I decided that I should build a Phaser using my PIC DDS LFO. I designed a PWM version using CD4066 analog switches but this had issues. It just drew to much current and had some noise artifacts. I got it working but it became more complicated than I liked. However, the design was easily modified to use a homemade vactrol. The vactrol uses four photcells glued together to make a square and then the LED is glued right in the center. The whole thing is then covered in a piece of heat shrink, electric tape or whatever. Performance is excellent and the circuit is simple. Of course the DDS can be replaced by some other conventional LFO circuit. The main issue is operating the LDR’s in a good range to get even and adjustable notch sweep. With this design, the sweep is adjustable and you can even eliminate one notch by pushing its position sub audio. The sweep controls the level of illumination of the LDR’s and thereby adjusting the total range of phase shift. The LFO uses my PIC DDS circuit and generates a Sine wave envelope. The code can easily be changed to generate other wave forms. I am going to include a link to the a zip file containing all of my source code. This was all compiled using MikroC. The program is small enough to compile in the freeware version of MikroC or you can just use my compiled hex file.
More detail on the PIC DDS is available on this blog in earlier post.
Link to source code and hex file: http://www.filedropper.com/ldrphaserdds
Etched Circuit Board: