Tips for altering feel or taper of Speed pot in my DiY trem.

[goldstache]

Wondering if there are any tips for altering the "feel" of a speed pot in my trem.
Series resistance ?  Lower pot value + Fixed resistor? 
I've tried all tapers available.  Linear, Audio, Reverse, and even "W"
I have reviewed many trem designs and can't figure out why some are so smooth while my EA trem speed control is so touchy
100k is my present value.
Thank you

[R.G.]

The feel of a pot is composed of at least three things.

One is the actual taper of the pot. The next is the response "taper" of the thing it's controlling. The last is the response of the human to what comes out.

The simplest example is the log taper for volume use. The human ear has an approximately logarithmic response to actual sound pressure changes. The thing being controlled is just signal voltage, which is linear; it's whatever comes out of the pot. The pot itself produces a very slow initial volume change, then increasingly larger. This compensates for the ear's changes in sensitivity.

When the thing being controlled is not linear, as the speed of a phase shift oscillator is not, then the taper gets odd. Reverse log is generally what is needed for even "feel" of an RC oscillator. However, there may be some nonlinearities in the response of the particular circuit, departures from a smooth response that no standard pot can even out.

There is an infinite variety of possible pot tapers. First, go read "The Secret Life of Pots" at geofex.com. That will give you an intro to what can be done. It is very likely that you will have to experiment with tapering resistors to get the degree of feel you like. Also notice that tapering resistors change the total resistance of the pot and may require you to tinker with the actual pot resistance to get a real range of min to max speed.

[goldstache]

I read that and loved the information.  I will tinker and learn.  Appreciate RG!  Thanks for dealing with my noobness!!!!!

[Mark Hammer]

In a great many instances, Speed/Rate pots tend to be reverse-log.  Why?  Because the speed of LFOs is generally dictated by how quickly a cap can be made to charge up, as a function of a resistance ahead of it.  Very slow sweeps (LFO rates) are difficult to differentiate, and the ear becomes more sensitive to the differences between swweps at faster rates.  So, you want the resistance that determines the speed to go from maximum to helfway more quickly than you want it to go from halfway to minimum: i.e., reverse log.  If you don't care about control direction, you can always wire a log pot in reverse, so that fast is at 7:00 and slow at 5:00.

But that general logic regarding use of pots for speed, is separate from the range of speeds that are of most interest to any given user/player, which is, again, different from the tolerance of the pot and how closely it follows the prototypic taper.  You can have a user who would normally be happy with a rev-log taper but the range of speeds in the pedal puts the ones they are interested in the range of "least dialability". You can also have a player who would be happy with a rev-log taper, but the pot itself has other ideas in mind and doesn't conform to that taper strictly.

The fork in the road, as far as custom tapers go, is to decide if you need more dialability at the slowest end or the fastest end of the range available.

[alparent]

What about a switch with different fixed resistors in series with the pot so you could change speed rates?
Something like a 3 positions switch (Fast / Med / Slow)
You could use a pot that allows for precise controle.....but change speed rates so you don't lose out!

[Mark Hammer]

Good point, and great idea.  Often, the problem is not that the speed you want is not in the range of the control, but rather, you simply can't find it easily.  Using multiple ranges makes it more findable.

[GGBB]

What about a switch with different fixed resistors in series with the pot so you could change speed rates?
Something like a 3 positions switch (Fast / Med / Slow)
You could use a pot that allows for precise controle.....but change speed rates so you don't lose out!

I did something along those lines for my EA trem.  I have two footswitchable ranges (fast and slow) with their own dedicated pots.  For the fast range a I am using a linear 20K pot - it is quite usable and can still go to moderate speeds.  The slow range uses a linear 100K in series with a trim pot to set the max speed of that pot, which I currently have at about 7K (but plan on lowering it slightly).  So there is a moderate overlap between the two ranges, but the big pot doesn't have to dial in the really fast speeds and the small pot is focused on the fast speeds.  This works quite well even with linear pots, although reverse logs would be better still - I just didn't want to have to place an order just for pots.  You could even go down to 10K for the fast range pot to have even better precision if you are willing to sacrifice some flexibility.  And if you don't care about really slow rates, you could replace the 100K with a 50K.  All this is really doing is allowing the full rotation of the pot to affect a smaller range of speeds, thereby providing more precision.

[smallbearelec]

Wondering if there are any tips for altering the "feel" of a speed pot in my trem.

Have you tried a dual reverse audio like what was used in the Univibe? I have it in 16mm as well. A lot of people have reported happy results with it in the EA and similar trems.

[goldstache]

I Love all these Ideas.  Thanks so much!  TO THE BASEMENT!!!!!!!!!!!!!!!!!!!