[sdiy] LAG circuit de-tuning VCO question

[Dave Kendall]

Hi All.

I have a playing with a simple expo lag circuit consisting of;

1V/octave input to an op amp wired as unity gain voltage follower, the 
output of which goes through a 1M Linear pot wired as variable 
resistor, then into a second voltage follower with a 1uF cap to GND at 
its input.
I notice that without even changing the input CV, setting the pot to 
max de-tunes the output by up to several 100 cents, judging by ear.

The effect is more pronounced the higher the input CV - around 0V to 1V 
input, it's hardly noticeable.

Is this normal, and is there a way to remove the effect?  it makes it 
pretty useless for accurate VCO use. One can mitigate the effect a bit 
using smaller resistors/caps, but then the lag time is very short.

Any ideas anyone?

cheers,
Dave