POT CURVE (how to make it more Log)???

[richon]

Hi,

I have a 500K-LOG (audio) pot that I use for GAIN control in a pedal alla dr. Boogey... but with 6 Jfet stages and a lot of diference in the filtering of the stages.

The Gain is HUGE, the TONE is awesome...   but!!!

With the gain pot over the 75% is WAAAY to much and bellow 20% it steals to much the gain.

any way to have the same pot with a even softer LOG super LOG curve to have a little more control over the low gain (even when it steals me the last 10 or 20% of the max gain)?

[R.G.]

You can further caper a log pot with the techniques of "The Secret Life of Pots" at Geofex.

[richon]

You can further caper a log pot with the techniques of "The Secret Life of Pots" at Geofex.

I know I should have looked there before 


Taper resistors work for Linear and Audio pots also???

the B value there get me confused as it seems to be calculated only for lineal pots, right?

[R.G.]

Taper resistors work for Linear and Audio pots also???

Tapering resistors mess with any pot they're put on. It's just simpler to do the math with linear.

the B value there get me confused as it seems to be calculated only for lineal pots, right?

It is only calculated for linears, as the most common situation is wanting to make audio/log or reverse audio out of cheaper and more available linear pots.

Without doing the math, you can mess with it a bit. A tapering resistor between wiper and "cold" side has no effect when it's infinity (open circuit). As you decrease from infinity, the effect gets more extreme. Values of about the value of the total pot should start showing some effect, and it gets more extreme as you approach 1/10 of the basic pot. So mess with values in that range and see if it gets you what you want.

[richon]

excellent!!!



will test right now!!!


last question...   does a 1/10 (50K for a 500K pot) resistor, as a TAPER RESISTOR, change the value of the impedance that "sees " a Jfet in the stage after the pot??

or is it that the high impedance of the Jfet would mind of the change in the pot and input resistor to ground?

[richon]

now that I thing, the JFET stage after the pot wouln't mind of the change in total resistance of the pot


BUT, the RC formed by the coupling caps and the pot (from previous stage) would change "maybe to much" with this taper resistor...


damn!

[richon]

after a lot of testing and looking everywhere i found that...

I could reduce the value of the pot with a paralel resistor and regulate the starting point of the pot (gain pot) and regulate the hole pot value for the RC

[Brymus]

You have peaked my curiosity,I will use a resistor in parallel to change the value of a pot.
But changing the taper is confusing to me,I must admit,I know it changes just not sure how ,or how to use it to my advantage.
Could you explain the graph a little more ?
And enlighten us with your findings ?

[John Lyons]

This thread is pretty all inclusive.
http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

Short answer:
Putting a fixed resistor from wiper to ground will give you an audio taper curve.
Putting the resistor onto a an audio taper pot will give you a G taper or "Super Audio Taper"
A value of 25% of the pot's resistance is a typical value.
This will lower the value of the pot 25% but it may not matter.

[Brymus]

This thread is pretty all inclusive.
http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

Short answer:
Putting a fixed resistor from wiper to ground will give you an audio taper curve.
Putting the resistor onto a an audio taper pot will give you a G taper or "Super Audio Taper"
A value of 25% of the pot's resistance is a typical value.
This will lower the value of the pot 25% but it may not matter.

Thanks John thats exactly what I was looking for,

[amptramp]

There is a way to get a linear-taper pot to act like an audio taper:  use it in an inverting op amp with the pot slider connected to the inverting input of the op amp, the input at one end of the pot and the other end connected to the output of the op amp.  When the slider is at the output, the gain is zero.  When the slider is at the input, the gain is infinite (OK, the non-ideal nature of op amps will take over before this).  If the resistance on the input side of the slider is X and the resistance from the output to the slider is Y, the gain is -Y/X.  Since Y or X can go down to zero, this covers a lot of variation.  A resistor in series with the slider can eliminate some of the extremes. YMMV.

[richon]

right, but both ways, with the taper resistor, would change the RC formed with a Coupling cap and the pot, isn't it???

This thread is pretty all inclusive.
http://www.diystompboxes.com/smfforum/index.php?topic=70732.0

Short answer:
Putting a fixed resistor from wiper to ground will give you an audio taper curve.
Putting the resistor onto a an audio taper pot will give you a G taper or "Super Audio Taper"
A value of 25% of the pot's resistance is a typical value.
This will lower the value of the pot 25% but it may not matter.

[John Lyons]

Slightly I guess. Probably not enough to notice though.
Just up the cap a smidge if your worried about it.