Transient Analysis for Audio Oscillator

[LarryJoy]

I have a twin-t 800 Hz oscillator that I want to simulate and see start up and oscillation. What I see/get on the output graph is the operating voltage of 9 V with the output voltage showing a blip, as if it is trying to oscillate, but goes to a 3.5 V DC steady line. I don’t know how it goes to a DC level as the output is taken after a 100 uF coupling capacitor. How do I properly setup and analyse this circuit?

[LarryJoy]

Okay all you good people, no response to my inquiry. Here is some more anomalous stuff I am getting. From the “Errors and Warnings:” box. Warning in ‘TR1’: Inserting 1 GOhm (should be Gohm) at node “_*” because it’s floating. What is this message trying to say? TR1 is the Transient box. There are no connections! What do I have to do to set this up correctly?

[SM6PGP]

Hello LarryJoy !

You did not attach a schematic, but I suggest you look at page 200+  in Gunthard Kraus, QucsStudio Tutorial, version 1.6, its about oscillators.

…from the tutorial “An oscillator simulation needs a “startup push” and this is done by programing the supply voltage as a ramp signal.” – did you use that ?

Attached a pdf of a simulation of a twin-T 800 Hz oscillator

/Hannes

 

Attachments:

1. 

   test-twin-T.pdf
   

[LarryJoy]

SM6PGP, Thank you for your response. How do I get to “Gunthard Kraus, QucsStudio Tutorial, version 1.6?” as I would like to read the information. I tried an online search but that was useless. What I did find was small print and no way to enlarge, I would have to use a magnifying glass–no good. I went to the main page for QucsStudio, there was a Technical article but no example circuits in the transient section. More help please.

–73 de WN8P

[SM6PGP]

Hi !

try this

https://www.gunthard-kraus.de/qucsstudio/index_english_qucsstudio.html

or his startpage

https://www.gunthard-kraus.de/

There is a lot of useful information, his homepage is still around, unfortunately he is SK  (DG8GB)

73 – Hannes – SM6PGP

[LarryJoy]

Okay, we are getting closer but still no cigar. I found the “file based voltage” source and now need to know how to setup the file. Where to set up the file and how to link it to the file based voltage source. Seems like should be able to setup the information directly in the schematic somewhere next to the source? More help needed. Thanks.

–73 de WN8P, Larry

[SM6PGP]

Hello again !

OK

from page 201 in the Tutorial

“An important detail is the (red marked) power supply:
An oscillator simulation needs a “startup push” and this is done by programing the supply voltage as a
ramp signal.
Vdd starts at time t = zero with a value of zero Volts and stays so up to 10 μs.From t = 10μs to t = 20μs the
amplitude rises linearly up to +12 V and stays afterwards on this value.
Therefore a “ramp.csv” file (= comma separated value file) must be written to use a “data based voltage
source” (= PWL source = piecewise linear voltage source). This file must be saved in your actual
oscillator project folder:
0 0
10e-6 0
20e-6 12V
40e-6 12V ”

…and now high lighted in the my pdf showing the simulation, the content in the ramp.csv file

GL – 73 – Hannes – SM6PGP

 

Attachments:

1. 

   test-twin-T_high_light.pdf
   

[LarryJoy]

We are getting closer. Here is what I get when going to the Projects tab:

Well that didn’t work! I did a snipping tool copy of the whole screen and it said it put it in the tablet? or wherever Windows 11 copies things to. I did a CTRL-V but nothing happened. So here it is in text.

Projects

CPO

Grok_Twin-T

Twin-t

Test circuit

*****I pick on “Twin-t” and select “Open”.

Content of ‘Twin-t’ | Note

> Schematics

Grok_Twin-T.sch

Twin-t.sch

Verilog

VHDL

Octave

C++ Sources

PCB layouts

> Data Displays

Grok_Twin-T.dpl

> Datasets

Grok_Twin-T.dat

Others

 

The large area to the right (yellow background) has “untitled” with red background with white X.

 

Next step? Where do I go to enter the file name “ramp.csv” and enter the information??

Again 73 de WN8P

[SM6PGP]

OK lets take next step !

You can create your CSV (comma separated value) file in any text editor, Notepad, Notepad++ or in excel name it to whatever…. but extension .csv *(you create this file outside of uSimmics, at least I do it this way)

Now save that csv-file in your project-folder (maybe Grok_prj folder, your project name), thats the folder where you have saved your schematic, Grok_Twin-T.sch

Now in uSimmics, edit your file based voltage source, right click, edit properties, browse and select your .csv file, apply and OK.

Now you should have a file-based voltage source up and running

73 – Hannes – SM6PGP

 

[LarryJoy]

I finally got a circuit with transient analysis and ramp source. Here is what I get:

I took a full screen snapshot of circuit and transient analysis with graph. The system stated the snapshot was saved to clipboard, but doing the CTRL-V does nothing.

All I get in my analysis is DC voltages no oscillations.

How do I enter a saved snapshot into this forum? I am using a Windows 11 OS on a laptop PC.

–73 de WN8P, Larry

Attachments:

1. 

   Screenshot-2025-07-12-160833.png
   

[SM6PGP]

So now you have to modify your circuit – maybe not enough gain ?

Try my circuit and check if it oscillates.

73 – Hannes -SM6PGP

[Author]

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