c Output stage switchoff Complex Variable Inherent
4 Non-linear VAS loading Complex Flat Inherent
5 Decouple return in ground Even Flat Topological
6 Rail induction Even 6dB/oct Topological
7 Wrong feedback point Even Flat Topological
8 Capacitor non-linearity Odd 12dB/oct Inherent
The distortions we have been discussing are distortions 3a, 3b and 3c, which he lists as "inherent", meaning they are fundamental to transistor function.
He then states: "In a field like Audio where consensus of any sort is rare, it is widely acknowledged that crossover distortion is the worst problem afflicting Class-B power amplifiers. The pernicious nature of crossover distortion is that it occurs over a small part of the transfer characteristic, and so generates high-order harmonics. Worse still, this range is around the zero-crossing, so it is present at all levels, the THD percentage potentially increasing as output level falls, threatening very poor linearity at low powers."
Furthermore: "To further get the measure of the problem, Fig 23 shows how HF distortion is greatly reduced by increasing the load resistance, providing further confirmation that almost all the 8 Ohm distortion originates as crossover in the output stage."
So, a typical loudspeaker load makes the situation worse and particularly at high frequencies. The lower the impedance, the worse it gets for a Class B amp.
Finally: "This leaves Distortion 3, in its three components, as the only distortion that is in any sense unavoidable, as Class-B stages free from crossover artifacts are so far beyond us."
THat sums it up. He found a way to mostly eliminate all the distortions on his list EXCEPT distortion 3, which are inherent traits of transistors when running Class B.
Doug Self, himself, has declared that avoiding zero crossing distortion in Class B transistor amps is IMPOSSIBLE with current semiconductor technology.
How many times does it have to be repeated before it sinks in? Your saying something without test measurements to show is NOT a fact!!I believe data not your words. So, until you can demonstrate with measurements a Class B amp without zero crossing distortion then it is YOU who is trying to gaslight me, not the other way around. I see you like project what you do onto others... sad...
Edits: 03/07/25
There is no plot of the residual distortion sine wave, the sine wave plots are all high level. So, you cannot tell from these whether or not there is zero crossing distortion.
Does Topping itself call this amp Class B or is that just Amir saying it?
https://www.stereophile.com/content/plinius-audio-sa-103-power-amplifier-measurements
Figures 8 and 9 are what I am talking about. Amir doesn't show anything like this, so it is not possible to tell otherwise. Please note that the high level sine waves look perfect in Figures 8 and 9 in both AB and A mode. Only the residual distortion plot tells the story.
So, until I see a measurement like that, I don't accept that this amp is free from zero crossing distortion, despite the very low overall distortion.
-why not do proper research on the topic?
I've measured AB amps on the bench. If they are improperly biased and running class B as a result, the crossover artifact is easily seen on the scope and the output level isn't very important. Its also (as you know) easily heard.
So I think we can assume this amp doesn't have that particular problem- users haven't reported it anyway...
So its either AB or Topping figured out a way to get around the problem. And there's evidence for the latter- Topping mentions the amp uses a 'module' of their own design and research. Clearly getting a lot of feedback and a microcontroller to prevent damage is part of it, but is that all? Could it be that they also figured a way to not have expensive heatsinks (which we've established they don't)? What could that way possibly be??
USERS ARE NOT EVIDENCE!!! A lot of users like Naim amps and some of the other so-called AB amps that exhibit zero crossing distortion. They likely can't hear worth a damn but that is another discussion...
Thanks for confirming what I have been saying, if an amp is AB or A and properly biased it doesn't have zero crossing distortion... If it is improperly biased and goes into cutoff or non-linear zone then it has zero crossing distortion and is effectively (regardless of mfg. claims) Class B because the bias is too low to keep the devices on through the handoff.
As I said, without a residual plot of the distortion component, we don't know if the Topping has zero crossing distortion or not. User feedback is not evidence.
Amir doesn't provide a residual distortion waveform and so we don't see if it is an issue or not. If it is not, then the Topping is not Class B and if it is there, even if small, then it is a Class B amp.
Honestly, the level of speculation in your responses is frankly amateurish and beneath the level of someone who has been an amp designer for a long time. You have NO idea if the amp has zero crossing distortion or not and the level of noise, distortion, and user feedback is not evidence of anything. Amir's measurements are not indicative either. One thing though is pretty clear is this, if an amp is underbiased then it will exhibit zero crossing distortion and is effectively Class B (even if claimed otherwise). There are no Class B amps that are completely free from this because it is inherent in the physics of the behavior of transistors.
