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Log or Lin pots?

C

chopthebass

May 20, 2009
9
1
#1
Hi,

I'm building a Jazz bass and will be installing Nordstrand Big Singles. I've found loads of wiring diagrams on the internet but can't determine whether to use Lin or Log pots. Even the Fender site gives no clues. All I found mentioned was 'audio taper' but I have no clue what that refers to.

I just know there is someone here with the answer!

Cheers
Ian
 
#4
The term "audio taper" refers to the resistance curve as a function of the angle which the potentiometer's shaft is turned from counter-clockwise to clockwise.

Pots with a "linear taper" have a straight line from Maximum to Zero.

Pots with an "audio taper" have a curve which starts falling gradually, then increases its rate of descent as you get closer to fully clockwise.

The reason for having an "audio taper" pot is to account for the human ear's natural tendency to hear logarithmically: it takes twice as much power to increase the apparent loudness of a signal by 3db, or something like that. The "audio taper" pot works against this by providing a predictable increase in power at any given start position, for a given increase in the angle of rotation of the shaft.

In practice, most "audio taper" pots aren't a smooth audio taper. Manufacturers long ago realized that making a pot with a perfect taper was too costly, so they usually approximate this by having two different sections of linear tapers. It may sound similar, but it's not doing quite the same thing.

A number of bassists have found that using a "linear" pot makes more sense, if you usually keep the volume of the bass turned all the way (or most of the way) to full, and only occasionally back the volume off for quieter songs. This is because it works a bit more smoothly, and gives you more usable range between the "sort-of loud" and "full volume" settings.

Guitarists usually still need an "audio taper" pot since they may be using this to control the amount of distortion that an amplifier or effects pedal may be introducing later.

Additionally, I've found that I get better response out of volume pots (audio and linear taper) by adding an additional resistor between the "ground" lug of the pot and the ground wire/bus in the bass. This effectively limits how "low" the volume pot can go (which also makes it impossible to mute the bass by turning the volume all the way down) but increases the smoothness and gives you more fine-grained control over your volume in a live situation.

For example, with a 500K pot, I would connect one lead of a 50K or 100K resistor to the "ground" lug of the pot, and then connect the other lead to my bass's ground bus. For a 250K pot, I would use a 25K or 50K resistor. I've tested this idea on several basses, and it seems to work well for me.

Hope this is helpful to you!
 
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#6
yes, linear volumes and audio tones will work the smoothest all around for bass, especially if you're blending between two pickups.
tubby.twins said:
Additionally, I've found that I get better response out of volume pots (audio and linear taper) by adding an additional resistor between the "ground" lug of the pot and the ground wire/bus in the bass.
Click to expand...
interesting.

i think this would also lessen the effective load on the pickup from the pot, making the sound a little brighter.
 
#7
On J-type in particular, greatest variation of tone comes within 12-24dB "window" around "both P/ups full on", if p/ups are well balanced (by means of construction and height). Covering this window is best achieved by linear volume pots. Also, fiddling with pot taper with external resistors is quite common in audio EE (you can get very nice reverse-log response over one decade from lin pot this way for EQ apps). Another way to fiddle around would be 1k-50k resistor from hot end of P/up to center connection on vol pot.
 
#8
Linear pots will give you most of the action at the end.
Log (audio ) pots will distribute the change over a longer sweep. This is why they are called AUDIO pots and used in all audio gear this way (stereo, amps, mixers, etc).

It is easy enough to try - see what you like.
 
#11
jazz jazz.jpg
Killed_by_Death said:
Yes, 1 MegOhm pots are fine for volume, but go ahead & replace both of them.
Click to expand...
the jazz is from japan (a custom gold hardware one) came with the dimarzios and gold badass w/gold tuners and 3 250k B pots (its the one in pic that i took the metal pickguard off of)
 
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#12
The problem with 1M pots is that there will not be a very useful taper. Expect the volume to drop very quickly, as you come down from "10," since the series resistance will be adding up fast.

Why would you want 1M/250k, when you can choose two 500k pots? The total load from one 1M pot and one 250k pot is 200k Ohms, while the total load from two 500k pots is 250k Ohms. Since your goal is to improve high end response, this is a better option. Plus, you have the added bonus of keeping a good taper, and not having to hunt down hard to find pots.
 
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#14
1000 ohm linears cropped.jpg
line6man said:
The problem with 1M pots is that there will not be a very useful taper. Expect the volume to drop very quickly, as you come down from "10," since the series resistance will be adding up fast.

Why would you want 1M/250k, when you can choose two 500k pots? The total load from one 1M pot and one 250k pot is 200k Ohms, while the total load from two 500k pots is 250k Ohms. Since your goal is to improve high end response, this is a better option. Plus, you have the added bonus of keeping a good taper, and not having to hunt down hard to find pots.
Click to expand...
ok, i have 1000 ohm linears already (military grade w/long solid shafts i will have to cut down), but if you think the 2 500k linears would be more user friendly i'll hold off till i get. are the mini pots of lesser functional quality than a bourne or cts full sized ones? appreciate it yall'z, p
 
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