Handling a complex load by power amplifiers

[Thorsten Loesch]

Maybe, just maybe, those SMSLs and Toppings are real amps

If they work correctly and do not suffer from serious flaws - they are fine.

The problem is that even two seemingly identical amplifiers from two different vendors or two different batches may be different. Parts may have been omitted that were present in earlier versions, or parts may have been substituted by different ones (not always inferior ones, but sometimes better arts will make things worse.

For example, I am very familiar with the problem that Pavel shows. It is normally dealt with by adding a 4 Ohm resistor of a few watt and a sensible value capacitor (usually a few 100nF) costing a few cent.

I actually get a ton of pleasure from getting the device that meets my desired parameters for as little money as possible.

Well, that presumes you can confirm the desired parameters objectively and reliably.

The problem is that most customers cannot do so. Hence they come a site like this and rely on what is presented here. So it is important they get correct and accurate information.

As I said above, an Amplifier with such measured behaviour is in my view broken by design.

The flaw is in my view fatal and excludes operating the amplifier, UNLESS YOU KNOW PRECISELY what the problem is and how it is triggered and how to avoid doing that reliably.

What can trigger this resonance?

Use a speaker with inductive characteristic (e.g. most dome tweeters) enable triggering it.

An external RC snubber could be used to compensate, if you an EE (try 4.7R / 10W Non Inductive resistor in series with 1uF).

Otherwise limiting yourself strictly to speakers with Planar or AMT Tweeters will also work to "disable" this.

If you use speakers with dome tweeters or full range drivers etc and you do not add a snubber, here is what can cause trouble:

1) Anything DSD whatsoever, even with the narrow filter setting.
2) Any Delta-Sigma DAC with modest filtering of noise.
3) Any DAC using some form of slow roll-off Digital filter or MQA.
4) Any DAC without digital filter.
5) Modern LP frontend with clicks & pops or playing DMM LP's.
6) Anything else that creates ultrasonic noise that I have not covered above.

I would not accept a device with such limitations as consumer goods.

Additionally, I'd also like see more compliance info in reviews here.

Does the device have a FCC ID? Technically sale and use without the blessings of the FCC are not permitted in the USA for devices that are "digital" or "switching" anything as they can radiate noise that interferes with radio transmissions or other equipment.

There are electrical safety requirements, ideally we'd see earth bond test (where applicable) and Hi-Pot tests according the international standards.

A lot of gear that comes out of Ch!na is not safe or FCC regulation compliance. In extreme cases the result can see the unwitting customer fined or worse for RF interference and I think we all remember the killer deal (literally) fake iPhone chargers that electrocuted people to death.

I'd think avoiding entanglements for breaking federal regulation or being killed are high up most people's "desired parameters".

Thor

 

[PeterOo]

[…]

Well, that presumes you can confirm the desired parameters objectively and reliably.
[…]

Might it be a good starting point to see if the effect of the actual speaker on the signal is identical to the effect of the equivalent circuit? So we know the measurements are not an artefact of our (possibly oversimplified) model.
Especially since @pma is reporting what he sees as troubling behaviour at just a few Volts, so no eardrums will have to die in the proces.
If I understand correctly pma provided an equivalent circuit for a speaker he owns in post 23.

 

[Deleted member 48726]

Might it be a good starting point to see if the effect of the actual speaker on the signal is identical to the effect of the equivalent circuit? So we know the measurements are not an artefact of our (possibly oversimplified) model.
Especially since @pma is reporting what he sees as troubling behaviour at just a few Volts, so no eardrums will have to die in the proces.
If I understand correctly pma provided an equivalent circuit for a speaker he owns in post 23.

Done right, an equivalent circuit simulates the driver, crossover and the cabinet. What it doesn't do is simulate non-linearities like compression and break-up etc.
There's more discussion on the topic in this thread-->

NC252MP (class D) vs. A250W4R (classAB) burst measurements into 4ohm//2.2uF load

Makes sense, thanks. So then what would qualify as a proper "equivalent speaker circuit"? In other words, much of this thread has been concerned with discussion of speaker loads that are atypical or particular to certain types of speakers. So logically it would seem that one would need to test...

audiosciencereview.com

 

[CtheArgie]

This is becoming a weird argument now. How many angels fit on the top of a pin?
Even if we assume that some of what PMA has stated is correct. How does it manifest in REAL life? How many "events" have been triggered or known due to this "design failure".
Do we have speakers using this particular Ayima amp that have "failed"? Either the amp or the speaker? Who owns ($$$) speakers that could trigger this issue and power them with an $80 amp? This seems to me like claiming that a factory VW beetle can't go over 250 kph in Nurburgring, thereby it is a failure as a car. Tell me with specific examples why I may be wrong. Who puts bicycle tires on a Bugatti Veyron?

 

[sarumbear]

You are only confusing the issue with these misleading tests.

Amen!

They are as useful as testing the torque required to turn the volume control.

 

[sarumbear]

But yes, we need much better measurement methods to be able to accurately be able to predict the suitability of an amp for a specific set of speakers and/or vice versa.