USERS ARE NOT EVIDENCE!!! A lot of users like Naim amps and some of the other so-called AB amps that exhibit zero crossing distortion. They likely can't hear worth a damn but that is another discussion...
Wait- huh? All people that listen to Naim amps can't hear worth a damn?
Your logic is terribly flawed.
If it is improperly biased and goes into cutoff or non-linear zone then it has zero crossing distortion and is effectively (regardless of mfg. claims) Class B because the bias is too low to keep the devices on through the handoff.
The amps you are talking about are not designed for class B. You seem to be ignoring that simple fact. So yes, when improperly biased (and so operating as a class B amp) they will have a problem. But if the circuit is designed to get around that problem with intention of being a class B circuit then your statement is false.
User feedback is not evidence.
Testimony is indeed evidence. What is is not is proof. You seem to be conflating 'evidence' with 'proof'. Do you see the distinction?
If you wish to be abusive that's on you. I hate to come back with something that might be considered abusive as well but in plain English you don't know what you're talking about. I've worked with amps that were operating class B because of insufficient bias and I can tell you they don't reproduce a sine wave properly. You don't need to have them at super low power- the problem shows up because at zero crossing the amp is low power at that point! Amirim's measurements don't show any evidence of a problem; if there was one the sine waves he showed would have been sufficient. Based on your comments though I fear this will be lost on you.
My recommendation is get an amp on which you can adjust the bias and put a scope on it, then adjust the bias and see what I'm talking about. If there's a problem at the zero crossing its pretty audible and you won't need a super low signal level to see in on the 'scope.
You've still not explained how the EV A-20C, which is a class B amp, can have no zero crossing artifact.
"Wait- huh? All people that listen to Naim amps can't hear worth a damn?"
Pretty much yes...same for 99% of the rest of hifi gear that sounds like crap.
Most people are not good critical listeners and the latch on to either advertisement (Naim is good at PRAT) or some specific aspect of the sound they like at the expense of most of the rest.
"The amps you are talking about are not designed for class B. You seem to be ignoring that simple fact. So yes, when improperly biased (and so operating as a class B amp) they will have a problem. But if the circuit is designed to get around that problem with intention of being a class B circuit then your statement is false."
Designed to get around it HOW??? You keep saying that but it doesn't mean that there is a way around it. Naim certainly hasn't found the way around it because they make Class B amps that have zero crossing distortion. If you know how to get around it then demonstrate how you would get around it. The fact that you haven't expressed a single circuit idea on how to do it tells me that YOU DON'T KNOW HOW to do it. Oh, and please provide measurements that demonstrate that it actually worked as claimed...claims aren't what they used to be you know.
User feedback is meaningless. You can always find someone who likes something, no matter how terrible it really is. It is evidence of nothing other than a subjective opinion and you don't know if that is in the minority or majority. You see the difference??
"'ve worked with amps that were operating class B because of insufficient bias and I can tell you they don't reproduce a sine wave properly. You don't need to have them at super low power- the problem shows up because at zero crossing the amp is low power at that point! Amirim's measurements don't show any evidence of a problem; if there was one the sine waves he showed would have been sufficient. Based on your comments though I fear this will be lost on you."
It's sad that you think a professional challenge is abusive. Stop being a snowflake Ralph and man up. You keep ignoring my point that Amir's measurements don't show the residual distortion in the sine wave plot. With low distortion amps the high level sine wave will never look distorted, you have to extract out the residual distortion and plot it like Stereophile does (so, we know it's possible but curiously Amir doesn't do it) and then you can see if there is zero crossing distortion. Until then there is no proof one way or the other. The fact that STereophile gets this and you don't seem to get it makes me wonder what you have really learned in 40 years of amp designing. Measurements don't seem to be your strong suit.
https://www.stereophile.com/content/naim-classic-200-series-nap-250-power-amplifier-measurements
Please refer to Figure 7 to illustrate what I am referring to. You see the residual distortion plot shows the zero crossing distortion in this Naim amp. No such plot was provided for the Topping.
"You've still not explained how the EV A-20C, which is a class B amp, can have no zero crossing artifact."
