Re: differant types of pots?!?
Where in the world are you Loz?
Here's a couple of US sites but there's no point me referring you to a US site if, say you are in the UK, there are easier places..
I got most of these links just browsing this forum BTW, and then there's Google...
http://www.stewmac.com/
http://www.allparts.com/
http://www.wdmusic.com/
http://guitarpartsdepot.com/
http://www.guitarpartsusa.com/
http://www.guitarpartscanada.com/
In answer to your q, the higher the impedance of the pickup coils, the higher the track value needs to be. Generally, humbuckers will use 500kΩ pots, single coils 250kΩ. In a mixed set you should use the higher value. Some manufacturers use 300KΩ and you will also find 470kΩ and 25KΩ. 25kΩ are used by EMG for their active pickups.
You will also find pots with different tapers; this refers to the way in which the track divides as the slider moves along it, or the sweep. the most common are logarithmic (sometimes called audio taper) and linear. Log taper is usually used for volume, linear for tone although some swear by exclusively log, others by linear and ther are some people who reckon it should be the other way around enntirely. Me, i just go with the flow and do whatever makes my customers happy..
Log pots are usually labelled B and linears A, i think. There is also antilog taper and these are labelled C but you don't see these very often.
It is more about orders of magnitude than exact values; 250kΩ pots will work with humbuckers and vice versa but may present a different taper to the sweep so with the wrong value you may get a bit of a "step" in the gain as you turn it up and down. 25kΩ will not work with ordinary high impedance pickups as, if you think about it, it would be like having the volume control of a 250kΩ turned down to 1/10th of its value.
As
7turns (see post below) says there is also an effect on the tone, although this is more of an issue with the tone pots than the volume controls. Any circuit which has a resistance and a coil or a resistance and a capacitor or all three, will have a resonant frequency to which it best responds; this is called the q-factor. Altering the value of any of the components of the circuit will alter the q-factor and therefore the perceived tone of the circuit.
The pot in a tone control is really just a variable resistor placed between earth and a capacitor. (pot is short for potential divider; I'll explain this later!)
Capacitors are good at passing high frequencies but don't like low frequencies, so without the resistor the high frequencies will tend to drain to earth. By altering the value of the resistor, we can control how much of the HF component of the signal is drained to earth, and therefore the percieved tone. this is called a low-pass filter. The higher the value of the pot track, the higher the value of the cut off frequency above which high frequencies are lost. The highest value of pot usually found in guitars is the 1MΩ (twice the value of a 500kΩ)found in early Telecasters, Broadcasters, Jaguars and Jazzmasters.
How the pot is wired also makes a difference. The volume control is usually wired as a potential divider: the signal goes to one end of the pots track, the other end goes to earth (so that the track is in parallel with the coil in a guitar circuit). This creates a
potential gradient (in DC terms) across the track which is then "tapped" by the slider, so that if you have a pickup with an RMS value of 200Mv, the output from the slider will be 200mv near the input track terminal, zero at the earth terminal and proportionate in amplitude at stations in between.
to be continued
