Falstad Circuit Sim

[morange]

Love of my life.

http://www.falstad.com/circuit/

and the newish, limited but cool, analog filter sim, fun for looking at the frequency response of high resonance circuits

http://www.falstad.com/afilter/

[moid]

Wow that's pretty cool - even though I don't know enough yet to use it properly, the list of circuits has a few things on it that I'm trying to understand and hopefully this will help me. Thanks for posting it.

[morange]

Yeah, he's made a great set of examples. It's easy to save circuits as text files or links, too. Here's a superfuzz octave circuit, for example:

http://www.falstad.com/circuit/circuitj ... 25+0+-1%0A

Or, the text to copy paste into the analog filter sim, for a bee baa tone circuit:

NSFW: show

$ 1 5.0E-6 5 50 5.0 50
% 0 24389.095776063856
O 416 96 528 96 0
g 384 224 384 256 0
170 176 96 144 96 3 20.0 1000.0 5.0 0.1
c 352 96 416 96 0 2.2E-9 0.0
c 384 160 384 224 0 1.0E-7 0.0
c 288 96 288 160 0 2.2E-9 0.0
r 352 96 352 160 0 47000.0
r 416 96 416 160 0 22000.0
r 224 96 224 160 0 33000.0
r 224 160 288 160 0 47000.0
r 224 160 224 224 0 10000.0
w 352 160 384 160 0
w 384 160 416 160 0
w 288 96 352 96 0
w 224 96 176 96 0
w 224 96 288 96 0
w 224 224 384 224 0
w 224 160 176 160 0
w 176 160 176 288 0
o 2 16 0 34 5.0 9.765625E-5 0 -1 in
o 0 16 0 34 2.5 9.765625E-5 1 -1 out

[morange]

Import this one into http://www.falstad.com/afilter/

NSFW: show

$ 1 5.0E-6 5 50 5.0 50
% 4 24389.095776063856
a 560 224 656 224 0 15.0 -15.0 1000000.0
r 560 240 480 240 0 100.0
w 560 208 560 144 0
r 560 144 656 144 0 100.0
w 656 144 656 224 0
c 560 240 560 320 0 4.9999999999999996E-6 0.0
g 560 320 560 336 0
O 832 128 896 128 0
g 736 304 736 320 0
c 736 224 736 304 0 4.9999999999999996E-6 0.0
w 832 128 832 208 0
r 736 128 832 128 0 100.0
w 736 192 736 128 0
r 736 224 656 224 0 100.0
a 736 208 832 208 0 15.0 -15.0 1000000.0
a 384 240 480 240 0 15.0 -15.0 1000000.0
r 288 176 208 176 0 100.0
w 384 224 384 160 0
r 384 160 480 160 0 100.0
w 480 160 480 240 0
g 384 336 384 352 0
r 384 256 304 256 0 100.0
c 384 256 384 336 0 4.9999999999999996E-6 0.0
a 208 256 304 256 0 15.0 -15.0 1000000.0
r 912 288 1008 288 0 800.0
r 832 240 912 240 0 100.0
g 208 336 208 352 0
w 288 176 304 176 0
w 304 176 304 256 0
w 208 176 208 240 0
170 832 240 832 304 2 20.0 4000.0 5.0 0.1
r 912 128 912 208 0 800.0
r 912 208 832 208 0 100.0
a 912 224 1008 224 1 15.0 -15.0 1000000.0
g 912 128 912 112 0
w 912 240 912 288 0
w 1008 224 1008 288 0
w 1008 368 1008 288 0
x 176 391 691 394 0 12 input and input added to feedback must be in phase at summing node for unity passband gain
x 513 73 1008 76 0 12 add equal parts filtered and unfiltered signal in feedback loop to retain unity passband gain
x 832 93 1008 96 0 12 feedback gain of 8 for oscillation
x 495 54 1008 57 0 12 60 degree phase shift per stage at resonant frequency instead of typical 4-pole 45 degree shift
r 208 272 208 336 0 100.0
r 208 272 144 272 0 100.0
170 144 272 112 272 2 20.0 4000.0 5.0 0.1
r 208 176 144 176 0 100.0
w 1008 368 80 368 0
w 80 368 80 176 0
w 80 176 144 176 0
w 288 80 336 80 0

3-Pole, 18 dB/oct low pass cascade filter, yes it's possible, but I've never seen it done anywhere. Basically a modified phase-shift oscillator, which is what the classic Roland (and others) 4-Pole lowpass circuit is, too, but with 4 stages. This could easily be implemented with OTA's for voltage control. Use 2 LM13700 chips and you could use a stage for voltage controlled resonance, and get nice sine shaping at the same time.

[lordgalvar]

3-Pole, 18 dB/oct low pass cascade filter, yes it's possible, but I've never seen it done anywhere. Basically a modified phase-shift oscillator, which is what the classic Roland (and others) 4-Pole lowpass circuit is, too, but with 4 stages. This could easily be implemented with OTA's for voltage control. Use 2 LM13700 chips and you could use a stage for voltage controlled feedback, and get nice sine shaping at the same time.

Dang, you just kinda pulled off one of my ideas with the wave shaping! haha...great minds think alike! Been messing around with the LM13700 myself a bit...cheers , keep up the awesome stuff!

[morange]

Old Roland trick, like adding input in feedback gain for unity passband. Check out the Mutable Instruments Shruthi 4-pole filter. Great minds think . . . like Roland.

Some Roland filters used diodes to ground for the shaping, the SH-101, for example; could be interesting to compare the two.

[Dr. Sherman Sticks M.D.]

this site was really helpful for me to visual wtf is going on. thanks for posting!

[morange]

Another thing I've noticed lately, is the pop up Java version of the program runs smoother than the new version that runs in the window.