Timestep Too Small Error (12ax7 circuit)

[moparman]

This message is for l. Knoblich; I was the person who originally designed the circuit and had the question. I have already changed the simulation options as you pointed out. In fact, this is the first thing I did after reading through the board, looking at the help file and reading a full description of the Error Advisor. I am using versions 8 and 9. I think I may just forget trying to even fool with tube circuits in multisim as this is more of a headace than it's worth. I have built the actual circuit before I even tried to model it in multisim and it works perfectly. I just wanted to simulate it in software so I could change things around and see the effects without having to solder/unsolder. I've found that I should have just done it the old fashioned way and just soldered/unsoldered or either use a breadboard and my real o'scope. Live and learn... I've not had any troubles with all the analog and digital circuits I've built and simulated with multisim. Just this problem when I tried a standard 12ax7 tube circuit. I'll know next time just to go straight for the real stuff when it comes to tube circuits. I do wish it would work though. The only luck I've had with it is if I change the Initial Time Step to a somewhat higher value in the Transient Analysis Instrument settings (under Interactive Simulation Settings). But when I do, the simulation is so S-L-O-W that I could have already built the circuit and tested it with real instruments! Just not worth the time or effort. Maybe I'll get some other simulation software and see what will actually work with tube circuits without have to constantly tweak the options. Thanks all for your inputs and comments. I appreciate it very much!

Brad (Electronic Engineer)

[Lars A]

Thanks for that input, Ingo, it solved my problem gettin a 12AX7 to swing in an RC oscillator.

I tried very hard to read the help file for my MS8.028, increased all sorts of stuff with no success, but your info was like the key...

Well it i is still interupted by "too small timestep" but last for a lot longer time. And its like Brad said, way too slow. I computer of today OUGHTA work faster.

I observed that the error comes when the risetime is steep and the voltage level high. Could it be that the calculations are not really prepared for hundreds of volts vs. short risetimes?  And tubes has their similarities to FETs ´but not those high voltage levels. Unless we talk about hexfets, but they are like nore ON/OFF devices, right?  Is there no chance that the Workbench tea, could concider looking at the calculations inner system for higher voltage levels / analog amplification factors / steep voltage level risetimes? 

I made this RC oscillator to check an old guitar amp that had a defective tre,molo circuit. All components measured the right values, but I found that the third RC circuit, connected to the gate of the tube, didnt have a 60 degree phaseshift, so I suspected a leaking capacitor. Now that capacitor measured correct with a simple LCR meter, but leakage requires the old Sencore to be dusted off.  B4 I did that I wanted to check with Multisim first what happens if I put a 1 MOhm resistor acroo one of the three RC links.  It faded the oscillation excactly as in the guitar amp...   I spended hours to make this, and I did it just to learn the workbench system better.
I really did. I found that I can add a comment to the circuit, describing hat changes had to be done in the simulation options.

Best regards,

Lars Ahlstrom

supertech, Sweden  

[ellendula]

hi...
when i'm simulating the circuit...i'm getting the error message...
------ Checking SPICE netlist for 555timercktthreephasefullwavenew - 2009-10-15 17:52:11 ------
======= SPICE Netlist check completed, 0 error(s), 0 warning(s) =======
Error Message From Simulation: doAnalyses: Timestep too small
Error Message From Simulation: tran simulation(s) aborted

i'm also facing same problem and put the values what u suggested......

but even then i'm getting the same error....
what may be problem...
please help me out...

[navya]

i have a problem with the circuit in simulating. please help me with getting the output

[navya]

i have a problem with the circuit in simulating. please help me with getting the output

[Miguel_V]

Hi,

Delete the floating nets that you have there (9, 10, 18) and delete the voltage source (v4) that isn't connected to anything. Then if you are not using vdd, vcc, etc, delete those as well, if you are using them then connect them. This makes your simulation run properly. Try not to have so many unconnected components, if you don't need them then don't place them on the schematic.

Kind regards,