Scoping out the Duos circuit, I found several numbered pads, labelled J1, etc.. These are probably used during functional testing. One of them has the Clock Out, which is a +/-11V square wave, another has the Rungler CV output. Two have the oscillator outputs, 0 to +10V, pre-LPG. I also found two LFO triangle waves, +/-2.5V, though LFO A does not have a pad; it’s on pin 8 of U1. But there is a pad for LFO A square. I decided to bring out the five signals that weren’t available on the Eurorack panel.

AO – A Oscillator

AT – A LFO Triangle

AS – A LFO Square

BO – B Oscillator

BT – B LFO Triangle

J14 has Oscillator A, U1 pin 8 has LFO A Triangle, J1 has LFO A Square, J15 has Oscillator B, and J13 has LFO B Triangle. I put 1K series resistors on all the outputs, and added 100nf series capacitors to AC-couple the oscillator pulse waves.

Scope photo above compares the main out of the LPG with the oscillator out. The LPG resonance was set to the lowest. (Turning up LPG resonance added sharper edges.) These waveforms will sound similar, but having the oscillator pulse prior to the LPG can get around the LPG internal modulation.

It will be handy to have the LFO triangle waves for coordinated external modulation. LFO A square is another rhythm pulse. Note that the triangle is +/-2.5V, but the square is about +/-11V.

See Duos Block Diagram, below. VC LFO A gets two new outputs, Triangle and Square; VCO1 and VCO2 (I labelled them A and B) now have direct outputs ahead of the Low Pass Gate; and VC LFO B has the Triangle output added.

Construction

I fabricated the breakout panel from a 2hp blank. But how to label it? I used Front Panel Designer for the panel design and printed it. Extra strong Scotch tape holds it to the panel.

Following my Bananut color scheme, the Red nuts signify pulse outs and the Black are normal outs, here the Triangles.

I found perfectly sized piece of perf board that even had an existing drilled hole I could use for mounting it. An M3 threaded standoff replaced the nut holding the Duos PCB.

I like to be able to separate expander panels, hence the connector. I had just a few IDC connectors left to do this. If I ever sell the Duos, the breakout panel will go with it of course. But the new owner might not have space for it. So it’s easy to disconnect.