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john curl 9th May 2007 03:23 PM

Spice emulations? I don't need no stinking Spice emulations! (think bandito icon)
Count me in with Bob Pease on this one. ;-)
I just measure them in REAL-TIME with capacitors and a square wave generator, as I learned to do at my mentor's side, 40 years ago.

x-pro 9th May 2007 03:29 PM

Quote:

Originally posted by john curl
Spice emulations, I don't need no stinking Spice emulations!
Count me in with Bob Pease on this one. ;-)
I just measure them in REAL-TIME with capacitors and a square wave generator, as I learned to do at my mentor's side, 40 years ago.

I am with you on that one, John, thought I do use Spice occasionally for some specific tasks ;) .

Alex

Bob Cordell 9th May 2007 03:37 PM

Quote:

Originally posted by john curl
Spice emulations? I don't need no stinking Spice emulations! (think bandito icon)
Count me in with Bob Pease on this one. ;-)
I just measure them in REAL-TIME with capacitors and a square wave generator, as I learned to do at my mentor's side, 40 years ago.


Hi John,

Either way works. I didn't use SPICE on my MOSFET power amplifier 25 years ago, and was able to get good results. It is also very important that people understand the limitations of SPICE, and don't just totally depend on it. Just as you have to LISTEN to an amplifier after you measure it, you have to MEASURE your built amplifier after you simulate it. I've rejected numerous JAES paper submissions because people claimed results based on simulation and never built the thing.

Having said all that, however, I find SPICE to be incredibly valuable in providing insights and in doing experiments and seeing what works and what doesn't have a chance. I have truly learned a lot when SPICING my own amplifiers, and have had several eye-opening experiences.

You should give it a try. It is never too late for an old dog to learn new tricks. I am also an old dog, and continue to learn new stuff every day.

Cheers,
Bob

Netlist 9th May 2007 03:49 PM

John,

Hope you donít mind us simulating an old PL? Perhaps not your piece of cake but you must remember them from the old days. :) I'm with those that think there is a lot to learn from it but the final arbiter should be the ears.

http://www.diyaudio.com/forums/showt...12#post1204712

/Hugo

Edmond Stuart 9th May 2007 04:08 PM

Quote:

Originally posted by Bob Cordell
.................... I find SPICE to be incredibly valuable in providing insights and in doing experiments and seeing what works and what doesn't have a chance. I have truly learned a lot when SPICING my own amplifiers, and have had several eye-opening experiences................

:yes:

And it saves a lot of time (and semiconductors!).

Cheers,

GRollins 9th May 2007 09:46 PM

Quote:

Originally posted by Bob Cordell



Having said all that, however, I find SPICE to be incredibly valuable in providing insights and in doing experiments and seeing what works and what doesn't have a chance. I have truly learned a lot when SPICING my own amplifiers, and have had several eye-opening experiences.



(italics mine)


Bob,
If you have time and are bored, read through the first part of the Aleph-X thread. (Yes, I know the thread's enormous; the first ten or twenty pages will do for current purposes.) I opened the thread and was immediately assailed by people whose first impulse was to simulate the circuit. Time after time I was told it wouldn't work. Why? Because their simulations said so! I knew differently because I already had a functioning prototype built with real, live parts. (IRF MOSFETs in case it matters.)
Now, the standard rebuttal is that "obviously" the person doing the simulation didn't know what he was doing. Once that argument runs its course, people begin pounding their chests claiming that their simulation software is better than the other guy's...etc. etc. etc. "Oh, bother!" said Winnie the Pooh, "Here we go again!"
My point is that simulations are capable of giving "false negatives."
I sometimes wonder how many marvelous ideas have been abandoned simply because someone didn't have the gumption to build a circuit after a simulation told him it wouldn't work.
If he did have the courage, why waste time doing the simulation? Go ahead and build the bloody thing and know absolutely, unequivocally, rather than guess.
Incidentally, the Aleph-X does not have an output network of any sort and somewhere in that thread I mention tossing a 4uF (I think...it's been a while) cap on the output. Nothing blew. Nothing got wonky. Film cap, I believe, for those who want something to gripe about.
Granted, the Aleph-X is not a "normal" topology, and I'm sure ten guys will post over the next hour pointing that out. However, I sometimes wonder just how much of the output network is necessity...and how much is "because it's always been done that way."

