The Q161 is connected to the Q106 by some
behind-the-panel wiring. Since the Q161 is sold as a separate item from the Q106, the good Dotcom folks came up with a clever no-solder way of performing the conversion. The Q161 comes with a set of 1/4" jacks that replace the ones in the Q106. The replacement jacks are two-way wired -- they connect to the MTA-100 connectors on the Q106 in place of the stock jacks at one end, and to a second set of MTA-100 connectors on the Q161 at the other end. So adding or removing a Q161 involves replacing the jacks in the Q106.
Here's Block 1 with the Q106, and the Q161 which is to be removed, to its right. (The module to the far left is a Q141 oscillator aid, which is unaffected by the conversion.)
If you look at the bottom of the Q106, you can see that all of the jacks except the sawtooth jack in the center (which is not connected to the Q161) have been removed. The Q161 is unscrewed and is ready to remove from the mounting rails.
Here's what Block 3 looked like before the changes:
The new Q106 and Q161 are to be installed at the far left. The Synth Tech MOTM-220 LFO and the MOTM-101 sample/hold are going to slide to the right; the Dotcom A/B switch and the Cynthia StereOspace are to be removed for installation elsewhere.
Block 3 from the back, after the new Q106 and Q161 have been mounted. The "sine" jack has been replaced with the one from the Q161, and you can see the behind-the-panel wiring that connects the two modules. One of the two sets of wires from the jack has already been connected to the Q161; the other end is awaiting connection to the Q106 and can be seen at the lower right. (These modules, like most Dotcom modules, have rows of MTA-100 connectors around the edges of the circuit board where all of the panel devices connect.) The other jacks from the Q161 have not been installed yet; they are off the edge of the photo to the bottom, but you can see the wiring going to them.
Block 1 is on top, with the Q141 oscillator aid and Q106 VCO at left. You can see the empty slot where the Q161 was; I haven't decided what I'm going to put there yet. Block 3 is on bottom, with the new Q106 and Q161 at the left, and the other modules moved over to the right. (I'm going to try to squeeze an MOTM-190 VCA in the empty slot.)