single transistor LFO?

[C Bradley]

I'm wanting a single transistor LFO for driving an LED/LDR setup for my auto-wah project. Anyone know of a circuit for this? I'd like to be able to use either a 2N2222 or a 2N3906 transistor. Can this be done with a dual polarity supply? I'm using the OPAMP wah from RG's Technology of the Wah page.

Chris B

[gez]

With many single stage designs you'll often still need another device to control the LED otherwise you'll load the LFO.  

For example, you could tap the junction of the cap and resistor which sets the rate in a simple op-amp relaxation oscillator.  This will give you a non-linear triangle wave, but you'd need something like a FET to control a LED otherwise loading would bugger up the LFO.

For a single transistor stage LFO, look at simple phase-shift designs as seen in tremolo schematics (EA for example).  Again, the output would need to see a load with a high input impedance.

[gez]

Have a look over at "runoff".  I think the phozer is a autowah?  If I recal that uses the EA LFO.

(Edit) Here it is:

http://www.runoffgroove.com/phozer.html

[bioroids]

You can use a relaxation oscilator with a 2N2646 (?) unijunction transistor. I dont know where to find a schem now. Is a sawtooh wave I think.

Anyway you may also need to buffer it as gez says.

Greetings

Miguel