"Popular optical tremolos from a single circuit"




The Earthquake tremolo rack effect module compares to the Demeter Tremulator, Fulltone Supa-Trem, and Joyo JF-09 tremolo pedals.  These tremolos all share the same basic optical tremolo circuit but have slightly different controls.  Optical tremolos generally have less noise than other designs, contributing to their clean tone and popularity.  



Tremolo is one of the simplest effects.  In its basic form, it just turns the volume up and down at some rate.  The depth is simply how loud and how close to silent it gets as the volume adjusts.  Deeper and faster tremolo can produce choppy, helicopter sounds, like the intro in Green Day's Boulevard of Broken Dreams.  Medium to low levels of depth at slower speeds can yield classic Creedence Clearwater Revival tones or give you some cool, subtle movement in your sound.  The Demeter Tremulator is considered by many to be the best tremolo pedal ever produced.  It has simple controls for a simple effect, just Depth and Speed.  The Joyo JF-09 is similar.  The Fulltone Supa-Trem adds a few extra controls to let you tweak your tremolo effect, but is essentially the same circuit as the other two.  Our Earthquake module compares to all three of those tremolo pedals.  It comes in three base configurations that differ primarily in the controls that are included.  Note that the Danelectro Tuna Melt also sounds and works similarly, but the circuit is just enough different that it isn't covered by our Earthquake module.

Overall, this is a very nice tremolo, pleasant and warm.  Ours is quieter than the stock Supa-Trem pedal we compared with.  There is no distortion if you have the Volume set properly, although our test Supa-Trem pedal does have bits of distortion or clipping now and then.

All the controls and optional controls interact to some extent, so you may have to fiddle around a bit to dial in the exact sound you want.

Without the external Volume control or internal volume trimmer, the volume in the circuit is set to a fixed level.  That level is generally OK, unless you use settings near the max or min for Depth and Speed.  Then it might be a bit above or below unity volume.  The Volume control lets you set your unity volume level.  Volume on a tremolo is a little funky.  Depending on your wave shape, Rate, and Depth, you are changing the amount of time the volume is cut, as well as the amount it is cut, affecting the perceived volume.  This usually isn't an issue with "normal" settings, but may cause lower/higher volume at some extreme settings.  Set it where you need it, of course.

Depth has a a good range, skewed more toward the shallow end, allowing good control over more subtle settings.  With the Hard/Soft switch set to Hard, higher Depth settings get very choppy.  Depth can be smoothed out with the Bias control when the Hard/Soft switch is set to Soft.

Speed also has a good range, although it probably goes faster at the max than is necessary.  The Half Speed switch option gives you a range of slower speeds and better control over them.  We do the Fast/Slow switch a little differently from the Supa Trem pedal,  Ours will tend to have a slightly lower max speed, although it seems unlikely anyone would use it near those max speeds anyway.  We've included a blinking Rate LED, too.

Bias changes from the Hard default wave shape to a range of smoother wave shapes when you have the Hard/Soft switch set to Soft.  This control isn't used when the Hard/Soft switch is set to Hard.  Setting the switch to Hard is the same as turning the Bias pot all the way one direction.



  • Earthquake Tremor - Compares to the Demeter Tremulator and Joyo JF-09.  Our version has Depth and Speed controls, internal trimmer for Bias, fixed volume level, and rate LED




  • Earthquake Aftershock - Compares to the Demeter Tremulator with extra controls or a simplified Fulltone Supa-Trem, whichever way you look at it.  Has Depth, Speed, external Bias and Volume controls, and rate LED
  • Earthquake Supa Tremor - Compares to the Fulltone Supa-Trem.  Has Speed, Depth, external Volume and Bias controls, Half Speed footswitch, and rate LED





