Quick wiring question. Is this correct?

[Steel Curtain]

I want to wire a circuit where I can blend a capacitor in and out of the circuit. The pot at max one way being fully open into the cap, and the pot turned completely the other way would be like taking the cap out of the circuit. I understand there would be a small amount of bleed through and the cap won't be completely blocked, that would be fine. I plan to use a L100k pot for this unless another value is recommended by folks more knowledgeable than I, which is pretty much everyone!

The top lug of the pot is unconnected in my picture. basically I want to allow signal through or block the signal to the cap all together with a turn of the pot.

Is my wiring in the picture correct for what I'm trying to do here?






Or would it be like a cap blend circuit with the main line open like this?





Thanks all

-Rob-

[J0K3RX]

You could do something like this... which I guess is kinda like your 2nd diagram..?

[Steel Curtain]

Thanks JOK3RX...

         I don't want to divert all the signal into the cap, just add the cap to the circuit with a pot leaving the main signal otherwise unaltered. The schematic you posted, unless I'm reading it wrong, has the cap in the circuit full time and blocks the would be unaffected signal path without the cap. Is this correct? If so, that's not what I'm after. If i were to modify that schematic and place the cap immediately after the pot in series and leave the bottom as the straight signal, would that have the desired effect? Or am I just confusing myself?

thanks.

[GGBB]

Actually both of the diagrams are wrong for the same reason - the pot and cap never have any effect no matter what setting the pot is on because they are always shorted by the direct connection between in and out.  J0K3RX's diagram works - when the cap is "off" the entire signal is basically passing straight through.  Another way is to connect the pot between the input and output (pins 1 & 3) and connect the wiper to your cap and the other end of the cap to output, but you will always have series resistance for some parts of the signal.  There is no getting around "diverting" signal into the cap if you want the cap to actually do something.  There are other ways to do similar things.  Maybe if you explained in more detail what you are trying to achieve we might be able to help you better.

[Steel Curtain]

Understood GGBB.. Thanks.

               I plan to put a cap between the base and collector of a transistor in a fuzz project. I've seen lots of different values of capacitors used in this manner to reduce or smooth out high frequencies in the circuit. My idea is to try to put a larger than average cap in there and use a pot to increase/decrease the amount of signal going to the cap to hopefully achieve a variable amount of the high frequencies effected.

               I have no clue if it will work, but I don't see why it wouldn't. But then again, I'm not even sure how to wire the pot! I'm still very much a noob.

Thanks again.

[GGBB]

That's freaky - I am planning on trying exactly the same thing when I build my next fuzz.  The way I intend to try it is to use a small cap (min cap) in parallel with a pot and another cap (max cap) that are in series.  It's basically the pseudo variable input cap idea from Joe Gagan's Easy Face but used between collector and base as a variable smoothing cap.  I still have to play with the values, but I figure that if I choose the right pot value and a small enough min cap, I should be able to blend between effectively no smoothing to whatever my max cap value is.  Another way I have thought about doing it is the way I described previously with the pot connected between the collector and base, and the cap across pins 1 & 2 of the pot (or 2 & 3).  Jim's diagram won't work here because it will short collector and base at one end of the pot and it will always leak some DC from the collector to base.  I will have to breadboard these things before I will know what does or doesn't work.

[Steel Curtain]

That's awesome! I'm glad I posted this when I did then..

          I had considered wiring it like an input cap blend circuit like you suggest, blending between big and small caps. After some thinking I figured that the small cap wasn't necessary because when the cap is wrapped around a transistor in the normal way, it of course works as intended, so, just varying the amount of signal that is allowed to pass the cap would be sufficient to get the effect I'm after. I also figured that the smaller cap isn't needed because unlike the input cap at the very beginning of the fuzz circuit, the signal doesn't NEED to be moving through the cap at all times, again, because it's not the main input cap. So just blending the one cap in and out of the circuit would be fine in this application. You don't think it would work properly and blending between two caps is necessary?

But, If I modify the cap blend schematic a little but still using the basic concept, it would look like this...




You like?  I feel good about this configuration. I have 1K, 10K, 100K, 250K and 500K linear pots and have no idea at all which would be ideal. I'm guessing the 10K or 100K. I'm going to need to get out the breadboard and try them out, the same as you.

Thanks again, GGBB.

[GGBB]

That should work as well, but there will still always be some signal passing through the cap.  The size of the pot will determine how much by shifting the frequency range above audible.