Nick wrote:Simon: keep shift pressed between the clicks
HM, 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. Gees, I thought I'd be designing optimised circuits by now .
Hi Simon
Well your not alone with this doesn't work for me either the probe just goes gray and nothing changes i guess we Will have to stay back after lessons tonight
This was a new one for me and at first, I was with you guys up the back
To see what's happening across a component, place the probe on one node, press CTRL and keep it down. Left click the mouse and hold it down too; the probe will turn grey. Move the probe to the other node. The probe will turn black when you are at that node. Let the mouse button go and remove pinky from CTRL.
Or click on node with probe and hold button down. Press CTRL and hold it down. Move probe to other node. It will turn black. Let the mouse go and CTRL.
Are we all happy so far, how about this as the next thing to try.
Assuming we wanted to do something with this, to se what could be dome about the initial peak. So lets see how changing the first cap alters things.
Run the sim with the first cap as 1uf. you can see the voltage stablises out at about 220v, and if you look at the current in the choke, and zoom in, you will see its a nice smooth sine shape. So thats running in choke input.
Now change the first cap, to 100u, and repeat, now the voltage is about 320v, but it takes a lot lonfer to settle and undershoots a couple of times. Also if you zoom into the choke current. its no longer a nice smooth sine.
We can show how the value of the first cap alters the results.
press S (when on the circuit window), a dialog pops up, and select the "Enter spice directive" option. Then in the text box, enter
".step param c1 1u 101u 10u"
This is a instruction, to make a parameter, called c1 change in value from 11u to 101u in steps of 10. Press ok, then click on a black bit of the circuit window, to add the text. Make sure there is a dot at the start.
Now we need to tell spice what component the parameter is used for, so right click on the first cap, and in ithe capacitance field, enter {c1}
Thats the text c1, the name of the parameter, in curly brackets to tell spice its a parameter
Then when you run the model, spice runs it ten times, once for each of the values of c1.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Well I clocked in for class had a go with nicks lesson and it worked fine I had a try changing C2 in the same manner but couldn’t get that to work I have a feeling there’s a lot of bits to remember with this prog
Yes, thats the thing Colin, its actually not for us, its for real electrical enginear types, LTSpice is a nice simple one, with a helpfull interface, but the real macho version just takes a netlist as input.
The thing to remember is Spice is as good as its models, now, manufactures produce very accurate models, so real big systems can be simulated, but the valve models we will get to eventually are only as good as the person creating the model. Having said that, they can get very close. Mr Bench has given us some very good models, as have others.
Just keep repeating "IT DOESN'T TELL YOU WHAT IT SOUNDS LIKE"
But for example, I have been messing with a 211 A2 amp, and the spice sim is good enough to allow me to work the two in paralell. The real thing lets me listen, the spice lets me mess with things and see if they are worth trying. Ok. maybe I will miss something great doing this, but I might also progress faster as well. as always, its about the balance.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
al newall wrote:But where's the rest of the class?
Oops, been caught twagging. Double homework tonight.
Ahh don't worry Simon
last nights lesson was easy with the destructions in front of you but nick says its the easiest spice prog he knows but remembering all these bits a pieces well thats a different story
PS. Seeing what's happening across a component it seems you don’t have to use the Ctrl key just holding down left mouse button and drag to next node and let go left button works
That's really good! I can start to see how powerful Spice is now, love the 10 traces. Funny isn't it how something like LTSpice is free but a glorified text editor like Dreamweaver costs so much.
Hurry up chaps, I'm feeling very swotty at the moment - I'm ready for the next lesson.
Yes I think some software is so over priced take PCB Designer EAGLE Professional for example at £2326.01 OK its a high spec prog but what?
LTspice looks good I have played around with different TX voltages and cap values just to try and get a feel for it interesting
. I'll try again tonight for my homework. Gees, I thought I'd be designing optimised circuits by now
.
the probe just goes gray and nothing changes i guess we Will have to stay back after lessons tonight 
