overview of the work to be done

 

In the image above, I have copied the portion of the Boss Dimension-C schematic relevant to the pushbutton interface.  As you can see, the pushbuttons alter the resistance values of key parts of the circuit.  The switch contacts on the left affect the depth of the LFO signal; those on the right affect the rate (LFO frequency).  I have made a video on Youtube with more analysis of how these buttons function:

https://www.youtube.com/watch?v=9X3oaw9NDnA

The connection points between the main board and the switch board, 12 and 14 for the depth and 11 and 13 for the rate, would be obvious and convenient places to attach pots.  In fact, it wouldn't be necessary to disconnect the button interface in that case, because in preset 1, there are no components connected by either switch: it is basically the "null preset".  Thus, in preset 1, any connected pots would be the sole elements altering the resistances.  For that matter, by accessing the contacts associated with button 1 (if indeed that button has contacts and is not just a means of turning off the other buttons), the pots could be attached to those contacts and thus button 1 would become the selector for enabling the pots, with the rest of the buttons operating as normal.  However, this would require finding enough space in the pedal enclosure to fit the knobs, without removing the buttons.

Instead, I will likely remove the buttons and install the pots in some of the resulting empty holes in the front panel.

Also, if possible, I will identify the fixed resistors (33k and 180k), assuming the TC circuit is sufficiently similar to the Boss original, and I will attach the new pot-based circuitry so as to completely bypass those resistors.  This will allow me to attain greater range from the controls than was afforded by the original circuit.  I will make the depth control a fixed 10k resistor in series with a 50k pot, and the rate control will be a fixed 100k resistor in series with a 500k pot (or perhaps a 1M pot, to make significantly slower rates available).  Thus, both the minimum and maximum resistances of the two circuit elements will be extended beyond the limits of the original design, but hopefully not so far as to cause circuit instability or malfunction (e.g., just two pots without any series fixed resistors, would permit the resistances to be dialed to zero, which would likely cause failure of normal operation).


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