SPDT or DPDT which is best for switching a capacitor on a toggle switch?

[daryl]

I'm new to electronics,  I am modding a Big Muff style pedal.

I want to add a toggle switch to change a single capacitor (Film or Ceramic) to a different value.

From what I understand it would possible to use a SPDT or DPDT switch, but i'm not sure if i'm correct.



Questions:
1. Can I use a SPDT or a DPDP? as in my above drawing?
2. Are there any other benefits or drawbacks from either method? or are they effectively the same?

[daryl]

Picture updated with correct picture now.

[daryl]

Anyone know? as I need to order some parts.

[JustinFun]

As you're modding an existing pedal, I'd definitely go for the DPDT option. That way you can solder the caps securely to the lugs of the switch rather than have them floating between switch and board.

If you were building your own you could use SPDT and mount the caps on the board.

[merlinb]

As you're modding an existing pedal, I'd definitely go for the DPDT option. That way you can solder the caps securely to the lugs of the switch rather than have them floating between switch and board.

If you were building your own you could use SPDT and mount the caps on the board.

Here is alternative arrangement that addresses both arguments:

[daryl]

Can someone explain how that works, I can't get my head around how it is switching between caps.

It looks like no matter which way the switch is the two caps are always in series. Or is it something to do with electricity following the path of least resistance and bypassing the capacitor when a path with less resistance is offered?

[Resynthesis]

I'm not an expert but I assume it's least resistance (reactance maybe). In the position shown the signal passes through C2 but takes the short circuit route to OUT and vice versa.

[slacker]

That's exactly it, as it's drawn C1 is shorted out by the green line, so the circuit only sees C2. Flip the switch and the opposite happens.
The benefit of this method over the other two is that there is no break in the circuit when the switch is flipped, which can lead to audiable pops when switching.

[daryl]

Thanks for the info guys, i'm learning.


Could you therefore wire the switch like this with the caps direct on the switch.



Surely that would work and no pop?

[slacker]

Yeah that would work fine.

[daryl]

What if I wanted a choice of 3 caps?

Is there a toggle switch I could use for that or would I need to use a rotary switch?

[merlinb]

What if I wanted a choice of 3 caps?

Is there a toggle switch I could use for that or would I need to use a rotary switch?

You could use an SPDT centre-off switch. In the centre setting the two caps would be in series, giving you a third value of capacitance.

You can also buy special three-way toggle switches, or use a rotary switch.

[aion]

This is the simplest. But, if C1 and C2 don't add up to your desired C3, there's a variation of this. The principle is that you'll leave your lowest-value capacitor connected all the time, and then you add another capacitor in parallel such that when added with C1 it creates the second value you wanted. Then do this with another capacitor to create the value of the third capacitor you wanted.

With the On/Off/On switch, the center position is going to be C1 only. Then one side of the switch is C1 + C2, and the other side is C1 + C3.

I can't do a diagram right now, but maybe someone else could if the description isn't making sense.

[daryl]

I'm learning more stuff, this forum is great thanks for all your help.

I diagram would help yes as I'm a real beginner. I understand the adding caps together part but I thought on-off-on meant that the circuit was broken when on the off setting?

I didn't know you could add caps like this. So say I didn't have the cap value I was looking for eg I wanted 1000nf but I only had a 800nf and a 200nf, could I put them together and get the same result as having a single 1000nf cap? or would it behave slightly different?


You could do it with an on-on-on DPDT switch like this I think:

[aion]

Here's a diagram of it:



C1 is always in the circuit. The switch selects whether C2 or C3 are added in parallel. If C1 was 0.01uF and C2 was 0.0047uF, and the switch had C2 selected, the total capacitance between IN and OUT would be 0.0147. No change in sound between using a single 14n7 capacitor. When the On/Off/On switch is in the middle position, the selector rests between the two poles and is connected to neither of them.

With this method you'll have to get different cap values for C2 and C3 than you had planned - but it'll work well.

[syntaxera]

I'm learning more stuff, this forum is great thanks for all your help.

better than any class or school for this sort of thing i have seen.   the best!

[ayayay!]

It still may pop.  Chances are high it will, depending on what you're using it for.  Look into using a high value resistor as a shunt.  

[nicolas]

You should use an SPDT and the circuit diagram earlier shown, it's easy to understand as well. When two terminals of a capacitor are shorted, it can't store any charge, therefore, it gets neglected. When you switch between two capacitors here, C2 gets shorted and hence only C1 will be the effective capacitance of this path. Hope this is simpler and easier for you to understand.