Tech Talk Friday Audio Amplifier Testing
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- Опубліковано 4 жов 2024
- This video 'Tech Talk Friday Audio Amplifier Testing Rant ', I will talk about the meaningful types of audio testing that we can do. #A07
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Eddie, great video. This subject is near and dear to my heart. It is as complex as RF is. You can try to simplify it down, but the interface between between human and electronic is loaded with disappointment. When you remove a major piece of the system, you will fail to understand and answer the questions. You touched on some of the key points that audiophiles incorrectly support. The electrical to acoustical interface is always left out of the equation because of the complex nature. There has been the desire to establish a set of standards to take the complexity of hearing out of the equation. Great subject matter discussion, please continue, but don't fall into dispare over the negative feedback that will follow.
Thank you! I appreciate you and your insight!
This idea of showing us the audio testing equipment and hopefully how to use good procedures when testing, along with the discussion... Really has my interest and let me explain... Over the years I've come across some quality amplifiers... But they need repair, my goal is to repair them but just because I repair them and I hear audio and music coming out like it should doesn't necessarily mean this piece of audio equipment has been repaired correctly or thoroughly back to original specifications by the designer of the piece of audio equipment... And getting an understanding about testing audio products really has me interested in hearing what you can tell us about these procedures, I think a lot of average technicians just don't have the knowledge to do these kinds of tests not to mention equipment to do it. So again it could be extremely informative. I kind of have the idea of repairing the equipment myself as best as I can and then find somebody who has some knowledge and equipment to test the equipment. At least that's my current thinking and I think this series that you are planning is going to be really helpful. P.S. your words about audio quality and testing and all that stuff audio people talk about... Was fantastic, I like your approach I like your thinking process and it also opens up the discussion. I have been a low-budget audiophile person since I was 16 years old and have some classic equipment meeting SAE, from back in the day and I also have Denon 5.1 receiver again just before all the digital stuff so that goes far back in time. So the continued thoughts and let's call it the analog world of delivering sound and the digital world of delivering sound.... And maybe what we can possibly measure to see what we see in the two signals kind of a thing. Either technology isn't something to necessarily argue about, because the bottom line is what a person hears and what a person likes, ... And manufacturers would love to create a product that a majority of people like the sound of their product... That's their goal making money 🙂🙂🙂😎 P.S.S. and you brought up the subject of temperature... And the equipment I have I enjoy,... And they truly sound great, but after living with them for so many years 🙂 you learn characteristics about these pieces of audio equipment and one of them is temperature. Again they sound great but... There are things you will learn once you really have gotten to know a piece of equipment...... I truly anticipate to learn quite a bit.
Thanks so much for this feedback! I can see this could really be helpful for many people. Not just characterizing amplifiers - but how to test them to see if hey work properly and to spec.
Without tossing out a list of aspersions (and believe me, I could do that very easily) UA-cam is *absolutely the worst place* to learn about electronics.
There's this little devil on the shoulder of most of these content creators called the "Dunning Kreuger Effect" (go ahead look it up) that leads people into believing they know a whole lot more than they actually do... and when that is fueled by the chance to make some money it gets even more exaggerated.
One of the most important things for a technician to appreciate is just how much he does not know. After 40 years in the industry I know a fair bit, but the list of stuff I don't fully understand is still growing daily and it is that bit of humility that keeps me from blowing up some very expensive equipment.
If you want to do amplifier repair ... and the world certainly does need more technicians... do yourself and your clients the favour of getting into an accredited course, with hands on learning, and earning that diploma.
Just stopped to comment at the bandwidth section. Bandwidth is incredibly important for particular designs that I've seen from '70s and I'm not sure about modern stuff but that's not where I spend my time. Beating high frequencies against lower frequencies was a technique I believe sansui used with high frequency ring emitter transistors. It was called TIM distortion. As a subjective listener obviously I can't hear anything pass around 15K at this point but I have noticed that certain amplifiers that go up to 50 or more kilohertz have a different sound than say a tube amplifier with an output transformer that rolls off at 20K. Just a personal experience and a note on higher bandwidth application. Keep it up man.
Thanks for this great feedback! I do like the idea of the TIM measurements, and I am aware that there are different frequency combinations for this test. I do want to run these tests to see if some types of amps show something more than others. I have tube amplifiers to test, and Class A transistor amps. It will be interesting to see how these perform with TIM compared to a Class D.
Excellent video , Eddie . I look forward to the amplifier testing.
Thanks so much
Great video Eddie.
I totally agree with your comments (as an ex lab tech).
I love audio am I an audiophile ?He’ll no, sometimes I use eq 😂
I’ve not got their “golden ears” 😂
The loud speakers have the highest distortion of any composing any HiFi system.
In the order of several %.
I’ve measured a few valve (tube) amps and even .8-1% thd still sound ok to my ears.
JBL and a few others used to quote distortion in their specs many years ago, now everyone hides that in a dark corner lol.
The marketing departments in the 80’s came up with a lot of the “wires you can hear type ” bs, and claiming the skin effect of silver etc (which has no audible effect as it happens around 6GHz and up).
Imagine the likes of EV, JBL etc missing a vital point that “special wires” would give better sound (not talking about too thin for rating as that’s a different issue).
I also agree a continuous power test run over several hours rather than a burp of power is the way to go, thermal limits have to be considered.
I’d love to know which noise and distortion meter you like best.
We had a nice AWA back in the 80’s (checked - calibrated at DSTO labs each year along with the cro’s, spectrum analyzer etc) as part of our certification (especially for mil spec).
Thanks for this fantastic - real world - feedback! Sounds like you have had some great experience!
HI Eddie, excellent Video, like the Rant. Thank you. 👍😃
Thanks so much! I appreciate you!
Best tech talk rant lol all facts said well done and i agree with you 100%.. The audio market is wierd lol
Thanks so much! I appreciate you!
Mulțumim!💯👍
Thank you for your generosity! I really do appreciate you!
