American Sine Language - How to adapt triangle LFOs to sine waves?

[Jdansti]

I'll throw my filter-noob opinion in the ring here. This did a decent job of rounding off square waves on the output of a 555.  The switch terminals shown here feed an LED in an optocoupler. I haven't tried this on any other LFO or directly applied to an audio signal.

I don't have a scope to view the waveform, but based on my calibrated ear, it seems that this affected the leading edge of the pulse much more than the trailing edge (and possibly only affected the leading edge).

Anyway, just wanted to throw this in the mix.   




SW1a... = Output to LED

[Mark Hammer]

Stupid me, I HAVE one of those boards, stuffed and sitting around, plus an uncommitted (and also populated) voltage-controlled delay board sitting around.  Man, I really have to take some vacation time and use these things!

The Shoemaker's Children come to mind.

Well, this shoemaker is spending the evening picking up one of his children from the airport, and harassing him to ignore the time zone difference and get to bed because there is school in the morning!  

[Jdansti]

^ I have that trouble with my own bedtime every night. 

OT- researchers now say that teens need about 9.5 hours sleep per night.

[Mark Hammer]

I think this is the revised schematic of the MXR Phase 90 with the sine-LFO modification suggested by RG.  If it is incorrect, someone please tell me.

[midwayfair]

This might help: The vactrols in my Cardinal trem get very, very sine-y with the waveform knob counter clockwise, almost identical to the EA tremolo at similar depths. It's a softened sawtooth like what the tremulus lune does (a friend scoped the LFO it's adapted from), but I got lucky discovering that with the multiple LEDs and the progressively smaller bypass resistor softens the waveform considerably. A vactrol's slow response also helps.
https://dl.dropbox.com/u/9878279/Cardinal%20Tremolo.png

You could fake this in a design with only one vactrol by subbing one of the vactrol LEDs with any old superbright inside the case. There seems to be an upper limit to the total voltage drop. At least one of the three LEDs here has to be a red, green, yellow, or orange diffused.

I'm also pretty sure that the right vactrol will make lost amplitude from softening the wave not an issue -- in the above design, it can completely bottom out at the highest depth setting regardless of the waveform.

Of course, this design is only useful for optical circuits, but it IS a very simple, small LFO. Maybe the diode drop/bypass resistor trick is other LFOs?

[brett]

Hi
LEDs are the perfect diodes to clip a +/- 4.5 V triangle.
e.g. this sine generator, based on a CD4049 (which has plenty of potential IMO)

cheers