Liquid Mercury Phaser combines an 8 stage analog optical phaser with a digital microchip (Electric Druid’s TAPLFO) providing modulation with multiple wave shapes and a tap tempo function.

The phaser circuit is derived from the Mutron Phasor II, adapted to operate with 9V supply and augmented with 2 additional non-swept phasing stages.

The phaser was built in in two different versions. One with identical phase capacitors, for a classic phasing and one with staggered capacitors as found in the Uni-Vibe phasers. The second one has a less pronounced phasing effect but a swirlier sound.

I could not really decide which one I like best so I will keep both on my pedalboard 🙂


The available controls are:

Multiplier – Sets the ratio for the tap tempo. Available multipliers are 1/2; 1; 3/2; 2; 3; 4
Rate – Sets the speed of the modulation manually
Symmetry – Bends the wave shape to the left or to the right
Mix – Blends between the wet and dry signal
Feedback – Sets the amount of signal that is regenerated and increases the phasing effect
Depth – Sets the depth of the modulation
Wave shape – select between the following shapes: Square, triangle, sine and random steps
Tap Tempo – allows tapping in the desired rate of the LFO
Bypass Switch – true bypass

These controls can provide a vast array of sounds, from classic swirly phase to vibrato as well as more extreme settings. The speed of the modulation ranges from ultra-slow to ultra-fast (creating ring-modulator sounds).

I decided to use only 4 of the 8 wave shapes available in the TAPLFO. This way I was able to use a 4 position rotary switch for the shape selection. I could not find any small PCB mounted 8 position switches. The lumps and sweep shapes that I left out, sounded too close to the sine or triangle anyway and the ramp up and ramp down shapes can still be obtained when setting the symmetry control completely to the left or to the right. When using the square wave, the symmetry control defines the ratio between on and off time.
I added a blend knob that was not in the Mutron Phasor. I borrowed the values and principle from RG Keen’s article “panning for fun”. It’s nice to have as you can dial in more subtle sounds when turning it CW or have a vibrato only if turned completely CCW

Here are the schematics:

Liquid Mercury Phaser1 Liquid Mercury Phaser2

3 thoughts on “LIQUID MERCURY Tap Tempo Phaser”

  1. Hi David.
    It’s beautiful, and sounds great. I’m on a long quest to make one myself, and I have a couple of questions, if you have a moment.
    1) Does the mix go from wet only to dry only?
    2) What are those two DIP switches for?
    -Dave Nash

    1. Hi Dave, the mix goes indeed from wet to dry.
      The dip switches disconnect a pair of optocoulpers each, disabling one or two phaser stages.
      So you can have 2, 4 or 6 stages being swept

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