Spice simulation

[MikeBettinger]

Originally posted by john curl
Mike, I don't know if you know this, but Litz wire is really lousy at very high frequencies, like TV, etc.

Like I said, It, a joke. I can remember in the early 80's when it was the thing to have. Remember the Polk Cobra Cable?

Mike

[GRollins]

John,
I call the phenomenon Science as Religion (I'll get the Nobel Prize for the concept someday). The irony is intentional. People who treat science as Revealed Truth refuse to question things in a manner precisely analogous to the most fervent religious zealot refusing to face the problems inherent in his faith. And, exactly as one would expect, they condemn most bitterly those who question the underpinnings of their faith as heretics, unbelievers, and worshipers of false gods.
Not to mention purveyors of snake oil.
(Speaking of snakes, it's interesting to note the reputation of the Serpent in Christianity. The analogy goes deeper than one might first think.)
Science, in order to be valid, must be tested against reality or it literally becomes another religion. In our case, reality means the listening room, not the test bench. This is not some abstract theoretical exercise--it's an attempt to build a real system that recreates music. But, oh Gussie, the cries of anguish from those whose Revealed Truth is found wanting. Just like all whose deity is mysteriously AWOL when put to the test, they blame everything except their belief system.
Don't get me wrong--although I gave up on simulation programs, I still think THD is nice. In moderation. I've got an HP 339. I even use it on alternate leap years. (Gasp!) But I've had far too many experiences that flew in the face of the Theory Uber Alles religion to show up on Sundays.
Reality dictates Theory, not the other way around. When people put theory above reality, it's no longer science...it's religion.

Grey

[GRollins]

Jeez, I should think it should be obvious--it's right there in the spec sheets. Devices behave differently when they get hot. But you can't simulate that because you can't know the ambient temperature in the room...
hence the efficiency of the heat transfer from the heatsink to the room...
hence the actual temperature of the heatsink...
hence the actual temperature of the output device...
hence the actual temperature of the semiconductor chip itself...
hence the actual, literal, real world behavior of the MOSFET's bias and transconductance in the practice of delivering music to the listener's ear.
For want of a nail, the kingdom fell.

Grey

[andy_c]

http://www.fairchildsemi.com/an/AN/AN-7532.pdf

And yes, this is about MOSFETs, not Vogon poetry.

[GRollins]

Originally posted by andy_c
http://www.fairchildsemi.com/an/AN/AN-7532.pdf

And yes, this is about MOSFETs, not Vogon poetry.

A quick browse indicated that the models are for low power. However, it is, no doubt, an incremental step forward.
I work with mainframe computers. At this point, meaning sixty or seventy years into the mainframe era, the technology is pretty mature. Your average mainframe works well into multiple "nines" of reliability. The system gets IPLed (more or less equivalent to rebooting a PC) every few months or so, whether it needs it or not.
Ah, but the network stuff is another matter entirely. I have a screen here above my head that lists problems on the network. At this moment, 21:52 on 5/9/07, there are 18 different things pending on the network here on campus. Reliable? Uh unh. Not even in the ballpark.
Yet the network guys are eternally patting themselves on the back about how great they are and how marvelous the network is.
Us mainframe guys? We're like the proverbial grandfather clock in a thunderstorm. We just keep on ticking. Reliable. Dependable. Always there.
No wonder anything important--student grades, accounting, dorm assignments, class roles, and so forth, gets run on the mainframe. Running that stuff on the network would be a recipe for disaster, no matter how cute the flashy graphics look on a PC.
There is no doubt in my mind that electronic simulation programs will someday be useful. At this point, though, it's a woefully immature technology and I question its utility for audio work. Like the network, they look good and give (false) confidence. Also like the network, they crash inexplicably and without notice.
Meanwhile the old-fashioned mainframe just keeps chugging along, doing the heavy lifting. Ain't sexy, ain't cool, ain't much loved, except by those who want to get the job done.
Kinda like using a soldering iron and real parts. It may not be the modern thing to do, but it works. And that's pretty cool in my book. I'll take results over flash any day.

Grey

[ingrast]

Originally posted by Christer


....Spice can also be useful to test concepts and compare topologies with ideal components. The latter may sound useless to some, but I think otherwise. By using ideal models, or models which are elaborate but not corresponding to a real component, one can get more general insight than if always only using specific component models or breadboarding with real components. It can even be enlightening sometimes to simulate non realistic circuits to understand things. .......

