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Old 21st November 2009, 10:32 AM   #1001
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Yup, agree uneqivocally Nico,

The reality is that simulation is just that - a fair stab at reality with untested models and a simplified program, a guide, and not much more.

Right now I'm doing compensation regimes for a power amp, and finding that the results of the simulations are at best a guide. The ear seems to be good at discerning tiny changes, too. Not very scientific, but the changes cause such sonic variations that telling the differences is easy.

The basic principles are elucidated by the simulator, but you still need to know precisely what is going. I'm using nested feedback, lag comp and phase lead, and the relationships are complex.

Cheers,

Hugh
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Old 21st November 2009, 11:46 AM   #1002
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Hugh, - we use simulation extensively in our products design and research phases, in fact CAD/CAM is an integral and heavily funded part of both our companies making extensive use of simulation, especially in safety critical developments such as an Anti-Lock Braking systems for road- and rail vehicles.

Professional simulators, provided with accurate data and run under all known conditions are exact, especially if your control loop includes actual measurements during prototyping it in fact becomes the system specification. It become accurate to a few fractional parts per million.

Your lag and lead compensation can be predicted very accurately after a few runs but you have to specify exactly or find from simulation which capacitors should be used to achieve the goal or would perform best in the required application.

The problem exists in mainly two areas, simple simulators assume perfect capacitors, and resistors and other basic components as well as perfectly matched semi-conductors with a few fixed parameters, this is not anywhere near reality. I see models of op amps based on a three terminal block and a macro describing it characteristic performance, which is absurd. Try simulating an op amp by building the whole circuit in your simulator, you would not know what to believe.

A simulator should be integrated with the PCB design program as well as the EMI program and this requires operators with an very good understanding of what they are simulating and what is displayed.

Very few companies can afford their own environmental test laboratories and third party testing is expensive, thus one has to be able to rely on a cost effective simulation during development in order to reduce the risk of performing any re-testing or the expense of lawsuits in the event of a critical failure.

Homologation testing both functionally and environmentally for an an ABS module at MIRA in the UK costs hundreds of thousands, if there were any failure, it requires rework and retest. How many amplifiers out there has actually been formally tested by anyone - legally it should. I know of only one that claims to have been tested at least for EMI by an accredited UK test facility, one of the Bryston models of three years or so ago, I cannot remember exactly, but this impressed me. There are at least one audio company out there that does more than listen to their product.

An expensive exercises and simulators provides a good alternative if you cannot afford to have such facilities available on your own premises.

I would say for simulating audio and the like were the result is really subjective, programs such as FREE SPICE could be a useful tools as you say, primarily because of its limited and very basic analysis. Unfortunately most seem to think it is the ultimate design tool and whatever it says is Gospel.

Anyway enough about simulators, I shall go back to sleep.
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Old 21st November 2009, 12:19 PM   #1003
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That was anything but a grand soliloquy, more a near-sighted, ill informed rant.
Anyone who has been using simulation for not much more than a year shouldn't hold himself up as an expert in it's use, even if he did buy the program.

As far as I know, all of the simulators (commercial or free) work on the same basic premise, that's why the models are pretty much interchangeable - I can use the same models in Multisim (NOT a "cheap" program) as one would use in LT or Microcap or Orcad.

I have seen one of the models Kean modified (I actually looked in the thread he linked to) and it looks like he is making some real progress with this, I would encourage him to continue. Andy_c has done some outstanding work, providing improved models for a few well known and often used devices - as far as I know he doesn't have the equipment that the semiconductor manufacturers have.

I have used the free utilities available, like RMAA to test my amps using the soundcard in my computer. It is not as convenient as a purpose-built unit, like an HP distortion meter but it can be very accurate. I have tested the same amp using both methods (brought it to Chris (Anatech) and he tested it's distortion on an HP meter) and the results concur.
Not all of us can afford to go out and buy a rack of equipment and the latest software. That is why some of these free utilities exist and you should try them for myself first before condemning them as useless, you might be surprised.
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Old 21st November 2009, 03:40 PM   #1004
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Hi John, Yes I would agree with you totally. These tools are helpful especially for the enthusiast. But you would not expect to find them were it matters. We were the first company in South Africa to purchase MicroCAP, I recall in 1993 and we have upgraded since then. We also purchase models of components that we use.

Spice is a universal simulation application but some uses more and other less model parameters. You can make a spice program that uses only one parameter. The accuracy of the models is quite important in order to obtain valuable information.

I have played a little with other spice simulators since I do not always want to bring a dongle home as I forget it in my machine and the next day have to pay an engineers salary for doing nothing. So yes these free programs do have their place and for that reason Hugh is absolutely right they offer great guidelines, like the calculator on your cellular phone, great for emergencies but not really an accountant's tool.

John I am not an audio know-all. I have been a qualified R&D engineer for about 40 years, keeping abreast with changes and advancements in electronics and also in software.

But in the audio forum there is much to speculate about since there is almost nothing anyone agrees with besides, everybody is an expert in this nebulous field of controversy and subjectivity. There is little science and very few proven rules.

In engineering the first thing that you learn is the theory of an amplifier, every single person with an electronic degree should be able to design a good performing amplifier in an afternoon. This was in the days of slide rules. Nowadays I guess it would take a good engineer about 10 -20 minutes to design a good amplifier from nothing. With the advent of simulators another 10 or so minutes to optimize it.

I used spice simulators and in particularly MicroCAP since 1993. It has been a great tool for almost any electronic simulation, whether it contains logic, mixed signal, etc. If the models are good and you know how to modify parameters then you will succeed with your design and can go from simulation to PCB.
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Old 21st November 2009, 04:10 PM   #1005
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Hi Nico,
I got a different impression from you here.

On this forum there are those that pretend they are experts and there are those that are genuine experts.
Of course, I am neither. I just give my opinion (see post #994 in this thread) and go about my business of learning and building.

Last edited by MJL21193; 21st November 2009 at 04:13 PM.
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Old 21st November 2009, 08:12 PM   #1006
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John,

Please stop taking cheap shots at Nico and other forum (= thread) members.

The experts who are pretending might get upset (including me!), and besides, are you really that clever?

Cheers,

Hugh
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Old 21st November 2009, 08:21 PM   #1007
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The way I see it, Nico is entitled to his self-confidence since he's been in the field so long. If he says something that's wrong, we'll figure it out between all of us, no problem. His input is valued; knowledge is knowledge, regardless of the giver.

I don't see the logic here, it just seems like a witch hunt to me. Nico does not need to be "exposed" by anyone, we can all think for ourselves you know...

For the record I don't think Nico has done anything wrong.

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Old 21st November 2009, 09:12 PM   #1008
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Thanks Anthony,

I have PMed John, asked him to moderate his comments. He indicates he won't be staying. I make it very clear I will not delete posts or ask individuals to leave. BUT, those who remain must be civil otherwise there will be conflict with me. I would say that while I'm not the best technocrat in the world I'm pretty good with words, and that is what these issues come down to.

Nico, I thought your response very measured, restrained even, and I take my hat off to you.

Cheers,

Hugh
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Old 21st November 2009, 09:35 PM   #1009
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Aye...

So, I suppose there is a little more experimentation to do with prototypes and then a final schematic will be drawn? Where are we really in the development?

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Old 21st November 2009, 09:46 PM   #1010
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Kean,

Crossfeed, possible revamp of tone control, level/balance, amp all ready, then we should be OK for a large schemat. Then it's the pcb layout, after a few important component choices.

Hugh
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