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Alpha Nirvana 39w 8ohm Class A Amp
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Old 14th June 2020, 10:55 AM   #1321
thompsontechs is offline thompsontechs  United States
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Originally Posted by xrk971 View Post
Actually, the voltage swings in the 4R amp are lower and that is what matters on the feedback resistor. So you are fine.

Do we need to stay away from Metal Film in those positions? I ask because there isn't much available out there in the 1%. I guess, I will have to do some matching if metal is out.
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Old 14th June 2020, 11:35 AM   #1322
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Originally Posted by xrk971 View Post
Actually, the voltage swings in the 4R amp are lower and that is what matters on the feedback resistor. So you are fine.
Aah, OK - thanks, X.

Andy
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Old 14th June 2020, 11:38 AM   #1323
thompsontechs is offline thompsontechs  United States
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Aah, OK - thanks, X.

Andy



Andy happy again?


I'm looking at one of my M2 boards sitting on the bench awaiting new resistors... Not real happy, but not pissed either, more resigned.
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Old 14th June 2020, 12:04 PM   #1324
andyr is offline andyr  Australia
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Originally Posted by thompsontechs View Post

Andy happy again?
Not happy, really - more resigned, JT. (The amp could be better ... but it's OK.)

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I'm looking at one of my M2 boards sitting on the bench awaiting new resistors...
That's not an extent I will go to (replacing resistors) - too hard!

Andy
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Old 14th June 2020, 12:25 PM   #1325
thompsontechs is offline thompsontechs  United States
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Luckily, I did mono builds and the board wasn't hard to remove. I've been looking at the two resistors in question and have two ideas. The first id extracting, which can be a real pain. I will try that first, and if it's to much of a pain, I will just cut it out and solder the new ones on from below. Not ideal, but workable.


I have to do something, just knowing they are not ideal would fester, lol
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Old 14th June 2020, 01:47 PM   #1326
xrk971 is offline xrk971  United States
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Do we need to stay away from Metal Film in those positions? I ask because there isn't much available out there in the 1%. I guess, I will have to do some matching if metal is out.
If you have quality metal thin film 1% like Dale CMF55’s or Takman’s or even Vishay’s - you are fine. Don’t change it to CF.

We are talking about a tiny difference. If you have carbon comp or metal oxide then maybe consider swapping.
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Old 14th June 2020, 04:03 PM   #1327
thompsontechs is offline thompsontechs  United States
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Originally Posted by xrk971 View Post
If you have quality metal thin film 1% like Dale CMF55’s or Takman’s or even Vishay’s - you are fine. Don’t change it to CF.

We are talking about a tiny difference. If you have carbon comp or metal oxide then maybe consider swapping.

Thanks X, ya they are what was on the Mouser cart and that is Carbon Comp 1/2 Watt. Once in a while I push a system pretty hard and I just feel better knowing that I have the what the designer intended and not just, good enough. Maybe we should edit the cart though, for future users.


It's a pain, but even if you had caught the carbon deal in the BOM I still would have to go back in anyway having the cart .5W instead of 1W. I appreciate the time it took to do all the cart work... it's up to the person that orders it to double check.



So it's on me....


JT
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Old 15th June 2020, 09:19 AM   #1328
danny_66 is offline danny_66  Belgium
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Here's an interesting post: beware the measurements.

Not directly related to the Alpha,
But Hugh designed his amplifiers and the Alpha with this philosophy.

Still happy listening to my Alpha20 4R
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Old 15th June 2020, 11:25 AM   #1329
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I first John Darko in 2008, IIRC. We got along very well; he is a very tall Brit, teaching ESL at that time, and I'm a very tall Ozzie, trained to teach ESL as well. We shared a deep love for music and audio (in that order!) and he then put my original NAKSA in media lights. I was very grateful, and wrote a long analysis of my design philosophy.
Here it is:
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“My approach is essentially informed by musical considerations. The human is unique in that he can make sense of cacophonous polytones – music by another name. But the inter-relationships must abide by certain rules to make mellifluous music – and chief amongst them is the rule that even orders are acceptable, where odd orders, particularly the fifth harmonic and beyond, are definitely not.”

