THD Usefulness Thread = Son of Opti-MOS ? - diyAudio
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Old 5th March 2001, 01:01 PM   #1
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I assume I have the attention of Grey, blmn, hopefully Pixie and others. I brought this out into another thread because many, I suspect, have tired from the length of posts in the last thread.

Anyhow, found this interesting website recently, thought you might enjoy the read.

It sort of relates to "is there more than THD/IMD?"

http://peufeu.free.fr/audio/

mark
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Old 5th March 2001, 06:03 PM   #2
blmn is offline blmn  Brazil
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Mefinnis,

Good reading. You´re right, again, but I think that thread is not finished, yet...

Regards
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Old 6th March 2001, 02:53 AM   #3
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You assume correctly, sir...
(Mark, I swear the first time I read the name Lavardin, my eyes reported seeing Lagavulin. Single malts are one of life's pleasures.)
Fascinating. I've been through it once at medium-concentration level, but will need to take more time and care with it.
Re: Tubes. I would assume that the same distortion mechanisms work in tubes, just at reduced percentages since plate dissipation is augmented by filaments, obviously.
Re: Transistors. Has anyone heard Lavardin gear? Does this concept actually work in practice, or does it simply look good on paper? I'm highly allergic to hand-waving, but this seems plausible. I don't own a good set of headphones, so I won't be able to try out this fellow's circuits as they stand. Does anyone out there have good headphones and the interest to reproduce what this guy does on his website? Subject to me getting a chance to re-read what this guy's saying, I'd like to propose a question. Since class A circuits (including the junctions inside) run at a more nearly constant temperature, is it possible that this distortion mechanism would be more prominent in AB and B circuits? Hence part of the class A sound. He may have addressed this issue. I'll be looking for it when I go back in.
Re: Current sources. They fascinate me. I use one under a differential as the first stage/phase splitter in my tube circuit. I can testify that the sound changes pretty noticably with I-source topologies, but I've not tried a cascode. Might have to give that a shot. On a related note, I believe the first stage of the Atma-Sphere amps uses a tube (6SN7) cascode as an I-source. They have a good reputation for sound. (I haven't heard one myself.) Could there be a connection? My current source topologies have all been solid state, as I wasn't willing to build another high voltage rail. Doesn't Horowitz & Hill have a bit on cascode current sources? (I'm at work and don't have all my stuff with me.)
Re: The parent of this thread: I can make my tube amp sound 'like transtors' with one of the I-source topologies I tried out. Just the one current source, mind you, and that from a portion of the circuit that some people don't even consider to be 'in the signal path.'
Mark, how'd you find this site, and are there any more like it? I'm always open to new possibilities as stuff like this sets my mind to fizzling with questions, and questions (sometimes) lead to answers.

Grey
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Old 6th March 2001, 03:24 AM   #4
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"I swear the first time I read the name Lavardin, my eyes reported seeing Lagavulin" .... I nearly cried laughing ;-)

(see the very bottom of http://www.health.adelaide.edu.au/icu/ss_finnis.htm)
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I have not had time to really dissect this paper yet, just posted because it seemed pertinent to the parent thread and I was interested to see what the higher-EE minds made of it - which is why I placed it "out in the open".

Found it on the http://www.audioasylum.com site, which I have only recently found and have not been overly impressed with ... people regressing to 4yo "sand-pit" level discussions with name calling and similar juvenile behaviour.

My suspicion is that this is a "cold amp" phenomenon, ie if you have a cool running amp then it would be much more susceptible, supported by the sonic signatures of A versus AB. Would also support the observation that SS amps sound "better" when they are at operating temp.

Note in his 2-stage example he has 20mA bias for both the pair and the output device. My 2S amp is closer to 20mA/3A.

The pulse signals he has used and graphed are going into cold devices ..... hell, after 20 mins there ain't nothing cold within my amp (or within about 1 metre actually!!).

