what about interconnecting two TC Electronic 3rd Dimension pedals to create a real dimension chorus?

Short answer: nope, the sound quality is just too wretched to make this worth it.  I tried adjusting the bias trimmer on my sample unit:

https://youtu.be/ucRMNt1bC2s

...and there seemed to be no way to get rid of the awful distortion, which is particularly audible on higher pitch single guitar notes.

Still, in case anyone else wants to try this, I'll include all my notes and a video about how it would be done.  Maybe some TC units sound better than others: the NE571 compandor that they use is supposed to have external trimming to bring its sound quality up to the level of the NE570 used in the original Roland/Boss units, but TC Electronic skipped providing this trimmer.  Maybe some units happen to be closer to the ideal trim setting, given component tolerances and variations in the NE571 chips.

https://youtu.be/9D7ya1y30Tc

Here is my notebook entry, showing the changes needed to connect the two TC units.

The modification is facilitated because the TC unit has a spare opamp section, IC1A, which can be used to produce the inverted LFO signal for the second unit.

As mentioned, to make a fully-functioning dimension chorus, it would also be necessary to include a DPDT stereo/mono toggle switch, and a bypass facility which could be implemented with two DPDT relays driven by a 2N2222 NPN transistor.  The transistor could be triggered either by a switch on the front panel, or by a footswitch via a 1/4" jack.

The notion would be to house all this in a 1U rack box (though it would also fit in a medium-sized aluminum chassis box such as those from Bud or Hammond, if one wanted to preserve the "pedal" format).

But I don't think I'll be doing this, even though it's probably the cheapest route to a dimension chorus, because the demos of the BBD-320 on Youtube (such as by Leon Todd) sound so much better.  I can't live with the sound quality of this TC unit.


Comments

Post a Comment

Popular posts from this blog

the Boss schematic

I don't want to simply place a copy of the full Boss schematic here in this blog, because I'm not exactly sure about its copyright status.  However, it seems to be "freely available" online, such as from this link: https://www.audioservicemanuals.com/b/boss/boss-dc/329776-boss-dc-2-dimension-c-chorus-schematic Thank you to Boss for permitting, or at least not obstructing, this!  I wish TC Electronic would follow suit, but so far in my searches, it appears they have not done so. Identification of the significant, "non-obvious" chips in the Boss circuit: BA634: flip flop NE570: compandor MN3102: clock generator for analogue delay line MN3207: 1024-stage BBD delay line One thing that I note about the schematic (this is the Boss DC-2, i.e., the original Dimension-C, not the newer WazaCraft version).  Although this unit provides "stereo" outputs, there are still only two delay lines as far as I can tell.  I haven't extensively analyzed the schematic...
Read more

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 an...
Read more

overview of the work to be done

Image
  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 associa...
Read more