How dose a Capacitor blend pot work?

[carboncomp]

Iv built and used a few Capacitor blend pot and appreciator the results, but don't really understand the function.  


Is there a good article someone could link to, or possibly take the time just to explain what is actually going on for a electrical point of view?  

[John Lyons]

Basically you send the signal through a small cap and when the resistance is high on the pot the signal is limited through the
larger cap, not all but mostly...compared to the small cap which is getting full signal current.
When the resistance is low or none, the large capacitor is parallel with the small cap which is add both capacitances.
So, small cap = small sound (less bass). Large parallel capacitance + full sound, more bass.
But with that said I don't wire it like the diagram you posted.  
I use this method.

[joegagan]

Hmmm, are you saying i can blend small and large caps? I will have to give it a go!

[earthtonesaudio]

Wut? John, yours is wired exactly like carboncomp's.   

[John Lyons]

Wut? John, yours is wired exactly like carboncomp's.
Yes but his is in color!  Missed the Grey wire....

Hmmm, are you saying i can blend small and large caps? I will have to give it a go!
Yeah dude! You have to try this. 

[bonaventura]

neat 

gonna try it tonight!

[carboncomp]

Thanks!

That makes much more sense now you explained using that layout! 

One last stupid question on this topic, Why dose capacitor size dictate what frequency get though it?   

[earthtonesaudio]

That's because capacitance as a physical property is frequency dependent.  The reactance of a capacitor is 1/(2*pi*f*C) where C is in Farads, f is in Hertz.  The main thing to remember is as frequency increases, the cap acts like a smaller impedance.

[John Lyons]

You can also think about it like a water hose. Bigger hose, more water gets through (more bass)
Smaller hose, less bass.

[mac]

I use a larger pot, 250k or 500k to decrease the residual effect of the bigger cap.
As the pot goes bigger it gets closer to a rotary switch with >5 input caps.

In my RM I have a 4.7n, and a 10n + 250kb pot. It goes from treble to full boost.

mac

[earthtonesaudio]

Note that as the resistance approaches zero, the filter changes from a shelf response to a simple high pass - if this is not desired you can keep a small value resistor always in line.  And if you don't like the sudden transition from ~no bass to ~LOTS of bass, a reverse log taper pot can help make the transition more predictable.

[John Lyons]

Good points. I use a different pot depending on the circuit.
100KB, 100KC, 250kB. Also different caps.
Even among fuzz face circuits (Ge vs Silicon) different caps
are more useful.