Question about how to choose potentiometers (kinda noobish electronics question)

[dap9]

I tried doing a search, but I'm at work and certain pages get blocked.  But it's a slow day so I'm posting now rather than when I get home.

Here's where I'm at:  I've been at DIY for about 2 years.  I've built several kits, learned to read basic schematics, built several pedals from schematics, and have a very basic general understanding of electronics.  I'm getting the hang of how components work, but I've yet to grasp Ohm's Law and how to apply it so I can make my own designs.  Hence my question...

How do people know what value potentiometers to use in a circuit?  For example, I found a schematic for a "Boutique" Marshall in a Box pedal (a Purple one ).  But I want to put the Marshall Tone Stack in there similar to the Smash Drive - both pedals are very similar in design. 

I breadboarded the "CLone" and I'm pleased w/ the sound.  It requires a 1k pot for the gain, but I only had a 5k (which the Smash Drive) requires.  But the 5k is too noisy (awful) when fully cranked.  What would I need to do to make it so my Clone works w/ the 5k pot?  And what's the rational behind that?  Is that an "Ohm's Law thing"?

Lastly, are there good books specific to this kinda stuff?  I have Anderton's Electronic Projects... and Electronics for Dummies, but what about Indyguitarist's books?

I hope this makes sense.  Thanks in advance

[drk]

it isnt likely that the noise comes from the pot. when the pot is fully cranked, its the same as having a resistor in parallel, so 1k or 5k doesnt make much difference.
the noise comes from something else

the pot value depends on what kind of effect you want the circuit to give, when you rotate the pot

[PerroGrande]

To answer one of your questions (design and selecting pots) -- well, yes, it *is* an Ohm's law thing.  However, that response alone probably won't help you very much.

Pots fundamentally behave in one of two ways, depending on how they're wired up.   

When it is wired up as a two-terminal device (with only two of the three legs connected OR with two of the legs wired to each other), it behaves like a variable resistor.  When turned one way, the pot has very low (nearly zero ohms) resistance.  When turned the other way, it has the rated resistance of the pot (within tolerances, of course).

When all three terminals of the pot are wired up, it acts like an adjustable voltage divider.  The resistance between the outer terminals is constant (the rated value of the pot), but the resistance between the inner terminal and the two outer terminals varies as you turn the knob.  To really get this concept, comfort with Ohm's law is an absolute must.  It explains the relationship between resistance, voltage, and current. 

So -- how does one choose which pot to use?  Well, it depends on what you're trying to accomplish and what precedes and follows the pot, circuit-wise.  Some choices are not particularly critical.  Others require absolutely the correct pot -- tone controls, for example.  The frequency at which a tone control does its magic is determined by resistance and capacitance.  The selection of the resistance (in this case, a potentiometer) is vital to get the desired control. 

I recommend checking out the geofex web site.  R.G. has some excellent articles that will head you in the right direction to get more comfortable with pots.

[GibsonGM]

R.G.'s site for sure, and if you can get any kind of Spice software, do so!  You really can learn a lot from things as simple as 'measuring' a pot part-way thru its rotation, or changing the whole pot's value and watching a Bode plot reveal how frequency response changes. 
Duncan's Tone Stack Calculator is good, too.    Experience and messing with circuits is invaluable!  Like Perro says, it's what comes before and after the pot that really determines what one to choose. 

[dap9]

Thanks a lot guys!  That was really helpful.  I fully agree about the importance of tinkering around w/ circuits.  I was feeling like I hit a plateau and now I have a better understanding of what's going on in the circuit, and what I need to focus my energies on to increase my knowledge.  Looks like I'll have to really sit down w/ Ohm's Law; learn it and find some introductory "worksheets" to practice the math on.  Man, I wish I paid more attention in math class back in the day, lol.  Again, thanks a lot.

[CynicalMan]

To make your 5k pot work as a 1k, check out:

http://www.diystompboxes.com/analogalchemy/emh/emh.html

Go to linear pot and input 5000 and 1000.