What is SPICE

Post by **Nick** » Mon Dec 03, 2007 8:25 pm

Well, the advantage of a phono, is its good at showing the effect of component change and the effcet on frequency response. also its a good way of showing how to step parameters.

Ok, maybe the first step is for peeps to install LTSpice. And a simple circuit, ,aybe a simple power supply, so its something we are used to, and may have used PSD to simulate in the past. So we can see how it can do what PSD can do, but then a lot more.

If its done using just the models that comes with LTS it will let us get started, and then we can add valve models later.

How about this

izzy wizzy · Post by **izzy wizzy** » Mon Dec 03, 2007 8:54 pm

I would start with something even simpler before we gets into transformers. They are a bit tricky so it might be better to get to grips with the basics before going into any transformers.

A line stage would be good and then build from there. A phono stage would be good after but then I would say that

simon · Post by **simon** » Mon Dec 03, 2007 10:20 pm

Excellent thread!

Okay I've opened the demo1.asc and in the complete absence of knowing what to do I clicked on Simulation-Run, which opened up another window, demo1.raw, but displayed nothing in it. So I turned some traces on (Plot Settings-Visible Traces). Current is obvious enough but for the voltage option I'm offered V(n001) to V(n005). How do I select the voltage on R1, for instance? Okay, I'm guessing it's V(n004) cos it's the only one that looks right, but that's not exactly scientific!

Post by **Nick** » Mon Dec 03, 2007 11:10 pm

Simon. ok. you cam select traces via a equation involving a node, but there is a much simpiler way.

Once you have run the simulation, move the cursor over the circut. You should see the cursor turn into a probe (for voltage) or a current loop (for current), click when either is showing, and it will display tge current or voltage at that point.

Further, if you click on the voltage at the choke input, whilst holding down shift, then move the pointer to the output of the choke, it will display the voltage across the choke.

izzy: yes, I thought that, but that circuit is something that most will have played with in power supply designer, its something all are aware of. To do something like a line stage would either involve transistors which many reading this are not that familier with, of introducing valve models, which involves copying files into the system and .include directives. I thought I would throw the coupling in, and worry about explaining it after folk had got used to messing with stuff.

simon · Post by **simon** » Mon Dec 03, 2007 11:27 pm

Nick wrote:Further, if you click on the voltage at the choke input, whilst holding down shift, then move the pointer to the output of the choke, it will display the voltage across the choke.

Can't get this to work. I can get it to display node 3 and 4 simultaneously, but not the voltage across the choke.

Must try harder. How are the boys down the front of the class doing?

pre65 · Post by **pre65** » Mon Dec 03, 2007 11:35 pm

Hi-got the pointers for voltage and current,even shows which way its flowing !

Sussed out how to remove a trace from the upper part as well.

It says the current flow in L4 is flowing right to left which is opposite to wot i thought !

Can you give more specific numbering to the measuring axis (ie amplitude) ?

al newall · Post by **al newall** » Tue Dec 04, 2007 12:02 am

I joined in as well.
Just about keeping up, from the back of the class.
Looks like school is over for today!

colin.hepburn · Post by **colin.hepburn** » Tue Dec 04, 2007 7:16 am

Hi All
after i click run i get a a pop up cannot find mur 460 error log
error no line 2 d1 n001 n003 mur480
error no line 3 d1 n005 n003 mur480
unable to find definition of model mur 460 default assumed

Andrew · Post by **Andrew** » Tue Dec 04, 2007 7:28 am

Nick wrote:
izzy: yes, I thought that, but that circuit is something that most will have played with in power supply designer, its something all are aware of. To do something like a line stage would either involve transistors which many reading this are not that familier with, of introducing valve models, which involves copying files into the system and .include directives. I thought I would throw the coupling in, and worry about explaining it after folk had got used to messing with stuff.

Just a thought, Steve's drop down models, if placed in the right folders, save on .includes and work extremely wellso make the task of using valves quite a bit easier. But, I agree, this seems to be a good place to start. I like the use of three L's to make a centered tapped TX. I'd not thought of that and generally use two opposing voltage sources connected to ground. I think the L's are more intuitive.

Good stuff.

Might be nice to try and show the hump caused by the resonant point of the LC based PSU next? Or this that better left for later?

-- Andrew

Post by **Nick** » Tue Dec 04, 2007 8:04 am

Simon: keep shift pressed between the clicks

Pre65: Current flows from negative to positive, always worth remembering, its the flow of electrons which are negative. At the beginning, they had to guess which way to assume current flowed, and they got it wrong.

Al: Hi, there is at least several days of things to discover from that model

Colin: Where did you get your copy of LTSpice, maybe you have a differemt set of models. Right click on the diode symbol, and press "select new diode", pick one of the list for the moment.

Andrew: Gret, I haven't used Steves modesl, so when we get there over to you I think

. Yes, the LC response would be a usefull thing to do with the model.

Other things to try, right click on the components, and see how you can add the hidden characteristics of them as well as the obvious. Should start to show that Spice is a very accurate tool, not just a "near enough" thing.

Also, try looking at the current through the diodes, then zoom in on the peaks, ans see how it shows the switching noise.

colin.hepburn · Post by **colin.hepburn** » Tue Dec 04, 2007 8:23 am

Just change the diodes as you suggested
Still got same error i got LT from link above maybe i try reinstalling and see if that Will fix the problem
Edit Yep thats got it

ed · Post by ed » Tue Dec 04, 2007 9:20 am

Nick, have you thought of a video lecture?.....you could be that mad prof!

I'm sure we can get a comenius board? together and elect you to the chair, no remuneration tho, sorry.

Post by **Nick** » Tue Dec 04, 2007 9:35 am

It should be in the style of 70's open university, cardigans to the fore.

Dave the bass · Post by **Dave the bass** » Tue Dec 04, 2007 9:36 am

Sorry I'm late Sir <adjusts tie and cap>

I was having snog with Betty Cartwright behind the bikesheds (you know the one with the big Guzoomers).

I'll have a play on a PC tonight, I'm out the workshop today and on a borrowed Mac for now.

DTB

simon · Post by **simon** » Tue Dec 04, 2007 12:21 pm

Nick wrote:Simon: keep shift pressed between the clicks

Hmmm, did that. Can't have been doing it right, though how one does that wrong I'm not sure

. I'll try again tonight for my homework. Geez, I thought I'd be designing optimised circuits by now

.

audio-talk

What is SPICE

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