pots: A/B; log/linear...

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andrei
hello, i've noticed that there are different types of pots with the same resistance. first thing i noticed: it says on them 500kA/500kB. now, snooping around on thomann (.de), i noticed in the descriptions, some say log (logarythmical?) and some linear. the only thing i could connnnect these with are the functions with the same names. is that so? does it reffer to the way the pot is increasing/decreasing the resistence when turned? i have 500kB pots with my duncans and they suck, cose when the volume is up, turning them doesn seam to have any effect at all and when turning it down, the sound cuts off abruptly. also: how come emgs only need 25k pots (kindo a big difference from 25 to 500)? i'll be verry grateful if someone with the technical knowledge could bring some light into this issue. thanks!
marauder

Volume pots should have logarithmic (A, audio taper) pots, when these are at 5 then the volume is half what it is a 10. This doesnt give exactly half the output voltage at 5, but it works the same as the way your ears work in response to the change in volume.

Linear pots (B) pots, these give half the voltage output at 5 compared to 10, usually used for tone pots. When used as a volume pot, 5 will not be 50% volume, this is the problem you have with your volume control.

EMGs need 25k pots due to the output levels being totally different to passive pickups.

metalhobo

I think the EMG pots actually control preamp gain, not output volume.

andrei

thnks for the replys!

i've searched on wikipedia and here's what it says:

Linear potentiometers

A linear pot has a resistive element of constant cross-section, resulting in a device where the resistance between the contact (wiper) and one end terminal is proportional to the distance between them. Linear describes the electrical characteristic of the device, not the geometry of the resistive element.

Logarithmic potentiometers

A log pot has a resistive element that either 'tapers' in from one end to the other, or is made from a material whose resistivity varies from one end to the other. This results in a device where output voltage is a logarithmic (or inverse logarithmic depending on type) function of the mechanical angle of the pot.
Most (cheaper) "log" pots are actually not logarithmic, but use two regions of different, but constant, resistivity to approximate a logarithmic law. A log pot can also be simulated with a linear pot and an external resistor. True log pots are significantly more expensive.

now it's pretty clear.

TheDevilHimself

For guitar controls I highly recommend you use logarithmic ones. The linear ones are really quite useless IMO when used on a tone or volume.

andrei

i've wired my guitars with 2 independent volume controls.
pickup -> pot -> switch -> jack

on clean, everything works just fine, but
when distortion is on, if one pickup is selectet and it's pot is turned down, but the other is up, i still get a weak signal when hitting the strings.

can this phenomenon be avoided (when still using 2 independent vol knobs)?
is it cose of the switch (3way)?

on emgs this works better then on duncans.

another one:
i've seen in some whire diagrams the signal in the vol pot goes "in" through the middle and "out" on the right and in others its the other way around, "in" through the right and "out" through the middle.

whats the deal/difference?

andrei

is there a way to get 2 independent output signals out of the switch (in1 <=> out1, in2 <=> out2), so i may try wireing:
pickup -> switch -> pot -> out

i've tried separating the two "outs" of the 3way switch, that are usualy soldered together, hoping i'd achieve this, but it didn't work.

andrei

thanks a lot Khali,

i get what your saying.
you're right, now it's done like the first schematics shows.

please explain what the difference between wireing a vol pot like the first schematics shows (in: middle, out: right) and whireing it as showed in the second (in: right, out: middle) is.

and why is it essential to use linear pots? do they "cut" more?
(people where recomanding log in previous posts, cose they fade in smoother)

i was actualy hoping in the mid position to be able to mix the sounds of both pickups, but well...

hopefuly i'll get to mess with them tonight and see how it turnes out,
thank you!

andrei

thanks a lot to all you guys for putting your knowledge into this and special thanks to Khali for his patience with this slow bastard.

i've wired the guitar as Khali described in the last post and it works just as it should.

allthou it's not exactly as i wanted it:
this way, in the mid position, each vol pot is master, so you get the same volume from both pickups, which is: min(vol1, vol2).
so, at all times the mix will be 50/50.

what i ment by "independent" is: in the mid position, each pup with it's own percentage, so if vol1=50% and vol2=100%, you get the output: 25% from pup1 and 75% from pup2.
this is how i had it set before, but this way i couldn't mute the damn thing by turning only one volume down, even if just it's pickup was selected.

so this is the compronise solution...

i've fryed some shitty new pots in the process and have ended up intsalling some the old ones from the EX (A/B)...
i'll order some decent (guitar) ones online since i can't find any suitable (big pots, long shaft) at the local electrics store.

thanks again and hopefuly this long thread will help someone thinking about rewireing his guitar, so he only has to do it once.

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