EFM VCO4E

The Electronics For Music EFM VCO4e is a pretty nice little oscillator. It is similar enough to the EFM Wildcat oscillators that I incorporated Yves Usson's Wildcat mods in the VCO4e. You can see what Yves did here.

I made changes for the Pulse Width controls (to center the manual sweep aroud 50 percent) and improve the Pulse and Saw outputs. All of the panel mounted pots are 50K linear taper, with the exception of the Initial Pulse Width control, which is 100K linear taper.

The modifications are mostly changes in resistor values. Beyond that, a pull-up resistor was added to the output of U4 and a divider resistor added between the pulse output and ground. This divider resistor is just soldered across the pulse output jack. The pull-up resistor was soldered to the exposed end of R42 on the component side. The free-standing end of this resistor was connected to a +V source (exposed upper end of R36) with a piece of red hookup wire (see photos below). The other addition was the 100pF compensation cap on U6 - soldered to the exposed leads of R41.

The modifications are mostly changes in resistor values. Beyond that, a pull-up resistor was added to the output of U4 and a divider resistor added between the pulse output and ground. This divider resistor is just soldered across the pulse output jack. The pull-up resistor was soldered to the exposed end of R42 on the component side. The free-standing end of this resistor was connected to a +V source (exposed upper end of R36) with a piece of red hookup wire (see photos below). The other addition was the 100pF compensation cap on U6 - soldered to the exposed leads of R41.