What an awesome video. There are so many valid points that need more discussion each one could be a video on its own. Recreating and amplifying analog signals to satisfy biological entities is super complex. What helps most is liquid fortification, lol. 👍
Thanks so much! I agree - liquid fortification helps;)
Since my channel is all about testing predominantly "vintage" audio gear, I have tested a lot of amps/receivers/integrated amps and preamps over the past few years. I use the QuantaAsylum QA402/3 that you mentioned and have. The square wave testing was usually called slew rate, and there was typically some capacitance in parallel with the 8ohm load. There are IHF specs/procedures for all of the audio tests- IHF has been replaced by CEA, but a lot of the spec's carried over. I recently started measuring the risetime of amplifiers (no cap in parallel with the load), as well as the phase change from input to output as well as between the two outputs, and that is just at 3 freq points- I mainly wanted to put my o'scope to use 😃 As for distortion, there is a great article in the May 1973 issue of Stereo Review, by none other than Bob Carver, titled "an informal test on the audibility of distortion"- an interesting read! There was a pre-conditioning period where amplifiers were run at 2/3 the rated power I believe, prior to taking measurements. I do not follow that most of the time, but am sure that tube gear has been on long enough before testing. What I try to do with my testing is see how well some old piece of gear- say a Dynaco ST120- measures compared to it's 40yr old specs. The QA40x does have a dynamic power test, but I don't understand it enough to use it. I will push the gear to it's rated output power into 4/8ohms and depending where the THD is at, may go higher. There is a new spec (CEA-2006/490a) that allows for output power to be measured to the point where THD reaches 1%- your opinion about this may change if you read the Carver article. My loads can take a lot of power, but once you start putting >200w into them they can get hot, so I won't keep the amps amp max output power for more than I need to- most of the things I test are friend's gear, so I'd rather not overstress them (so far, so good). But as you go up in power it is interesting to see when protection circuits come into play- for heat or clipping/indicators. Powering the Aiyma/Fosi amps with one of your larger p/s bricks or nice linear Power supplies is a good idea- the higher voltage and current supplies should allow for more power to be delivered, of course, but I am very interested to see if there is any difference in the noise level, particularly at 60, 120 and 180Hz. Good rant!
Thanks for your great feedback!! I sub'd and will be happy to hear more feedback on my testing to come. I'd love t hear your input.
@@KissAnalog Thanks for subscribing and if for some reason you are in Tucson on July 13th, we will be having a little get together and doing an A/B test- I will supply the beer. BTW, I has a weekly "audio club" zoom call last nite and one of the guys provided a link to a $150 ac power cord he purchased that made the sound better. I could only bite my tongue for so long and asked him what sounded better. "It just did" was the reply. We got into measurements not telling the whole story and I would have liked to have your "we can't hear what dogs can but can measure it" analogy at the time....
Hey Scott ... good to see you chiming in here.
LOL... every group has "that guy", don't they?
@@Douglas_Blake_579 I get around just a little bit on some channels. There was more than the one guy- I am in the minority in this call.
@@vintageaudioreview
Yeah, I've been there too.
Just recently I got something of an eye opener as a client and his wife were listening to my latest "sound bar killer" system... and it was the wife who started on about wires and cables. Kind of took me by surprise. Apparently in their family she's the audiophile and he's the one who just listens.
Cheers, my friend!
Hi, interesting subject. I think as audio electronics have got closer to truly "transparent" rendition of the audio, it's caused a kind of meltdown of our evaluation as music listeners. Archimago has written well about this. For music creators, shaping beautiful distortion is an essential part of their artistic palette, hence love for vintage recording gear, tube guitar amps, etc. For listeners, we should aspire to the absolute most accurate rendition of the source media; that way we get to hear exactly what the creator intended. The complications are (1) some of us listeners are hooked on the distortions we have grown used to hearing, hence the appeal of vinyl, and (2) some music creators are second-guessing the deficiencies of playback equipment and shaping mixes to sound good on car radios, ear buds, etc. Personally I'm persuaded that tests like THD, IMD, slew-rate, etc, are taking us in the direction of literal high-fidelity, without subjective waffle, and I'm happy to be led in that direction.
Thanks for your fantastic feedback! I'd have to agree with you. I am on the hunt for a test that might show an actual difference between 2 amps with similar specs. It might turn out to be a simple matter of meeting the spec;)
Eddie, great video as all your videos and I.E. rants always are. 👍
Thank you! I appreciate you!
Look at the Ampeg Bass guitar amps.
They have some wicked harmonics and they are some of the best out there.
They aren't a straight up "music" amp but they are required to hit most of the same, if not more frequencies.
Great point - guitar amps are on another level - not linear at all;)
One power amp I had rolled off the output at 20kHz to prevent speaker destruction in case of oscillation above the useful audible band.
Most actually do that ... but at about 30khz.
Yes, I think this is a matter that the crossover could take care of;)
@@KissAnalog
Trust me ... the absolute last thing you want is an amplifier spitting out 100 watts of power at 30 or 40 khz .... Not only does that fry speakers, it kills amplifiers too.
Wow you just attacked me on my last video where I showed an amp resonating at 60kHz… I generally like your comments but then you don’t stay consistent with your comments/attacks.
This idea sounds interesting.I used to hear ''slew rate'' as an important factor in amplification.Maybe you could explain this among the many other audiophile tests.Also a lot about power supplies(as you say with the dynamic aspect).Also the whole business of the different classes and why the lack of switching distortion in a Class A amplifier gives it a superior sound?
Lots to get your teeth into here I should imagine.
Thanks for the great feedback!! I'll go over slew rate;)
Slew rate is overrated, it just shows max frequency at which amp can push its rated power into load.
Yes - class A has the best behaved output stage.
