New phaser with Homebrew 1×4 Vactrol and DDS LFO

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:

Completed Phaser:



LDR phaser

Etched Circuit Board:

etched phaser brd

Completed Board:

phaser board

Homebrew Vactrol:

quad vactrol

6 thoughts on “New phaser with Homebrew 1×4 Vactrol and DDS LFO

  1. Hello, at Circuit Salad. I think that i like the sound of the Vactrol Brainwash Phaser, but i would love to hear it with some different EQ. settings, and with the knobs at different extreme settings, simultaneously. Got to give it a good work out. Strum a chord, and hold it. Like i said as far as the EQ goes, i’d like to hear this pedal with alot less midrange at the amp or by scooping the mids with an outboard EQ. My favorite phaser pedals are those with vactrol circuitry. Also, i would be interested in purchasing more than one of these phaser pedals, but i like the exterior colors i see hear on your web site. But, the one pictured at Sherwood Music, i do not care for. Silver, black, and blue yea ! Silver, black, and Purple yea ! But i don’t like or want the orange thrown in, ney ! But definately, very, very interested in your pedal.

    • You’re a strange person…that’s not an insult!

      Yes my videos are geared toward conveying basic performance to builders and experimenters and not promotion to make a sale. As a player your requests make sense and I will try and heed your advice in general as to demonstrating the full range of performance. At least I don’t bloviate for five minutes at the beginning of the videos – wasting everyone’s time.

      The pedal at Sherwoods is actually a pwm switching version…just to clarify.

      If you want a pedal I can make you a really cool 8 stage vactrol job with multiple modulation choices and speed, sweep range, mix and resonance would do it in a 1590bb form factor with a custom etch which you could design if you like.

      Normally, I don’t make a vactrol version for sale…but I like the sound also.

  2. Hello again, at Circuit Salad. Thanks for the reply back. To be honest, i am basically interested in 4-stage Vactrol designs. But since you took the time to write me back. My other interest as far as parameters would be : speed, depth, +/- resonance, wet/dry mix, sweep range or frequency range. As far as colors and finish, it’s not that big of a deal, but i do like the color combinations of the phaser on your site. And yes, i understand, that you may have no interest in building a pedal that i have described. But it sounded so good that i felt i had to at least leave a reply on the great job you did, even if i didn’t may it clear in my first post to you. But i would be willing to pay, for your time and expertise and build quality if you were to choose to build a pedal or pedals for me. Anyways that’s about it for now. God Bless ! foggy !

    • Hey Foggy
      thanks for the feedback… I like LDR stuff as well, in general, the response time, and resistance curve of LDR’s give them a unique sound that is very pleasing.

      I build some pedals here and there to sell for fun…right now I am really swamped. If I build one in the near future, I’ll let you know

  3. I really want to speak to you about a project. How can I call you? BTW, i have one of your brainwash pedals, and it’s really great.

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