Explain what? You have not provided any evidence that this is in fact true. I cannot explain something that has not be demonstrated to exist. When you can do that, then perhaps there is something to discuss here.
"My recommendation is get an amp on which you can adjust the bias and put a scope on it, then adjust the bias and see what I'm talking about. If there's a problem at the zero crossing its pretty audible and you won't need a super low signal level to see in on the 'scope."
I have first-hand experience with a Plinius SA-103, which has a Class AB and Class A bias setting (push of a button on the front panel). The sound quality difference is very significant and the measurements on Stereophile show clearly the effect of the AB setting vs. the A setting.
https://www.stereophile.com/content/plinius-audio-sa-103-power-amplifier-measurements
It's sad that you think a professional challenge is abusive. Stop being a snowflake Ralph and man up.
Name calling like this is abusive and earlier you used the word 'amateurish'. What is sad is that you have to resort to this sort of tactic. It literally means you have nothing.
I explained how a solid state class B amp can be designed to have no zero crossing artifact. My assumption is you didn't read that post or have chosen to ignore it.
You have not provided any evidence that this is in fact true. I cannot explain something that has not be demonstrated to exist.
I did ask what sort of evidence would be acceptable but you didn't respond.
Furthermore, the EV A-20C is a tube amp, not a transistor amp. Tubes behave differently around cutoff than transistors, which get really non-linear. It could be that a tube amp in Class B is not as troubled by zero crossing distortion as a transistor amp clearly is. Therefore, it is unfair to use that as an example when discussing transistor amps.
This sure looks like backpedaling to me... I explained how its able to have no zero crossing artifact. Clearly you're not reading.
Robert Heinlein once said "Ignorance is curable, stupid is forever."
If one refuses to read, and therefore chooses to remain ignorant, how is that not stupid??
It means you have offered nothing and then acted offended when challenged...you can say that is name calling but it is a fact.
"You have not provided any evidence that this is in fact true. I cannot explain something that has not be demonstrated to exist.
I did ask what sort of evidence would be acceptable but you didn't respond."
Not true. I told you that the residual distortion wave form would be proof. You didn't provide that for either the Topping or the old EV amp.
"This sure looks like backpedaling to me... I explained how its able to have no zero crossing artifact. Clearly you're not reading."
No, clearly we were discussing transistor amps in the thread and then you chose to throw something else into the mix.
"Robert Heinlein once said "Ignorance is curable, stupid is forever.""
Project much?? You're the one who misinterpreted what the thread was discussing and decided to throw some old tube amp into the mix. I read your posts but didn't google the exact amp until recently. You still didn't provide any technical proof that it doesn't suffer from crossover distortion. WHat few measurements I found would not tell you this.
So, it is you who are dodging the requests for data to demonstrate.
Did you miss the point that the Topping is a solid state amp?
You're the one who misinterpreted what the thread was discussing and decided to throw some old tube amp into the mix.
I didn't misinterpret anything. Here is the text again:
https://www.audioasylum.com/forums/amp/messages/25/254430.html
I explained what was different about that amp and so it became relevent.
I also explained how a class B solid state amp can get around the problem you described. But you didn't read that.
I also asked for what would be considered 'proof' since its pretty obvious that if I just put up a nice looking sine wave you would challenge its source. I'm not playing that game.
No dodging anything; just dealing with the fact that you tend to obfuscate when presented with the truth of technical things about which you don't have training or experience.
Some old tube circlotron design is IRRELEVANT to a discussion about Class B solid state amps. I showed you examples of Class B commercial amps that clearly demonstrate zero crossing distortion. You just keep using words!
You can't even show me evidence that your one example doesn't exhibit the zero crossing distortion issue. Not one piece of evidence from you! Claims are just that...claims. I have showed you numerous examples of underbiased AB and B amps (class B is by definition underbiased so that the transistors go into cutoff) that exhibit the issue.
On top of that I tell you clearly what is missing from the Topping measurements that would confirm it to have or not have zero crossing distortion and then you pretend I didn't tell you what was missing! Who isn't reading?? Clearly you.
I've mentioned several times how a solid state amp can be designed to avoid crossover or notch distortion.
You're not interested so around and around we go...
You need to showed data, your explanation is worthless without data to prove your claim.
I guess you would rather play the victim while projecting...
