Isolating two op amp amplifiers from each other

Question

My circuit consists of two oscillators: one VCO in audio range and an LFO (low frequency oscillator - below the audio range). The signals from the two oscillators are amplified with two non-inverting op amp amplifiers. The two amps (LM358) share the same split voltage supply/virtual ground source. Because of that the LFO effects the frequency of the VCO. The two oscillators should be entirely independent. How can I avoid the two oscillators effecting each other?

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

R3 connects to the half rail supply but consider that it could be on its own half rail supply - instead of using one 8k2 for R3, use two 16k4 (or nearest preferred value); one down to ground and one up to 9V.

Ditto R11 - it can become two 16k2 resistors in the same way. The two half-rail generators are now independant.

About noise and interference

The proposal I've made will neither improve nor reduce the effects of noise and fluctuations on the 9V power supply. However this type of design could benefit from 100uF decoupling caps on the 9V near these chips.

Answer 2

At the very least, you want to reduce the equivalent resistance of your virtual ground.

You could repalce R14 with a 4.5 V zener or shunt regulator. However this would not track like your current setup if your 9V supply drifts. You might also need to worry about noise and thermal drift if you use a zener.

You could buffer the virtual ground with another op-amp configured as a voltage follower.