Spice simulation

[Nelson Pass]

Originally posted by john curl
and declared to me that I was a washout and a has-been at the old age of about 40.

Oh yeah, I was washed up at 40 too - those analog skills weren't
going to have any value in the coming golden age of digital...

[GRollins]

Originally posted by Christer


Greg, aren't you missing the point?

My name is spelled Grey, not Greg...like I said, it's a matter of reading comprehension.
Go back and reread my posts and you will find that I've already addressed your point.

Originally posted by Nelson Pass


Interestingly, some of the best insights into these issues come
from negatives. You start with a circuit that has the qualities
you want, and you make a small change that degrades them.

Nelson's post addresses my experience exactly. Case in point: When I was in school, I thought negative feedback was the ultimate answer. It cured all ills, right? The professor said so and I believed him. All you needed was enough open loop gain and you could conquer the world. Of course, a lot of other people felt the same way, so we ended up with junk like Nikko amps (amongst many others) with THD specs featuring a zillion zeros after the decimal point. Only they sounded like crap, didn't they?
(John, this is your cue to cover alternate distortion measurements.)
That was, as Nelson put it, a negative. A big one. What should have been better, wasn't.
A more subtle question that never seems to get asked, much less answered, is how those circuits made it from the test bench to the shelf at the retailer. Could it be because they skipped the listening room? No wonder the tube manufacturers of the day gained such a large market share--their solid state competitors were their own worst enemies. Tubes really did sound better than most solid state, and by no small margin.
I often wonder where tube gear would be today had it not been for the low distortion craze back in the 70's and early 80's.
I do not claim to have the circuit-related expertise that John and Nelson have, but I've done a little here and there and have found that theory needs checking a lot more often than some would have you believe. If it makes it more palatable, think of it as negative feedback; use your ears to tell you when you've gone too far. It's for sure that simulations won't tell you...they're positive feedback; they will confirm all your preconceived notions. Of course it's better! Look how many extra zeros we've tacked on behind the decimal point!
Audio history says otherwise.

Grey

[Christer]

Originally posted by GRollins


My name is spelled Grey, not Greg...like I said, it's a matter of reading comprehension.

Of course it is Grey. I was tired when posting. I am terribly sorry. Please accept my apologies.

Go back and reread my posts and you will find that I've already addressed your point.

I really cannot see that, so one of us must be seriously misunderstanding the other. It still seems to me that you are trying to say that Spice is useless because it doesn't do what you want it to, totally disregarding that it is not and never was intended to do that. I could say that cars are useless since we cannot fly to the moon with them, but it would be unfair and pointless to do so.

Please note, however, that I am not trying to convince you, or anybody else, to start using Spice. As I said, Spice is not necessary, but it can be very useful for those who realize what it can be used for.

[GK]

Originally posted by GRollins
I would like to thank those who responded to my last couple of posts for participating in an impromptu experiment in reading comprehension and human psychology. (One of my degrees is in psych--old habits die hard.)
I trust the parallels between my post on Science as Religion and some of the responses are obvious enough.

The content of your own post was a greater parallel and you come off as more of a patient than a practitioner.

Someone who makes a dogmatic assertion that spice simulation has no application audio engineering clearly isn't in touch with reality and doesn't have much authority with which to denounce others as religious dogmatists.

Also, what remarkable powers of perception do you posess in order to berate certain people here as being at the "but-end" of your incoherent analogy - people whose knowledge, careers and achievments you know absolutely nothing about?

[Edmond Stuart]

Originally posted by GRollins
.......................
You can simulate THD until the cows come home (English idiom meaning "for a long time"), but those numbers have only the loosest of correlations with reality because you're dealing with cloned parts; perfect in every way. Monte Carlo analysis can shake up the numbers a bit, but it's still a badly flawed approximation of reality.
................
Grey

Hi Grey,

I've simulated a lot of amplifiers, just to see how reliable the THD predictions are. According to my experiences, those number do have a close correlations with reality, say +/- 3dB, just what one would expect when taking into account the lot to lot spread of the various semiconductor parameters.
As for cloned parts, do you really think spice adepts are so naive using only clones?

Regards, Edmond.

[jacco vermeulen]

Originally posted by Nelson Pass
washed up at 40

Dude,

that was '91, you were too busy washing cash in your "little laundrette" then.

The car shop owner in the village i reside in needed a week and a thousand bucks to figure out the thing refused to start because the $2 chip inside the car key had taken off to the twilight zone.
However, the guy still knows how to flatten my engine head by sanding it on a mirror with diamond paste.

Not talking Spice, without simulation tools i'd be a goner.
Just like a range of other applications, Spice has progressed a long way compared to a decade ago.
But i'd gladly trade software for 30 years of experience, a wet finger, and a set of ears.

A quote from someone we haven't seen here in quite some time, regretably :

Originally posted by jcarr
The key is to understand the topology and operating conditions of the circuit, and know what characteristics are required from individual components at each location in the circuit.
To summarize: "Do you understand what you are doing?"

[Workhorse]

Jacco, do you have skinny legs

[jacco vermeulen]

Kanwar,

i've got Monster amps, but i'm a neanderthal retard.
Just pulling the Master's leg, but not for very long.

[Workhorse]

Bad manners Jacco, cut your nails...

[Bob Cordell]

Originally posted by john curl
Actually, we just take SPICE a little less seriously than some others. (dog barking)

If you don't use it at all, that would truly be an understatement.

SPICE is just another tool, but a very good one. Comparing it to ECAD of 40 years ago is just plain silly.

I didn't avoid using PC's because of the limitations of the Commodore 64.

As I said, you can design a fine amplifier without SPICE. You can often do the same without a spectrum analyzer in your toobox. I also do not SPICE everything in sight.

And yes, it is important to have the basic design understandings and insights BEFORE you SPICE the circuit, and YES, you are a fool to believe all that SPICE tells you without subsequently building the design and measuring it thoroughly.

You can also drive a car without a seatbelt, and yes, there is the infrequent occasion when the seatbelt doesn't work perfectly, or makes it more difficult to exit the car. That is not a reason not to wear one. Our Governor just found that out the hard way.

Cheers,
Bob