Learning LT Spice

[lowell]

I've finally downloaded this program. I think I tried playing round w/ it once and got a headache... I did not know where to start. Could someone suggest some things to do w/ this program to get familiar w/ what it can do for me. I generally fix tube amps but have fixed some ss amps and would like to be good at both. If there's a good tutorial somewhere I'd like to try that, can't find one in the help menu. Otherwise maybe I should simulate a power supply for a push-pull Class AB circuit? Anyone to steer me in the right direction...

I am currently working on a Blues Deluxe and do not know what a specific voltage should be... was told LTSpice could simulate it and tell me... hence why I've downloaded it and am giving it another go.

[raiken]

The search engine is your friend...

User's guide:

http://ltspice.linear.com/software/scad3.pdf

Getting started guide:

http://www.linear.com/designtools/so...artedGuide.pdf

Demo circuit collection:

http://www.linear.com/designtools/so...o_circuits.jsp

LT spice guide:

http://kom.aau.dk/~hmi/Teaching/LTsp...pice_guide.pdf


Beginner's guide to LT Spice:

http://pages.suddenlink.net/wa5bdu/ltguide.pdf

LT Spice introduction:

http://www.uwm.edu/Course/ee301/LTSpice.pdf

LT Spice instructions and support files:

http://highered.mcgraw-hill.com/site...ort_files.html

LT Spice tutorial:

http://denethor.wlu.ca/ltspice/

Basic guide to LT Spice:

http://www.itee.uq.edu.au/~elec4400/...LT%20SPICE.pdf

[lowell]

well that should do.... thanks!

[MarkusBass]

Lowell,

Please find attached simulation for channel switching in Fender Blues Deluxe - I think you are talking about it . Unzip the files to any folder, open the *.asc file in LTSpice and click Run icon (in the toolbar). In order to see Average and RMS signal values you have to left-click(+ hold down the Ctrl key) on V(tp30) label on the graph - you will see a meassage box with values.
If you connect D5 and D6 diodes, you will see that the voltage drops down to 2.5 mV. The next stage (not shown on the simulation) compares 0.6V with 2.4V (or 2.5 mV) and switches channels of the amp.

On the LTSpice group Web site: http://tech.groups.yahoo.com/group/L...ec=group&slk=1 there a complete Fender tube amp simplated. Please check it.

Mark

[lowell]

Markus,
thank you very much for that. that helps for sure. do you use this for tube simulation too?

[MarkusBass]

I'm not that much in tubes amps so the answer is no. But on LTSpice site: http://tech.groups.yahoo.com/group/LTspice/ in the Files section there is a complete simulation of one of Fender tube amps (Bandmaster if I remember correctly). You can search for the simulation and see how it is done. And yes, LTSpice can be used for tube amps simulation .

Mark

[lowell]

cool thanks!

[BackwardsBoB]

Tonight, the Santa Clara Valley Chapter of the IEEE Power Electronics Society hosted Mike Engelhardt, the man at Linear Technology Corp. that brought you and continues to bring you LTSpice.

You gotta see this guy if you can. He goes around occasionally training groups to use the tool. He got a physics background, and started simulating all kinds of things on computers, back when computers were primal.

Meanwhile, in Berkeley, around 1970, some guys developed CANCER, Computer Analysis of Non-linear Circuits Excluding Radiation. Big man in the EE department got Larry Nagel to come up with a better name. He packaged it as SPICE, Simulation Program with Integrated Circuit Emphasis, and wrote a manual that spilled the beans on the heart of the algorithm used by the program.

So Mike cames along, looking for books on non-linear simulation, and he found Larry's manual. He started writing a simulator for electronics, and Linear Tech hired him to re-do SwitcherCAD, which wasn't very good. He finished the first SPICE-based SwitcherCAD, and Linear started delivering it to customers along with accurate models of their huge library of regulators (now up to 1000 LT models, and all start up accurately). They wanted to sell regulators, not software, and the .com thing was heating up, so they opted to give it away.

Being free, it's much cheaper than HSPICE or PSPICE, two programs that I haven't even purchased at work because they're so pricey for the little use I'd give them. The thing is, its faster, it's more accurate, it's the only multi-threaded SPICE implementation, it's easier to use...