Furthermore, the EV A-20C is a tube amp, not a transistor amp. Tubes behave differently around cutoff than transistors, which get really non-linear. It could be that a tube amp in Class B is not as troubled by zero crossing distortion as a transistor amp clearly is. Therefore, it is unfair to use that as an example when discussing transistor amps. I don't actually know of any current commercial tube amps that are Class B for comparison.
Offer a better solution to crossover distortion when NPN output devices are tightly matched? Just a question. :)
My Edge Electronics M8 power has this type of output stage but the output transistors are very tightly matched. If I remember correctly the Bias is set at 8mVdc @ 120AC input. This amp is a really nice sounding amp and has better many I have tried in my system at low or higher volume levels. My Amp uses the Toshiba 2SC3281 NPN transistors.
So much depends on design and of course, matching.
-
he has been pitching that concept for years.
You can buy "Blameless" boards here as referenced on his own website.
I didn't realize that was a class B design.
The distortion rise with frequency at 1KHz is a bit concerning. I have a theory that sort of thing can be audible as harmonics of signals below the cutoff frequency can be considerably higher in amplitude than one might expect, and those harmonics also being higher orders, to which the ear is keenly sensitive.
I've not heard one, so I really do wonder if its 'blameless'.
building the equivalent of a Toyota Corolla. Plenty of market space there.
Low price and very accurate but they don't have the cachet of 'audiophile grade' time pieces, i.e. expensive and less accurate.
"So, one transistor completely shuts off before handing off to the other one. That is Class B."
The argument is there is always some leakage current flowing so for those that think the full definition of Class A is "as long as there is current flowing for the whole input signal cycle it's Class A" that makes all Classes of amplifiers Class A amplifiers.
My point? There is much more to Class A than just duty cycle. That goes for all the Classes.
Tre'
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Every amp has some bias and therefore at least a tiny amount of class A.
Them's fightin' words for some. ;)
nt
Dmitri Shostakovich
Based on the B100 being class B. I'm assuming the 'B' means something.
Is then the LA series class LA?
the "NFCA discrete outputs" are switchers? They clearly say the PA and MX series are. Doesn't look like it to me!
NFCA (Nested Feedback Composite Amplifier)
So it is not class D. But the size is on the small side for a 200W amp.
What is class A/B?
Runs class A at lower power levels (the all important First Watt or more) and switches to nearly B at high power.
What I've used for fifty years and just like your Cary V12
"Runs class A at lower power levels"
No it does not. Class AB is nothing more than Class B with a little idle current in both devices to limit crossover distortion.
In a Class A amplifier the output devices are biased at the mid point of the most linear part of the operating curve (transfer curve) allowing linear and symeterical operation in both directions (increase and decrease of current) from the idle point with the input signal limited so that the operation stays away from the non-linear cutoff and saturation regions of the devices.
With Class AB the devices are biased at a point that is already down in the non-linear cutoff region. None of the power made by a Class AB amplifier is Class A power. There is a small amount of power produced while both devices are on and conducting but that does not make that power "Class A" power for the reasons given above.
I think there are some designs that operate in both Class A and (when needed) Class AB but that requires "sliding bias".
Tre'
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For a solid state push pull output I think it is fair to say that when it is delivering all the required load current without either device switching off it is in a class A region. So, if a 50W class A/B power amp has enough idle current to deliver 2W to the load and you're actually delivering less then it is fair to call that region class A operation. At higher power a push-pull stage will move to class B.
For single-ended stages the device must be biased to deliver all the rated load current.
I can't argue against your definition of class B. How would you define the bit of class AB that is not class A? Not that it matters as pure (!) class B is a rarity.
A Class AB amplifier is always operating in Class AB.
It never operates in Class A but at times it shares one of the characteristics of Class A. Namely that at low(er) power all of the output devices operate without reaching cutoff. This is something that a Class A amplifier does all the time.
It never operates in Class B but at times it shares one of the characteristics of Class B. Namely that at high(er) power half of the output devices do reach cutoff. This is something that a Class B amplifier does all the time.
A Class AB amplifier is neither Class A or Class B.
It is, at all times, Class AB.
Tre'
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" At higher power a push-pull stage will move to class B."
No, a Class AB amplifier is never a Class B amplifier. In a Class B amplifier all of the output devices are biased to off and they only conduct when presented with the positive portion of the signal. The devices presented with the negative portion of the signal stay off for the full half cycle and only conduct once they are presented with a positive signal.