We can also develop better tests to detects ghosts and spirits!

 

[levimax]

Uncontrolled amplifier oscillation, even if not readily apparent when listening, is always sub optimal. It happens more than one would think with any class of amplifier including tube amps. Stability should always be part of a good amp design. While these tests are approaching being edge cases they are none the less interesting and I have learned a lot from them. It seems like some people get all "tribal" on certain amp topologies or brands and don't want anything discussed that shows any "weakness" even if it is just an academic exercise showing issues that could be improved with better engineering. The SINAD chase, even though it has no audible effects past a certain point, is cheered on as show casing good engineering, so why should less than optimal stability be overlooked?

 

[Thorsten Loesch]

Might it be a good starting point to see if the effect of the actual speaker on the signal is identical to the effect of the equivalent circuit? So we know the measurements are not an artefact of our (possibly oversimplified) model.

An actual speaker will behave worse, for a variety of reasons.

Thor

 

[Thorsten Loesch]

The SINAD chase, even though it has no audible effects past a certain point, is cheered on as show casing good engineering, so why should less than optimal stability be overlooked?

Well, I have asked here repeatedly for the science behind all of this SINAD (aka THD&N).

What Pavel measures is very real, probably > 90% of all speakers are affected and we need the combination of amplifier, speaker AND source to cause the system to show problems. It may even be recording specific.

It does of course not show in an overly simplified AP Dashboard (it would if, like JA at Stereophile measured amplifiers with a simulated speaker load and to high enough frequencies) and if it cannot be measured with the most simple AP dashboard and has not been confirmed by at least a dozen Audio ABX tests it does not exist and is a mythical "unknown factor" that is brushed off as meaningless.

The issue is, people need to believe into something. And here they like to believe that chinese copy/pasta "engineers" produce world class gear that bests the most expensive seriously engineered (if overpriced) gear based on a very limited set of measurements.

Wherever belief enters into the equation rational discussion is impossible, even if the belief masquerades as "science" (but in reality is utter bunkum and at best cargo cult science.

So naturally, should anyone dare to throw spanners into the works, the bunch believers comes down on them.

USUALLY it is me in that situation with Pavel joining in beating on me with the rest, so it kind of gives me a perverse pleasure to see him at the pranger...

Thor

 

[Thorsten Loesch]

You are only confusing the issue with these misleading tests.

Yes, let's just stop making measurements of gear that show problems, when we can instead focus on only the good parts.

Let's be like the Curate and if we get a bad egg, let's focus on the parts that are excellent. Unless of course it is an expensive audiophile egg...

Thor

 

[NTK]

What Pavel measures is very real, probably > 90% of all speakers are affected and we need the combination of amplifier, speaker AND source to cause the system to show problems. It may even be recording specific.

If it afflicts >90% of all amplifiers/speaker combos, but seemingly nobody notices, is that the dictionary definition of a non-problem?

 

[Thorsten Loesch]

If it afflicts >90% of all amplifiers/speaker combos, but seemingly nobody notices, is that the dictionary definition of a non-problem?

FOR THIS SPECIFIC AMPLIFIER, around 90% of speakers will be inductive enough to allow the output filter peaking to be substantial.

ONLY FOR THIS AMPLIFER, because it is faulty by design. But for most speakers.

MOST Amplifiers do not have this problem at all, be by design or by luck.

And yes, we need some source of excitation.

Next, how does the problem manifests itself?

Fun part, as a variability in sound quality. CD recordings may sound great, but only with DAC's using brickwall filters. Playing MQA for example may sound aggressive, cymbals may sound harsh.

Without a "good design" Amplifier to directly compare, it will be hard to nail down exactly what is the cause, especially if we do not know about the peaking and the interactions.

It is just plain utterly awful design, this output filter and indicative of systemic failures at the company that makes it. This thing, just like the virus should have never been allowed to escape from it's lab and enter the wild.

Thor

 

[NTK]

It is just plain utterly awful design, this output filter and indicative of systemic failures at the company that makes it. This thing, just like the ch!n353 virus should have never been allowed to escape from it's lab and enter the wild.

This is just a copy of the TI reference design Blame TI.

 

[sarumbear]

Well, I have asked here repeatedly for the science behind all of this SINAD (aka THD&N).

It’s the result of a noise and distortion test. What science you are looking for?

 

[IPunchCholla]

Uncontrolled amplifier oscillation, even if not readily apparent when listening, is always sub optimal. It happens more than one would think with any class of amplifier including tube amps. Stability should always be part of a good amp design. While these tests are approaching being edge cases they are none the less interesting and I have learned a lot from them. It seems like some people get all "tribal" on certain amp topologies or brands and don't want anything discussed that shows any "weakness" even if it is just an academic exercise showing issues that could be improved with better engineering. The SINAD chase, even though it has no audible effects past a certain point, is cheered on as show casing good engineering, so why should less than optimal stability be overlooked?