I used to be all about objective measurements when deciding on which components to buy. Every component was top of its category spec wise and convinced myself that it sounded great. Then I read a debate about subjective vs objective evaluation and took a step into what you obviously consider the dark side of audio. Using my ears to match components sonicly to compliment each other to achieve a final synergy. I put my spec based system aside till I was done matching components subjectively. Then after a bit of burn in came the day of truth on several pairs of speakers. The subjective system based on what I heard blew the measurement based purchases out of the water. Richness detail and soundstage far surpassed my spec based system at less cost. I'm pretty sure those aspects of audio can't be tested and only can be evaluated by the human ear and brain. Everyone I've had over to compare agreed. I also did a gated response at 1w at 1 m between the two systems, source, pre, and amplification of each with the same speaker and the results in frequency response were identical. So why the big difference in sound? Your the engineer, you tell me. I no longer give a rats ass about objective measurements anymore. They actually kept me trapped in mediocre sound because I convinced myself my system sounded good because of the numbers. Just my experience.
Thanks for the great feedback! This is not a comparison of subjective vs objective. This is a comparison to what is written in specs. This is my point, we need to measure honestly and in a way that someone can compare the 'real' numbers. I'm sure that we can measure the difference between the two systems - no question! Our instrumentation is far superior and more resolving to the human ear - not question. This is not even up for debate. Use a microphone position in the same place relative to your speaker placement and where you listen - and you will see a difference. And then you will know what you like. Wouldn't it be great to select equipment based on 'real' measurements?
Subjective tests are still BS - the only true way is the blind test. Also keep in mind preference vs best - for example good bass response is hard to achieve and to most sounds flat and weak - problem is that most ppl have no idea how it should sound and instruments are way better at discerning this than any ears.
There is the issue of counter electromotive force generated by the speaker magnet and voice coil assembly that could influence why one amp sounds different from another. Some amp designs might be more prone to the interactions with the speaker than others, even though their normally measured specs with a pure resistive load are pretty much equal.
Thank you for bringing this up! Yes - this could be important! Some amps - depending on the topology, could be more affected by this.
Thanks!
Wow!! Thank you for your continued generosity!!!
One thing to keep in mind for the frequency respone aspect is that if an Amplifier rolls off at any frequency, the phase response starts changing further into the pass band. Moving the -3DB points out reduces phase shift in our hearing range.
Thanks for pointing this out. Some think that the phase can not be heard, but I think that this might be true at low frequencies, but at higher frequencies where this occurs - it might not be.
Also Eddie I did mention on another post about even harmonics being consonant with "western music". By western music I meant western civilization, music based on the well-tempered scale where the frequency of adjacent octaves is simply a doubling of the frequency. I think you may have thought I meant country and western music :) If a second harmonic is imposed on a piano playing the note "A", the distortion is also the note "A" except an octave higher. An odd harmonic like the 3rd, would be producing a note that doesn't even exist in the musical scale, thus out of tune, not consonant.
Thank you for clarifying this for me:) You have a great insight and I find this very interesting:) I think noise / harmonics might be less of a problem then other parameters of the amplifier - maybe. Thank you!!
Gday Eddie, Testing at 1w so amp to amp comparisons make sense, then test at rated power, -3db and maybe -10db. I wonder if slew rate testing would reveal interesting results, the slower the amp the more distortion the better the sound?
Thanks - I think this is a great place to start! A test series like this might show a difference;)
I find a lot of testers don't test the speaker response with a given amplifier. A given amplifier will have different response with different speakers systems. The best amplifier, home built or commercial will either have a good sound or sound like crap depending on what is driving it to what the output sees and if the system has resonant inputs and outputs. Here is a test I haven't seen anyone do: have the same frequency from a single source feed into both inputs at the same time and see if the 2 outputs are the same waveform when overlaid or are they out of phase. Another words if at a given response would the cone on speakers left side and right side be extended at the same time or will one speaker be extended and the other be retracted.
I like this - thank you! I will add this to my tests. This could be something important!!
Something to consider....
Accurate measurements only happen when you eliminate all but the device under test.
If you add a second variable you will be unable to determine which is causing what to happen. Then it becomes very easy (per your example) to blame the amplifier for something the speaker is doing... and vice versa.
The goal is to measure the amplifier in isolation.
Yes I agree with you here. I think the question is what is the test that brings the challenge to the equipment that makes sense and is most revealing.
Also about the audiophiles and measurements. Its not about that we cannot measure stuff but can still hear it. I think maybe we're not measuring everything to explain the differences. Some simple S/N or THD or stuff like that may not be nearly enough to explain sound quality. I know some amps are more sensitive to reactive or inductive loads..etc Maybe some amps get out of sorts depending on the speaker they are driving as an example. Who knows, but definitely we can measure everthing, if we know what we're after.
Thank you!! You hit the nail on the head! I agree completely!
@@KissAnalog Thank you :) I've actually been trying to figure this out myself. About a year back I picked up a budget single ended tube amp and subjectively for me and also a few friends that have listened to my system, this amp is better sounding in many ways. I've not done any testing on it but at least measuring the FR of the loudspeaker between it and solid state amps shows minimal deviation at the speaker side.
So maybe the even harmonics or gradual clipping or something else accounts for why we all feel it sounds more detailed and more real somehow. No idea but I need to know LOL :)
Thanks for your feedback!
Audiophiles can measure? Oh that's funneh, those 3 words don't even belong in same sentence.
If you're good at measuring and suspect that phase angle changes the sound - why won't you slap together a dummy load that requires lead/lag and remeasure. The only true test is a blind one, but who would bother with those - those take effort to set up and analyze and do so correctly.
Another important consideration when thinking about amplifier performance is undoubtedly the power supply. They need to be sufficient enough to deliver immediate power in responce to what one might call transient sound particularly when listening to classical music, such as Beethoven's 5th , otherwise it sounds flat. So a nice big transformer is usually the case. Personally I find valve amplifiers in class A to be most pleasant which I understand to be attributed to harmonic distortion which is pleasant to the ear. Also when listening to music i dont care about the inefficiency of class A so long as it sounds good to me.
What does a big transformer have to do with "immediate power response"? The instantaneous power demand will be satisfied by the decoupling capacitors throughout the power distribution system.
