modifying the TC Electronic 3rd Dimension pedal

The TC Electronic 3rd Dimension pedal is essentially a clone of the Boss Dimension-C pedal.  These are so-called dimension chorus pedals.  The audio travels through two parallel BBD analogue delay lines.  The delay line clocks are modulated by a single LFO, but one delay line gets the direct LFO signal, and the other gets a 180-degree out-of-phase copy of the LFO signal.  Thus, when one delay line is at maximum delay time, the other is at minimum, and vice-versa.  These two delayed audio signals are then combined with the dry signal.  The result is something which sounds like a chorus effect, but the distinct "warble" from the LFO waveform which is clearly perceptible in most chorus pedals, is largely obscured.  This is thus called a "motionless" chorus.  It gives the shimmery ambiance associated with the chorus effect, but without the pulsating vibrato sound of the LFO.  It is a relatively subtle effect, which I have always found pleasing and more musically-useful than the more "blatant" sound of standard chorus effects.

However, for some reason, when Boss created the dimension chorus effect, first as the rack-mount Dimension-D unit and later as the Dimension-C pedal, they chose to provide an unusual interface to control the sound.  Instead of the usual two-knob controls as found on almost all chorus units, i.e., rate and depth of the LFO signal, Boss provided a set of pushbuttons which selects a few fixed choices for rate and depth.  Perhaps they felt that the effect is so subtle, and the nature of the effect is inherently to conceal the action of the LFO, that only a few basic variations would be needed, and maybe people would find the knobs "disappointing", since the amount of obvious variation would be small regardless of the settings of the knobs.  This, to me, seems like a bad choice.  For one thing, of course musicians like to have lots of control and adjustability; if there are certain settings that are useful to repeat, there could be preset buttons provided as an option in addition to knobs, or frankly, probably just the numeric markings of the knob positions would suffice, as on most other pieces of music gear.  Also, having only a limited collection of fixed presets, particularly as concerns the LFO rate, means that in multi-track recordings, there might be objectionable, audible "synchronicity" between multiple tracks recorded with the same dimension chorus settings; with knobs, it would be possible to give a slight variation between tracks which would immediately erase the synchronicity.

Unfortunately, though perhaps understandably, when TC Electronic made their version of the dimension chorus, they copied the Boss scheme with the preset buttons.

Tomorrow, I expect to receive a TC Electronic 3rd Dimension pedal in the mail.  My intention is to first record sound samples with the pedal, unmodified.  Then, I will take it apart and attempt to make the modifications necessary to replace the pushbuttons with a two-knob interface.  I will document my work here, since I think others may wish to do the same.  The TC pedal is significantly cheaper than the Boss original, so it seems like the right candidate to modify.  Its only drawback is that it is not stereo.  The original Roland/Boss units had mono-in, stereo-out, so they could be used to create a stereo soundscape from a mono guitar signal.  The newer WazaCraft reissue of the Dimension-C has stereo in and out, so it can be used in a pre-existing stereo signal chain as well as creating the stereo itself.

There is, helpfully, a schematic of the Boss Dimension-C available online.  There isn't one, as far as I could find, for the TC unit.  So part of my work will be to figure out how to locate the necessary components and connections in the TC unit.