Does Op-amp Rolling Work?

[solderdude]

The discrete is larger in size and seems to have picked up slightly more hum.
Could have been caused by the position or size.
Probably the lid was off.

Now... look at the levels and then take the equal loudness contours in consideration.
This is inaudible anyway. Even when the 1kHz tone would be reproduced at 90dB SPL you simply can't possibly hear 60Hz tone -50dB down.

The 3rd harmonic in both op-amps is way below audible levels and is -95dB.
For that to be audible (listening to a pure tone, it would be masked with music) you would have to listen to the 1kHz tone at 110dB SPL or thereabout.
You would immediately cover your ears as that is VERY unpleasant. The 3kHz would be 'whisper quiet compared to the extreme loud tone.
On top of that... look at plots for masking and you will find you can't even hear it.
And when one would be listening at lower levels the 3kHz would be below audible levels and as the 1kHz signal would be lower and not reach the level where the distortion measurement was done at the distortion would (very likely) be below the noise level anyway.

Nah inaudible and measurable at differences that are in the realm of measurement error.
Ears aren't analyzers and analyzers don't work the same as ears.

This is exactly where hearing sucks big-time opposite test equipment which is magnitudes more discriminating.

Edit... ha... cross-posting with MAB

 

[antcollinet]

I disagree, without a proper baseline test i.e. stock, we can't rule out the discrete changed the Sinad. You can see by the 60Hz noise that the discrete changes something.

even if a baseline test were needed - we don't have one. We only have the channel comparison testing - which is good enough. One channel is stock - the other has the discrete op amp in it. Everything else is the same excepting component tolerances.

Of course, Amir, could have first run a base line of both channels before swapping the op amp in one. He didn't, presumably because he knows the tiny changes in Sinad between channels (when you are already down at -90dB a few dB here and there are totally irrelevant.

If you want to get an idea of what you are expecting to hear, think about the "shoutometer" Trying to hear the difference between Sinad 87dB and Sinad 90dB is like trying to hear the difference between someone shouting from 14 miles away versus 20 miles away (the distortion) while simultaneously having someone shout 3 ft away from you (the music)

Yes, you are correct - the person shouting from 14 miles away is just as inaudible as the person shouting from 20 miles away.

 

[DavidR]

I recently bought and tested three Douk A5s. Definitely will NOT be doing any Op Amp rolling! I'm very pleased with them.

 

[Whatsthephuss]

I disagree with the premise that THD and frequency response describe everything that we can hear. What about impulse response or phase/timing differences? Slew rate?

 

[voodooless]

I disagree with the premise that THD and frequency response describe everything that we can hear. What about impulse response or phase/timing differences?

Opamps are minimum phase systems. If you have the frequency response, you also have phase and impulse response.

 

[voodooless]

Slew rate?

For an audio opamp very much irrelevant.

 

[antcollinet]

I disagree with the premise that THD and frequency response describe everything that we can hear. What about impulse response or phase/timing differences? Slew rate?

For an audio opamp very much irrelevant.

Apart from anything else, a slew rate limited device will create distortion, hence measured.

 

[Doodski]

I disagree with the premise that THD and frequency response describe everything that we can hear. What about impulse response or phase/timing differences? Slew rate?

To consider phase response and leading and lagging phase response one needs to consider the entire system from beginning to end. The consideration of this phase response is all about the proportions of phase leading and lagging response. The source(s) and amplification phase changes are miniscule proportionally when compared to the phase leading and lagging response in all speakers which is massive as in humongous. So... To consider phase changes of leading and lagging phase with OP amps because it is proportionally insignificant when compared to the huge phase changes occurring in speaker is not meaningful in a system wide analysis.

 

[oleg87]

I disagree with the premise that THD and frequency response describe everything that we can hear. What about impulse response or phase/timing differences? Slew rate?

the impulse response from an op amp in an audio circuit should ideally be very unexciting - otherwise, you’ve got problems. insufficient slew rate will cause distortion at high frequencies, though maybe a 1khz test won’t shake that out, but a CCIF intermodulation test is probably sufficient.

 

[Whatsthephuss]

Opamps are minimum phase systems. If you have the frequency response, you also have phase and impulse response.

Do different op amps not have different bandwidth? That would imply that their phase and impulse response could be different as well.

Different DA filters affect the impulse response even if the change to the frequency response is minuscule…

 

[voodooless]

Do different op amps not have different bandwidth? That would imply that their phase and impulse response could be different as well.

Sure.. but that will influence the frequency response as well, they are all different aspects of the same thing.

 

[voodooless]

Different DA filters affect the impulse response even if the change to the frequency response is minuscule…

It’s not… and most of these filters are not minimum phase either.

 

[MaxwellsEq]

Do different op amps not have different bandwidth

Different op-amps have different Gain-Bandwidth Products. They are designed for different uses, such as Radio Frequencies, video amplification etc. Modern audio op-amps all have sufficient Gain Bandwidth to cope with the audio range.

BUT, what happens in a real circuit is set by the circuitry around the op-amp, not the op-amp itself. If you read enough on ASR you will find many tests proving this.

 

[Whatsthephuss]

To consider phase response and leading and lagging phase response one needs to consider the entire system from beginning to end. The consideration of this phase response is all about the proportions of phase leading and lagging response. The source(s) and amplification phase changes are miniscule proportionally when compared to the phase leading and lagging response in all speakers which is massive as in humongous. So... To consider phase changes of leading and lagging phase with OP amps because it is proportionally insignificant when compared to the huge phase changes occurring in speaker is not meaningful in a system wide analysis.

