Really stupid question-- capacitors in parallel on DPDT

[crazynoises]

Let's say you had a circuit with a 2n2 capacitor. But you wanted to vary that value via a switch, maybe for some kind of boost.

The simple way to do it would be to simply have a 2n2 capacitor on one side of the switch and a different one on the other side, so the switch changes between the two values. Which is the way I've always done it.

But couldn't you also just take a DPDT switch and attach the 2n2 capacitor between the middle input/output pins, and then the second capacitor to the "up" or "down" pins? That way the 2n2 is always in the circuit. When the switch is one position, the path really goes nowhere so you just have 2n2. But when it's in the other position you would have two capacitors in parallel, giving you a capacitance of 2n2 + the other capacitor, right?

[Dr Satan]

Yes, and you don't even need a DPDT, a SPST would work just as easily. Connect the caps in question together on one end, switch the leg of the second cap on the other end. Easy peasy. Or you could use a SPDT to switch between two different values, either paralled or in series or just in and out. Or you could also use a SPDT center off switch and have 3 different values to switch between.

[crazynoises]

Thanks, man. Yeah it works. Of course it works. Why wouldn't it work? I needed someone to slap me upside the head.

It suddenly hit me yesterday that I could do it the way we are talking about. I couldn't figure out why I never did it that way because it's actually much better and it's so simple. I was thinking there MUST be a reason, but I couldn't come up with one.

I think what happened is whenever I try to build out a circuit, I don't worry about the switches at first. I just try to get the circuit working. And then I swap out components to try various options. If I end up liking capacitor A and capacitor B then I just think about it like "oh okay. That's what a switch is for. Capacitor A is on one side of the switch and B on the other." And then never thought about it any further. If I had thought about it putting a switching option in that place from the get-go when laying out the circuit, I guess I probably would have figured it out way earlier.

So I guess there was a reason I never did it that way, and the reason is that I'm an idiot. Ugh.

[LaoWiz]

If you search for input cap blend at diystompboxes boxes you can find a neat little trick where you can blend a small cap with a large cap with a pot. Doesnt need to be just for input cap. Adds an extra knob/control on your enclosure but can be useful for some circuits. Basically, a variable capacitor. Ive thought about doing this method but using a trim with the caps on the board as a set and forget. Otherwise, itt's a nice ultility to have around when breadboarding, as well. Switches work, too!

[crazynoises]

Thanks, good tip. Simple enough. 0 resistance=C1+C2. Infinite (or large enough not to matter anymore) resistance shuts off that parallel branch so capictance is just C1. Twiddling the pot gives you values between C1 and C2.

Makes sense to rig up that partial circuit on a pot so you can just drop it into a circuit whenever. Twiddling a pot beats constantly swapping out capacitors trying to zero in on a good value. Plus you can twiddle and play at the same time so you get a better feel of what effect changing the capitance does vs playing something, stopping and swapping and then playing again.

I guess I need to up my game and stop focusing solely on the schematics/theory and just getting them working and only tthen thinking about possible changes I should take a more practical approach to wiring as well as modding and testing and making the circuits more flexible from the start.