9V through patch lead

[spruce_moose]

Hi, I'm posting this outside the sharktank, as I figure it wouldn't be relevant to people searching for pedals. Please delete if not allowed and i'll repost somewhere else.

I'm wondering if anyone has tried sending power through the audio TRS to make a tidier board? For example run power to sub groups that only have a single plug each.

I've designed a MOSFET circuit that has around 1ohm resistance with @9V but only sinks 10mA with a mono lead. It would take a board per I/O a connect to another compatible pedal, but if no one ever used the feature it would only cost 10mA per channel.



If anyone wants to give feedback I'd much appreciate it!

I'd like to make it open source but would be cool to develop it with others so it could be released with some easy filtering application notes as a result of some testing, allowing that it ended up being bug free. Seeedstudio or someone could sell them

Initial tests seemed to be on par with daisy chaining for noise, but the circuit did distribute power after the host's RC filtering.

Maybe someone could make TRS patch leads too, although I figure you might be able to use Stereo RCA cable, which would be fairly cheap if it didn't present issues with high impedance signals for some reason

[crochambeau]

Just so I'm clear, the idea here is to do away with the DC wiring loom and provide power along the signal cables in a manner similar to phantom power (but without the need of AC coupling at interfaces)?

Conceptually, this is a cool idea. Pragmatically, it would need to be *exceptionally* easy for a less than electronically adept end user to retrofit this into their existing devices.

[spruce_moose]

Just so I'm clear, the idea here is to do away with the DC wiring loom and provide power along the signal cables

Yes, so each pedal can still receive power, but it can create a 9V bus through the input and output along the ring connection of the stereo jack.

It's not too difficult as a mod from the module- 3-4 wires soldered between the ring, 9V and ground.



If open source then maybe modded pedals could eventually work with any smalltime builder who wants to add a few components or drop a module on before putting it through the oven.

I think you could go way further and explore the concept of having open source modules designed to provide really handy functions. For example, every type of useful signal mux with all caps and pullups/downs on the board. You could probably order most of them for less than a dollar, save space and a fair bit of time. It could allow people to make complex designs with simplistic trace layouts.. design stuff faster etc.

Would be cool if there was enough interest for somewhere like seeed/adafruit/sparkfun to stock them.

SMT/stencil soldering isn't rocket science..The board turns up, paste it, drop the modules on and apply hot air - That stuff is super cheap and accessible these days. Most people would figure it out in 5 mins with a good vid - have also worked out how to paste pretty much anything with a $20 elecrow stencil, a razor blade and a thin rubber mat, so could make a video to help.

[DRodriguez]

Quite like the idea. The main issue I see is accidentally sending power to a non compatible pedal, or double powering the same pedal. How does it handle with chains of hungry digital pedals?

[BetterOffShred]

When you plug the jack in the tip will slide past the switched portion of the ring lug too right? Not sure what that would sound like.

[spruce_moose]

When you plug the jack in the tip will slide past the switched portion of the ring lug too right? Not sure what that would sound like.

My guess is that the pop you get from plugging in a lead is from the high impedance input of the following circuit, likely biased to 4.5V getting momentarily shorted to ground as the decoupling cap charges. E.g. a big AC pulse. In this case if the tip was shorted to the ring/9V momentarily I'd suspect it'd do the exact same thing, but in the event of an input being 5V or 3.3V i.e. digital, then perhaps it'd need a Zener to clamp any transients.

The main issue I see is accidentally sending power to a non compatible pedal, or double powering the same pedal. How does it handle with chains of hungry digital pedals?

The circuit switches off if it sees a high load/short, so at this stage I think it shouldn't be able to do anything nasty to incompatible pedals, but I'm hoping someone into beta testing can verify that! It would also not notice power coming from two sources. The circuit would just prioritise one or the other.

The resistance is around 1ohm and can supply whatever the host's input is capable of. E.g. if the first circuit has a 100ohm series resistor on 9V, then the load of the following device will drop the voltage across 101ohm, the third being 102ohm etc. I think the capacitance would be additive too, so assuming two pedals have a 100ohm + 47uF inputs, then patching them together would disregard one of the DC input resistors and increase the capacitance to 94Uf

There's certainly a potential issue if a digital pedal wanted 100mA and pulled the rail down, but perhaps there's an inductor /cap config recommendation that could work around this.. Haven't really schooled myself of that yet, but my basic understanding is that this might only be practical if the supply's switching frequency is known and the LC is set accordingly... but it would be fair to assume DC supplies are all over the place..

[eatyourguitar]

where is the power entry? is this a Y cable? is there a power injector box? have you measured voltage drop? will you disclaim damage to speakers with a shrink wrap contract? open source does not protect you from liability. it only exposes you with no possible way of getting paid. you are in NZ so maybe this does not affect you as much.

people would need to buy all new cables

I would rather see something like 500 rack for guitar pedals with the remote switching midi controlled and all integrated. or maybe keep going with your power injector idea but make a comprehensive spec sheet on standards that apply to the entire guitar rig. without that I would be skeptical that this solves more problems than potential problems that it could create.

[DRodriguez]

Is there any limitation to 9v, or could i run 12, 18, or 24v through them?

Power entry, i assume you could wire it to the dc in jack on your compatible pedals. So you would only need one compatible pedal to start the chain. Alternatively you could build a tiny voltage injector box.

[Dr Satan]

I do like the idea, but just don't see the practicality of it. It's essentially useless to someone who needs isolated outputs on a power supply because they are using positive ground pedals like a PNP fuzz face, treble booster, tone bender, etc etc. But honestly, that digital caliper working without a battery is the real witchcraft I'm focused on here. What in the actual fuck is going on there?

[DRodriguez]

Tested this out quite successfully. Left pedal is running on power from the right. You can always use a seperate power supply for positive ground effects or build in an isolated dc converter into those pedals etc.