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M³ Project Announcement - Page 4

post #46 of 565
8/21/04 at 7:55pm
Thread Starter 
JCX: Regarding power issues, we could do it just like the PPA with 3 TLEs, or with a single supply for all 3 channels separate from the output rails, or one supply for everything. We could use capacitance multipliers, or voltage regulators, or FET isolation. There are many options. We are waiting for some FETs to arrive from Mouser so we can do more testing. This includes testing the performance difference between 2 and 3 channel operation. I would like to cut out anything that does not significantly contribute to amp performance, to keep the price reasonable while still providing excellent quality. As for using rail splitters, I like them. They are only being used to supply the opamps, which have miniscule power requirements. We will keep you posted on the results of our power supply tests.
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post #47 of 565
8/21/04 at 11:04pm
Quote:
Originally Posted by morsel
Hey Tangent, are you listening to this? We found someone besides Kurt who wants so8 pads. Glassman, where were you when we were working on PPA v1.1?
Count mine as a vote for SO8 pads as well! The way that it's set up on the PIMETA is great - a choice between DIP or SO8. Very flexible.

-Drew
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post #48 of 565
8/21/04 at 11:08pm
thay are complementry j-fets 2N5457 and 2N5460 and are available everywhare
http://www.onsemi.com/pub/Collateral/2N5457-D.PDF
http://www.onsemi.com/pub/Collateral/2N5460-D.PDF

You can also use the 2Sk170 and 2Sj74 J-Fets from Toshiba
http://www.ampslab.com/PDF/2sk170.pdf
http://www.ampslab.com/PDF/2sj74.pdf
Thanks to amplabs for hosting these and other data sheets
http://www.ampslab.com/
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post #49 of 565
8/21/04 at 11:59pm
Thread Starter 
PPL, you are right, they are readily available, what aos and I meant is that they are nonstandard in the sense that everyone has been using 2N5484, 2N5486, and 2N4392 FETs. By specifying yet another kind of FET, it forces people to order and stock more parts. There is some nuisance factor involved. I'm sure some people would be happier if we used the "same old" FETs as before.
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post #50 of 565
8/22/04 at 12:51am
Nah, FETs are cheap. And if they are available from Digikey, it's a non-issue. I was just wondering why, since when you experiment you tend to pull something out of your drawers and go shopping only if you absolutely need to (or you're depressed).
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post #51 of 565
8/22/04 at 2:50am
Quote:
Originally Posted by aos
Nah, FETs are cheap. And if they are available from Digikey, it's a non-issue. I was just wondering why, since when you experiment you tend to pull something out of your drawers and go shopping only if you absolutely need to (or you're depressed).
LOL since im depressed dose this imply if i go shopping ill feel better never thought of that one
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post #52 of 565
8/22/04 at 11:38am
Quote:
Originally Posted by Earwax
Is a crossfeed a good use of board space? Which circuit would be used? I like the Meier crossfeed best, but maybe someone else wants a Linkwitz or something else. Overall, wouldn't a daughteboard approach for crossfeed be better?

Any opamp at all, including Bipolar types (LM6171)?
I have tried the Meier one, and it is absolutelly stunning, after two weeks of using it, there is no way I could remove it from the system. I like it so much to the point of opening it and replace all the internal wiring by silver solid wire....
I know that many people do not like it and others never had tried it, for the ones who have not tried it, my advice is, go for one and try it.......
The problem with doughter boards is that they need a lot of additional wire in the signal path, if you include it at the input near the jack in the circuit you minimize this, you can even use a few levels of crossfeed with bass and highs compensation similar to the Corda Cross-1...
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post #53 of 565
8/22/04 at 11:58am
Quote:
Originally Posted by aos
Also, you can't use Meier's circuit without permission. You can add it on your own amp if you wish but I don't think it could be included on board as default.
That's why a daughterboard (or another kind of allowance for crossfeed)
is a good approach to adding crossfeed.
Meier circuit is of the public domain, it is on the Headwize projects section, and for DIY use, since a long time ago, and this amp will be for DIY, not for commercial use. I don't think that Jan will have any objection, that someone use his project, and circuit (or part of it), in a completely personal DIY project.
But of course, there will be, as usual, some of the DIYFSE that will begin to make them for others, and get some profits, out of it, (this is always a consequence of the free projects, and in fact some of us that really wants them do not have the tools and knowledge to do it for ourselves) But even though not everybody is so reserved with his intellectual property. Of course if some of those DIYFSE are going to use his, it will be very polite to contact him first, just to be sure he won't mind.

As for the impedance issues, I don't know how he implement his in his amps then, maybe some kind of compensation or the like, but it works with any source on his amps, for sure.....
Anyway any other circuit that works will fit as well, I'm just suggesting the one I have tried, and liked....
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post #54 of 565
8/22/04 at 12:08pm
Add me to the SO8 statistical poll.

Does the design take into account that the ground channel buffers will be sourcing/sinking twice as much current as the drive channels? And thus will require twice as much heatsinking.

If power consumption is of no concern, why not use single ended pure class A output stages. Like the Nelson Pass DIY amps. Two N-type mosfets, the bottom as a constant current source. Should be more linear.

