creating an external lfo controller box for the rebote - tech guys pls help

[ulysses]

i was interested in creating an external lfo box - specifically as an add-on for modulating the delay speed on the rebote delay.

the delay speed pot on the rebote is 50k.

so i would need to create an lfo that could modulate between 1k and 50k - have depth control ie, change to between 10k to 40k - and have various wave forms, sine, triangle, sawtooth, and square waves..

anyone able to point me in the right direction?

cheers
ulysses

[Seljer]

copying and pasting together the delay control from the Rebote and the LFO from the Tremulus Lune, I made this thing


(I think you'd want to isolate the jacks if you're going to build the LFO in a seperate box)
I Just realised that that schematic wont do anything in the minimum delay time unless you move the wire thats going to jack directly from pin #6, not after the 1kohm resistor

the LFO lets you get a triangle->square wave shape out of it. There a bunch of other mods you could do to it as well, hooking up a diode across the LFO speed resistor makes it into a sawtooth wave (either rising or falling depending on what direction the diode is oriented)

but I'm not really sure on whats the best way to implement the LDR with the existing potentiometer. The thing is LDRs usually have a rather high resistance, where for not-too-screwed-up sounds, you'd just need the total resitance hooked up to pin#6 of the PT2399 to be chaning for a couple of kiloohms max.
(looking at the data sheet for it, 1kohm = 10 to 12ms difference in the delay time)



though yeah, you could also use the schematic on this page here that shows you how to do it with a transistor
http://sdiy.org/destrukto/vc-echo.html#pt2399
if you want to build yourself a fancy LFO that would work with outher control-voltage stuff (if you have any aspirations to build a modular synth or buy one of those moogerfooger pedals) http://www.musicfromouterspace.com/analogsynth/NewAugustSIN_TRI_SQR_LFO.html

[ulysses]

thanks for the reply Seljer!

do you have a sound clip you can post so i can see how that simple lfo mod sounds?

cheers
ulysses

[Paul Perry (Frostwave)]

but I'm not really sure on whats the best way to implement the LDR with the existing potentiometer. The thing is LDRs usually have a rather high resistance, where for not-too-screwed-up sounds, you'd just need the total resitance hooked up to pin#6 of the PT2399 to be chaning for a couple of kiloohms max.
(looking at the data sheet for it, 1kohm = 10 to 12ms difference in the delay time)

If you are worried about the LDR maximum being too high, you can just put a suitable resistor across it. Experiment with a  pot & then measure to get the value you want.

[Bassmanfox]

I added the aux LFO from http://commonsound.org/tremulus/auxlfo_add.pdf to my Pt-80 and it sounded great.  I tried a few different LDR's, hand made and store bought and settled on the VTL5C2.  I then added a dpdt switch to turn it on and off.  It only doesn't do much when set to minimum delay, but when its anywhere else sounds can go from totally screwed up pitch shifts, to beautiful chorus/vibrato sounds.  The "depth" control of the LFO actually becomes the pitch shift range/amount control.  Just make sure if you use it in the same enclosure that you isolate the power and grounds with a 10-22 ohm resistor otherwise you can hear a VERY slight clicking from the LFO at high speeds.