[sdiy] RC filter questions + SPICE RC filter simulation questions

[Veronica Merryfield]

This post...

> On Apr 16, 2010, at 4:40 PM, cheater cheater wrote:
> 
> No, it's just messy set of handscrawling; it's not something I'd particularly want to post. Basically I ran through a series of making Thevenin equivalents, and then did a truckload of algebra.

has prompted me to post a reply I wrote and thought about not, to this previous post.

> You're analysing intermediate stages in the whole circuit so expect the responses to be different from single circuits.  In your extended circuit =
> 
> R1 + (C1 || (R2 + (C2 || (R3 + (C3 || (R4 + C4))))))
> 
> (where '||' denotes parallel connection and '+' denotes series connection).

I can't believe I am about to write this, but in days of old (ok, pre the advent of home computers which is when I started in synths), these were analysed by hand using the impedance equations and network analysis formula, such as above, Kirchoff, Thevenin etc. Later in life, I used spreadsheets to do the number crunching. Today, despite having a few spice packages at my fingertips, I still find myself turning to a spreadsheet fairly frequently for this sort of thing. Using Kirchoff/Thevenin/etc or frequecy-impedance formular, series/parallel analysis and so on, setting up the cell equations is pretty quick, add some frequency numbers down the side, copy and paste the formula to get the result and then as much graphing as your heart desires. Whilst I am not laying down a challenge, for something like this I would think it would take me longer to put the schematic in, set up the stimulation, run the simulation to get the results than to create the spreadsheet. I also think that I would gain more insight using the spreadsheet.  

Just an observation.

Veronica