DIFFERENCES BETWEEN LINEAR POTS & LOG POTS?

[siaoguitar]

Hi, just started out to do my own stompboxes, nice forum u guys have here.-wonderful.
Well, i was trying to get some components for my projects, but the shop do not hav the log pots that was specified in the bill of materials.
So i bought the linear ones instead, can it still function? will it give me the same result?
What's the difference between linear pots & log pots?

I am using them in my proco rat clone & minimixer(generalguitargadgets)

[mikeb]

Linear pots can be subbed for log pots,sure,  so it will 'work'. Log pots are used to give response that matches the human ear (we hear in a 'log' fashion, i.e. to be twice as loud the source needs to have 10x as much energy). You'll find that the response of linear control (when subbed for a log) is bunched up early in the pot travel.

HTH

Mike

[guitarhacknoise]

right on!
a linear pot goes from zero to ten like a wheelchair ramp,
and a log pot looks like a skateboard ramp! make sense?
-matthias

[MartyMart]

Thats a nice analogy Mr Hacknoise !
could you please explain to me how to wire up a Baxendall tone circuit using a surfboard and a baseball bat !!  
Marty.

[remmelt]

... and you can check the difference with a multimeter: connect one side of the MM to the middle lug, the other side to one of the side lugs (doesn't matter which).

turn the pot entirly to one side. note the readout (say: 0). now turn the pot all the way to the other side and note the readout again (say 50K). we have now established the pot is a 50K pot. now turn the pot to roughly the halfway mark. if it is anything near half the value you measured before (say 25K in our example), it's linear, if it's more like a quarter (say about 10K), it's log or audio.

have fun!

[markr04]

right on!
a linear pot goes from zero to ten like a wheelchair ramp,
and a log pot looks like a skateboard ramp! make sense?
-matthias

I was under the impression that the skater quarter-pipe shape was that of exponential (at least in math it is). And that log is closer to the shape of a parabola. And, of course, linear is a straight line.

Now I'm confused! How far off am I?

And is there such a thing as exponential pots?

[markr04]

Ooops. Let me try that again.

Exponential:
a line from (-5, 0) to (0, 5), the curve leans toward (0,0) = skate ramp shape.

Logrhythmic:
with same coordinates, bows away from (0,0). More of a rounded curb shape (parabola). The opposite of the exponential skateboard ramp shape.

Unless resistance is measured differently? I'm sorry, I'm just confused.

[zeta55]

Check this out.


http://sound.westhost.com/pots.htm#chg-law

[niftydog]

in it's true meaning, exponential functions are closely related to natural logarithim functions.

(e is a constant = 2.718, log as shown is a natural log [base e not base 10])

say;
x = e raised to the power y
(this is an exponential function)

then;
log x = y

[R.G.]

OK, I tried to bite my tongue.

Go read "The Secret Life of Pots" at GEO, http://www.geofex.com.

[siaoguitar]

HOW ABT REVERSE POTS? ANY DIFF. FROM NORMAL LOG pots, coz' i got schematic for mxr phase90 and microamp, they uses reverse log pots, so how? can use other type of pots?

[Kent S.]

What's the difference between linear pots & log pots?

Although the question has been answered, I'll throw a simple explanation ... the pots will work just most of their *action* will happen at one end or the other for using a linear in place of a log, or anti-log taper.
Here are some idealize numbers for you or the division between the CCW and wiper, and the wiper and CW lug of a two section commercial *audio taper* (read cheap log) ... For a 500K pot ...
CCW .......W ....... CW....... @Position
........500k.......0................@10
........410k.......90k.............@9
........320k.......180k...........@8
........230k.......270k...........@7
........140k.......360k...........@6
........50k.........450k...........@5
........40k.........460k...........@4
........30k.........470k...........@3
........20k.........480k...........@2
........10k.........490k...........@1
..........0..........500k............@0

[Kent S.]

Linear Taper would be ...
500k.......0
450k.......50k
400k.......100k
350k.......150k
300k.......200k
250k.......250k
200k.......300k
150k.......350k
100k.......400k
50k.........450k
0............500k
For the same positions ...

In short a log pot is -6dB @ 7.5, while a linear is -6dB @5;
A log pot is -20dB @ 5, while a linear is -20dB at 1 ...

A reverse log is the same values as a log, but starting say going from 0~10, but with a reversed rotation. The rotation is the same, but the ratios are swapped ... the CCW to W value being swapped with the W to CW value.

[mikeb]

OK, I tried to bite my tongue.

Go read "The Secret Life of Pots" at GEO, http://www.geofex.com.

Some questions do seem to keep on coming up, don't they? Weekly even!

Mike

[Kent S.]

... and you can check the difference with a multimeter: connect one side of the MM to the middle lug, the other side to one of the side lugs (doesn't matter which).

turn the pot entirly to one side. note the readout (say: 0). now turn the pot all the way to the other side and note the readout again (say 50K). we have now established the pot is a 50K pot. now turn the pot to roughly the halfway mark. if it is anything near half the value you measured before (say 25K in our example), it's linear, if it's more like a quarter (say about 10K), it's log or audio.

have fun!

The easier, if you will, way is to just check the two outside lugs CCW and CW, that's the pot's total resistance; now where the issue comes into contention with me is, with a log pot, you check between the CCW and W lug ... for linear, yes, 50% of the pots total value (or close to it); for log, you should get about 10% for an audio (not 25%) the remaining 90% between W and CW lugs) Fender has some pots stated to be 30% at center(from the CCW to W lug) they are used for some of their mid boost control pots for their on-board midboosts, they are more of a semi-log.
A reverse log (lefthanded pot) ... would be 10% between the W and CW lugs (the remaining 90% between the CCW and W lugs).
A cold lug to wiper value of 20%, 25%, or 30% does not yield the proper voltage level to match an audio curve at the center ...remember from 10 to 0, 5 if half way down (half volume ...1/10 the voltage) ... -20dB (ref voltage). Now those other tapers may be pleasing as tone controls, but as far as a log taper, they are not.

[siaoguitar]

Can i use a normal log pot for my phase90 clone? (just reverse the wiring the other way round)  coz' phase90 uses a 500k reverse log pot

[markr04]

Can i use a normal log pot for my phase90 clone? (just reverse the wiring the other way round)  coz' phase90 uses a 500k reverse log pot

I'm pretty sure they're not referring to the direction you turn the pot. It's probably the shape of resistance.

But, yes, you could use a normal log pot.. It may not behave exactly (as in the pot itself) like a phase90, but you may not even know the difference.