One of the most important uses I find for simulators, apart from sparing charred silicon after some silly mistake.

Rodolfo

[jan.didden]

Originally posted by GRollins
Jeez, I should think it should be obvious--it's right there in the spec sheets. Devices behave differently when they get hot. But you can't simulate that because you can't know the ambient temperature in the room...
hence the efficiency of the heat transfer from the heatsink to the room...
hence the actual temperature of the heatsink...
hence the actual temperature of the output device...
hence the actual temperature of the semiconductor chip itself...
hence the actual, literal, real world behavior of the MOSFET's bias and transconductance in the practice of delivering music to the listener's ear.
For want of a nail, the kingdom fell.

Grey

Actually, Grey, all of these things can and have been simulated. IsSpice has published several newsletters in the past addressing these kinds of issues. Guess you'll have your kingdom after all .

Jan Didden

[Christer]

Sorry for yet another Spice post, but I cannot silently stand by when people post the most surprising nonsense about simulations and computers.


Greg, I don't know if your lengthy discussion of mainframes vs. networks was intended to say anything about simulations. But if so, I cannot see the relevance of network reliability issues for a discussion on simulations, unless you are doing distributed simulations over a network, which probably none of us are doing.

Originally posted by GRollins

There is no doubt in my mind that electronic simulation programs will someday be useful. At this point, though, it's a woefully immature technology and I question its utility for audio work.

There is no doubt in my mind that that that day did come long ago, and you just missed it, since Spice has been used regularly by the industry for a very long time. Except for IC design maybe, simulations do usually not tell the whole story, but they are undoubtedly ver useful. Do note that Spice is an electronic circuits simulation program. It is not intended for modelling spatial issues like component placement or heatsinks. However, with a lot of effort you could probably make an electrical model of your PCB and a model for the electrical effects of the thermal arrangement (heatsinks, component placement etc). However, it is most likely not worth the trouble to do so for a specifik design. Neither is Spice intended to simulate psychoacoustics, which would be necessary to giva an accurate simulation of what you will think an amplifier sounds like. To simulate what an amplifier sounds like would also require simulating the speakers and the room acoustics, also something Spice was never intended for. So please, do not call Spice useless just because it doesn't wash up your dishes or move your lawn or any other thing it never was intended to do. Also do not accuse Spice for the errors that the users are responsible for.

Like the network, they look good and give (false) confidence. Also like the network, they crash inexplicably and without notice.
Meanwhile the old-fashioned mainframe just keeps chugging along, doing the heavy lifting.

Sorry, but I am afraid you do sound quite confused. Trying to compare network reliability with simulation results seem like a very strange and useless analogy. And what is it that crashes like the network and in contrast to the mainframe? The simulation program? Not the one I am using at least.

Is it that you are trying to compare network technology, simulation programs and computers (but only mainframes)? A very strange comparison indeed, whichs leads me fear you don't have a clue what you are actually talking about.

[GK]

Originally posted by Christer
Sorry for yet another Spice post, but I cannot silently stand by when people post the most surprising nonsense about simulations and computers.

I had a similar reaction, but I only broke from silence when my jaw hit the table.

Your response is most reassuring. Some times I question wether it's me that's barking mad, or if it’s everyone else around me.

[john curl]

Bark, Bark! SPICE is OK, but you should know its limitations and that it can sometimes be misleading.
When I was young, SPICE was only a concept, but we had specific electronic analysis programs that worked on mainframe computers, mechanical calculators, and slide rules. When we wanted to evaluate a design, we built it. I used to build them for others, at first, then I finally got to build my own designs. This was the way of the engineer of 35 years ago and more. Like the proverbial: "When I was young, I had to walk to school." often said by parents to childern, when I was young we had to actually build our own circuits in order to see how well they work, and we got used to it.
You, newbe engineers, are taught in school how to use Spice, and you can't see a world without it. You also tend to rely on it, perhaps more than is completely wise in all situations, but there is nothing wrong with using it, if you wish.
This question came up when Bob Cordell apparently was surprised that I had not made a SPICE emulation of the JC-1 power amp. I told him (in so many words) that it was not really necessary, since Parasound did it the hard way, we built it and tested it.
The SPICE scare stories are to point out that no emulation is perfect, and to keep that in mind when designing.