[sdiy] Becoming better at understanding difficult analog schematics

[David G Dixon]

I have only ever had to make my own model once, simply because there was no model in Multisim -- for the 2164 quad VCA, a pretty important component in synth-world.  I made the simplest possible model of it -- a current amplifier with exponential voltage control -- and it has served me extremely well for about 14 years.
 
Like Tom, I use simulation as a virtual breadboard.  Also, sometimes I am just too lazy to calculate component values for a certain application (such as, for example, what are the correct input resistors on a non-inverting summer to get the output I want from several inputs), so I just set up a quick simulation to get the right compoent values.
 
If you think you will be able to use simulation to determine the effect of, say, sharp corners on a PCB trace, then you have the wrong idea about simulation.  It is mostly useful for confirming that a given circuit will actually do what you intend for it to do, before taking the trouble to build it.
 
Also, I almost never breadboard.  I just etch a PCB and build the circuit to test it.  If it works, then I've already got it.  If it doesn't, then it still didn't take as long as breadboarding would have taken.  Yes, it's quicker and easier to lay out a PCB, print it, etch it, drill it, stuff it, and solder it, then it is to build a significant circuit on a breadboard.

  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom Wiltshire
Sent: Thursday, May 16, 2024 1:29 PM
To: Jay Schwichtenberg
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] Becoming better at understanding difficult analog schematics


[CAUTION: Non-UBC Email]	
Maybe I'm a newb, but I don't agree about "more than likely add your own models". There's a lot of useful stuff you can do in LTspice without going near making your own models. 

Perhaps we're just working towards different objectives? Mostly I use it for testing ideas instead of breadboarding, generating frequency responses for networks that would be a pain to work out manually, checking filter responses, that sort of stuff.

I definitely don't think it's going to give me a perfect answer - the first time I got the ideal op-amp model to spin out to a 15KV output voltage firmly dissuaded me of that, and that's surprisingly easy to do. The concept of "op-amps with no supply rails" is pretty weird, if you're coming from a more practical background - and since it clearly leads to behaviour which is far from realistic, I did wonder a bit why they included them at all. Now I'm better at it, I know when I can use the basic models because it doesn't matter and when I need something that actually has a rail limit. So yes, I totally agree that you need some understanding of what the thing is doing and what you're looking at - but 15KV output is a give-away to *anyone*, right, newb or not?!?



On 16 May 2024, at 19:58, Jay Schwichtenberg via Synth-diy <synth-diy at synth-diy.org> wrote:


I wouldn't recommend noobs using simulation without them having some understanding of it. Main reason without knowing how it works they assume that a simulation is going to give you the perfect answer or close to it.


To get good simulations you really need to know what you are doing and more than likely make your own models. A lot of the models for components are simple and don't go into the details of the components. So that can make a big difference in the simulation.

There are things like noise, power supply ripple, transmission lines, PCB layout ... that you have to manually add to get really good simulations that they have no idea how to do.

Jay S.




On 5/16/2024 11:21 AM, Paulo Constantino via Synth-diy wrote:


What about the Falstad simulator? It's the best for quick and dirty sims!!!!!!!

On Thu, May 16, 2024 at 7:11 PM Chris McDowell via Synth-diy <synth-diy at synth-diy.org> wrote:


Simulation, yeah! I learn a ton from popping stuff into LTSpice and try out anything new or novel there first. 

Cheers, 
Chris 


On May 16, 2024, at 8:21 AM, ben gebhardt via Synth-diy <synth-diy at synth-diy.org> wrote:



 
Not sure if mentioned already, but I learn alot by simulating circuits and then doing time and frequency domain analysis.  


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