Dan D'Agostino interview on measurements

[Matias]

I posted this on another thread but it is too interesting and deserves its own discussion.

Dan is a legendary amp designer formerly from Krell and nowadays with his own company.

Went from designing deeply based on measurements on the later Krell days to less reducing distortion and more subjective designs at Dan D'Agostino Ma$ter Audio $ystem$.

 

[NTomokawa]

What is "musical sounding"? Why is feedback a "band-aid"?

If measurements do not correspond to "how it sounds", then what does? What is this "thing" that cannot be measured, yet makes amplifiers sound "musical"? If this "thing" cannot be measured, how, then, could the designer properly control and implement it in their amp design?

 

[macauley86]

Magic. The head of the transistor department is Hermione.

 

[NTomokawa]

Magic. The head of the transistor department is Hermione.

Sure it's not Snapes? Austere and rigid, just like how transistors sound...

 

[Doodski]

What is "musical sounding"? Why is feedback a "band-aid"?

If measurements do not correspond to "how it sounds", then what does? What is this "thing" that cannot be measured, yet makes amplifiers sound "musical"? If this "thing" cannot be measured, how, then, could the designer properly control and implement it in their amp design?

Musical sounding usually involves speakers that present a more difficult load to the amplifier. To make a amplifier musical it needs enough RMS power output for the desired sound pressure levels and then it needs to have as linear of power output as is possible. Linearity being RMS power doubling with each halving of the impedance. We see that Ohm's law is being followed to some degree for better or worse in different amps. Hence in another thread we where discussing Krell and Mark Levinson amps that can arc weld and lay down some bead because they have good linearity and can output power continuously into a very low impedance or a direct short without protection circuitry engaging or the amplifier overheating and going into thermal runaway or outright just letting loose some smoke. So class A/AB amps' power supplies get heavy, big and beasty to ensure they have good linearity by having a large reserve of current available. Basically in a very simplified schematic the power supply would have a internal resistance and the amplifier is a variable resister creating a voltage drop across the entire amp circuitry or the amp circuitry being a very low resistance and then dropping the voltage across the load. So in class A/AB linearity is musicality. Testing for linearity will let the smoke out of many amps at 4 Ohms never mind at 2 Ohms and so linearity can be a destructive test and is not recommended in many situations.

 

[Doodski]

Sure it's not Snapes? Austere and rigid, just like how transistors sound...

... and FETs following a transconductance curve sound better? I think it is imagination there.

 

[raistlin65]

Magic. The head of the transistor department is Hermione.

Yep. And sadly, he can probably can make more money if his marketing copyrwriter describes the sound, instead of designing amps for accuracy. He's already got the name to create the expectation bias.

 

[Matias]

Nelson Pass is another legendary amplifier designer who is not concerned at all with lowering distortions, but rather "tuning" them to taste.

 

[pma]

Nelson Pass is another legendary amplifier designer who is not concerned at all with lowering distortions, but rather "tuning" them to taste.

I do not believe in "tuning" distortions "to taste" at all. It does not work. Take some complex classical music like Mahler or similar and all the magic of those "tuned distortions" is gone in one unitary hazed sound. Low distortion is the key which has to be accompanied by wide bandwidth, enough slew rate and good immunity against interferences of all kind - air coupled, signal coupled, PSU coupled. Then we get "good sound" even with complex music.

 

[despoiler]

What is "musical sounding"? Why is feedback a "band-aid"?

If measurements do not correspond to "how it sounds", then what does? What is this "thing" that cannot be measured, yet makes amplifiers sound "musical"? If this "thing" cannot be measured, how, then, could the designer properly control and implement it in their amp design?

He didn't say feedback was a bandaid. He said using feedback as a bandaid isn't good which implies if you use feedback as such your amplifier circuit wasn't properly designed in the first place. He straight up says its use sparingly is OK.

 

[Wes]

"tuning" distortions "to taste" works if all humans share a common taste, and if eliminating the distortion is impossible or impractical

BTW, what studies or data is the even vs. odd distortion claim based on? anybody know?

or is it such ancient audiophile lore that is buried in some geological stratum that is yet to be probed?