That never happens in a Class AB amplifier. In a Class AB amplifier all output devices are conducting with no signal and half of the output devices only stop conducting when they are presented with enough negative signal to cause them to reach cutoff. The next half cycle, the roles are reversed.
"For single-ended stages the device must be biased to deliver all the rated load current."
Yes, single ended circuits for audio use have to operated Class A but push pull can be Class A as well.
Tre'
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No it does not.
your broad stroke of the brush misses reality. Many exceptional amps designed by John Curl, Nelson Pass, Dan D'Agostino do just that!
I'd hardly consider 500-600 watts as "a little idle current". ;)
Regarding the Parasound JC-1+, As the JC 1+ operates in class-A up to 25W into 8 ohms when its bias is set to Normal, it runs hot.
used to make a monoblock, think that was its idle current. Damn thing sounded like jet engine.
.
/ optimally proportioned triangles are our friends
"Regarding the Parasound JC-1+"
What they are calling Class A power is the power that the Class AB amplifier can make before any of the output devices reach cutoff.
That is not the same thing as true Class A power. The devices in a Class A amplifier are bias at the mid point between max current and cutoff.
The output devices in Class AB amplifier are biased at something lower than that, otherwise the amplifier would not be able to produce power beyond when half of the output devices reach cutoff because the other half of the output device would be at max at that same moment.
The JC-1+ can do 25 watts while all of the output devices are conducting 100% of the time and 450 watts total. Clearly the output devices are not biased at the mid point between cutoff and max current.
Tre'
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The JC-1+ can do 25 watts while all of the output devices are conducting 100% of the time and 450 watts total.
Yes, that's the thing.
Yes, that is the thing a Class AB amplifier does.
All of the power produced by a Class A amplifier is produced while the output devices are conducting 100% of the time. Saturation and cutoff is reached at the same time and at that point the amp has no where else to go.
The amp has no way to produce any more power.
That is Class A. If the amp is not doing that, then it's not Class A.
How can an amp that is not Class A produce Class A power?
Tre'
Have Fun and Enjoy the Music
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!
The Mind has No Firewall~ U.S. Army War College.
who design, test and sell them since you seem to be confused.
You are confusing sales hype with knowledge.Tre'
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Edits: 02/08/25
Yeah, these guys (among others) don't know what they're doing. ;)
What is the collective noun for audio gurus?
among engineers.
Constant correction unnecessary.
?
A-ha, I do now see that it is a young Bernstein. But, I wouldn't know Copland if he a blew a fanfare in my face.
Edits: 02/11/25
Bernstein and Copland.
Another pair of distinguished artists in their craft.
.
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their AB amps run class A for tens of watts at lowest power levels.End of ridiculous discussion.
Edits: 02/08/25
A output device (tube or transistor) can't be operated all the way down to cutoff (or saturation) without entering the non-linear cutoff region.
A proper Class A amplifier is biased to idle in the middle of the most linear part of the operating curve, half way between cutoff and saturation and is intended to never be driven into those non-linear regions. (non-linear cutoff and saturation regions shown above)
A Class AB amplifier is driven into the non-linear cutoff region even while producing its so called "Class A" power. Just because someone chooses to call that Class A power doesn't make it Class A power.
Tre'
Have Fun and Enjoy the Music
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Howard Tremaine Audio Cyclopedia second edition
Page 543 "What is a Class A amplifier. An amplifier in which the grid bias voltage is set to approximately one half the cutoff voltage to obtain linear operation."
Tre'
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Tre'
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"When a bipolar transistor is biased so that the Q-point is near the middle of its operating range, that is approximately halfway between cut-off and saturation, it is said to be operating as a Class-A amplifier. This mode of operation allows the output voltage to increase and decrease around the amplifiers Q-point without distortion as the input signal swings through one complete cycle. In other words, the output is available for the full 360o of the input cycle."
Tre'
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"The Last Word on Class A
First of all, what is a class A amplifier?
A class A amplifier is defined as one which is biased to a point where plate current in all the output devices flows for the entire 360 degrees of an input cycle, at the full, unclipped output of the amplifier. Or, as stated in the RCA receiving tube manuals: "The classification depends primarily upon the fraction of input cycle during which plate current is expected to flow under rated full-load conditions". The key phrase being "under rated full-load condtions", which is a requirement for amplifier classifications to be meaningful.. This is typically done by biasing the output stage halfway between cutoff and saturation, with the plate load impedance to an appropriate value that gives maximum undistorted output power."
