This is the measurement Richard did on one amp at 50W/8 ohm not long time ago.
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John, however you slice it, this amp is mediocre at best in this time and age. We actually DID progress audio quality in the last 50 years or so but you refuse to see it and come up with examples like this to deny it.
And please, what´s this ´measures very well with a normal THD meter´? And this from someone who maintains that THD doesn´t tell a lot anyway? Now THAT is disappointing!
Jan
Sorry Richard I cannot parse this.
The issue was that full OLBW and consequently constant feedback factor with F does not generally guarantee constant distortion with F. Is this post meant to refute that in some way?
Jan
This is simulated LG of the same amp, and no, VAS is not resistor loaded to get that.
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I think that slide it taken out of context. If you read his F-word article he goes into more detail. What he is discussing there is that small amounts of feedback make things worse.
If you imagine the case where you have 250dB of negative feedback at DC and only 50dB at 20kHz this does not apply.
Yes it was taken out of context. The article gives a much clearer picture and reasoned position. But you need to spend an hour on it to read it thoughtfully.
The reward is that once and for all you can separate the chaff from the wheat here 😎
Jan
Richard,
Have you measured the distortion profile of the MiniDSP you are running your M2's through? They have clearly rising distortion with frequency based on measurements I did years ago. Still, you proclaimed your M2's to be the most transparent etc. loudspeakers you have ever owned.
This just to underscore my earlier point that, once low enough, distortion does not matter, either rising or constant with frequency. For the simple reason that our organic audio analyzer has its limitations, beyond which awareness of certain phenomena just becomes impossible.
I meant for the miniDSP in answer to vacuphile
power amps are no longer the largest sources of distortion in the system! (if we ignore the speakers).
power amps are no longer the largest sources of distortion in the system! (if we ignore the speakers).
I measured the Electrocompaniet (Otala) power amp at 25W (4ohms) because it hard on a small power amp to test it there. Of course, I make better measuring amps, but not necessarily better sounding ones.
Talking about big amps, how about this one?
3050 Mono Power Amplifier - Boulder Amplifiers
It has been hardly ever mentioned here, why?
Its smaller brother, 2150, has fantastic set of measurements in Stereophile.
Boulder Amplifiers 2150 monoblock power amplifier Measurements | Stereophile.com
3050 Mono Power Amplifier - Boulder Amplifiers
It has been hardly ever mentioned here, why?
Its smaller brother, 2150, has fantastic set of measurements in Stereophile.
Boulder Amplifiers 2150 monoblock power amplifier Measurements | Stereophile.com
But also, if that's roughly its distortion level, it's very very much pushing the boundaries of our hearing. So may not sound much different to newer designs. (not that I disagree with the rest of your sentiment in the least)
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Unless the author had some false feedforward premontion in place, I'd argue that you're wrong 😀 ... The slides were published in 2007.. the f word article in 2011. In any case, a thorough reading of the later article does not debunk, in any way, the point made in the slides.
'Open-loop bandwidth is no indication of speed and tells us nothing about the qualitative behaviour of the feedback system. The distortion products that we hope to attenuate using feedback are all at audio frequencies, so what matters is loop gain at audio frequencies. If at some impossibly low frequency it is much higher, we don't care. If at the other end of the audio spectrum it's not enough, we do.
Later on ....
A second step in the experiment consisted of placing a resistor across compensation capacitor C that reduced DC gain to the same value as that at 20kHz (Figure 12, trace 4). The test amplifier was of the folded-cascode persuasion, which allowed this. At this stage, loop gain has indeed been reduced across the full audio range. I surmise that since the amplifier's distortion was never negligible, making it constant across the audio band makes it fly under the psychoacoustic radar more easily. My own subjective experience would support this.
To my ears, amplifiers with the normal 20dB/decade behaviour but whose distortion is not negligible at the end of the audio range have glassy mid-highs, a "superglue stereo image" as KK once put it, and the illusion of spectacularly, unnaturally tight and impossibly controlled bass. Some love this, and seceded into a subculture of ultra-beefy amplifiers.
I don't and when forced to make a choice I'll take higher but consistent distortion across the band."
[emphasis added by me]
That's not so suggest I agree with every argument made in article. The point about too little feedback was extremely sloppy - it applies only to a unique and special case started by baxandall and continuously regurgitated and consumed uncritically. Any amount of feedback applied around a push-pull amplifier with reasonably matched p and n channel parts (and thus negligible h2)therefore will reduce total measured distortion, not increase it. So the example needs huge neon lit qualifiers saying "only for single ended or h2 dominant cases"
Unless the author had some false feedforward premontion in place, I'd argue that you're wrong 😀 ... The slides were published in 2007.. the f word article in 2011. In any case, a thorough reading of the later article does not debunk, in any way, the point made in the slides.
'Open-loop bandwidth is no indication of speed and tells us nothing about the qualitative behaviour of the feedback system. The distortion products that we hope to attenuate using feedback are all at audio frequencies, so what matters is loop gain at audio frequencies. If at some impossibly low frequency it is much higher, we don't care. If at the other end of the audio spectrum it's not enough, we do.
Later on ....
A second step in the experiment consisted of placing a resistor across compensation capacitor C that reduced DC gain to the same value as that at 20kHz (Figure 12, trace 4). The test amplifier was of the folded-cascode persuasion, which allowed this. At this stage, loop gain has indeed been reduced across the full audio range. I surmise that since the amplifier's distortion was never negligible, making it constant across the audio band makes it fly under the psychoacoustic radar more easily. My own subjective experience would support this.
To my ears, amplifiers with the normal 20dB/decade behaviour but whose distortion is not negligible at the end of the audio range have glassy mid-highs, a "superglue stereo image" as KK once put it, and the illusion of spectacularly, unnaturally tight and impossibly controlled bass. Some love this, and seceded into a subculture of ultra-beefy amplifiers.
I don't and when forced to make a choice I'll take higher but consistent distortion across the band."
[emphasis added by me]
That's not so suggest I agree with every argument made in article. The point about too little feedback was extremely sloppy - it applies only to a unique and special case started by baxandall and continuously regurgitated and consumed uncritically. Any amount of feedback applied around a push-pull amplifier with reasonably matched p and n channel parts (and thus negligible h2)therefore will reduce total measured distortion, not increase it. So the example needs huge neon lit qualifiers saying "only for single ended or h2 dominant cases"
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