 

[Matias]

Well, there is this article on harmonics from Bob Katz, famous mastering engineer, written on Innerfidelity website.

https://www.innerfidelity.com/content/katzs-corner-episode-25-adventures-distortion

 

[0bs3rv3r]

I keep reading threads like this, because, even though I basically believe in measuring things such as distortion figures, power output etc, I am very aware of enjoying listening to my 2 watt SET amp - which can hardly be called low distortion. Doesn't prevent it sounding good.

 

[FrantzM]

We are at a point where electronics issues are virtually solved:
$9 gives you a transparent DAC
$500. a 200 x 2 wpc. Transparent Stereo Power Amplifier
$99 a Headphones amplifier with close to perfect performance...

What is there left to sell at elevated price (>10,000 amplifier , $30,000 preamps, etc...) ? ... Magic, BS. Perhaps steampunk aesthetics and casework...

And this is a case of selling BS and acting as if you believe in it ... This strategy works and has made some of them, very rich.

I no longer waste my time watching or listening those BS peddlers. There is too much to learn to extract the best from our system.

 

[ta240]

I keep reading threads like this, because, even though I basically believe in measuring things such as distortion figures, power output etc, I am very aware of enjoying listening to my 2 watt SET amp - which can hardly be called low distortion. Doesn't prevent it sounding good.

and in all fairness the argument also goes this way:

 

[audiophile]

If this "thing" cannot be measured, how, then, could the designer properly control and implement it in their amp design?

They use measurements up to some point and then listen to evaluate sound quality. They use their experience in understanding how different changes of the circuit affect sound, try them on the fly and judge the result by listening. Here's Paul McGowan from PS Audio, fine-tuning the crossover of their new speakers in PS Audio's listening room:

On this last picture Paul explains that he knows 5 different ways to make this frequency response curve look smooth, but they'll all sound very different, although measure the same.

Darren Myers, on PS Audio's new phono stage: "I designed a phono stage that had very very low distortion and very good measurements and I listened to it. And it sounded ok, but wasn't what I was after. It sounded closed-in, a bit stuck to the speakers, so I redesigned it all... I started to play with the amount of feedback and quickly realised that it sounded better and better the lower i took the feedback... so I struck the balance with the amount of feedback that's applied...and kept designing until the moment when I just forgot about designing and started listening..."

 

[audiophile]

We are at a point where electronics issues are virtually solved:

$500. a 200 x 2 wpc. Transparent Stereo Power Amplifier

Audioholics: "Power costs money"

 

[Billy Budapest]

We are at a point where electronics issues are virtually solved:
$9 gives you a transparent DAC
$500. a 200 x 2 wpc. Transparent Stereo Power Amplifier
$99 a Headphones amplifier with close to perfect performance...

What is there left to sell at elevated price (>10,000 amplifier , $30,000 preamps, etc...) ? ... Magic, BS. Perhaps steampunk aesthetics and casework...

And this is a case of selling BS and acting as if you believe in it ... This strategy works and has made some of them, very rich.

I no longer waste my time watching or listening those BS peddlers. There is too much to learn to extract the best from our system.

And that is why after 35 years of reading Stereophile and the Absolute Sound, I discontinued my subscriptions last year. I get far more utility from this forum and Archimago’s blog. I still will watch some subjective reviewers’ videos to see demonstrations of product features—primarily Darko and Zero Fidelity, but never New Record Day which makes my B.S. meter go crazy.

 

[ta240]

On this last picture Paul explains that he knows 5 different ways to make this frequency response curve look smooth, but they'll all sound very different, although measure the same.

If only there were some medium where he could show us the different setups measuring the same and possibly even capture the sound too. Someday we will be able to store and send moving pictures with audio. For now we will just have to take his word on it.

BTW, I've solved cold fusion but you will just have to take my word for it.

 

[pwjazz]

Ah the things one must do to stay relevant working on a solved problem. I wonder if toaster designers come up with similar rationale for creating new toaster designs? "I got tired of always designing stuff that heats evenly and fits four bagel slices at once. So I took out some of that temperature regulation and focused more on taste tests. If stuff gets stuck in the bottom or comes out a little burnt every now and then that's okay, what matters is if it tastes good."

Seriously though, I would be sympathetic to the argument that maybe we're measuring the wrong stuff, but no one who argues against measurements ever seems to propose better measurements, it's always just sighted listening tests, usually performed by elderly gentlemen who likely can't hear much above 12 KHz. No thanks.