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VERY Low MIDI OUT Voltage?
Old 28th May 2020
  #1
VERY Low MIDI OUT Voltage?

Hello can we talk MIDI voltage for a second? I need to understand this: I'm having an issue with my Novation Impulse 49 controller. Every other MIDI device I have (keyboards) I can measure 5v on the end of the MIDI output cable (even USB only powered devices), between the center pin and the one next to it (counter-clockwise). However, this Novation keyboard controller (USB power only) doesn't register any voltage or it's like .005 or something.

Never noticed or cared much until I wanted to split the MIDI output to some of these new lunchbox sized boutique synths. I bought a MIDI solutions "MultiVoltage" unit for just this reason, yet it still doesn't register or receive power from this controller. I tested others and it works if there is enough voltage. Apparently I should have first visited their site to read the fine print...

After reading that, there is a laundry list of other keyboards that won't work too! (some that you might have!) So why bother creating a MIDI standard again?

Now, before I go any further, if you have a suggestion for a better way to split MIDI output from this low voltage, grounding bastardized controller you can just drop me a comment. Actually, can I send to my interface then take that output to the splitter? For all the geeks, read on:

So next up "MIDI solutions" recommends doing the below (next paragraph). So my question is, how would creating this ground provide more voltage, or better yet, without it, why does it still work for devices but not a splitter?? It sounds as if this "missing ground" is by design; to eliminate an audible ground hum from the PC when using the controller, but I'm not convinced,. But, if I do this, will I have grounding problems? Lastly, just to be clear, they are actually talking about performing this on the output jack inside the controller and not on a cable right? I'm a bit ignorant on this so it makes me nervous to open it up without some photos or something. Easy answer is return it, but it's out of warranty, and I do really like the way it plays. So I'm on my own unless the Slutz have any suggestions:

From Quadra Thru:

If a device won't provide power to a MIDI Solutions MultiVoltage product then this is likely due to the omission of the connection from pin 2 (the center pin) of the device's MIDI output to ground as indicated in the MIDI specification. Pin 2 of a MIDI cable is connected to its shield, so even if the device will not be powering a MIDI Solutions product it is important that pin 2 is connected to ground so that the other conductors in the cable that are transmitting MIDI data are shielded from outside interference. This problem can be repaired by making a ground connection from another ground point on the device to pin 2 of its MIDI output. In some cases a ground connection can be found on the shield of an external jack, so opening up the product to find an internal ground connection may not be necessary and this external ground can be tied directly to the MIDI Solutions product's ground. The ground connection of the MIDI Solutions products is available at pin 2 of any of its MIDI jacks (with the exception of merger inputs 2 and higher). When making this connection be absolutely sure that the point on the device you are connecting from is ground – MIDI Solutions will not be responsible for products that have been damaged by incorrect interpretation of the above instructions, attempting this modification is not recommended for those unfamiliar with electronics. It would also be wise to first do a continuity test between the device's ground connection and pin 2 of the device's MIDI output to confirm that this is in fact the problem and this connection is missing.
Old 29th May 2020
  #2
Lives for gear
 

The MIDI signal is actually more of a current loop than a voltage. It's designed to drive an LED (inside an optopcoupler or optoisolator--different names for essentially the same thing) with a 220 ohm resistor in series at around 5mA. While many do this from 5V rails (and so when unloaded, such as when measuring with a voltmeter, you'd see 5V), it is possible to do it at higher or lower voltages as well, as the FAQ from MIDI Solutions mentions somewhat obliquely.

The center pin (pin 2) on the MIDI connector is for the cable shield, and is not part of the signal. On properly implemented MIDI inputs, it's not connected to anything; so having it connected atypically on the output port causes no general problems for compliant inputs (but, if it's not connected to a ground, does lessen the effectiveness of the shielding in the MIDI cable). The MIDI data is on pins 4 and 5 (the two next to the center pin--pin numbering on the DIN connectors is unintuitive).

MIDI Solutions seems to me to be playing pretty fast and loose with the MIDI specifications. MIDI was not designed to provide power to devices, save for the one solitary LED in the optoisolator of the input. The MIDI Solutions box is assuming that the devices are using the same ground reference for the shield as for the MIDI data output, something that the specification doesn't specifically require (even with their sample circuit). They are also specifically and explicitly ignoring the requirement that MIDI inputs be optoisolated, since doing so would mean they couldn't steal power from the MIDI input.
Old 31st May 2020
  #3
Thank you for the reply. So what are your thoughts on modifying the keyboard MIDI output vs modifying a cable? It sounds like there is potential to introduce some ground loops hum with their approach. I can try it, but could you confirm if they mean the output jack on the controller, or can I do this to a cable (a cable which runs from controller MIDI output to boutique device)

The only mnethod I've found to work is; I have a Behringer Model D that has a MIDI through which must output a higher voltage that what it receives, but then I have to have that powered at all times while I'm using other gear and it's just less than ideal. Is there anything you can purchase to boost the voltage to standard values, a powered MIDI through connection that's not an analog synth?
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