adding a switch to go from positive to negative ground.

Magnetar Effects · Post by **Magnetar Effects** » 11 Sep 2012, 21:50

This is my very first post, and I am looking forward to opening a dialog with the freestompboxes community. My question is: What is the best way to add a switch to change a pedals power from a negative ground 9V supply to a positive ground 9V supply? I would like this to be incorporated into a 9V battery powered pedal with a 2.1mm kobiconn jack. I use a solder lug washer around the power jack for a chassis ground connection from the board as well if that makes a difference. The powering scheme is the standard TRS jack on the input with the ring connecting to the battery and DC jack. I am finding it much harder to envision this because of the fact that I would like this to be done with a true bypass pedal that also has an LED, since the LED wiring is based on the polarity of the ground. Is it even possible to add this switch while having a perfectly functioning LED as well? Thank you for reading my post.

IvIark · Post by **IvIark** » 11 Sep 2012, 22:05

You'll also need to swap the polarity of any polarised capacitors in the effect so you'd probably need a bank of relays to do it even with something simple like a Fuzz Face. What would your reason be for wanting to do this?

Magnetar Effects · Post by **Magnetar Effects** » 11 Sep 2012, 22:16

There is no caps or anything else in the circuit to change the polarity of. It's for a new pedal I'm bringing to market. Pretend there is no effect circuit to worry about. Is it possible to do this while also switching the LED? I imagine a dpdt switch would do the trick without the LED, so perhaps it can be done with the LED by using a 3pdt switch?

Duckman · Post by **Duckman** » 11 Sep 2012, 22:35

What portion of the market are you pointing with that feature? Just curiousity...

Magnetar Effects · Post by **Magnetar Effects** » 11 Sep 2012, 22:57

I haven't thought about that. I was just hoping somebody could help me figure this out. Thank you for taking the time to reply to me.

Duckman · Post by **Duckman** » 11 Sep 2012, 23:56

Don't tell me you're the curious! I'm the curious!

One more Q: you're thinking in a device that can accept different polarity from any power supply or you, specifically, needs to change the polarity inside the circuit from a given power supply?

Magnetar Effects · Post by **Magnetar Effects** » 12 Sep 2012, 00:12

I just want a switch in my pedal that will switch the pedal from positive to negative ground. Normally a pedal is wired for one or the other, and I want a switch so the pedal is wired for either at the flick of a switch. I don't know how to accomplish this while still getting the LED status to work properly.

Duckman · Post by **Duckman** » 12 Sep 2012, 01:11

So, you have always the same power supply

How about... power the LED before the polarity change?
Just two dedicated traces or wires directly from the power to the I/O switch?

Magnetar Effects · Post by **Magnetar Effects** » 12 Sep 2012, 01:24

I'm not quite sure what you mean by always having the same power supply. So when you are in the positive ground position, its the exact same setup as a pnp fuzz wiring scheme. When you switch to the negative ground position, then it's the same wiring scheme as npn wiring schemes found in most effects, like bc108 fuzz, or just about any op amp distortion. Hope that clarifies what i'm looking for. Can you describe further what you mean by powering the LED before the polarity change? I can't quite picture this schematically.

Duckman · Post by **Duckman** » 12 Sep 2012, 13:43

Ok, I hope to explain myself better with this drawing of the power distribution inside the pedal.

~arph · Post by **~arph** » 12 Sep 2012, 15:11

Just a thought.. There are LED's which can be wired either way. Just search for duo color LED's with just two leads. One way it's green, flip polarity and it's red.. Will even give you a polarity indication

Duckman · Post by **Duckman** » 12 Sep 2012, 18:32

~arph wrote:Just a thought.. There are LED's which can be wired either way. Just search for duo color LED's with just two leads. One way it's green, flip polarity and it's red.. Will even give you a polarity indication

I was just about to write the same!

Two solutions in one

earthtonesaudio · Post by **earthtonesaudio** » 13 Sep 2012, 02:04

I wish I could hear the reason why you'd want such a thing, but anyway here are some methods to achieve it:

1. Simplest: floating power supply and DPDT switch. Since one terminal of your power jack is grounded, that is your ground. Ground is always ground is always ground is always ground. In order to make ground "more positive" than the power supply you need a power supply which is more negative than ground. So your power supply has a magnitude of 9V and can be either polarity. Simply ground the more positive side and make the other side your supply: instant -9V supply. Using a DPDT switch you can swap both positions at the same time (hint: use a break-before-make switch to avoid burning things), to achieve a +9V supply.

2. Convert whatever your single-ended power supply is to bipolar, and select one or the other.

3. Gather up all the ground connections (except in/out pull-downs) and all the power connections and wire those two nodes to a DPDT switch. Wire the other side of the switch to the power input. This allows you to reverse + for - in your circuit.

All of these methods will result in a broken pedal for probably 99.9999999% of all circuits ever designed. So, uh, yeah.

Magnetar Effects · Post by **Magnetar Effects** » 13 Sep 2012, 05:18

Thank you for your replies! The bicolor LED solution is pure genius. Thank you to earthtonesaudio for your insight as well. It's funny that you mention 99.9999999% of all circuits, because this pedal is one in a million. Once I release my pedal to market you will understand why I wanted to have feature. I'll post a link when it's available. I was going to use a rocker switch. Not sure if it's break before make. I just need something low profile that has a high quality metal washer and nut if possible. I found the perfect one in google image search, but the website is down for some reason. Here's the google image link:
http://t0.gstatic.com/images?q=tbn:ANd9 ... diQNSEykNQ
I don't think burning things or destroying the circuit will be a problem, but I'll definitely test it first. My surreptitiousness must be really annoying! I will reveal my reasons in time though. Thanks again, all!

Duckman · Post by **Duckman** » 13 Sep 2012, 05:31

Good luck!

Magnetar Effects · Post by **Magnetar Effects** » 19 Sep 2012, 04:41

I wanted to update everyone reading this post that the switch works perfectly. It functions exactly as I intended it to, and the bicolor LED was the perfect solution to having a polarity reversal with a DPDT switch, while enabling me to have a visual indication of polarity and status at the same time. I am so grateful for the wisdom of the freestompbox community. Thanks again!
Augie Esposito
Magnetar