Low Frequency Oscillator
There are two Low Frequency Oscillators on the main circuit board of the Z-5. The output of these oscillators are used to Frequency Modulate the VCQO's, Amplitude Modulate the VCA's and handle a function known as Sweep. By design, LFO 2 runs significantly faster than LFO 1 though a large part of their frequency spectrum does overlap.
Frequency Pot Modification - Similar to the other oscillators, I wanted to increase granularity with the LFO's. The challenge here is the required potentiometer is somewhat hard to find. For best results, you need a 1Meg, Reverse Logarithmic potentiometer. Also known as a C1M. The Z-5 currently uses standard 270 degree C1M pots for this function which can make dialing in a specific frequency a bit of a challenge.

On my console, I have decided to replace the C1M potentiometer with a B1M multi-turn potentiometer. The 'B' indicates linear response of the potentiometer. The part I selected is a 3 turn Bourns potentiometer which gives much better control over the frequency. Being a linear pot, you end up losing a bit of control at the higher frequencies but the improved control over the lower frequencies makes this improvement work doing.

I would rate this modification as being very easy. Aside from soldering 4 wires, you will also need to increase the hole size in the panel to support the larger potentiometer shaft.