Thanks for your feedback! I do have an MC30 amp that I can test. I'll have to see if I can characterize this amp;)
@didgeridooblue I think the transformer might help if low impedance and large magnetic field, but the bulk capacitors after help with the immediate response;)
@@didgeridoobluealright let's say it this way then, anectdotally a bigger transformer helps. This is one of those things Eddie could actually test, looking at lower and higher VA against peak demand, threshold levels and diminishing returns, etc.
Some amps need to be left powered for extended periods for best results is also a consideration.
Thanks John!!
I don’t understand why class d sound reinforcement powered speakers have such ridiculously inflated power output ratings. For example a QSC 12.2 powered speaker (a well regarded speaker) is rated at “2000 class d watts”, while its current draw is rated at 2A at 120v or 1A at 240v. These current draw rating don’t even come close to the 2000 watt supposed output. I’m sure it’s some sort of marketing hype, but still - 2000 watts with a 2A fuse? Did they suspend Ohm’s law?
Thanks for bringing this up! I don't think the ratings have to be blown up so much - just teach people what is really needed vs this inflated fiction.
It's just my opinion - my references - the maximum power at 8 ohm and at 4 ohm - the maximum heat dissipated at maximum power, at what values does distortion start - and for me an important thing is the starting frequency - some amplifiers start from at 50 Hz others at 7 Hz - unfortunately no manufacturer says this - although it is quite important. and the rest of the measurements, if any - are welcome
Thanks for this great feedback! I appreciate you!
We're not testing in the time domain and I think that's a mistake. Also we should test at 100mW or max 1W power (if we use constant test signals like multi tone).
1)Bass control: we need to connect a big speaker and play a bass kick or a timpani "bong" and then autocorrelate input and output signals (amplitude normalized). Amps with bad damping will have output signal less equal to the input signal compared to amps with high damping
2) Dynamics: create one music stream filtered to be 20....500Hz (e.g. drum content) and one filtered 1...3kHz (e.g. sax, percuss. with a bit of room echo / spatial information). Measure/cross correlate the output of each stream and the combination of both streams. See if the dynamic stream influences the fidelity of the high freq. stream
3) Detail reproduction: Play mid to high complexity music (e.g. good choir recording) and measure fidelity (autocorrelation between input and output signal
All tests above should be done with both resistive and complex loads as well as real speakers (where the swinging cone of the bass driver acts as a electrical generator)
There are some python modules dealing with audio waveforms. If we find one that also can filter and correlate signals it might show how different amps with equally low noise/THD and linear frequ. resp. can measure in the time domain.
There are multiple (good) reasons we don't generally test using actual music and that's because music is a really messy signal, the denser it is the harder it is to measure. By using isolated frequencies to test the various attributes of an amplifier we can draw very specific conclusions about it's behaviour. Unfortunately with messy signals, the best we can conclude is how messy the signal is.
In the time domain (testing transfer function) an amplifier is very immediate. It takes the instantaneous input signal and multiplies it by it's gain and produces an output signal. This is actually all it knows how to do, so there is no reasonable expectation it will behave differently with a constantly changing (messy) signal than it would with a steady one.
@318ishonk @Douglas_Blake_579 this is exactly the dilema - how do we achieve this in test - to predict "messy" with 'clean' signals?
@@KissAnalog
You are assuming that an amplifier behaves differently with a music signal than it will with properly applied test signals... and, except for some seriously brain dead designs that assumption is false.
Audio amplifiers are essentially voltage sources. The input signal is a voltage that changes over time. The output signal is that voltage multiplied by the amplifier's gain. That's it. That's all these things know how to do... _Input Voltage times Gain_ .
The only design goal in just about every amplifier in existence has been to do this one simple task _accurately_ With a gain of 10, 1 volt in = 10 volts out, every time.
In the case of a power amplifier, the output stage is required to deliver enough current to drive a speaker load.
Current delivery is an artifact of Ohm's law which tells us that _"Current is the _*_result_*_ of applying voltage across a load"_ That is, if you put 10 volts across a 10 ohm load 1 amp of current will flow... every time. This is a fixed and well understood relationship.
Speakers are transducers. The technical description is that they are _"a linear servo motor with a spring return to center"_ Thus they are designed to position a pistonic cone on either side of a restive center position in reaction to voltages applied to their motor assemblies... and, again, the only credible design goal is to do this _accurately_ .
Take a scope grab of any music signal, then expand it out to see the component waveform. What you will find is a single voltage with small fuzzy bits of varying sizes superimposed on larger transitions. There are no separate signals for guitar or bass or tweeters or woofers.... The signal is a single voltage that changes over time. In fact it is nothing more than a map of how to move the speaker cones.
When testing this stuff there are only 3 actual points of analysis... _Accuracy, Capacity and Speed_ .
What we call Distortion is actually a measurement of how accurately an amplifier can apply gain to it's input signal.
What we call Power is really just a measurement of voltage and current capacity of the amplifier's output.
What we call Frequency Response is just a measure of the speed with which it can follow the input voltage.
There's no magic here. These devices do not know, or care, what they are amplifying. They are simply applying gain to a voltage at their inputs.
Thus, there is no valid premise for the belief that an amplifier will behave any differently on music, speech or sound effects than it does on the nice clean tones used on our test benches.
@Douglas_Blake_579 I'm sorry - but you describe an amplifier as an ideal part - that is the whole point here - is to find where it does break from your ideal description. There is a reason so many amplifier Topologies and even types of components are used. If an amplifier was so Ideal to meet your simple description - then we wouldn't be here talking about how to test them.
@@KissAnalog
Where did I say that wasn't the goal?
A technician's job is simply finding out where things go wrong.
Okay ... To begin, the most important thing to understand ... _"Tools do not the mechanic make"_
You can have every last piece of test gear in the world and if you don't understand how the device under test actually works you can't hope to measure it accurately.
So, here's how I measure an amplifier...
