Kenton Pro Solo MkIII

I use this to control a Yamaha CS-5 analogue monophonic synth from Ableton. It's a rugged little box that's easy to get up and running and can be configured to suit pretty much any CV protocol. Midi thru port is a bonus.
UK customers - note that my unit shipped with Kenton's continental power supply, Thomann will send an aftermarket adaptor if asked but unless the stock changes, you won't have the original UK supply.

I bought this to control my little Eurorack setup from my MIDI controller, it has a huge menu of settings to tailor it to your synths & is made like a tank. Good value when you compare the features with other similar products.