Tre'
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I think it fine to classify an amplifier that is class A only for a fraction of its specified output power as Class AB even if it might end up spending most/all of its time operating in a class A regime. But, as pure solid state class A amplifiers are uncommon and class B is very rare (AFAIK) I also think classification with such fervor pretty pointless.
In your follow-up posts I see the inclusion of single-ended amplifier load lines. These are not relevant to solid state push-pull output stages, which can produce load current above their bias point as required (but only in one direction, hence the need for push-pull). And then I remebered having this discussion once before on AA and after a search it turned out to be with you!
As I told you more than 6 years ago, I'm not a SS guy."I see the inclusion of single-ended amplifier load lines. These are not relevant to solid state push-pull output stages, which can produce load current above their bias point as required (but only in one direction, hence the need for push-pull)"
Should I understand, from what you said, that a transistor can't idle at the mid point between cutoff and max current?
The single ended load line may not be relevant as the current moves up from the idle point but isn't it relevant as the current moves down from the idle point?
Or do transistors magically drop all the way to cutoff in a perfectly linear way?
If they don't then that's my point. In a true Class A tube amplifier (single ended or PP) none of the devices are driven into the non-linear regions, up or down. It transistors are linear all the way to cutoff then there is no need for Class AB, Class B with be notchless. (crossover distortion less)
As the dynamic operating curve chart (not a load line plotted on a set of plate curves but derived from that) shows, with a tube circuit Class A only operates the tube(s) in the "most linear part of the dynamic curve". I forget which book I'm quoting but that is a quote.
An AB tube amplifier doesn't do that and neither do SS circuits (unless transistors are linear all the way down to cutoff).
Side note, with a PP Class A tube amp, it you drop the idle current a little to get more power then it's not a Class A amplifier anymore and none of the power is Class A power. Even the part that is still operating in the "most linear part of the dynamic curve". The total rated power of the amplifier has to be power produced while all the tubes are operating most linear part of the dynamic curve. That is what all the old books discribe and show as examples of Class A.
Maybe with SS it's different. If a transistor stays linear all the way to cutoff. Tubes don't do that.
Tre'
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Edits: 02/10/25 02/11/25
And likewise I'm still not a tube guy :)
I've kind of lost the thread a bit but to answer your question nothing is linear! The further up and down the output current vs. Input voltage curve you go then the more distortion there is. The smaller the current excursion around a bias point then the less the distortion (with the limiting case being zero distortion for zero current change = small signal conditions). I don't know what the load line for an emitter/source follower would be but it would probably show the analogous effect that you are describing by tending to cut off the follower if it has to sink current from a load. Followers are great at supplying current to loads but that only works in one direction hence the need for push-pull unless you went with a single-ended follower biased so that it can sink the maximum load current before turning off (or getting too close to turning off) and that would be class A. But, IMHO, even if you did go class A, a push-pull would have the advantage of going into class AB for lower load impedances e.g. it could be 'pure' 50W class A into 8 ohms but give 100W into 4 ohms class AB, whereas a single ended 50W class A could only provide 25W into 4 ohms (current limited).
Transistors do not stay linear all the way to cutoff...otherwise, there would be no need for Class A to begin with as you would not have serious distortion at the handoff between transistors in a push/pull amp.
With push pull, there would be no need for Class AB because there would be no notch distortion in Class B.
I just thought of an analogy. It maybe not a good one but here goes.Class AB is a "fix" for Class B much like a suppressor grid in a pentode is a fix for the tetrode.
When they added the screen grid to a triode to block internal feedback path between the plate and the screen that lowered the gain and reduced the distortion, they created the problem of secondary emissions and had to add the suppressor grid to fix it.
When they went from Class A (push pull) to Class B (push pull), the non-linear behavior of amplifying devices in the cutoff region created cross over distortion and they had to put some of the idle current back to "fix" it.
A pentode is a fix for a tetrode but that doesn't make it a triode.
A triode is it's own thing.Class AB is a "fix" for Class B but that doesn't make it Class A.
Class A is it's own thing.I warned you that the analogy might not be very good. :-)
Tre'
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Edits: 02/11/25
!
The Mind has No Firewall~ U.S. Army War College.