For power :
Use a signal generator, feed in a sine wave at 1khz. Hook up to a dummy load. Monitor the output right at the speaker connector with an oscilloscope and adjust the input signal until you see the first hint of clipping (flat topping of the sine wave), now back the signal down by 1%. Using a volt meter take note of the RMS voltage across the speaker connectors.
Power = Voltage squared divided by load impedance ... P = (E x E) / R ...
20v rms on 8 ohms = (20 x 20) / 8 = 400 / 8 == 50 watts.
If you suspect power supply issues, repeat the test with 100hz signals.
For class D or Bridged class AB, you can use one side of the bridge for your scope, unless the amp is defective, the other side of the bridge will be identical but inverted.
For THD :
With the same setup as above, using the FFT function in your oscilloscope, measure the 1khz fundamental and the third harmonic at 3khz ... THD = (H / F) x 100
So if you get 20 volts at 1khz and 0.1 volt at 3 khz (0.1 / 20) x 100 = 0.005 x 100 == 0.5%
At 100% output (i.e. the onset of clipping), there is a knee point where harmonic distortion starts shooting up wildly. You want to measure just below that point.
For noise:
While still on FFT mode in your scope, take a look at the average noise level below your 1khz test tone. You calculate it the same as THD. But remember to ground your scope probe after and subtract the noise level from your own test equipment.
For frequency response :
Still with the same setup as above, set your scope to single trigger on a 1 second time base (i.e. to capture 1 second of data). Send in a one second sweep from 5hz to 50khz. Now with the captured waveform, look for the average as well as any dips and bumps... measuring the difference gives you your frequency response as a voltage ratio, which is easy to calculate as a percentage. But the most useful information is not little bumps in the middle... it's at the ends, when does the low frequency roll-off begin and where does it taper off on the high end? For most amplifiers 3hz to 30khz with no large deviations is "flat" enough.
For gain:
Just take the ratio between the input signal level and the output level at 1% below clipping.
Once you get this sorted so that you can "just do it", measuring an amplifier should not take more than a couple of minutes.
It's not about fancy test rigs (although I have used them)... Most people will be amazed at the details you can get with just very basic test gear and a decent understanding of how these amplifiers actually work.
Many of the "measurement" guys will also be amazed at the things they miss by allowing automation to do the work for them... For example: things like stability or oscillations will not be caught by automated tests, but they will be plenty obvious on a scope if you know what you're looking for.
Thanks for the fantastic feedback!! I too test much the same way. Even with the new gear that I have - I like to investigate and look at things before I start the auto testing - and even then - I like to watch the signal on the scope to see what it looks like. Thanks for this procedure!
@@KissAnalog
You're welcome.
I've used both AP and Panasonic in the past and I am often surprised at the stuff they miss... simply because they lack the human ability to go "hey, what was that?"
Most recently all the measurements guys working with the V3Mono amplifiers missed a stability issue when used with a shared power supply. It was initially caught by a subjective reviewer who noticed they were running really hot and making noise ... a sure sign of oscillation. One guy even fried one of the little amps trying to get reliable readings, instead of first checking with a scope to be sure everything was working right.
Like I said ... Tools do not the mechanic make!
This is fantastic feedback! I like the automated tests, but I use a scope to watch what is going on. I don't like the tests that people say - hey this is a dynamic test... I'm like, OK, what is this 'Dynamic' test?? ;)
🙂Takk!
Thanks so much for your generosity!!
I think the best test would be to feed a fast rise-time square-wave into the amp, and view the output on a spectrum analyzer. We know, from the Fourier series, the frequencies & amplitudes of the harmonics that should be there. Anything else...TIMD...THD...noise...etc. ?
Thank you! I think this is a test that I want to add to my list. Even though music does not have sharp edges - it might tell us something about dynamic behavior:)
The best indication with square waves is the Rise Time and Decay Time.
Rise Time (the slope of the vertical edges) can be back calculated to tell you the maximum frequency response.
Decay Time (the slope of the top) can be used to determine the minimum frequency response.
Of course any harmonic that is out of grade is an indication of other problems.
It should be noted, however, that for audio purposes, these tests are mostly useless above 100hz.
@Douglas_Blake_579 I have been asking for the rise and fall time of these square waves for some time now - but I don't get any answers. So, I agree this is the most important part of the square wave test - but it is not the only important aspect. There's the frequency and the duty cycle that is also important. I'll explain this in videos to come.
@@KissAnalog
It's very simple, really .... the period for 1/2 cycle is T = 1 / (F x 2) ....
Always test with 50% duty cycle...
For 20khz the rise time is ... t = 1 / (20,000 x 2) = 1 / 40,000 == 0.000025 seconds or 25 microseconds.
Thus: An amplifier that can't reach full output in less than 25us is going to struggle at 20khz.
For the sustain/decay at the top of the square wave... At 20hz that is 50ms so any amplifier that can't sustain full output for 50ms will struggle at 20hz.
These rise and sustain times should be easy to measure with any digital scope.
Yes you are correct that this is easy to measure - I am just trying to understand if this IS what we should be doing.
Hey Eddie, I did a test with my two young sons who have excellent hearing. I played some rock music that has a lot of symbol crashes, lots of highs, through a preempt that has parametric tone controls and I can adjust a high Q filter at around 14khz, then I can enable it and disable it while the music's playing.
They could not hear any difference with a complete cut and frequencies over 14K. So, I suspect, given that most musical notes only go up to 8K, 20,000 hertz is ridiculous and just a marketing scam.
Actually the highest standard musical note, c8, is at 4,186hz ... above that it's all harmonics... by the time you get beyond about 12k, the rest of the bandwidth is practically silent.
On my personal site (search for "DBPages music") I even have a musical clip I chopped off at 4200hz... and some say it sounds better!
Thanks for this great feedback! Yes, I know 20kHz is just a band that has stuck around. A nice round number;) However, that is a great fact to note, why take the amp BW so far out that might create other issues with the crossover and speaker drivers... Something to pay attention to.
I think that usual set of tests performed by Amir from ASR is quite reasonable. Surely you could do something similar with your AP and QA. Btw, it seems that you have got there some brand new OWON oscilloscope. I hope you are going to review it.
