LFO circuit

[Heemis]

I'm interested in using the LFO circuit from the EA tremolo in another circuit.  I think I know how to do this, but I just wanted to double check with some of the people here to make sure before i start experimenting.

I'm thinking that the LFO is basically everything to the right of the "Depth" pot in the EA tremolo schematic.  Am I correct in assuming that if I built the circuit to up to the depth pot, and then connected the wiper of the depth pot to the variable I want to control, that would work properly?  Or are Q2, the 22uf cap, the 180 ohm resistor, and the 1.2k resistor part of it as well?

Here's the schematic for quick reference:  http://www.runoffgroove.com/EAtremolo.png

[frequencycentral]

I'm thinking that the LFO is basically everything to the right of the "Depth" pot in the EA tremolo schematic.  Am I correct in assuming that if I built the circuit to up to the depth pot, and then connected the wiper of the depth pot to the variable I want to control, that would work properly? 

I think that's correct. It looks like a single transistor phase shift oscillator to me.

[cpm]

take into account that its not a sinusoidal type waveform

[Lurco]

take into account that its not a sinusoidal type waveform

always looked siney to me 

[cpm]

well, i mean, the effected volume in the EA is not sinus... even if the LFO is... so yes, the LFO alone may be siney 

[R O Tiree]

I haven't built it, but I just simulated the LFO in LTSpice and it's about as sinusoidal as it gets.

[oskar]

You know the way we hook up volume controls with audiotaper. Little gain in the beginning to big gain in the end...
A sine wave modulating the volume is like the opposite... sure it's smoother than a squarewave but still it comes on relatively percussive, staccato like. A trianglewave would be less hard.

[R O Tiree]

...and then I put the rest of the circuit in and it went seriously non-sinusoidal...

[PerroGrande]

The remaining portions may be loading the output of the LFO to the point where it is no longer sinusoidal.  In the original EA Trem, the LFO drives the gate of an FET -- talk about a high impedance load!

A simple solution, if you need to maintain the sinusoidal nature of the LFO would be to essentially do the same thing.  Stick a simple FET source-follower (or similar buffer of your choice) after the LFO and before the next stage of your circuit.

[R O Tiree]

Yes - that looks like what is happening on the simulation. Not only that, but the LFO trace is not pure - it's getting some of the original signal mixed into it... and when you feed the input with a pure 200mV sine wave, the final signal out is like a row of UUUUUuuuuuUUUUUUuuuuuUUUUU... that's right - the bottom of the wave doesn't seem to vary its level more than about 20mV - it's only the top half that varies. Lastly, that input buffer is very sensitive to set correctly with the trimmer to get bypassed signal equal to processed signal - set the trimmer only very slightly off and you get a 3V output or tweak it slightly the other way and it drops to 20mV!

I much prefer the Danelectro Tuna Melt circuit - uses an LED/LDR combo to alter the gain of an opamp.

[puretube]

You know the way we hook up volume controls with audiotaper. Little gain in the beginning to big gain in the end...
A sine wave modulating the volume is like the opposite... sure it's smoother than a squarewave but still it comes on relatively percussive, staccato like. A trianglewave would be less hard.

[oskar]

     
-Yeah... that didn't work too well for me either...  somewhere I left half of the sine ( and probably did something else for my inner vision to make it come true ).