linear pots and audio taper pots

[67polara]

My question is when does a linear pot work better than an audio taper pot?  I know the audio works best in volume controls but what in the circuit makes the linear pot better for tone control and such?

Tony

[shortfuse]

I have asked myself the same question and have no clue so I look forward to answers on this also.

[navdave]

Linear pots work great for treble, midrange, and presence I like em for master volume to.

[67polara]

Would you agree with this statement?  An audio pot starts out slow and gains more resistance toward the end of travel.

Would you agree with this statement?  A linear pot when rotated has a constant even increase in resistance.

Now here is what I find strange, if you use a linear pot for a volume control the volume ramps up very quickly to about the number 4 point and then has a very slight increase in volume to the end of rotation.  Why?

Tony

[alerich]

One place where I find that an audio taper pot works better than a linear taper pot is in the reverb intensity control on Fender amps even though Leo put linear taper pots in that circuit position by design. The audio taper pot affords greater control since the lower part of the taper covers less resistance. Makes the reverb much more user friendly.

[kagliostro]

Linear and Log pot exist because of the response of our ears that are non linear in sensitivity

so is preferred to use Audio pot (Log pot) for some use where is more relevant the fact that our ears are'nt a linear sensitivity device

Kagliostro

[tubeswell]

Linear pots are good for mixing/balance controls

[eleventeen]

Our brains want everything to make sense or they rebel, at some level.

If we were twisting the "volts" knob on a power supply and watching the output meter, we'd surely like the pot to sit at about 12 o'clock when the supply is cranking out half its rated output. We would want the proportionality of the pot's rotation to match the range of operation it is supposed to trace out. It would, in contrast, bug us if we turned the knob 10% off zero on (say) a 0-100 VDC power supply and the meter was reading 40 volts. This would happen because we are looking at this linear output (meter) scale with our eyes and formulating this scheme of things where the more we turn the knob, the higher the output. It would bother us if the supply reached 100 volts before the midpoint of the pot's rotation. It would bug us if we could not get good adjustability because upper end of the voltage range was crammed into the last 15% of the pot's rotation.

Audio pots are formulated to create a resistance curve that can drive a circuit non-proportionally to the rotation of the pot, because we don't have that linear output readout...we have instead our sensitivity to volume levels, which is far from linear. There are of course reverse-audio taper pots, and I happen to believe that this is very frequently not notated on many schematics, nor is it much discussed. On a Super Reverb, both tremolo pots are reverse audio. It's in some ways a matter of "programming"; the designer of the circuit wanted to make the user feel like when user twists the knob, there is a perceivable effect.

As Chubby Checker once said, "I twist, thus I exist".

[67polara]

Thank you eleventeen.  Now where are linears used most and Audios used most?  I also notice that many of the schematics shown on these forums do not state as to whether it is an audio or linear so if I know what it does I could figure out if it should be linear or audio.

Tony

[eleventeen]

I think to answer that question you'd have to essentially take a poll, by viewing a few hundred schematics which I'm sure you do anyway, but with that additional data point in mind.

We know that volume controls are pretty much audio taper, universally. We know that tone controls are generally linear. I recall adding MV controls to Fender amps in my early modding days and it was always annoying that the operative range was crammed into a very small arc of the pot's rotation. Why that? No doubt because I grabbed a loose 250K or 500K pot from the junkbox, and most (though obviously not all) pots in that ohms range salvaged from other consumer audio gear are going to be volume = audio taper pots when they probably want to be linear. I can likewise recall using nice Allen Bradley pots salvaged from more industrial gear (almost guaranteed linear) for volume controls and having to turn the knob up to "7" before I was really running the amp...when all my stock Fenders were happy at 3-4.

[simonallaway]

I recall adding MV controls to Fender amps in my early modding days and it was always annoying that the operative range was crammed into a very small arc of the pot's rotation. Why that? No doubt because I grabbed a loose 250K or 500K pot from the junkbox, and most (though obviously not all) pots in that ohms range salvaged from other consumer audio gear are going to be volume = audio taper pots when they probably want to be linear.

Ah! That explains the behaviour of an overdrive pedal I built. All the activity on the 'drive' control is bunched up in the first very small arc. I think I bought the wrong part.  Thanks for confirming that.