Power the midihub

Midihub
1

Hi all.

Still struggling to power the Midihub from my classic (guitar and bass-) pedalboard- Strymon Zuma 9v/12v/18v DC powerbrick.

  1. I will build a 9v DC to 5v USB power-converter, to power the midihub from the 9V dc output from the Strymon Zuma powerbrick. Everything will be build under / in a pedalboard used for touring / on the road. No computers involved.

  2. If I want to access the midihub to change or adjust settings, I don’t want to tear down the setup, unplug the power-usb and plug in the computer usb. That’s a hassle in the way I want to build it. I want the midi-out ports easy accessible (to add synths), but when I do that I can not also make the USB port accessible. :frowning: …

So, I am looking for a way to power the Midihub with USB (without computer) from the 9v (should be ok …) AND ALSO accessing the midihub with my computer when I want to do that, without unplugging the USB that powers the midihub.

Can I do that with this cable? The red one will come from the 9v-5v converter. The black one I can use to link a computer. Will it work?

Thanks for everything. It would have been amazing if the midihub had an extra 9v power input. So simple, so effective in so many cases when you do music :slight_smile:

Thanks a lot!

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Hi, such cables are meant to be connected to the same device, there are some caveats when mixing devices, as it can cause back-feeding of power in the undesired direction (the current flows from the higher voltage to the lower voltage, so if PC has 5.0V while 9V to 5V might have 5.1V level, so the current would flow into the PC which might or might not be protected from by the PC. It could be the other way around too).

Here’s some options:

  • This might not work for all USB hosts, but it might work if you cut the VBUS line that is supposed to go to the USB host, so only D+, D- and GND contacts are connected to the PC, while the power itself is provided by the USB power supply. Some hosts may be expecting to see some current to be drawn from their VBUS line, so they may refuse to properly enumerate the USB device connected.

  • Use a low voltage drop Schottky diode (digikey search) to prevent back-feeding of power on both VBUS lines. If you build the 9V to USB voltage levels circuit yourself, you should aim at providing around ~5.3V before the diode, so after the drop, the Midihub sees the expected ~5V level. You’d have to figure out how to get the diode into the VBUS line that goes to the PC.

  • Build a custom PCB with 9V to 5V circuit, that would include the necessary diodes, and would have a USB B connector for connecting the host PC with a standard USB A ↔ USB B cable, and a USB A connector dedicated for Midihub. The VBUS lines would be joined internally through the Schottky diodes and D+, D- and GND lines tied directly. This would be the cleanest solution, and would require no special cables.

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Searched for a ready to go PCB that would do this, but didn’t find any, however, there’s this discussion with pretty much the schematic I had in mind: https://electronics.stackexchange.com/questions/443325/usb-splitter-circuit

Another thought - use an externally powered USB hub, it can likely power Midihub while the host is not connected, and you might be able to find a hub taking 7V - 12V DC input through a barrel jack, but I’m not aware of any particular models.

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