I hope I am not being tribal. It is just that there seems to be a subtext that somehow these amps are not fit for purpose and are toys. The implication is that if I like them, then I must be a child. When in reality, it looks like we are talking about putting a lot of energy into an amp at 40kHz, far more than would ever be seen with music, unless you were listening in the instant ear damage range to music being played at a 96kHz sampling rate, that contains a lot of information at 40 kHz on an amp that is aimed at low end consumer market. All of that is important context to have, if we are not going to oversimplify things.

Should all amps be designed to handle any possible situation they may see? Sure. And they should be free too. But that just isn’t realistic. Engineering overkill is easy. But it is also very, very expensive. It is an engineering feet to make something ”good enough” at a the target cost.

 

[IAtaman]

Credit is where credit's due Mr. Loesch. These last couple of posts you wrote were one of the most masterfully executed pieces of demagogy I read since Orwell's Animal Farm. Bravo. When I found myself asking "do I wanna break the law or even die because I am using Chinese products" I knew I was reading a masterpiece.

Story of poor Thorsten and Pavel being attacked and tortured by the cruel, blind and ignorant SINAD cult all the while trying to bring light to masses and save them from the lethal Chinese audio gear. So sad and yet so heroic - so Biblical even.

I think you should consider setting aside a chapter in your auto-biography for the events surrounding ASR .

Cheap stuff gets too high of a praise and expensive stuff too harsh of a treatment sometimes, yeah maybe, but I think you are stretching the case a bit too far. 90% cases this amp will perform poorly statement is empirically incorrect. Check out Amazon, there are literally a thousand reviews of this amp and 90% of the reviews are positive, i.e. 4 or 5 stars. Or is it because all those reviews are purchased by the Chinese mafia or written by ignorant cult members as well?

And I am not sure what this ch!n353 stuff you keep repeating is supposed to be - whatever it is, it is not tasteful.

 

[Thorsten Loesch]

This is just a copy of the TI reference design Blame TI.

My reply was harmonised it seems. Aparently posts referencing the TI EVM design are not welcome.

Put simply, the TI EVM does not show this behaviour. What is more, the EVM contains additional non-populated positions for parts that can be added, if changing (for example) the filter inductors lead to problems. Their purpose is explained in the EVM Documentation.

Bottom line, copies of the reference designing do not have peaking filters. So don't blame TI. Blame the designer.

Thor

 

[Thorsten Loesch]

Credit is where credit's due Mr. Loesch. These last couple of posts you wrote were one of the most masterfully executed pieces of demagogy I read since Orwell's Animal Farm. Bravo. When I found myself asking "do I wanna break the law or even die because I am using Chinese products" I knew I was reading a masterpiece.

Really. So you mean all far eastern budget priced are tested for electrical safety and EMC according to all relevant international regulations and pass the requirements?

I have seen a LOT that I am certain would not pass.

And there have been quite a few well publicised cases of unsafe electrical/electronic products killing their unweary users.

And depending on the country you are, you will be breaking the law if you operate a device that causes interference to Radio system.

Simple facts, simply stated.

Cheap stuff gets too high of a praise and expensive stuff too harsh of a treatment sometimes, yeah maybe, but I think you are stretching the case a bit too far.

Well, have a look. Carefully. It is certainly an impression one might gain.

90% cases this amp will perform poorly statement is empirically incorrect.

It is not a statement I made.

I stated that peaking of the output filter will happen with any speaker that has an inductive impedance at high frequencies, which applies to ~ 90% of speakers out there.

Check out Amazon, there are literally a thousand reviews of this amp and 90% of the reviews are positive, i.e. 4 or 5 stars. Or is it because all those reviews are purchased by the Chinese mafia or written by ignorant cult members as well?

You said that, not me. But that is a common MO for companies in that part of the world.

Thor

 

[levimax]

Should all amps be designed to handle any possible situation they may see? Sure. And they should be free too. But that just isn’t realistic. Engineering overkill is easy. But it is also very, very expensive. It is an engineering feet to make something ”good enough” at a the target cost.

Recently a Buckeye amp using Purfi modules had a slight increase in distortion as it approached peak power and was not recommended despite SINAD over 100 because it did not match the reference design. It was then "fixed" by replacing the binding posts of all things and SINAD increased by 3 points and it was recommended and applauded which was well deserved. In this case an amp potentially becomes unstable because it did not properly copy the reference design and it is supposed to get a pass. It does not require heroic or expensive engineering to copy the reference design.

I think people here are thrown off because as bad as this oscillation looks it may not be all that audible in many cases. I built a DIY amp and used it for a couple of years and was very happy with it. I then got an Oscilloscope and noticed over a certain output it would being to oscillate (at HF I could not hear) I then fixed it (it was easy, changing a cap value in the feedback loop) and I can't say it was a big improvement for my use case. None the less not fixing it and keeping a defective amp the way it was because it was not noticeable to me would not make sense and I am surprised how many people seem to think potential instability is OK when it could be easily fixed.

 

[thecheapseats]

fascinating dialog exchange...