Are really AB in that they operate with significant idle bias current thru the finals. Theory indicates that a unity coupled OPT could operate successfully with B biased finals but that's not what Mac did in practice, at least for their consumer stuff.
Marketing is a very important part of any business. It is just easier to explain it that way rather than trying to explain that it is not really Class A, it just sort of acts like Class A.
Tre'
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....it acts as A sometimes but it is not A in the true sense of the definition.
Yes, I think it is just easier to call the power an AB amplifier makes, while not reaching cutoff, Class A vs. trying to explain that it only acts like Class A is one narrow way but it's not real Class A. I believe that is the most likely reason designers (who for sure know better) say what they say.
I wish the wouldn't do that. They are confusing people. :-(Tre'
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Edits: 02/08/25
One thing is for sure, the distortion behavior is not the same as a Class A amp. Also, if you look at measurements, you can see that not all Class AB amps are sufficiently high bias to remove the zero crossing cutoff distortion.
As an aside, newish brand Infigo claim to operate always in class A using a novel sliding bias scheme but JA's measurements showed it rife with cross-over distortion though THD was still low and the reviewer loved the sound. I've no idea how much bias is required for a 'smooth' handover between push & pull and vice versa but many years ago Douglas Self wrote a series of articles about audio power amp design and claimed, IIRC, that optimally biased class B actually produced the lowest distortion. I didn't pay much attention at the time so don't know his reasoning but think it was that the variation of composite transconductance of the push-pull pair could be made much less through the cross-over region than for an AB pair. This was set in the context of applying as much loop gain as possible so, perhaps, with the right class B bias and a lot of feedback Topping has gone in this direction and try maximize efficiency to go against class D designs.
I found that amp review on Stereophile (see above). I don't take too much stock in what the reviewer liked and didn't like. You can always find someone to like your product. Having had amps early in my audiophile career that were both Class A SS and what I would call close to Class B (meaning later measurements revealed zero crossing distortion), I can tell you the one with zero crossing distortion sounded nasty and congested and was not very long in my system.
The Naim measurement I found also has zero crossing distortion and I don't know about you, but I find all Naim amps to sound dry (as in no harmonics and poor low level resolution needed for ambience retrieval) and flat. Horrible amps that traded on the selling point of having PRAT...because they had nothing else that sounded like music.
To the best of my understanding, you cannot remove distortion caused by zero crossing with negative feedback. I would need to read the reference I learned that from again to know the exact reasons why. Might have something to do with the fact that it is not an inherent transistor property but related to the stitching together two transistors to make a whole waveform and the glitch created by the imperfect handoff.
Distortion is created if the transfer function is anything other than a straight line (with slope = gain). For a push-pull output stage, if there is a little wiggle in the line around the zero crossing that creates cross-over distortion. The larger the deviation, the higher the distortion and sharper wiggles create higher frequency harmonics. Feedback can only suppress any open loop distortion by the amount of loop gain at the frequency of interest. So, higher frequency harmonics are suppressed less because amplifier loop gain is always rolling off as frequency increases, and this applies to all distortions not just cross-over.
One danger, I think, is that biasing too hard into class B could create a 'dead-zone' at the cross over point where there is a small region with no transconductance and that will give low, or no, loop gain in that region and, hence, no suppression. It would be interesting to study but I don't get much spare time and I'd rather listen!
Conversely, class AB output stage should have twice the slope in the region where both devices are conducting (class A region) and a signal transitioning between A & B regions will be distorted by that slope change and there will also be a halving of loop gain in the class B region. So open loop distortion is created by that transition and the amount of suppression is modated. This is the so-called 'gm doubling' effect that is in the literature. Most recently it was tackled by Jason Stoddard in his blog, he came up with something he calls a 'continuity bias'to get around that problem. But, IIRC, that biasing burns significant power that is still lower than staying class A all the time but much more than a traditional AB.
Where both finals are in cutoff at idl, it's class "C" not "B" . . . Not good for audio. Almost all audio amps claiming "B" operation are really "AB" with idle bias current set low but high enough to prevent both finals from being cutoff simultaneously under real-world conditions of manufacturing and operation. It could be argued that true class B exists only at a single operating point where "AB" and "C" have an infinite number of points.
:)
Interesting how this amplifier class discussion arises every few years and involves some of the same persons each time. The basic amp classes were defined nearly a century ago . . .
