I'm putting together this FM radio module. The CV input picks up stations between 1.5v and 3.1v.
I'm using the 3.3v source that powers the FM module on the 'start' pot - the op amp is powered with a normal +-12 split supply.
On the module I want a 'start' tuning pot and a CV input pot (attenuator) just like any standard oscillator.
I'm trying to follow the summing amplifier from Art of Electronics.

The 'start' pot works as I'd expect, until I connect the CV pot (the 38k resistor is to keep the voltage above 1v, to increase the useful sweep of the pot)
My problem(s):
- When the CV input is zero (i.e. the output from a pressure points row with all pots at zero, or just unplugged), changing the CV pot still changes the output voltage - it rises around the middle of the sweep, falling at each end
- There seem to be other interactions between the pots that I don't expect - i.e. the total voltage doesn't seem to get much beyond 3.3v. I'd assumed that 3.3v + 5v from the Pressure points would give 8.3v - not ideal for this implementation, but it's what I expected - I'm just testing this part of the circuit without the radio module connected
What am I doing wrong?
Thank you!