Volume pot ground leg - why?

[burningwater]

Ive noticed looking at a few overdrive projects that the volume controls have one of the legs going to ground. I dont really get what the purpose of this is. If the pot is there to add resistance to limit the amount of signal passing through why have one leg grounded.

This came up when I was trying to reduce the overall volume of a simple fuzz circuit by adding a resistor to the input or output signal of the volume pot (which was at the end of the circuit). Though it did lower the volume it also effected the tone Im guessing because of the ground connection.

Please explain. Thanks!

[sfr]

What happens when you short a signal to ground?  You get no signal.  This is often times what happens to broken guitar cables, the hot and ground conductor short out.  If you open one of your pedals so you can access the jacks and connect the tip off the cable to the chassis, you'll get the same thing - no signal. 

Connecting one of the lugs of the pot to ground allows you to do the same thing - short the signal to ground and get no signal - but by putting a variable resistance in there, you can do this by increments.  Simply tacking a resistor on there w/o connecting to ground will simply mess up the impedence.

I'm someone else here can explain this much better than I, however.  I think it's covered in the FAQ as well? 

[MartyMart]

It's simply providing a path to ground between your circuit out and the output jack.
More to ground = quieter
Less to ground = louder.
The pot is a handy control for this = volume 
For a fixed amount of output level , such as an MXR P90 , a fixed value resistor is used to ground
just before the output jack - 100k/150k etc .

MM.

[burningwater]

Thanks guys that makes sense. I guess if you just wired to lugs of the pot it would lower the volume but because its not shorting to ground it wouldnt necessarily cut the volume all the way at full resistance.

So that leaves me wondering. I put together a fuzz circuit but it is way too loud. I tried adding a resistor after the pot between the output lug of the pot and the bypass switch out. It worked but it cut a lot of the high end, any suggestions on how to cut the vol without effecting tone?

Thanks!

[DuncanM]

It's not there to act as a variable resistance - it's called a "potential divider". A whole different idea.

The voltage at the wiper will be related to the voltage at the top of the pot according to the ratio of (the resistance of the wiper to ground) to (the resistance of the top of the pot to ground).

For example - a 100k pot with the wiper measuring 10k to ground will give an output of 10/100 times the input. i.e. one tenth.
This is a rough approximation because the impedance of the following stage will load the pot.\

http://en.wikipedia.org/wiki/Potentiometer

[burningwater]

Interesting. So would you say that the reason Im getting a change in EQ is that you are in effect changing the voltage to ground or the amount of signal to ground therefor effecting everything else connected to ground, in this case the tone caps?