Thanks for this feedback! I do like Amir and think that's a great place to start, but I don't know if those tests show the difference in sound that some claim to hear. The OWON is new on the bench;) Thanks for noticing. I did do a first look video: ua-cam.com/video/_bYCnCIAVKI/v-deo.html
@@KissAnalog I agree. I remember that Single Ended Triode amps used to sound noticeably different that push-pull transistors or push-pull pentodes. But distortion of SET is rather big compared to decent P-P and easy to measure, so no mystery here.
I have noticed that their are some combinations of Speaker and Amplifier that seem like almost magic. I have wondered if that has to do with the design of the global loop feedback circuit.
There's no such thing as an "open loop feedback circuit" ... Open loop, by definition means "no feedback".
Great point! So, if we knew the response of an amp - then we could say - not only does this amp work - but this one should too based on these tests... That's what I'd like to be able to achieve;)
@@Douglas_Blake_579 Thanks for pointing this out. My mind was thinking Global Loop Feedback but my typing wrote Open Loop Feedback (getting old), my mistake!!!
@@davidlucavish7948
Ordinarily I would let it slide but in a technical discussion, it kind of matters.
(You should see some of the goofs I've pulled over the years)
That person's channel doing the power test that goes to 1% and burst..etc, they do mostly car audio so the !% is more inline with car amps belting out power for SPL competitions. The device used is made by a car audio company. It gives a good representation of power to a reasonable amount of distortion. There are studies done that imply that THD of 1% may be the limit where it starts to become audible by the average person.
Thank you! Yes - and I love that channel. But other amps like this A07 Max was tested as well, and the 1% is beyond what the amp should put out - so it is essentially breaking down at that point. I think that should be pointed out.
@@KissAnalog Yes I will agree that the testing on audiophile type amps to 1% may be excessive but one thing it could show is if the manufacturer is lying. I mean if they claim say 100wpc at 0.1% and the test to 1% only gets like 70W, then for sure at 0.1% its likely even lower. So in that way its still kinda useful :)
Yes - I agree that the marketing for amps is not truthful or correct. But I do not think the burst testing at any one of these distortion levels (1% 10% and dymanic) are correct in testing an amps specs. They are all dynamic or transient. The heatsink is the largest and the most expensive component in the design - but isn't even exercised in these tests. They are fun to watch and actually help manufactures lie about their power ratings - oh, and isn't this test device made by an amplifier company;)
@@KissAnalog Oh thats true. I guess even if an amp can deliver undistorted output at a certain level, we dont know if it can do it for any length of time. Though I guess most music is very dynamic so maybe a sustained output is less important than delivering undistorted transients. Who knows, all good things to think about for us :)
So true - so maybe a test below max continues that can do a max level?
Is there a engineering explanation why ac phase matters on 2 plug amplifier. Meaning switching the two prong plug around in the power socket affects amplifier sonics?
Thanks for asking! No - there is absolutely no effect to how the amplifier performs - with polarity of the 2 prong plug. It simply supplies power to the transformer - which is isolated - and then the bulk capacitors make DC. This power processing does not care.
Thanks for answering, figured so much. Find physical difference to be in circuit. In that one way hot wire goes first through the fuse, or through the switch. Unfortunately always notice a difference. Could be time to clean the switch.
As a nother question, can i replace the power switch with any power switch. Have seen some real bizarre things posted by people on audiokarma, like if transformer or power switch die amp is dead, tha5 surely is not the case?
To my understanding can replace it with any modern switch or transformer as pong as voltage/amps match the originals?
12:00 So can CATS (the most marvelous creatures ever to slink upon the face of the Earth!)
Yes you are right - sorry I forgot about them;)
Where is the test gear that can measure the image created by good gear? This is the end all be all for me and my QA403 isn't able to tell me much about these types of detail.
Thanks for this!! Yes - that is what we need to do somehow. I think the QA403 might be able to get close - if we use it right...;)
If you're referring to the "stereo image", you should know this has nothing to do with amplification. An audio amplifier is simply applying gain to an instantaneous voltage ... Gain of 10; 1 volt in 10 volts out ... that is all it knows how to do.
The stereo image in your room is a result of A) the source recording, B) Room acoustics and C) Speaker placement.
Yes, the image you hear is actually burned into the source recording and there is nothing in the home electronics that can change or create it.
I don’t intend on testing stereo source recordings and playback. I just want to verify that two channels can amplify what’s at the input regardless of what’s at the input of the other channel and that they don’t affect each other.
a little bit disappointed I never got a response to my last comment on power cables, I thought you might be able to clear it up!
Thanks for asking - I try to respond when I see your comments. Can you tell me what video that comment was on?
@@KissAnalog didn't show up I'll just repeat it here! its about shielding on power cables that old chestnut 😉 the guy said you have to shield it at the wall what we've disproved, but he says if you shield it at both ends it becomes an aerial I don't believe that's the case, how can shielding a cable both ends turn it into an aerial is that correct?
Let me solve the power cable quandry for you...
Ask what manufacturer would be outright stupid enough to sabotage their own equipment with bad cables...
Save your money. 99% of the time the cables in the box are more than good enough.
@@Douglas_Blake_579 yeah I can understand and agree with you but that's not my question? I'm talking about if you put a shield on it I both ends connected to ground does it become an antenna?
@@hoobsgroove
No, not if both ends are grounded. BUT, if you have a ground fault on your outlet it will not only become an antenna it will become a shock hazard.
Any power supply worth salt will incorporate both RF and DC filtering in it's input stages then every step up to the final delivery of DC for your amplifier will be filtered and compensated. RF on the power cord simply does not matter.
If two differently-designed amplifiers are set to output the same power, have the same THD+N, have an identical frequency response, and you are using the same speakers, but yet sound very different, what exactly is leading to that sound difference? Is it measurable and if so, how?
I've come across many amps (for both speakers and headphones) that have this; one of them just sounds more "full".
