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Yes – opamps swapping may make a measurable difference in a preamp

restorer-john

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Not out of spec's, but out of common use cases. Interesting to engineers, but not to the end user.

Pavel is looking for measurable differences between OPAMPs when used in a common circuit. He has successfully found there are differences. The resolution of the COSMOS ADC means we can see anomalies way below normal floors of resolution.

The increase in THD as frequency goes up, and load is low, is significant, though not unexpected. I applaud Pavel's demonstration of that. Sure, maybe outside the specified range of the device, but illuminating, nonetheless.
 

Mnyb

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I think members here can ( or should ) understand that a measurable difference is just that in this context and does not imply anything else at all.

Just keep on educating what different op amps do in circuit if your in the mood I’m quite enjoyed my free op amp class :)
 

BDWoody

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The thing about real science is that it isn't deaf to what human beings report. ABX and hearing threshold tests aren't telling the whole story because they don't reflect the often very consistent subjective listening results from people who listen rather that just read papers and measure.

So those consistent reports from uncontrolled subjective listening come from people who haven't read those other consistent reports?

"My cable risers really bring out the detail from the plankton."

"Really?! Same for me!"

Here's an idea...how about someone provide evidence.
 

Geert

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The thing about real science is that it isn't deaf to what human beings report. ABX and hearing threshold tests aren't telling the whole story because they don't reflect the often very consistent subjective listening results from people who listen rather that just read papers and measure.

And part of the problem too is that so many of those on the high-horse of "science" aren't scientists but merely engineers.

You're clearly not a scientist, and not even a worthless engineer. Nevertheless you think you are in a good position to get on your high horse?
 

Geert

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I applaud Pavel's demonstration of that.

Absolutely. But intentional or not, there's another suggestive or at least confusing message between the lines.

I think members here can ( or should ) understand that a measurable difference is just that in this context

'Should' yes, 'are' no I'm afraid. Hence the importance of clear communication.

I'll leave it at that. It was just a remark I had, not worth and not interested in a fight.
 

Geert

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"Merely" engineers, hah! I'm going to start using that with my engineer friends.

You probably better loose that type of friends.
 
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Gorgonzola

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So those consistent reports from uncontrolled subjective listening come from people who haven't read those other consistent reports?

"My cable risers really bring out the detail from the plankton."

"Really?! Same for me!"

Here's an idea...how about someone provide evidence.
Strawman: I don't use cable risers. :)
 

Gorgonzola

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I cannot see definition of measurement conditions - the load impedance. As such, the plots at the Sparkos site have mainly marketing importance. The measurement conditions must be carefully described, otherwise the plots are pointless.
No dispute, but consider that Sparkos tested other op amps, (as shown at the link I provided), under the same conditions with pretty different results for some those op amps, so there is presumably consistency at least. Yes, maybe they tweaked their own results or outright lied but there is no reason to assume that.
 
OP
pma

pma

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Measurement of OPA1622 - perfect! Cleaner than D10s-E1DA loop. And balanced input impedance is 2kohm, instead of 500ohm without OPA1622.

D10s-OPA1622-E1DACosmos_1k.png
 
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lashto

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Blind tested with 2 amps and the only difference being the usage of different opamps or a switch of opamps and subjective evaluation knowing what opamp is in there ?
Measurements of both situations (or rather all 4 mentioned) with at least the quality of measurements PMA did.
Measurements of the entire amp incl. dummy load ?

Posting a plot made by a vendor in not similar conditions isn't real proof.
Could it be that you did not even look at the provided link and measurements?!
Those were not plots by the vendor (Sparkos) but, as mentioned on that page, "independently generated by ATM Audio of Spain". Measured in the same circuit/amp and "entire amp".
6 different opams were measured there and the THD diffs look pretty big to me. Some of those diffs might be audible (in that particluar amp/circuit). There are no claims of audibility in that article, they just provide the plots. Looks quite legit to me.
 
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lashto

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@Gorgonzola
Many thx for those measurements, I was looking for something like that.


Some years ago I did a similar experiment with ~the same opamps in a DAC output stage:
  • NE 5534 (original ones): they did sound very good to me and I could have lived with those "happily ever after". But after hearing the others, I thought the NEs were kind of veiled/boring.
  • LME49720: very clear/clean sound ... yes the proverbial "veil was lifted" thing, shoot me! Maybe the cleanest/clearest of them all. Cannot find any explanation for that in the measurement plots.
  • SS3602: also very clean/clear, maybe a tad less than LME but somehow with more "weight". A bit more bass energy and the whole soundstage was somehow 'heavier', like it contained more sound (or 'air' if you wish). A sort of relaxed sound, the kind you'd want with jazz/chillout music. No idea how to correlate any of that with the THD measurements. (also not 100% sure if it was the same 3602 model, AFAIR it looked same as the ones on the Spakos website.)
  • Burson V5. Did sound pretty close to the Sparkos. A tad less clean/clear, even more "weight" to the soundstage and pretty much the opposite of the 'relaxed' Sparkos sound: the kind of sound you'd want with hard-rock music. That actually seems to correlate quite well with the Sparkos & Burson THD graphs. (at least from what I know about the audible effects of THD.)
My choice/idea was to use the Sparkos for the late night music sessions and the Bursons for party-time. But since swapping was not so easy (and I am lazy) the Bursons just stayed in. I guess my Burson choice correlates quite well with my preference for tube amps (the Bursons THD spectrum looks quite tube-like).