Has an input buffer



  • Level Trimmer - Adds an internal trimpot so you can adjust the volume for unity.
  • Level Control - Adds an external control so you can adjust to unity volume.  Can be handy since changes of Depth and Speed can change the perceived volume.
  • Hard/Soft Toggle Switch - Adds a the Hard/Soft switch like the Tuna Melt, Joyo, and Fulltone pedals.  It changes the wave form for a choppier flavor of tremolo.  When this switch is set to Hard, the Bias Control (if you choose to have one) will do nothing.  This option makes it a toggle switch on the front panel.  Not really needed since you can get all the settings with the Bias control alone.
  • Hard/Soft Footswitch - Gives you the Hard/Soft switch as a footswitch instead of a front panel switch, like the Fulltone.  You'll also have the override switch on the back panel in you don't want to use a footswitch.  Not really needed since you can get all the settings with the Bias control alone.
  • Half Speed Toggle Switch - Gives you the ability to switch between the normal speed and half speed.  This makes it a toggle on the front panel, which gives you an extended range of Speed control.  Good if you want better control over very slow speeds, otherwise the default range of speeds is pretty good.
  • Half Speed Footswitch - Puts the Half Speed function on a footswitch, like the Fulltone.  Not sure how useful this is, but if you need it, we can do it.
  • External Bias Control - The circuit has an internal bias trimmer that controls the shape of the LFO wave.  When you use the Hard/Soft switch, you are selecting to either use this trimmer (Soft) or bypass it (Hard).  So if you have Hard engaged, your Bias trimmer or Bias control will have no impact.  Otherwise, the External Bias Control will allow you to more conveniently adjust the wave shape to a range of generally smoother, less choppy shapes.  By default, we give this control a bit more range than you might need, so you may find the best settings in the first half of the control - or maybe not!  Definitely changes up the character of the tremolo and gives you some options.  If you want to keep it simple, skip this option, set the internal Bias trimmer as you like, and forget about it.
  • No Rate LED - By default, we include a blinking Rate LED.  If you don't want it, we can leave it off.
  • Custom Components - The audio path in this circuit is tiny.  About the only tweak would be to change the op amp used in the buffer.  But all the original pedals use the same type (not model) of op amp because it sounds pretty good.  We don't recommend any component changes in the LFO that controls the wave form.  But if there's something you would like to change up, just let us know.


Front Panel

  • Depth - tremolo depth
  • Speed - tremolo rate
  • Rate LED - blinking Rate LED
  • (Optional) Volume - external unity level control
  • (Optional) Bias - external bias control
  • (Optional) Hard/Soft switch - change between Hard/choppy tremolo and smoother tremolo using Bias control
  • (Optional) Half Speed switch - switch between normal and half-speed ranges of tremolo rate


Rear Panel

  • Audio In
  • Audio Out
  • On/Off Footswitch
  • On/Off Override
  • (optional) Hard/Soft Footswitch
  • (optional) Hard/Soft Override
  • (optional) Half Speed Footswitch
  • (optional) Half Speed Override
  • DC Power
  • DC Power LED


Module Width

  • 1.5" for most configurations, 2" with options
  • Wing configs available for some combinations of controls, but not available for configurations with more than one footswitch


Power Consumption (aprox)

10 - 25mA, depending on configuration


Base Configurations

Part # Description List Price
MOD-EARTHQUAKE-TREMOR Earthquake - Tremor module configuration $179
MOD-EARTHQUAKE-AFTERSHOCK Earthquake - Aftershock module configuration  $199
MOD-EARTHQUAKE-SUPA Earthquake - Supa Tremor module configuration  $229



Part # Description List Price
MOPT-EARTHQUAKE-HARDSW Hard/Soft Toggle Switch  $19
MOPT-EARTHQUAKE-HARDFSW Hard/Soft Footswitch $29
MOPT-EARTHQUAKE-SLOWSW Half Speed Toggle Switch $19
MOPT-EARTHQUAKE-SLOWFSW Half Speed Footswitch $29
MOPT-EARTHQUAKE-BIAS External Bias Control $19
MOPT-EARTHQUAKE-CUST Custom Components $0 - TBD



Part # Description List Price
MPT-EARTHQUAKE-CA Replacement pot, switch, jack, LED cable assembly $19
MPT-EARTHQUAKE-KNB Replacement control knob $2
MPT-EARTHQUAKE-PB Replacement power board $29
MPT-EARTHQUAKE-SB Replacement switching board $29