I both agree and disagree with this. For sure the most audible components are the leading edge of THD and impulse response, but to say that the other components make no difference is what I struggle to agree with. if the view of ASR is that >80dbSINAD is inaudible so a waste of money, then wouldn’t that mean that Topping and TI are just releasing snake oil designing DACs and OP amps with better specs? What’s the point of technological advancement if these things are already good enough?

 

[voodooless]

What’s the point of technological advancement if these things are already good enough?

Because you buy it..

 

[MaxwellsEq]

Different DA filters affect the impulse response even if the change to the frequency response is minuscule…

This is nothing to do with op-amps but to do with Impulses into filters. Irrelevant.

 

[Doodski]

I both agree and disagree with this. For sure the most audible components are the leading edge of THD and impulse response, but to say that the other components make no difference is what I struggle to agree with. if the view of ASR is that >80dbSINAD is inaudible so a waste of money, then wouldn’t that mean that Topping and TI are just releasing snake oil designing DACs and OP amps with better specs? What’s the point of technological advancement if these things are already good enough?

Why the, "What-about-isms?" You asked the question. I answered it clearly with no bias, no spin and just the electron flow physics facts. The physics are what they are for the reasons of the limitations of the various technology of the circuits and it's components. The mind struggle is not related to the physics. You are off into the politics of the market and it's spin. The speakers are always the overall majority of all the stuff/sound issues that you mentioned before in your previous commentary and all the other stuff once at a decent level of quality is just spin, micro-managing and the politics of the market and it's products.

 

[Whatsthephuss]

This is nothing to do with op-amps but to do with Impulses into filters. Irrelevant.

All analog components have limited bandwidth, so in theory that would put a bandpass “filter” on the impulse sent through op amps, would it not? My point using DA filters was an exaggeration but not exactly irrelevant.

 

[Whatsthephuss]

Why the, "What-about-isms?" You asked the question. I answered it clearly with no bias, no spin and just the electron flow physics facts. The physics are what they are for the reasons of the limitations of the various technology of the circuits and its components. The mind struggle is not related to the physics. You are off into the politics of the market and its spin. The speakers are always the overall majority of all the stuff/sound issues that you mentioned before in your previous commentary and all the other stuff once at a decent level of quality is just spin, micro-managing and the politics of the market and it's products.

The reason for what about isms is because I’m struggling to comprehend how engineering advances can reach the point where they are merely market fads. That’s what this whole thread is supposed to expose, but if it holds for one sector of the market (op amps) why shouldn’t it apply to other sectors? ASR doesn’t only exist to provide scientific data, it provides product recommendations as well which is not purely about the physics…

 

[Doodski]

The reason for what about isms is because I’m struggling to comprehend how engineering advances can reach the point where they are merely market fads. That’s what this whole thread is supposed to expose, but if it holds for one sector of the market (op amps) why shouldn’t it apply to other sectors? ASR doesn’t only exist to provide scientific data, it provides product recommendations as well which is not purely about the physics…

OK. Good points and I appreciate you stating them for me. I see your concern and I agree that things are too often occurring as you stated. The entire industry is permeated with market fads and the manufacturers propping them up. I worked in the home audio industry for 24 years. First 9 years in sales and I was very successful because I was unfailingly refusing to not succeed, I had some simply fantastic influential people around me, I had Yamaha home audio gear to sell is the main reason and I had a great old German business man old school service oriented and no BS corporation owner/employer who was the real deal person. Then I returned to study, got educated and was the electronic technician for another 15 years. The entire industry is full of wankers of various sorts. In sales there is issues and in service there is issues. Some manufacturers are all about the integrity and cause few if any issues and other manufacturers are issues reoccurring. The same with the sales and management and then service is full of wanker employers wanting it all from the employees but not supporting that with proper wages. The entire industry is permeated with scammers scamming the employees and some as we know scam the customers too. I had 2 terrible employers in sales and then I was able to walk into the main head office of a major player and get an on the spot interview and then 1.5 hours later I was hired by the old German fellow who owned the chain of major player AV stores while he inspected concrete forms at a new store that was under construction. Very hands on boss man. He told me if I worked hard then he would make sure that I got my pay on time and I would make lots of money and he would always support me doing that. He did just what he said over the years of being my boss and any corporations(They did) that tried to mess with me got his wrath. He was a great influence and a great business man. The customers are good and bad too. They are people and people come in all the good and bad variations possible. The entire mass of people involved is permeated with fictional beliefs, half truths and using the convenient facts while ignoring the inconvenient facts that do not prop up the various peoples' agendas. The manufacturers are comprised of as I mentioned various agendas too. Sony is known to be very protective of it's developments and many people around Earth have never figured out what all the various agendas where for. Then there is Panasonic, Technics, Quasar/Matsushita who in my 24 years of sales and service not once caused a single issue and every time all the time was an upstanding good corporate citizen and did stuff that was simply kind, generous, the right stuff and proved it everyday by actions and no spin. The issues that you speak of are caused from all angles of involvement of the various people. Then add in the media/magazines/web sites/influencers and it all gets even messier. There are the very good people in the industry and they generally make it all operate. They are known to generally be responsible for about 85% of the profits and responsible for the majority of the product movement and without them all of it would not work. The engineering advances sometimes make sense and then other advances simply are blocked or made to fail for reasons nobody has figured out sometimes.(See Sony). I can make sense of some of it sometimes but I don't use a crystal ball to attempt to figure out what I don't know. There are so many people with so many agendas.