Input Blend for Caps Gagan vs

[Mcentee2]

Been searching and absorbing the info for Capacitor Blend circuits and came across these two, that to me appear "most similar", set up to always have a small cap in the circuit and then to progressively dial in a larger cap in parallel.

This is different to the version that simply has the input into the wiper and then two caps on the outer lugs ie going from one side to the other moved the signal progressively from one cap to the other cap - that's not the one I am asking about

For these two versions of the former, however, one has one of the pot ends hanging, the other connects it up shorted to the wiper.

What is the electronic difference between the two ?



and....

[thermionix]

Other than the specific component values, it's the same thing.  In parallel with the smaller cap, you have a larger cap and a variable resistor in series.  The order of the the series components doesn't matter.

[Mcentee2]

Other than the specific component values, it's the same thing.  In parallel with the smaller cap, you have a larger cap and a variable resistor in series.  The order of the the series components doesn't matter.

Thanks, my brain was hurting trying to work it out, it *looked* the same.

[PRR]

> one has one of the pot ends hanging, the other connects it up shorted to the wiper.

We need a variable resistor, two leads.

But IF the wiper gets dirty, bad contact, the resistance goes to INFINITY.

In some circuits, that might be real loud. (Here it just puts you at the small-cap setting.)

Since all our "variable resistors" are made as THREE-leg potentiometers, it gets to be habit to tie the wiper to the un-used end. Now the resistance only goes to max, not infinity.

It is often not important.

[Mcentee2]

> one has one of the pot ends hanging, the other connects it up shorted to the wiper.

We need a variable resistor, two leads.

But IF the wiper gets dirty, bad contact, the resistance goes to INFINITY.

In some circuits, that might be real loud. (Here it just puts you at the small-cap setting.)

Since all our "variable resistors" are made as THREE-leg potentiometers, it gets to be habit to tie the wiper to the un-used end. Now the resistance only goes to max, not infinity.

It is often not important.

Thanks 😀

Sort of failsafe design, makes sense.

[pinkjimiphoton]

i do it slightly differently. i like a small cap and a large cap to taste, and a pot, can be anywhere from 10k to 250k or so. put one cap on each side of the pot, tie the free ends of the caps together. input to the wiper, output where the caps join. its weird, but works fairly well.

[Mcentee2]

i do it slightly differently. i like a small cap and a large cap to taste, and a pot, can be anywhere from 10k to 250k or so. put one cap on each side of the pot, tie the free ends of the caps together. input to the wiper, output where the caps join. its weird, but works fairly well.

I have seen this as well but strikes me that at any point between the two you are introducing some series resistance to the circuit.

In a fuzz face circuit input this changes the input impedance, so is fairly critical, in other circuits maybe it is less critical.

[pinkjimiphoton]

the bigger the cap, the bigger the ESR. thats where ya play with the value of the pot to feel what works best.
at about 50k you get for all intents a passive buffer which helps with oscillations if ya put your wah first.
look at the fulltone 69 pedal. there's a lot of ways to do this. ya can go the EE route, or ya can use your ears.
but there's the thing... EE's are taught to MINIMIZE distortion, not deliberately create and influence it. too many kemzars for my pay grade, i go with a breadboard and a curious george approach.
i really don't care what it looks like on paper, i only care about what me earholes tell me generally. right or wrong. all the time.
this does indeed increase the series resistance. if it works for ya, it does, if not, it doesn't.
don't let the numbers throw ya in this kind of case,  if ya gotta breadboard, try it.
adding resistance in line can help make a si fuzzface sound a whole lot sweeter sometimes.
increasing the esr as ya pan between the caps, to my ear, at least, gives a very smooth and natural sweep to the pot.
the other way is a more abrupt sweep as i recall.
to me, kills two birds with one stone. but depends on how ya voice the rest of the circuit, gain, biasing etc
but right on with the ESR and how it affects the circuit. i think it was actually RG who mentioned that to me first years ago, thats how faking a variable cap works.
not claiming to be right. just built a LOT of fuzzes.
there are myriad ways to skin a cat
ymmv... and should
peace

[Mcentee2]

the bigger the cap, the bigger the ESR. thats where ya play with the value of the pot to feel what works best.
at about 50k you get for all intents a passive buffer which helps with oscillations if ya put your wah first.
look at the fulltone 69 pedal. there's a lot of ways to do this. ya can go the EE route, or ya can use your ears.
but there's the thing... EE's are taught to MINIMIZE distortion, not deliberately create and influence it. too many kemzars for my pay grade, i go with a breadboard and a curious george approach.
i really don't care what it looks like on paper, i only care about what me earholes tell me generally. right or wrong. all the time.
this does indeed increase the series resistance. if it works for ya, it does, if not, it doesn't.
don't let the numbers throw ya in this kind of case,  if ya gotta breadboard, try it.
adding resistance in line can help make a si fuzzface sound a whole lot sweeter sometimes.
increasing the esr as ya pan between the caps, to my ear, at least, gives a very smooth and natural sweep to the pot.
the other way is a more abrupt sweep as i recall.
to me, kills two birds with one stone. but depends on how ya voice the rest of the circuit, gain, biasing etc
but right on with the ESR and how it affects the circuit. i think it was actually RG who mentioned that to me first years ago, thats how faking a variable cap works.
not claiming to be right. just built a LOT of fuzzes.
there are myriad ways to skin a cat
ymmv... and should
peace

Thanks! All good advice, and very pertinent re using one's ears.

Admittedly all my understand so far  is based on theory reading and trying to ask "informed" questions, so am easily confused as to "rule of thumb" practicalities such as "for this circuit it doesn't matter, but for that one it matters more" type of thing!

Thanks again.

[pinkjimiphoton]

i think all theory will always apply, but with fuzz?
whatever fuzzes, is

rock on mate!

[PRR]

> at any point between the two you are introducing some series resistance to the circuit.
In a fuzz face circuit input this changes the input impedance...

It adds series R at low frequency.

At high frequency the signal always takes the short-cut through the small cap.

I'm not sure what the implications are to a FF.

[pinkjimiphoton]

depending on the impedance, it either makes it "brighter" or a bit mellower, kinda like turning the guitar down a little bit, paul

[Mcentee2]

depending on the impedance, it either makes it "brighter" or a bit mellower, kinda like turning the guitar down a little bit, paul

Exactly, like the input pot on something like a Fulltone 69, one of those things you need to know is affected strongly build it.

In the middle of a tube screamer tonestack probably not so much.

[pinkjimiphoton]

well,. maybe... variable caps seem to offer less gain loss than shunting to ground tone controls.
never liked toob skreemers so never bothered to build one.

they workGREAT as snubber caps on transistors... just as it will take the "hiss" out, it can be exploited to modify the tone, too