LFO + FETs question

[midwayfair]

I'm trying to figure out if something would work.

I have this LFO (specifically A):


The output where the LEDs is connected settles at 4.5V. They blink out of phase simply by changing the voltage rail they're referenced to, with the 4.5V being either the "ground" or "supply rail" for each LED.

Let's say I wanted to use FETs like in the EA Tremolo instead of the LEDs.



When RG Keen did his Harmonic tremolo (see here: http://www.geofex.com/FX_images/FakeFenderVib3.pdf), it looks like he hooked up the source FETs to a 4.5V voltage reference and then fed them an out-of-phase signal.

The oscillation with the FET works by dropping the resistance when the voltage swings negative, and increasing its resistance when the voltage swings positive.

So here's the question(s):
If I hook up one FET's source to ground (as in the EA Tremolo) and the other FET's source to +9V instead of ground, and then feed them the output of the LFO that centers at 4.5V, will I get out-of-phase modulation of the two bands similar to what RG did in his harmonic tremolo? Or would I instead need to use P-channel devices? Or do I absolutely need to use out-of-phase LFO signals to get the devices to change their resistances counter to each other?

Although I could probably answer this myself on a breadboard, I'm feeling lazy ...

[jubal81]

I can see what your getting at, but I'm wondering what your specific design goal is here.

Is it just a matter of making a smaller circuit? Or don't you like the waveform of the quad op-amp version?

[midwayfair]

Is it just a matter of making a smaller circuit? Or don't you like the waveform of the quad op-amp version?

I like the waveform just fine. I'm trying to figure out if there's a different way to go about this that doesn't involve $9 photocells. Not that matching FETs is much more fun ... also, I have a friend who prefers RG Keen's version and I'm trying to figure out if there's a way to get this LFO into that design's modulation method.

[jubal81]

My gut reaction is I don't think the voltage changes will be congruent and you'd have two different wave shapes. Looking forward to seeing what RG has to say about it, though.


Also, if that worked, I think you'd have seen it already in other circuits.

[midwayfair]

Also, if that worked, I think you'd have seen it already in other circuits.

This may be the most damning evidence ...