Schematics / Magic Smoke LFO Design By Tim Servo
Magic Smoke LFO ,design by Tim Servo , more on this thread : http://electro-music.com/forum/topic-32372.html as he explains : Here's one of the LFOs I've cooked up recently. This runs on a +/-15V supply and puts out standard +/-5V outputs. For the most part, it's a basic triangle oscillator built around a comparator and an integrator. I wanted something with a LOT more range than the other LFOs I was finding, so I made a few tweaks and came up with a design I really liked. This one goes from 0.017Hz (1 cycle / 60 seconds) to 150Hz, or a factor of 8,800:1 (hence the name). A few points: 1) You can use Linear pots for the tuning controls, but it's MUCH easier to make fine changes in the lower portion of the range with Audio taper pots. 2) You can eliminate the Fine Tune control if you want. This reduces the range to 0.033Hz to 150Hz (approx 4,400 : 1) but this will probably do the trick for many applications. 3) The Fine Tune pot is set up so that it really does have less range than the Coarse Tune. When Coarse is at maximum, Fine will adjust from 50Hz to 150Hz. When Coarse is at minimum, Fine will adjust from 60 sec/cycle to 30 sec/cycle. 4) The timing cap can be found in polystyrene (23PS233 or 23PW233 from Mouser) if you want the best frequency stability, but you can also sub a film cap or other type. 3300pF works out to 3.3nF or .0033uF
I'll be making a few additions to this (sync, additional waveforms, Indicator LEDs), but the basic core will remain the same. Any thoughts?
Tim (got my LFO hat on) Servo
and about the waveshaper add on :Here's a coupla add-ons for the 8K LFO. The first (TSW) uses the Tri and Square to make a Saw, or even a 2X Saw. The second (TSQ) takes a Tri and puts out a wave that is continuously variable from Tri to Square, with a "Trapezoid" shape in the middle. You can even take the output of the TSQ and put it into the TSW, and now you have a Tri to Square on one output and a Saw to Square on the other (both varied at the same time with the Waveshape control on the TSQ). By the way, a 1458 or other "low bandwidth" op amp works a little better for the TSW because it helps minimize the glitch in the reconstructed Saw output. I've got some more add ons that I'm still working on, but I thought I'd throw these out here because these variable outputs are so much fun.
Tim (also looks like a trapezoid in the middle) Servo