AX8 MIDI Power Spec Question

RossE

RossE

Inspired
I want to connect a Midi Solutions Relay to the MIDI out of my AX8.

Cliff or AdminM can you answer this for me? Is the AX8 MIDI power old vs new standard or rather +5 or +3.3v?

Here is the blurb from Midi Solutions FAQ.

MIDI Solutions products draw power from either a MIDI Out or MIDI Thru connected to their MIDI input. MIDI Solutions products were originally designed to be compatible with the 5V MIDI electrical specification, however the MIDI specification has recently been updated allowing a lower voltage of 3.3V, so devices that follow the new specification will not power the original MIDI Solutions products. We are currently working on MultiVoltage versions of the MIDI Solutions products that are compatible with both the original 5V and new 3.3V MIDI specifications. These MultiVoltage products resolve most compatibility issues, however we have received reports of a small number of products on the market that do not provide the ground connection to the center pin as indicated in the MIDI specification (this FAQ provides more details).
 
The MIDI h/w interface using the DIN 5-pin connector doesn't support sourcing power for connected devices. Afaik the spec describes a current loop that should drive 20mA on the data line. That's different with USB-MIDI where the USB standard defines the limits.
 
You may be correct. I was thinking this +5 or +3.3v power on pin 4 was part of the MIDI standard, as opposed to the 7-pin DIN power the Axe FX, Ultra and II would provide to say the Voodoo Labs Ground Control.

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Have to correct myself: the hw interface spec describes a 5mA current loop. Using the opto-coupler in your schematic it takes 3 220 Ohms resistors to achieve 5mA at 5 Volt. If the circuit was using 3.3V the resistors would have to have smaller values. The spec doesn't say which voltage should should be applied to pin 4. The usage of a 7-pin DIN connector is a proprietary extension. Rocktron used to feed 12V AC on those extra pins, FAS sources DC (afaik)
 
The schematic is the standard from the MIDI Org and shows +5v on pin 4. Not arguing whether the AX8 would work with the Relay or not, just seems it is part of the base standard. Surprises me that Fractal wouldn't adhere to the standard, but maybe actually providing voltage on pin 4 is a common opt-out for designers. The other thing that puzzles me is that Midi Solutions states some devices won't power the Relay due to providing 3.3v rather than the required 5v. They don't say due to some device designers choosing not to implement power voltage on pin 4.

Anyway, I appreciate your input.

I wish someone from Fractal would step in and clarify implementation.
 
RossE said:
The schematic is the standard from the MIDI Org and shows +5v on pin 4. ...
Click to expand...

It's the reference implementation but technically not ideal as it is not a true current loop. Did you notice the resistor between the 5V source and pin 4 ? The current loop will draw power from there if a 0 level is sent across the data line and this will cause the voltage at pin 4 to fall below +5V. This means the voltage level at pin 4 will vary with the data sent across the line. The voltage will remain at 5V only if no data is sent.
 
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