How do you decide pot taper?

Usually I decide what I'm going to use it for, and then go with the taper that gives me the most control over the usable range for that use.

Most of what I do is guitar pedals, so the volume control is usually a lot less important there -- there's not really gain staging a lot of the time, just trying to get the thing the right volume when it's turned on. I think the most frustrating tapers I've ever had to deal with are depth controls on some tremolos, where the usable range doesn't neatly box into any particular range.

Anyway, I don't think my general rules for deciding the taper are very different from Dualflips, but from what you've described it sounds like they used an audio taper and needed a linear taper, or a linear taper and needed reverse log. In fact, I'd say that the range you described sounds like they used an audio taper when they needed a reverse log. If they're sticking a pot between a cap and ground hanging off the emitter of a transistor or the ass end of an op amp, they wanted a reverse audio taper, or even, as John said, a REALLY reverse log taper, which might require fiddling with some extra resistors across the pot lugs.

If the design is more finicky than that, to the point where none of the common tapers work, then there's always a stepped rotary switch.

EDIT: The guitar pedal reference I have for this behavior is the stock fuzz face's fuzz control. Nothing nothing nothing nothing ALL THE FUZZ.

midwayfair said:

I'd say that the range you described sounds like they used an audio taper when they needed a reverse log

Click to expand...

try lifting then swapping the connections to pot ends, then try how it feels "the other way around", i.e. highest gain CCW.. If it's a log and sjuddabina neglog, it will feel right but mirrored. If nothing really changes but the mirroring, it's lin where itsjuddabina something-else..

/Jakob E.

After a week with these pres, the manufacture contacted the studio to get our opinion. We told him everting from how they sound to how they measure. We mention to gain pot and they replied that it was normal
And working in spec. That they have found  that it sounds best when the preamp is at full gain and that is why it does that. Totally normal

..not boosting confidence very much, that reply.. 

working as designed.
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Most preamps have a fixed and variable noise component. At low gain the fixed noise floor is more significant (while presumably the input signal is hotter). At high gain the fixed noise fraction is least significant delivering best overall test bench S/N numbers.
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Normal for "that" design... The luxury of full custom pot tapers is only enjoyed by large volume manufacturers.

If it is a competent design (low distortion, flat frequency response) it will likely sound similar to other competent designs. Gain law is a human factors engineering concern and noticed by consumers.

I have shared this story before but last century during an upgrade, model refresh, of a best selling powered mixer, my lead engineer redesigned the one knob channel gain/mix control for improved signal kill when turned down. In inadvertent side effect of this circuit redesign changed the 12 o'clock gain output to be something like -2dB versus the previous model. The maximum gain was identical, and the power amp module was identical to the previous model........ but we got a tsunami of customer complaints that the new model had less power    :

The customer/dealer/market expectation for normal operation was to turn the channel knobs up to 12 o'clock and then roll...  We decided to retool the gain pot taper to deliver the same gain at 12 o'clock as the previous model, and the field complaints immediately subsided.


JR