[sdiy] help adding a 1/v oct input to an MS20/50 vco core?

[dan snazelle]

Tonight I got a Korg Vco built on the breadboard.. 
just the CORE..


.i did not want to deal with building the expo until I KNEW I could get it working.

it sounds great!

for now I am just controlling the pitch with a resistor into the FET (q5 on this schematic)


http://www.korganalogue.net/korgms/images/service/ms20/circ1.gif



 which connects to a pot going to ground and +v

my question is this....
Do i need to build the transistor pair OPamp hz/v converter Korg shows
 on the schematic or can i plug ANY old regular NPN pair expo converter into the bottom of Q5?

thanks for any help!