VCO and LFO

I have breadboarded a VCO capable of producing four wave shapes. I have attached the schematic. I want to know how to I could modulate the signal with an LFO before it gets to the output. I want to create it as a separate module and connect it like a modular synth. The VCO as two outputs phono and a 2 way terminal block but I'm not going to have the two way terminal block in the finished product. I don't know how I would connect the LFO so any help would be appreciated.

Thanks

Stu

I have also been looking at midi to cv converter to add control to this oscillator but that look a little out of my league just yet. So I thought I could possibly add a ribbon control like the Korg Monotron has. I have attched the schematic as I don't know where the ribbon control is? Any help would be greatly appreciated.