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HELP me with my crazy LFO ideas


 
8/22/1998 3:22 PM
nic
email
HELP me with my crazy LFO ideas
Can anyone help me find some schematics for a few of these things:  
 
-Ramp and reverse Ramp wave generator.  
-a push pull deal so I can run dual LFO's out of phase with eachother for stereo operation.  
 
Or if soemone can help me in my direction. I hope that I can come up with a LFO that has the following selectable waveshapes:  
 
Triangle  
Square  
Ramp  
Reverse Ramp  
 
I like to be able to control the symetry, rate, intensity, and anything else I am missing like maybe bias. The LFO is heavily influenced by Roger Mayer's VooDoo Vibe, I just want to add on... Could someone help me, or am I on my own here????
 
8/22/1998 5:06 PM
nic
email

okay so I should have first scrolled down to an earlier discussion... R.G. how would I go about controlling the symetry and bias settings that are found on RM's VooDoo Vibe? Also, if I hacked a ramp generator in with this thing would it's rate and symetry and stuff be dependant on the normal LFO's settings. In other words could they share the same pots? I am also still puzzled on how to run the thing stereo.  
 
 
nic
 
 
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8/23/1998 1:25 AM
Mark Hammer
There was just such a project in Elektor Magazine in the late 70's, called "SEWAR" (Sound Effects With Analog Reverb). It was intended to drive a bucket-brigade device. It does almost everything you describe, except for the dual thing, although I imagine you had envisioned separate LFO's.  
 
One place to look is any book on analog synthesis from the 1975 to 1983 period. Most such books will have a schematic or two, based on an 8038 function generator chip or an XR2206. Come to think of it, there was a series on the 2206 in Radio Electronics, in the mid to late 80's.
 
8/23/1998 9:04 AM
paul perry
email

weird LFO ckts?  
most of these are based on the concepts of level shifting (that is, adding or subtracting a fixed voltage to give a new 'baseline) and full wave rectifying (see the ckt in Jung's 'Op Amp Cookbook' for example).  
Also check out 'pan' circuits, a voltage controlled panner likely has in it what you want.  
And if you want a continuously variable waveform, try feeding a triangle to an OTA like a LM3080. By overdriving it, you go from triangle to sine to square.
 
8/23/1998 12:42 PM
nic
email

I need that book!!! I can't find it anywhere! The library where I used to live had it and I loved the thing... An amazing idea enters nic's head... Maybe one of you guys have two and would like to give me a copy? :)  
 
Hopefully it is at Amazon.com. They had one by the same title for $30, I don't want to buy it to find it is the wrong one... Does anyone have it's ISBN number handy?  
 
 
 
nic
 
8/24/1998 12:23 AM
Preben Hansen
Hi nic.  
 
I have found this document on the net.  
It is in PDF - format. It contains a scem. for a lfo with Ramp - Reverse Ramp - Triangle and Square wave output.  
Follow this link:  
http://www.tellus.vallentuna.se/gymninfo/personal/anders/gep.pdf  
 
Regards  
Preben.
 
8/24/1998 8:08 AM
paul perry
email

Thanks for the ref, Preben!  
It wouldn't be hard to add a rectifier and give an envelope following wah option as well.. but the filter doesn't look all that extreme. Should be as good as a DrQ, though.
 
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