Clearly haven't heard any of this gear.

not a convert just yet, but it was interesting me'thinks!

mark

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Old 6th March 2001, 01:55 PM   #5
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Mark,
A quick brain tickler for you:
If we're talking thermal distortions of operating points, here, would it be better to use a small device closer to its limits (smaller mass, hence quicker settling times), or a larger device that is well over-spec'ed so that the thing hardly heats at all due to having larger junctions, etc.?
I vote for the larger device (subject to further thought--this just occurred to me) even though the hysteresis would be worse if it ever did start warming significantly.
In other words, there may be other ways to approach cures for this thermal distortion mechanism. (Can you say IRF9610 used in place of typical small signal device? Sure, I knew you could. Food for thought, there.)
Re: Ethanol. And you've got Penfold's Grange down there, you dog. Something I'd love to get acquainted with...excepting you could buy a complete high end system with one bottle around here...

Grey
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Old 6th March 2001, 04:18 PM   #6
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MeFinnis this is a very cool site. I need a few hours to read about it. I well tell you what I think when I finish with it.
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Old 6th March 2001, 09:03 PM   #7
Thunau is offline Thunau  United States
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Thumbs up Son of a Gun!

I wish I was more electronics literate. Even with lack of understanding of particular concepts, from what I can understand this is a serious contender in quest for quality. I hope it will not turn out to be another "ho-hum break through". Anybody going to give it a shot and build an actual working amp? Seems to me that existing cuircuits could be modified to accomodate a few extra parts , even if it means a couple of p-t-p conections. But, I could be totally wrong on this one. Anyway, I would buy some PCB's if one of you guys decide to make a prototype based on this design. I can handle assembly.
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Old 12th March 2001, 08:39 AM   #8
peufeu is offline peufeu  France
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Default Thanks guys

... for your feedback.

I am the writer of the page on memory distortion... I appreciate your comments. I plan on making a PCB available for download for anyone who might want to experiment on it. I think the Internet is a great collaborating medium for that ; so when I run out of ideas, others can take over and add theirs to the melting pot.

By the way the 20mA bias is normal (it is 100mA in real life actually)... for a headphone amp. Yes, I do test with headphones...

Regarding my sources : yes, the CD63SE sounds grainy and compressed. Now, I do all my evaluation with my Harman Kardon DVD1, which is not perfect, but much better yet.

Cheers !
Pierre
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Old 12th March 2001, 03:56 PM   #9
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Cool Opti-MOS, finished.

I built the Opti-MOS Saturday. It wasn't difficult at all using the kit! :) Of course, I had to build my own power supply. That's OK though, I built a huge power supply. If it came in the kit, it wouldn't have been as good.

I spent all day Sunday listening to it and comparing it to my McIntosh on both my Legacy and Klipsch speakers.

This is my opinion, and only MY opinion. Not anyone else's. My opinion means nothing to anyone but me and those who trust me. Opinions are opinions, nothing more. I will accept no argument on this point. So, if you don't like my opinion, tough. :)

I love it. It is indistinguishable from my McIntosh, except , and this may be my imagination, but I think it has better control of the bass. The highs are perfect. I can detect distortion in the treble very easily, but I heard none. It blew the hell out of the Zen. I listened to my Zen for hours before it fried. The fact that the Zen is missing the upper quarter of audible frequencies kills it. It's a fun first circuit, but it's not a real amp.

I was able to get 100dB peaks out of my Klipsch and not hear any distortion or lack of bass. That's about as loud as I can stand. So, by every meassurement that's important to me, the Opti-MOS is perfect.

I highly recommend building this one. If you like clean perfect sound, It's the best I've heard yet. And at a total cost of $250. I'm a very happy man. If it is reliable for the next two or three months, I'm going to build three or four more.

Later,
pixie
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Old 12th March 2001, 05:24 PM   #10
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Pierre,
Many thanks for posting the circuit idea. I have not yet had time to go back and give it a more thorough reading, but it is high on my list of things to do. I find it conceptually fascinating, and hope that it has relevance in the real world.
I had a posting above about device ratings vs. thermal (memory) distortions. I'd like to get your input on that one, since you've had longer to meditate on the idea.
Pixie,
Glad to hear that your Opti-MOS worked out okay for you. Just for fun, you might want to keep an eye out for surplus caps to add to the power supply. You might just find that the bass tightens further still...
Regarding your Zen, I'm curious as to how it came to be missing the upper quarter of the frequencies. I know that it had a difficult birth and, apparently, a short life span. Just wondering if some ambiguity in the schematic was responsible for one or both. In any event, it doesn't sound as though it had enough power for you--hope the Opti-MOS fits the bill.

Grey
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