Small gain differences between two amps, less than a dB, can result in different sound with a given signal.
Thanks for setting the stage. This is exactly what I want to see if we can find out. For one, power ratings are not done in a way that actually describes the power. It is generally done at one setting. So, a rating at 4 ohms at 1kHz might be completely different at 8 ohms and not linear.
@@jim9930
While I can agree that "idiot proofing" has it's influence on some amplifiers, I have to disagree that output compensation, stability and protection circuitry is useless.
If you've ever seen a high quality amplifier (Crown DC300 in my case) sitting there hammering out 30khz square waves at about 50 watts, slowly melting itself into the table top... you will understand why protection and stabilizing circuits are absolutely essential ... even around smart people.
Most recently I've been playing with TPA3255 based Class D amplifiers, both on pro-audio boards and in the current batch of mini-amps. Now these chips are something exceptional... Along with some of the cleanest sound available, they incorporate current limiting, clipping and temperature warnings and autonomous protection circuits... none of which are being implemented by the Chinese designers. Now given the choice between automatic power limiting and watching the chip self-destruct in the middle of a live concert, which do you think we should choose?
Really throwing a lot of nonsense shade here. BigD Tests primarily to show what people are getting vs what was advertised, and nearly everything he tests is intended for a subwoofer. CTA-2006 defines power rating at 1% thd+n, so i'd say for a consumer watchdog test 1% thd seems right to me, if that really bothers you then just drop the volume 1% and you're probably back to 0.1% thd anyway. 10% thd is a general rule of where its just heating the voice coil rather than increasing spl, its not a test for people that care about sound quality. The 1% thd, some people may be more sensitive than others, some speakers/boxes make it more apparent than others but likely no one would be able to identify a perfect signal vs 1% thd on a 12" sub at 500watts playing nothing over 70-80hz. A lot of interchanging thd and noise here, those are different things, thd is distortion of the input signal, in any half decent modern amp thats clipping. Noise is extra that was not present in the signal. Its all static load testing so a much harder load on the amp than it would ever see on a same rated speaker, not sure how this could be done better as every speaker has a different impedance rise curve across its range and this changes again depending on the the enclosure the speaker is installed in and even the room it is operated in. The 1% thd into a static load is the test, 10% I doubt many care other than it shows a little character of the amp if its right on about the same power or a good bit higher, maybe the spl comp people that dont care too much how it sounds want to know about output that far into clipping. Dynamic seems to be like a kick drum, if you actually watched more than one of his videos you can see the power cables jumping with the load current and have a pretty good idea of whats going on, or just google the manual for the D’Amore Engineering AD-1, its all in there, you can even download the test tracks, no need for a uninformed off base rant on what someone else is doing. It gives a decent idea of what the amp will do on music rather than say a constant 40hz in the other tests and if this number is much higher than the 1% tests you have a pretty good idea the amp is running out of power supply but has enough caps internally to hold it up for some musical peeks. At any rate, its all done to help people when the industry on a whole likes to sell things that say 1000watts rms on the tin and reality is closer to 300 if you're lucky. We're all pretty sick of buying shop vacs and air compressors that say 4-6hp on the sticker but plug into a standard 15amp 120v outlet also. 100% efficiency the best you can do there is 2.4hp, so anything past about 2.25 is a total lie but still going with blow the breaker, burn the cord, locked rotor current ratings on everything. Who knows maybe those 300w amps actually make 1000w for a ms on a dead short. You should really understand what someone is actually doing before going on a public rant about it. BTW, meaningful testing unless we're talking about electric guitar amps or other musical instruments should not include personal preference/bias, this is exactly what even bring up the topic of harmonics/warmth is, an ideal amplifier has none. Also doubt there is too many people out there that care much about the chip amp junk, most of them are too cheap to even come with a power supply and then market them on being small while the repurposed laptop power brick is bigger and still doesn't properly supply them, 200wat amp on a 135watt power brick, yeah sure.
Thanks for your feedback. I can see you were triggered by my reference. Sorry about that. I didn't bring up his name or his channel, but I did bring up the testing explaining that I don't think that is a good test to tell the difference in the sound quality from one amp to another - and you essentially supported my claims.
BTW, I do a lot of research - as any good engineer would;) But I am also asking for everyone to share their knowledge and/or ideas, comments, remarks. I have watched his channel many times and I like it - but it is misleading. I'm also familiar with the AD-1 and almost bought one - but have my reservations...
Since you brought it up. You say his tests are to show us if the advertised claims hold up. But his tests do not show that - not at all. And you say he tests amps for subwoofers - and yes he does, but he also tests the chip amps that he think so poorly of. Example, he tested the Aiyima A07 Max that is on my bench. The advertised claims are for 0.007% THD (not THD+N). So pushing it to 1% to get the numbers is misleading.
Burst testing is only valuable if there is a duty cycle and then another burst. Unless you only care about the cannon shot on AC/DC sounding good. If it is a kick drum - how many times do you see the drummer kicking it then taking a long break?
What is "static" testing to you? What does that mean? Continuous? If an amp is rated well under 1% distortion - then you push it to 1% - it is on its way to clipping. BTW, clipping is not the only reason you get harmonics - a distorted waveform in any way will cause harmonics. The noise is also a factor of many things - and power level can be a huge factor. And 10% distortion is when clipping becomes visually obvious - and doesn't have to heat up voice coils. It's just bad sound at that point.
Real power testing is not this. Not for people that don't care about sound or do care about the quality of sound. As I said in this video - temperature effects come in a big way - especially with these chip amps.
I did not throw shade on anyone - I simply used those tests as an example of tests that do not show the quality of sound - which you seemed to agree with me. So, not sure why you were so triggered... I hope you will have more input on my testing that I come up with and what tests might be of value.
_"Also doubt there is too many people out there that care much about the chip amp junk"_
You may want to rethink that one... The little mini-amps are outselling traditional cement block sized gear by a factor of 3 or 4 times, right now.