What do you need the 10ohm output resistors for? My understanding is they are useful in bipolar output stages with multiple transistor pairs to keep any single one from running away. But mosfets have a negative temperature coefficient so that doesn't happen. Plus there is only one pair.
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post #55 of 565
8/22/04 at 1:03pm
Thread Starter 
Cameron: The MOSFETs are going to dissipate about 1W assuming 12V × 80mA. This is no problem for the Aavid extrusions. Most of the power is due to bias, so the ground channel will not be double the signal channels. As for the Nelson Pass amps, aren't they capacitively coupled? Not my personal preference, although he does great work.

You are free to reduce the value of your source resistors, or remove them if you dare, but AMB feels they need to be 10 Ohms to adequately balance the differences between the N and P channel MOSFETs and limit the maximum output current. I originally wanted to go with 1 or 2 Ohms. Perhaps AMB will say a few words on this subject.
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post #56 of 565
8/22/04 at 2:20pm
I figured the biasing would be closer to the expected maximum load current. I usually go 2x to be on the safe side. But if you are going for a larger fixed bias current for everything, that should work okay. With any given bias current, I would still check to make sure the ground buffer isn't switching to class B or doing anything else weird. Just to be sure.

The Nelson Pass amplifiers usually do have a DC offset at the output. But since the output stage would be inside the feedback loop, the opamp will take care of that. No need to worry about current limiting with resistors either. The lower mosfet current source is your limit but without adding to the utput resistance. Also why would you want to current limit anyways? There have been many instances where it was noted that buffers without current limiting sound better.

Attached is a butt basic no-gain example schematic:
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post #57 of 565
8/22/04 at 2:39pm
http://www5.head-fi.org/forums/showp...0&postcount=50
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post #58 of 565
8/22/04 at 3:33pm
Thread Starter 
Peter, thanks for that link. The entire thread is worth reading:
DC Coupled Szekeres Power Supply l7815 and lm317

Quote:
There have been many instances where it was noted that buffers without current limiting sound better.
Cameron, in principle, I agree. The Hafler DH-200 power amp (circa 1980) does not use source resistors. I am theoretically in favor of lower or no source resistors, however AMB is the supergenius among us and he has his reasons, so I'll let him answer.
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post #59 of 565
8/22/04 at 4:01pm
OT:

Quote:
LOL since im depressed dose this imply if i go shopping ill feel better never thought of that one
I'm dead serious here. Shopping helps a LOT when you're depressed. I thought it's well known. Shopping as in go-look-buy, not online because it's a time-delayed thing. It's even logical, you go and see stuff, get excited, buy it, run home and play/fiddle with it, changes your mood easily. It's also a form of addiction unfortunately so if you can't control your shopping implulses you'll end up with house full of gadgets and no money.

OnT: I'm going to place an order with Mouser so I'll get a few of these parts. Eventually they'll come in handy .

Meyer circuit is NOT in the public domain, except for your own personal use. The fact that these boards WILL be used by some for DIYFSE eliminates it from being on the default board - or eliminates possibility of DIYFSE of the boards, whichever. I'm sure Jan would object (because he mentioned that in the past) and he has every right to. If I were to include his crossfeed I'd personally be willing to pay royalties, as would be only fair. I've tried several crossfeeds over the years and Meier crossfeed was the only one that
gave me the desired effects and made me want to use it myself.
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post #60 of 565
8/22/04 at 4:25pm
Quote:
Originally Posted by aos
Meyer circuit is NOT in the public domain, except for your own personal use. The fact that these boards WILL be used by some for DIYFSE eliminates it from being on the default board - or eliminates possibility of DIYFSE of the boards, whichever. I'm sure Jan would object (because he mentioned that in the past) and he has every right to. If I were to include his crossfeed I'd personally be willing to pay royalties, as would be only fair. I've tried several crossfeeds over the years and Meier crossfeed was the only one that
gave me the desired effects and made me want to use it myself.
There was a long discussion on what is, or not, allowed to be used, and registered, and copyright ownership in the past (IIRC was in that same thread in which Jan complained about one member using one of their same crossfeed circuits) so I will not go into that again.
IIRC there was enough posting regarding that, from even a person that use to work in a field related to the patents registration, etc....but anyway, this will cause some problems as you wisely stated in the case of the DIYFSE part of the project that we will be sorry of that, we as customers, need that and some others as manufacturers also....here is part of that discussion....anyway, nevermind....


Quote:
".......Jan can copyright the article text as well as any images, PCB layouts, and schematic diagrams, but he cannot copyright the circuit design itself. Here is the US Copyright Office's description of what can and cannot be copyrighted:
http://www.copyright.gov/circs/circ1.html#wnp
In other words, the disclaimer text at Headwize does not prevent others from selling copies of Jan's design, as long as they make their own PCB layout (as appears to have happened here).

Copyright simply doesn't protect device designs. The only forms of intellectual property that protect device designs are patents and trade secrets. He obviously gave up trade secret protection by publishing it online........etc....."
Just for the records, I have one of his Corda Cross-1, and made by him, so even if they won't include it, I will have it anyway.....I don't care if it will be part or not of the circuit, but I would like others to have it as well, as I'm extremelly pleased with it....
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