“Psychoacoustic studies reveal that to humans the fifth harmonic, sometimes called H5, is musically discordant and unappealing. H2, the second harmonic so redolent with valve circuits, adds warmth and engagement; H3 adds a certain sharpness, and H4 adds ‘body’. H7, H9 and H11 are quite unattractive, sometimes described as ‘machine’ tones, since they do not sound sympathetic to music and in fact contribute to listener fatigue. Crossover distortion on push pull amplifiers is often made up of these components.”

“Even order harmonics are produced by distortions to one half of the waveform – but NOT to the other half. This type of distortion is sometimes called asymmetrical, because it manifests on one half of the waveform, but not the other. Most amplifier designers strive to have the amp clip at the same amplitudes of the two waveform halves; this is electrically efficient, and gives a pleasing symmetry.”

“However, there is a trap here. The human animal is primordially drawn to symmetry, after all, we have two arms, two ears, two eyes, two legs, and two hands. We are irresistibly attracted to symmetry in art, in our visual appraisal of others, in mathematics and in science. Much of our architecture is symmetrical, and even automobiles are often marketed on the basis of symmetry, so there is clearly something to it.”

“The trap is that symmetry of waveform distortion means that any distortions will be odd order. Be mindful that distortion is inevitable; it is a fundamental part of the amplification process, however small, so we must design to accommodate this distortion. Corruptions of the upper half cycle duplicated in the lower half cycle will manifest as odd order harmonic distortion, and this sounds very bad to our ears. In fact, there is a pronounced asymmetrical quality to our hearing; the transfer function of air is different in compression to rarefaction, and this means that everything we hear is slightly corrupted by the very medium through which we hear it! It transpires that the human ear also deals asymmetrically with compression and rarefaction; and as a result all incoming sound waves are augmented with H2 as they enter the ear canal. Estimates of this phenomenon vary, but some experts put the figure in excess of 30%. This is a shocking revelation to those who insist on vanishingly low THD, since, along with huge distortions added by the speakers, the amplifier issues are, on the face of it, dwarfed by other phenomena occurring in the human hearing system.”

“This all has repercussions for audio systems, particularly digital sources and power amplifiers. It means that if odd order harmonics, even at very low levels, are delivered to the speakers then the human ear will respond to them, perhaps not directly, but certainly at a subliminal level. This may cause us to cry out in sonic rapture, or quietly leave the room after only ten minutes.”

“At Aspen we believe that these considerations are pivotal to audio amplification, and our many careful tests over the years confirm that an amplifier with higher even harmonics than odd harmonics is more musical. This has informed all our recent designs, with the NAKSA series following this philosophy to the letter. We fervently believe we are on the right track, have developed a series of metrics to assist with the design cycle, and would ask that you listen carefully to the new NAKSAs and hear for yourself just how musical is this novel approach.”
I was always fascinated with X's measurements using carbon resistors v. metal film resistors in the feedback networks of the Alpha. He demonstrated conclusively that metal films bring up the third harmonic over the second; the carbons do the opposite.
Best sounding amps have a monotonic decrease of successive harmonics, and the more linear, the better. This is from Jean Hiraga in the 60s - nothing is new and demonstrates how the marketing speak drives the equation rather than the truth.

Cheers,

Hugh
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Last edited by AKSA; 15th June 2020 at 11:28 AM.
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Old 15th June 2020, 12:01 PM   #1330
bucks bunny is offline bucks bunny  Germany
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taking this Quote
"but some experts put the figure in excess of 30%. This is a shocking revelation to those who insist on vanishingly low THD, since, along with huge distortions added by the speakers, the amplifier issues are, on the face of it, dwarfed by other phenomena occurring in the human hearing system.”
I consider any discussions of amp THD signature that amount to a total THD below 0.00xxx% as pretty irrelevant. This includes the actual hype about post-filter feedback as well. If there are any serious reports about audibility of THD levels that low I would be very interested in link(s).
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