In particular gear based on the Texas Instruments TPA32xx series and on the Infineon MA series are capable of surprisingly good quality reproduction. The TPA3255 is particularly popular right now and it can reach an honest to goodness 220 clean watts of output on 4 ohms with a 48 volt 10 amp supply.
Remember the good old days when we all went gaga over 50w/ch from amplifiers weighing 50 pounds or more... well now we can fit that into our jacket pockets. It's called progress.
@@KissAnalog ("I did not throw shade on anyone" "but it is misleading") You should probably have a watch of your own video. "I'm also familiar with the AD-1" If this was true then you wouldnt have been acting like its some mystery or anything other than what it is, it took me all of 15 seconds to find all the info on it, why play dumb about it? That other channel does not test for sound quality. You say i'm triggered, you're the one that made a whole video and uploaded it to youtube to rant about someone else doing testing that is not what you personally want, disparaging them for being misleading on top of it. No one was ever led to believe a test of output power into a fixed ohm load is a sound quality test. Again its 1% thd+n because that is the closest thing there is to a standard (CTA-2006) for output power in the mobile audio industry, it is not a statement of sound quality. I've never got the idea Derek thinks poorly of chip amps, and what is pushing it to 1% to get the numbers? If he tested it then it was tested to 1% like everything else, if its truely a 0.007% thd amp then it should have easily made its claimed output by then, I don't see the issue here. Again its not a sound quality test, it is a "are they lyin to ya" test, sure only holding a 0.007%thd amp to a 1% standard still leaves a lot of room for lies from the manufacture but its still better than blind trust of this weeks amazon or alibaba flavor. If anything he made a amp you claim he thinks poorly of look far better than it would have if the test was stopped when it reached 0.007% thd, thats assuming that chip ever has a output that clean. Thats the capability he has to test with, if you think you can do better then by all means get at it but already trying to disparage someone who is doing what they can with what is available to them within their niche of interest while you have yet to do anything yourself on the subject is pretty low class IMHO.
Its obvious you want a sound quality test, not just an output power test, so why talk down about someone only testing for output power? Good luck testing for sound quality, if you are the engineer you say you are then you already know that is basically impossible to do in any meaningful way. Speakers are reactive loads and are not all the same, how many thousands of different speakers are you prepared to test an amp against to get a true measure of sound quality? A fixed 4 or 8 ohm load is not going to cut it. Personally i'd find simple signal to noise testing and something like does the gain stay flat across a sweep from 15hz-22khz(lots of older class D and many chip amps dont do well here), maybe range sweeps following 0.1% or 1% thd, or similar could be interesting but when a 4 ohm speaker presents as a variable inductance with an aparent load varying from 4.5-20ohms in use just as an example, I dont see how any of it tells us anything solid about an amp. Thermals are worth mention but its a pretty unrealistic use case to say an amp is not whatever power because it couldnt run a constant 1000hz signal at its rated output for an hour straight. Maybe something like find some actual music other than subwoofer test tracks that does stress the heat management and loop that for an hour or just figure out where the 100% duty cycle is and what the duty cycle at max output is(likely going to vary with frequency), people could make their own conslusion about what that means vs what they listen to.
Clipping to 10% thd at a drivers rated power into say a 500w sub is a great way to kill that voice coil. That is an eletrical signal that the speaker simply can not mechanically follow and that shoots the aparent load way up, the result of that is as you should know a lot more heat. Unfortuantly speakers generally dont get rated for actual measured power and in most cases attempting to force that much in will have them way past xMax, so any ideas of 500w is 500w is right out the window when that 500w rating is some magical nonsense of an amp setup to provide 500w into a fixed 4ohm load is what they figure the max rating of their 4ohm 500w rms sub is. In reality the apparent load will likely be at least 5 or 6ohms so more like ~300w rms actual, a clipping amp can easily turn that aparant load into something that is going to pull far more than the voice coil can cope with for long.
We (people who are not deaf) can all hear 10% thd, I can see clipping on my cheap scope way before I can hear it, not even squinting, no clue what you're talking about "10% distortion is when clipping becomes visually obvious". Fully understand not all distortion is clipping but also aware most modern stuff, even the cheap stuff is likely staying under 1-2%thd if its not clipping.
@@Douglas_Blake_579 Small vs a traditional receiver sure, we've hardly had any big transformer supplied tanks around in the last 20 years through and those chip amp units arnt really so small once you stack them on top of a power supply. There are amps just as small that are are mosfet class D or even traditional class a or a/b. TPA stuff has an output across the range that is anything but flat, they are not that cheap and having to deal with a sound processor to tune around where they let you down is just more expense. If you have one just run a frequency sweep though it. They are cheap for mfg's who buy them by the 10's of thousands and its no issue for them to tune their product to work with it, it is an issue for any of us trying to run them as a dumb amp.
50w/ch even back in the 70's i'd still consider a toy, my marantz 2385 or the 2500/2600 or pioneer sx1980, technics sa-1000 and fancy turntables that would stay on track without carving away vinyl while you rattle the windows are more the things people were oogeling, and quad... 50w/ch in home audio wasn't anything special in the last 50ish years, even mid 90's i had $100 chip amp STK4192 mini systems that were doing 50w/ch.
Edit: It is kind of crazy how far prices have come down on high power stuff, I'll give you that.
@@celiturbo
Gees man ... chill out... take a nice deep breath, maybe a sip of brandy, relax.
I've been working with and testing these chips for nearly 8 years now. I've put dozens boards and mini-amps through my test bench, even done mods and recommended changes to the manufacturers. And the one thing I can tell you is that you are dead wrong about most of it.
Don't let biases or the urge to gatekeep on behalf of the old school cloud your judgement. Time and the world will march on just the same.
Speak with writeing lurn bord no only speak
I'm sorry - I don't understand what you are saying...
@@KissAnalog writing on bord lurnig all subscribe weaver
You what, mate? Use google translate or something.
@@KissAnalog आप सिर्फ बोलिए नहीं बोलने के साथ बोर्ड पर सर्किट बनाकर समझाये कृपया