11-16-2006 08:25 AM
11-16-2006 06:39 PM
11-16-2006 09:47 PM
11-18-2006 10:00 PM
O.K. Here's what I have so far. Keep in mind I am using 2001 and I am not a tube expert. First I did away with your power supply and ran the voltages direct to the tubes. The only thing I have found is that the two 1Mohm resistors seem to be causing a problem for some reason. I eliminated the input resitor R9 and output resistor R6 from your original file (not the revised circuit). After doing that the circuit seemed to work normally. Why these two resistors would cause a problem I don't know.
The simulator also seems to be having problems with your power supply when it is hooked to the tubes. I haven't quite figured that one out yet. I will continue working on it to see if I can find a solution.
11-18-2006 10:37 PM
11-19-2006 08:10 AM
I don't really understand why Multisim (in all forms) has trouble with circuits that work in the real world. You would think that iif it works in reality, then the simulator shouldn't have one ounce of problems with it, but that just isn't the case.
I may have jumped the gun when I said I had it working. I found out that as long as R10 was set at 100% then it did work right and the volume control spanned correctly. Anytime I tried to adjust R10 below 100%, the error would return. I am going to continue playing around with this to satisfy my curiousity and also to get more tube experience. I will let everyone know what I find if I find anything.
11-20-2006 10:41 AM
SPICE takes a text netlist describing the circuit elements (transistors, resistors, capacitors, etc.) and their connections, and translate this description into equations to be solved. The general equations produced are nonlinear differential algebraic equations which are solved using implicit integration methods, Newton's method and sparse matrix techniques.
To cut a long story short: If Multisim displays a "Time Step to small" or similar message, it only means that SPICE can't find a mathematical solution to the given circuit. Even if your circuit looks real, it is possible that through ideal models (e.g. don't take 'real' parasitic effects into account), ideal sources (e.g. high rise and fall time for a clock source) it doesn't behave like in reality. "Playing" around with your circuit (e.g. changing resistor values etc.) may or may not solve the problem. But as a rule of thumb, it is always recommended to match the components to their real counterparts.
A good approach to overcome convergence problems is to understand more about the SPICE Engine Options. They define what is rated as a "good" solution and what will become a "Time Step to small" or similar error. You can find the settings for the SPICE Options in the Analysis tab (part of setup for all analysis and the Interactive Simulation Settings for instruments).
Steps to solve "Time Step to small"
Please consult Multisim's online help for further assistance on convergence problems and SPICE options.
A great online resource are the SPICE Simulation Fundamentals on ni.com.
11-20-2006 03:32 PM
Thanks for your explaination on this subject. I have never really fooled around too much with the default settings in Multisim other than chaning the maximum timestep setting. I am going to give this a shot and see what happens.
I am no expert when it comes to Multisims internal workings that is why I have always tried re-working circuits to make them work in the simiulator at the default settings. I knew you could change the way the simulator does it's thing, but I never told anyone to adjust these settings based on my experience level with Multisim. I just didn't feel comfortable with my level of knowledge on the matter to recommend anything like this.
Thank you so much for taking the time to help and increase our level of knowledge about Multisim.
11-20-2006 03:50 PM
11-20-2006 04:26 PM