It's really good SPICE. It's had 1,100.000 downloads. That means that Linear gives away more SPICE in a day than Cadence ships in a year.

Lowell - Stick with it. It's really easy to use. Here's incentive -- you can send your output to a file, and you can make that file a .wav.

Imagine simulating a negative bias generator driven off a HV secondary line, making sure that it comes up before the screen voltage, then printing the schematic.

[Steve Conner]

+1, we actually used LTSpice for all our simulation needs at my last job, because we didn't really do that much, and we were too tight to pay for Microsim/Cadence/whatever abortion.

Personally, I think any computer simulation is overkill for tube circuits. Part of the charm of tubes, for me at least, is that they're a simple technology. I've yet to come across a tube circuit that I couldn't get working with a copy of RDH4 and a few different sized mallets. However, I'll admit that I've used simulation when working with hybrid amps.

[MarkusBass]

The difficulty may be related to problems with proper simulation of output transformers in valve amps. Here is a link to Fender Bandmaster simulation:
http://tech.groups.yahoo.com/group/L...Examples/Apps/ (search for Fender5E7Bndmstr.asc file).
Lowell, it is possible that you may be required to sign up to the LTSpice group if you want to download this simulation (I'm not sure whether it's required).

Mark

[lowell]

Anyone use any Duncan spice models? I am trying the http://www.duncanamps.com/zips/el34_push_pull.zip. The schematic loads, however the inc. files don't seem to work. They show up on the schematic, however when I hit "run" I get "could not open include file "6ca7.inc" I'm still very new to spice. Could someone help me figure out why this isn't working?

[Steve Conner]

It ran fine on my computer! I extracted the contents of the zip file, creating a folder with three files: 6ca7.inc, dmtriodep.inc, el34_push_pull.asc.

Then I double clicked the el34_push_pull.asc file to load LTSpice, and hit "Simulate".

The two .inc files need to be in the same folder as the schematic (.asc) file.

[Wombaticus]

It ran fine on my computer! I extracted the contents of the zip file, creating a folder with three files: 6ca7.inc, dmtriodep.inc, el34_push_pull.asc.

Then I double clicked the el34_push_pull.asc file to load LTSpice, and hit "Simulate".

The two .inc files need to be in the same folder as the schematic (.asc) file.

[ATTACH=CONFIG]20219[/ATTACH]

You will also find that if you try and put libraries or include files in the LTSpice->Lib->Sub directory (where LTSpice puts its own subcircuits) that it is often necessary to restart LTSpice before it will see them properly. There is a further issue, I think with Windows7 (probably Vista too), in that if you put user files in this directory, they actually end up in Windows "virtualStore", and are not actually written to that directory, unless you override that behaviour, which is something of a pain, and I could never get to work quite right, even after taking ownership of the folder, etc. So on my Windows 7 machine, I just do as Steve suggests and put libraries directly into my schematics documents folder. And I keep my schematics folder in my user documents hierarchy, not as a subfolder of C:\LTSpice\Program Files (x86)\LTC\LTSpice, because again, you run into virtualStore issues if you try and keep things there.


Incidentally, those interested in modelling tubes with LTSpice should definitely investigate the tube libraries developed by Stephie Bench (formerly Steve Bench for those that might recognize the name). The latest versions of these can always be found over at the Intact Audio forum, which is Stephie's preferred online hangout. Look in the "Sim City" section, and the sticky "Drop down menus for selecting your tube" topic for her latest tetrode and triode models. I've so far only played with a few, but the 6L6GC model, for instance, seems to be much superior to both the Koren and Duncan's Leach derived models.

[lowell]

Yeah I saw the "vitualStore" window popup and didn't know what that was. That must be what's happening, as I am running Windows7. I'll try the "my documents" folder, and add all inc. and schematic files to their own folders.

Thanks for the help, and also thanks for the info on Intact Audio Forum. I'll certainly be checking that out.

[lowell]

Wombaticus, you nailed it! I moved all 3 files to a new folder under "my documents" and it worked!