And no, I did not do any DBT/ABX tests, the only realistic way to do that would be to have 2 devices. I did not. And I am lazy :)
No idea if I can reliably identify NE/Burson/Sparkos in a blind test, the diffs were not exactly night & day. But I am pretty sure that I can identify the LMEs: their 'clarity' also had a sort of metallic/glassy sheen which gave me a slight pressure/discomfort/pain in the ears (and a sort of light headache) after 1h or so. Yes, I tested that multiple times on different days, same strange effect. I expected to see some H5/H7/H9 in the LME plot but there is only one feeble H2 ... seems to contradict all I know about the sound of THD. But then, my test and the THD plots were done in two very different circuits.

And to finish with another beloved cliche: my ẃife/kids/neighbors/dogs/cats did not hear or confirm any of those differences and I have a strong suspicion that they couldn't have cared less.

All that is of course just subjective "stuff" and one guy's anecdote. Take it as you wish.
It's all free though, so you are not allowed to complain (too much) :p
 
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solderdude

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6 different opams were measured there and the THD diffs look pretty big to me. Some of those diffs might be audible

What makes you think -80dB H2 could be potentially audible (for the worst one Muses01) ?
H5 at -105 isn't exactly near any audibilty levels either.
At lower levels distortion is likely to improve even more.

And yes, all opamps do measure differently but as long as it stays below audibility levels it is moot.
If anything... if I had to choose between input opamps for that circuit it would just not be the Burson or the Muses... just to be sure.
Will that make an audible difference (assuming FR is flat) ? Not very likely.
 

lashto

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What makes you think -80dB H2 could be potentially audible (for the worst one Muses01) ?
H5 at -105 isn't exactly near any audibilty levels either.
At lower levels distortion is likely to improve even more.

And yes, all opamps do measure differently but as long as it stays below audibility levels it is moot.
If anything... if I had to choose between input opamps for that circuit it would just not be the Burson or the Muses... just to be sure.
Will that make an audible difference (assuming FR is flat) ? Not very likely.
As you can see from my other post, I actually chose the Bursons, i.e. the "worst" distortion.
I had no measurements at the time and no other 'incentives': the whole opamp package was actually a gift and I kept them all (should still be in a drawer/box somewhere).

That's where I relate to (some of) @Gorgonzola's posts in this thread. There are actually quite a few of those "consistent subjective listening results" that he mentioned. And many are dismissed on ASR (and generally in the so called objective audio community) for no good reason.

E.g. millions of people still buy and enjoy tube devices, turntables etc... Looks to me that those "distortion-generators" do get a lot of ear-love and some extra research-effort in that area would be useful and well justified. Instead of that, I see lots of "haha distortion-generator" or "haha sucker likes distortion" comments. Often with lots of likes. Very helpful & very scientific those ones ...
 

lashto

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Lack of experimental controls is a very good reason for dismissal.
it surely is. Especially if you are lazy :)
Last time I checked, lack of experimental evidence/controls only means that there is no (strong) evidence. Does not mean that the 'phenomenon' does not exist.

Why would anyone talk about "suckers who like distortion", when the truth is that we just don't have (enough) evidence?! And generally don't know that much about the subject. I haven't seen/heard anything but "maybes" on the subject: maybe it's just imagination .. maybe it's some sort of collective psychosis ... maybe its something inbuilt in our brains and/or auditory-organs ...
 

SIY

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it surely is. Especially if you are lazy :)
Last time I checked, lack of experimental evidence/controls only means that there is no (strong) evidence. Does not mean that the 'phenomenon' does not exist.
Read up on Russell's Teapot.
 

Gorgonzola

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Read up on Russell's Teapot.
Yes, to be sure. But poster @lashto is making no pretense of proof, only offering his impressions. Impressions are anecdotal at best and per se proof of nothing ...

Russell'sTeapot.jpg


But when serious listeners have consistently similar impressions over long periods of time, there are a couple of possibilities:
  1. The folks are simply reinforcing each other's specious beliefs, (kind of like religion as Russell was alluding to), or
  2. What it is they are believing is worth investigating objectively and without bias. (Scientists' confirmation bias is no more a friend of the truth any more than anyone else's.)
 

solderdude

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As you can see from my other post, I actually chose the Bursons, i.e. the "worst" distortion.
I had no measurements at the time and no other 'incentives': the whole opamp package was actually a gift and I kept them all (should still be in a drawer/box somewhere).

Even the worst measuring one still is well below audibilty thresholds so cannot be the reason for 'hearing' better sound quality. Even if signal fidelity is slightly worse and some claim (without scientific evidence which is not impossible to obtain if one really wanted to) that small but not too big distortion of a certain type would be 'pleasant'.
This comes no where near most (but not all) tube amps so the comparison with tube 'goodness' is not in play in this particular case.
Furthermore the plots only show 1kHz HD at a certain level (+14dB) and most likely this will not be reached and thus distortion in practice, under normal usage) may well be even substantially lower.
 
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