LFO Pots - Log or Linear?

[mimmotronics]

Just wondering about standard/basic design practice...is it standard to use log pots for constructing LFO rate controls? I have an LFO breadboarded with a linear pot and have no log pots around to test.

[GGBB]

Typically they are reverse-log so that clockwise rotation increases speed evenly. If you use log then wire them in reverse, otherwise nearly all of the speed change happens in the last little bit of rotation. Linear works find but there will be some adjustment crowding at the higher speeds.

[Mark Hammer]

Small proportional differences in slow speeds are not as noticeable as similar proportional differences in faster speeds.  So, the change from 5 to 4hz is more easily noticed than the change from 0.75 to 0.6hz.  The way that LFOs work requires that smaller resistance values are used to charge up a cap more quickly.  So, putting both of those together, the pot needs to be able to dial in smaller distinctions in low resistance to produce small noticeable differences in LFO rate.  HOW you do that is your business, and the direction it happens in is also your business.  An anti-log pot skips very quickly through the high resistance changes, from the 7:00 to 12:00 position, and then inches its way through small changes in resistance as you continue.  A log-taper pot will do the reverse.  So, you can wire up an anti-log toproduce faster speeds going clockwise, or a log pot going counter-clockwise.

If you are stuck tith a linear strap a parallel resistor between the wiper and one of the lugs to achieve something approximating a log or antilog taper.

[DrAlx]

Depends on the LFO. Compare the LFOs in the two circuits below.

First one has a fixed voltage source in series with a (rev)log pot that feeds the timing cap.
The second uses a linear pot acting as a voltage divider on the voltage source, and then a fixed resistor in series to the timing cap.

http://www.metzgerralf.de/elekt/stomp/mistress/images/deluxe-electric-mistress-v2-schematic.gif

http://www.metzgerralf.de/elekt/stomp/mistress/images/deluxe-electric-mistress-v5-schematic.gif

I seem to recall that the trick of approximating a log by shunting a resistor between the wiper and one end of a linear pot only works when you are using the pot as a voltage divider.