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Author Topic: Troubleshooting electrical (grounding?) issue  (Read 2372 times)

Offline Jon

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Troubleshooting electrical (grounding?) issue
« on: September 02, 2015, 05:51:35 PM »
Hey Sam,

Huge fan of your work, long time listener, first time caller...

My friend Joe and I were at an event this past weekend and had some issues getting the MIDI Sprout to function. The MIDI Sprout was running fine with only the electrodes connected and MIDI interface plugged into our laptops' USB port. However, as soon as we connected the laptops to a power source we stopped receiving MIDI from the Sprout and the LEDs on the board no longer registered connectivity.

We also lost functionality when running the MIDI Sprout into our battery powered laptops and then inserted an 1/8'' cable to connect to the PA. This was an outdoor show in the backyard of a house. We took our setup inside and experienced the same issues.

We assume that it was some sort of grounding issue but are pretty confounded beyond that. Have you had a similar experience? Do you have any suggestions on what to do in a similar situation?

Thanks for your time,

Jon

Offline sam

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Re: Troubleshooting electrical (grounding?) issue
« Reply #1 on: September 08, 2015, 09:15:08 PM »
Thank you for your question Jon! 

There are a few things at play which can impact your MIDI Sprout when performing.  Your MIDI/USB interface, your laptop/synth connected to a PA amplification system, and the basic wiring of a house Power System can cause the effective 'sensitivity' of the MIDI Sprout to decrease.   

The Grounding of a power system can affect both a laptop and a PA system, bad wiring can allow the flow of electricity but also present much noise or loading in the system.  One common issue is called a Ground-Neutral-Reverse (GNR), where an electrical outlet is miss-wired such that the Neutral (Common/White) wire is switched with Ground.  If even a single outlet on a string is wired incorrectly, the entire system can be impacted.  Of course, we can't always prevent strange (or dangerous) power setups, but we can try to 'Isolate' ourselves! 

A power issue can be seen when connecting the MIDI Sprout to a laptop through USB, if you disconnect the laptop from its power adapter, and run only on batteries, you may notice a change in the 'activity' or the variation of notes.  On macbooks, you can even see a difference in the MIDI when you touch the aluminum frame of the book.  Well then, what is going on?  Why can't I get a clean signal?  The issue is Isolation! 

MIDI device standards dictate the use of an optically isolated transistor on MIDI input, and a Voltage with ~220ohm current limiting resistor for MIDI output.  Essentially the MIDI out port sends a voltage to a little tiny LED which then flashes at 31250 bps through a tiny photo transistor inside the MIDI input reading that data and sends to a computer or synth.  This type of optical isolation can keep the two electronic systems completely independent, and is one of the primary reasons i am using MIDI to communicate Galvanic Conductance Fluctuations.

Real-world MIDI interfaces vary drastically, and cost != quality.  I get great isolation through my ancient Akai ME30P 8 port MIDI Hub and also with a Griffin iOS-MIDI interface(pads and phones are battery powered, hence isolated), but lower cost USB-MIDI devices may omit the opto isolation circuitry or may contain an isolator but still attach Ground-to-Ground (odd but true), both conditions can potentially impact the sensitivity of the Galvanometer.

The Red USB-MIDI included with some MIDI Sprout kits is 'not' isolated, meaning there is no optoisolator inside the MIDI input, rather there is a ground-to-ground connection between the USB and MIDI port.  In my experience, this works just fine the majority of the time and in many different venues and situations, BUT i can guarantee that if there is a grounding issue either in the power supply, computer, synth, or PA system the Red USB interface will not provide Isolation.  There are simple solutions.

Thinking about the PA system, when performing with electronics I strongly recommend brining your own/using a Stereo Direct Box.  A DI contains a transformer, which consists of two 'coils' of copper which are 'near' each other and 'induce' the flow of current without physically connecting the electrical systems.  A DI can additionally allow you to isolate your setup from the house PA system using the Ground Lift switch, removing the PA ground connection from the transformer.  Using a DI is also 'polite' in electronic music, as it protects the house mixer from any erratic signal inputs (ie crazy voltages from circuit bent toys or modular synths ;) By Isolating the output of your computer (or Audio Interface) through a DI you can gain a level of confidence in your signal.

For the computer power supply, there are many isolated/regulated surge protecting power strips on the market. I also will mention that a laptop power supply tries really hard to isolate itself from any trouble in the mains.  By isolating your audio output using a DI you are effectively removing the worst of the trouble but please note: If you are a performing electronic musician and not already isolating and regulating your own power (or at least bringing your own power strip) ... immediately research further on the topic, too many synths have died (and hands been shocked) when shady power meets DIY modular!!

Grounding and Isolation issues in a PA system or MIDI port can impact the MIDI Sprout, proper isolation through a MIDI interface and a Direct Box can partially resolve these issues.  Remember that you are measuring miniature fluctuations in galvanic conductance, if you can 'get shoked' from a microphone just imagine how the plant feels attached with trodes!?   #isolateyourMIDI #BYOpowerstrip

-sam