Grey

P.S.: Please don't ask me to try this load or that or any of umpteen other imaginable tests--at least not right now. I've got six month-old twin boys and a four year-old daughter that I watch over during the day and I work at night. What little time I have for electronics is currently aimed at conjuring an Aleph-X Ver. 2.0 out of thin air.
(And to the nay-sayers who might wish to point out that lightning ain't likely to strike twice, my response is simple: I know. But Nelson kinda tossed out the challenge and I try to accommodate the guy, 'cuz he's been good to me. So there.)

john curl 9th May 2007 10:07 PM

My first negative experience with computer modeling was in 1967 (yes, 40 years ago) with ECAP (Electronic Circuit Analysis Program) written by IBM, most likely for the military.
We (I was immediate supervisor) were running worst case simulations of many of our motor drive circuits. Sometimes they would show (FAIL) even though a simple slide rule calculation would show OK. The computer analysis was wrong, but what could we tell the client? We were caught short.
Computer analysis is just fine, for what it is and does, but don't think that everything that the computer gives you works, or visa-versa.

MikeBettinger 9th May 2007 11:19 PM

My experience with simulations, that keep me chuckling when they are put forward as hard facts, is that the simulations don't take into account the physical layout from input, to output, to power supply, not to mention the PCB layout. I've spent 30 years stumbilng through this maze and there are quite a number of the instabilities that result from the thousands (?) of ways to physically implement a circuit that do occur, that aren't really covered in the textbooks.

If a zobel network or coil is necessary in some cases but not in others, what is the variable? If two (or 30) people build a chip amp and they all get different results, what might be going on? What is actually happening when you place a ground plane around your circuit? If you hook a 8ga litz wire ground (that's a joke, son) to your heatsink, is it really grounded? Why are some implementations plagued by hum and RFI and others quiet as a they should be? What is a ground?

I won't go on, but the concept deserves some thought.

Mike.

john curl 9th May 2007 11:25 PM

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

Christer 9th May 2007 11:35 PM

Quote:

Originally posted by john curl
My first negative experience with computer modeling was in 1967 (yes, 40 years ago) with ECAP (Electronic Circuit Analysis Program) written by IBM, most likely for the military.

Honestly John, by similar resoning you and many other EEs would probably still be using valves because the transistors were so bad 40 years ago. :-)

Since computer science is a younger discipline than electronics, I think it is fair to assume that it has advanced much more than (at least analogue) electronics has in the same time. Furthermore, with the computing power we have today in an ordinary PC, we can easily do simulations of a kind that nobody would have dreamed of then, because the models we use today would have been too complex to be used on 1960s computers. Most probably the models used in that ECAP system were extremely crude and inaccurate to make computer simulation possible at all.

Quote:


We (I was immediate supervisor) were running worst case simulations of many of our motor drive circuits. Sometimes they would show (FAIL) even though a simple slide rule calculation would show OK. The computer analysis was wrong, but what could we tell the client? We were caught short.
Computer analysis is just fine, for what it is and does, but don't think that everything that the computer gives you works, or visa-versa.

This I totally agree with. How long didn't some aerodynamics experts tell us that bumble bees can't fly? (Fortunately for the bumble bees, recent research has shown that they were right all the time, so they can go on flying happily).

One should never trust computer results as a truth. First, you must have a fair understanding of how the circuit is supposed to work, and what the component models look like. Then you must consider if the answers are reasonable, just as with any calculation. Obviously Spice simulations can be very accurate and reliable if you know what you are doing. ICs are regularly designed using Spice as the verification tool, since a breadboarded model would be both impossible and too inaccurate. But ICs are simpler in the sense that it is a more controlled environment. For discrete circuits we do get a lot of added error sources, like parasitic, mutual induction between PCB wires etc. etc. So a perfectly accurate simulation of how a finished circuit will behave is hardly practically feasible.

It is probably true as you said, that occasionally someone has decided not to build a working circuit because it didn't seem to work in the simulator. However, then it is most certainly mishandling of the simulator, just as you can mishandle an oscilloscope or any tool you use. I think on many more occasions, people have been spared from building a prototype that never had a chance of working, because they detected it already in simulation. In fact. I once found a problem when simulating a circuit that I most probably never would have found if building a prototype. I don't think I have the instruments i would have needed and even if, I wouldn't have found the problem unless I already knew I should look for it. Since I didn't think of it when inventing the circuit, why should I have thought of trying to look for it?

That said, I see no need to convince experineced EEs like you to start using Spice if you are happy without it. You have found your ways to think and design long ago and are comfortable with them. I am sure Spice could help you to get new insights, like Bob suggested, but of course only if you are curious about it yourself. Spice won't do it for you.

For less experienced people, I think Spice can be a great tool to experiment with circuit behaviour in general, to check if one has understood the theory correctly. It should not replace the theory, though. It would be utterly stupid to use trial and error in Spice instead of learning Ohms law, to take an overly stupid example. 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. But of course, if the goal is to build a working prototype, one eventually has to build it, measure it, and most probably redesign it. There might be less of redesigning though, if one makes the right simulations first.


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