However, that means the performance around zero crossing is very non-linear and will create a lot of distortion that is of a very obnoxious nature.
Look at the stereophile measurements I shared above. You can see the sharp discontinuity they have around the zero crossing. As one can imagine, this is essentially only high order dissonant distortion components. Even very low levels of these harmonics will audibly damage the sound.
As Tre was pointing out, even AB is not putting the bias in a very linear part of the transistors transfer function, which will also result in increased higher order harmonics.
Yes, sliding bias is a whole different thing. I mentioned that early on in this thread.
"I think there are some designs that operate in both Class A and (when needed) Class AB but that requires "sliding bias"." See link.
"with the right class B bias and a lot of feedback"
I wasn't aware that there was different types of class B bias. I thought class B was biased to where the devices are just off and ready to come on at the first sign of a positive signal voltage? I thought all Class B amps were biased at the same spot?
Tre'
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I think bias is a spectrum so you could under bias heavily into class B such that both devices are off for a region and make a dead zone around the zero crossing (which would be bad) or over bias until you end up in class A. I suppose an optimum class B is something that gives the best trade off between distortion and power dissipation. I don't have direct experience of this but, I think, Self delves into it and his work is online and he justifies his choice of output stage biasing.
There are some amps are high biased in such a way, the first several tens watts are class A watts.
For example, Pass Labs, Plinius, Krell.
But part of the definition of Class A is that the output devices are biased half way between saturation and cutoff.
A AB amp can be biased so that more of the first watts are delivered when both devices are remain on through the full cycle but that, in and of itself, does not make those watts "Class A watts". It is easier to say "Class A watts" than to explain with I just did.
Again, in a Class A amp all of the amplifying devices are biased in the middle of the most linear part of the operating curve and never allowed to reach into the non-linear portions of that curve approaching cutoff or saturation.
Tre'
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Please see the picture
There is more to Class A than the short definition.
"In a class A amplifier current flows for 360 degrees"
A class C amplifier meets that definition, there is always some leakage current flowing.If you take the time to read the Radiotron Designer's Handbook and Tremaine's Audio Cyclopedia (and read beyond the short definition) you will see that with all of the examples of Class A (and a lot of the discussion of Class A) the bias point of in the middle of the "most linear part of the dynamic curve". You will also learn that with Class A the input is limited as to not drive the device into the non-linear regions (saturation and cutoff). Again, with Class AB the device is ran into the non-linear cutoff region (if not biased there to start with).
I don't know how you (or anyone) can call the circuit you showed Class A.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/07/25
This is from stereophile review
"Looking inside the KSA-250, the emitters of the 12 pairs per channel of output-stage transistors appear to standing on series resistors of nominal 1 ohm value. The average voltage drop across these resistors was 110.5mV, implying a standing bias for each of 110.5mA; ie, a total of 1.33A. This will give a maximum power for true class-A operation into 8 ohms of 28.5W (14.5dBW) rather than 250W."
Most Class AB amplifiers are bias low. So low as to be in the non-linear cutoff region at idle. Even though there is some power while both devices are conducting all the time, that power can not be considered Class A power. A device biased that low is not "operating in the most linear part of the operating curve".
If there is a Class AB amp that is biased high and does have some operation (or even a lot) where the devices are both conducting all the time and not dipping into the non-linear cutoff region, then that is closer to Class A but again, the devices in a Class A design are biased in the middle of the *most linear* part of the operating curve (for the device choose). The devices in a Class AB amplifier are not.
If the KSA-250 can output 250 watts but only 28.5 watts with the devices conducting all the time then it is a Class AB amplifier and it is biased as a Class AB amplifier (lower than the mid point between cutoff and saturation) and regardless of what the review says, none of it's power is true Class A power.
None of what I am saying is hard to understand. Class A amplifiers produce Class A power. Class AB amplifiers produce Class AB power.
Class A biased devices are idling at half the max current, Class AB biased devices are idling at something less than half the max current.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
in the forums?
If you are asking about the manufacturers that will tell the buyer that their amplifier operates in Class A for a certain amount of watts then it operates in Class B for the rest of the watts then I have to remind you that marketing is an important part of any business.
It is just easier to explain it that way rather than trying to explain that it is not really Class A, it just sort of acts like Class A.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 02/08/25
I don't need to ask you about anything.
But I don't know what is class A/B.
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