Build a special “3,5mm TRS jack” to “dual banana jack” adapter (with additional female pin headers for grounding the connection). The TRS jack has two pairs of wires coming from it. Both pairs transport a signal (Tip or Ring) and the ground (the sleeve of the 3,5mm jack). The signals (Tip/Ring) go directly to the banana jacks and the ground (Sleeve) is connected to a set of female pin headers, which I glued on the outer plastic shells of the banana jacks.
I added 3 pin female headers to my Lorre-Mill uTone “prototyping area” which connect to the ground (the negative terminal of the DC power connector -> to the negative terminal of the battery). When using the adapter the ground connection can be made using a jumper wire. I’ve used the adapter to connect the uTone with a Bastl Kastl unit. Kastl can send out control voltages via a TRS female connector on the back of the device. It can send out an LFO, random sequencer voltages, gate pulses, etc. Signals can be routed from the top of the device to the left (Tip) and right (Ring) channels (Should there be resistors inside the adaptor?).
I can now sequence the pitch of the uTone and send other kinds of voltages to it’s other input. Sending a gate signal to the input in the middle of the board introduces pretty rhythmic distortions. The only weird behaviour I can identify is that the uTone produces lower tones when powered from an adaptor and more high pitch sound when a battery is used. This might be due to the Kastl, the voltage might drop when it’s grounded. I imagine the connector will work the same with a softPop.
Works well and looks cute.