Phozer mod---runoffgroove.com--- question

[jimbob]

A 1k pot wired as a variable resistor can be inserted between the 22uF cap and the junction of the 680pF and .0068uF caps. This will allow control of the sweep Q.

How would i do this? I have a 1k pot where do i put the wires from the board? Above it shows how to put them "on" the board but then they need to be attached to the lugs of the pot ; and there are 3 logs..which wires go to whick lugs?


thanks,

jimbob

[B Tremblay]

Connect a wire from lug 3 of the 1k pot to the junction of the 680pF and .0068uF caps.  Connect another wire from lug 2 to the positive lead of the 22uF cap.  Lug 1 can be connected to lug 2 or simply left unconnected.

This will provide a control that gives the most pronounced peak at full clockwise rotation.

[jimbob]

Very cool! Thanks for the quick response! May you make a million someday..Your site is awsome! On my 7-8 ROG project!

[Samuel]

Read "The Secret Life of Pots" at GEO. A pot is basically a resistive strip that connects the two outside lugs (call them 1 and 3). Lug 2 is connected to a "wiper" imagine the arm on a record player, with the "needle" coming into contact with that resistive strip. When you turn the pot, you are moving that needle closer to one end of the strip, and further away from the other.

Say for example you turn the pot counterclockwise. As you turn the pot, the wiper attached to lug two moves closer to lug 1 along the strip. Since the amount of material between 1 and 2 is now reduced, resistance between those two points decreases. At the same time, resistance between lugs 2 and 3 increases, since there is now more  resistive material in the path.

The result is, that at one end of the turn, the resistance between 1 and 2 is close to zero, and the resistance between 2 and 3 should be the full value of the pot (in this case 1k). Turn it the other way and its vice versa. Regardless of where the pot is set to, however, the resistance between lugs 1 and 3 will always be the full value of the pot, since any signal traveling between those two will always have to traverse all of the resistive strip.

This is a long way of saying that, with a linear pot (audio or logarithmic taper pots have an uneven distribution of resistive material to change the manner that the pot affects resistance dependent on the wiper's location...) you can use *either* 1 and 2, or 2 and 3. The only difference in operation will be the manner in which turning the pot affects the signal. ie if you were putting a volume pot into a circuit you'd want to turn the knob clockwise for more volume. If you wired it backwards, you'd get just the opposite.

As an added note, many people are in the habit of connecting the "spare" lug in this setup to the wiper, which can reduce noise across the pot as it ages and wears.