2-in-1 Pedal Wiring: How Are They Able to Share Power?

[Caldo71]

Regarding this from the Wiki...

2-in-1 Pedal Wiring (Single Footswitch) - PedalPCB Wiki

wiki.pedalpcb.com

I was just curious as a newbie builder what the electrical theory is behind the seeming fact that you can power two builds from the same 9V power supply? Which assumedly is the case, or that diagram would not exist.

I guess as a novice it would seem to me that those 9V would only be enough to make one of these miraculous gizmos run, and that they'd "run out of juice" if you try and hook up more than one to the same power. Obviously I'm wrong. So how does that work: does it have something to do with how they draw amperage? Bear in mind I know next to nothing about how current works. Talk to me like the dummy I am ;-)

And that leads my brain to the next illogical question: is there some alternate version of this same wiring that could power several pedals (like four, eight, whatever) if they were in the same huge housing? Or is there some kind of practical limit?

Sorry if this is all reeeaaaly f%&*ing dumb: I'm learning...

 

[TravisM]

Voltage divides is series but is the same in parallel. Current divides in parallel but is the same in series. So, effects in parallel, it will draw the extra current if you use a source with more on tap than the required amount.

Same way a daisy chain power supply can power multiple pedals.

 

[Dan M]

As Travis said, just make sure you have enough current from the supply. You can take a look at the current requirements for some production pedals to get an idea. For example: a DOD Carcosa lists 4mA in the specs, a lot of Boss pedals are between 10 and 50 mA, but a Strymon Big Sky needs 300.

Just double check what you are building compared to your power supply. Most likely you will have plenty of current available.

 

[Caldo71]

@Dan M @TravisM is the current draw for any given PedalPCB build listed somewhere on the build docs? I still suck at reading the schematics but I don’t believe I see it in there or elsewhere. Guess I have to go read the specs for the original pedal that the PedalPCB build is cloned from?

 

[TravisM]

If they are both analog, you'll be fine. The digital stuff takes more in general.

@Dan M @TravisM is the current draw for any given PedalPCB build listed somewhere on the build docs? I still suck at reading the schematics but I don’t believe I see it in there or elsewhere. Guess I have to go read the specs for the original pedal that the PedalPCB build is cloned from?

 

[TGP39]

The current draw can be measured on any pedal.

How to measure current draw – stinkfoot.se

stinkfoot.se

 

[Caldo71]

Okay so I THINK I understand the current draw thing when chaining pedals under a common power supply, but let me just give you guys a “hypothetical rig” to check my math.

So lets pretend this is my pedalboard (I’m inventing this all arbitrarily):

• Phaser: 5mA
• Clean boost pedal: 8mA
• Lo-gain drive pedal: 20mA
• Crunch pedal: 10mA
• Searing lead distortion pedal: 20mA
• Post-overdrives EQ pedal: 17mA
• Gate pedal: 40mA
• Reverb pedal: 15mA
• Delay pedal: 15mA

…would that therefore mean that I could run the whole rig off of a power supply that provided 150mA? It’s cumulative?

 

[TGP39]

Your cumulative theory is correct, but remember that current draw for each pedal will increase and decrease depending on what the pedal is doing. Want to turn on that LED? Your current usage for that pedal just went up. Want to switch on that feedback loop which activates an optical circuit? That’s going to require more current as well. When you look up current draw for almost any pedal, they’re going to show you the current when the pedal is on, but it’s most idle state. I would say give a pedal 25% wiggle room for current draw. So your above example would need approx 200mA. Hope this helps.

 

[Caldo71]

Your cumulative theory is correct, but remember that current draw for each pedal will increase and decrease depending on what the pedal is doing. Want to turn on that LED? Your current usage for that pedal just went up. Want to switch on that feedback loop which activates an optical circuit? That’s going to require more current as well. When you look up current draw for almost any pedal, they’re going to show you the current when the pedal is on, but it’s most idle state. I would say give a pedal 25% wiggle room for current draw. So your above example would need approx 200mA. Hope this helps.

Yeah that makes total sense, because as I was looking up these specs on all the original pedals, most of them showed a RANGE for the draw…now I know why.

And that garden-variety OneSpot chained power supply that everyone out there in the world uses supplies 1700mA for just that reason.

So, final devil’s advocate question: I’m assuming there is a correct argument for NOT daisy-chaining your power on a huge host of pedals in this fashion? For years I’ve been supplying all my pedals with individual power leads from one of those ubiquitous “isolated power brick” units, which claim they are better at protecting your pedals from noise and power drops. Is there real hard science to this, or is it all kinda negligible?

 

[Robert]

Noise.... ground loops and interference between pedals.

 

[Caldo71]

Noise.... ground loops and interference between pedals.

…but in the case of the two-pedals-in-a-single-enclosure wiring that is presented in your Wiki entry, one would be pretty much “safe” from ground loops etc? Given the specific pads that your +\- leads from the inputs/ouputs are connected to?

 

[Robert]

You could certainly find a combination of two effects that would be unusable garbage... heck you can find that in a single pedal.

For the most part though, you shouldn't have a lot of issues unless charge pumps and digital (or BBD) circuitry are involved.... just be aware of how your offboard wiring is routed.

One of the first commissioned builds I did years ago was a 2-in-1 Fuzz Foundry into a Tremulus Lune...

Did it work? Absolutely. It sounded like a pack of banshees in a Chinook.
Should it have existed? ... It sounded like a pack of banshees in a Chinook.

 

[Caldo71]

You could certainly find a combination of two effects that would be unusable garbage... heck you can find that in a single pedal.

For the most part though, you shouldn't have a lot of issues unless charge pumps and digital (or BBD) circuitry are involved.... just be aware of how your offboard wiring is routed.

One of the first commissioned builds I did years ago was a 2-in-1 Fuzz Foundry into a Tremulus Lune...

Did it work? Absolutely. It sounded like a pack of banshees in a Chinook.
Should it have existed? ... It sounded like a pack of banshees in a Chinook.

Haha awesome!