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Graham Armitage

Fri May 02 2014, 12:49AM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Hi,

I am still having major problems with the MIDI output from the laptop. The interference from the coil is clearly causing a problem with the USB port, as when the note hangs, the laptop often has to be rebooted to get the USB port to work again. Probably not good for the laptop

When I have the laptop power cord plugged in the problem is magnified 100x and it won't even play the first note without hanging. I have tried several laptops and same problem. Moving further away definitely helps but even at 20ft it will hang with a ground strike.

From my observations it seems to be the ground on the USB that is picking up the signal and causing the problem. The USB to MIDI cable is shielded but the shield is grounded as is the MIDI controller's metal box. Not sure what else I can do other than a full faraday cage to sit in, but really don't want to have to go to that length. Anyone had any success in overcoming this kind of problem?

Steve Conner

Fri May 02 2014, 07:46AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

USB is notoriously sensitive to interference. Try wrapping the USB cable through a large ferrite toroid as many times as it will fit.

Graham Armitage

Fri May 02 2014, 12:33PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Oh boy - can't believe I didn't think of trying that

Well, I gave it a try this morning and actually had enough cable to wrap around two toroids and ran it at full power from about 10ft and never had a single note hang. Cannot thank you enough - it looks like that did the trick.

HV Enthusiast

Fri May 02 2014, 07:58PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Are you using a fiber optic link to the coil, or copper?

Graham Armitage

Fri May 02 2014, 08:03PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Using fiberoptic from MIDI controller to coil. After Steve's suggestion it's still behaving. Hoping it continues to work.

Hydron

Sat May 03 2014, 12:10AM

Registered Member #30656 Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208

You're not the only one to run into this - USB uses single ended signalling for a few things on the bus (e.g. bus reset), and is extremely susceptible to common mode noise.

I have seen the same thing on my USB-MIDI converter (these seem particularly bad, probably not helped by the dirt cheap construction and lack of shielding), my scope when running with USB, and also USB-serial converters when doing EMC testing.

I solved the MIDI thing by just moving further away, and the ferrite toroid choke worked somewhat for my scope, though the real answer was switching to ethernet connection. For EMC testing we ended up using real hardware serial ports, which are far superior to the USB imitations in other ways too.

Intra

Mon May 05 2014, 05:30AM

Registered Member #2694 Joined: Mon Feb 22 2010, 11:52PM
Location: Russia, Volgograd (Stalingrad).
Posts: 97

I have had same problem. This can runs under grounded Faraday's cage and into it you should put the laptop, midi-usb adapter and interrupter. Between interrupter and coil you should use fiber optic cable.

Graham Armitage

Mon May 05 2014, 10:20AM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Faraday cage is ideal but did not want to go to that extent. The two ferrite toroids and moving further away seems to be working really well. I have been doing more testing and still no problem with hanging notes. This is the most stable it's ever been.

Goodchild

Mon May 05 2014, 03:39PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

I have had seen amazing improvements after eliminating the USB to MIDI converter. My current working theory is that the non-differential un-shielded MIDI cable between the converter and the DR controller is the largest culprit in picking up noise.

In my latest design I have built a custom USB to MIDI converter right onto the same PCB as the micro running the DR controller software. This way I only have a USB link between the computer and the controller. The ground referenced serial MIDI signal is reduced to only about a half inch of trace onto of a ground plane.

This made a huge improvement, I was able run my old controller right beside the new one and I was able to get the controller almost close enough to arc to the coil without it locking up. The old version of the controller however locked up per usual when it was brought to within about 10 feet of the coil.

USB if used as a standalone link is very noise immune being fully differential, particularly if you run with ferrite chokes. As soon as you add the unshielded ground referenced MIDI into the same cable USB becomes as useless as the MIDI serial, because your link is only as good as the weakest part of the chain.

Graham Armitage

Mon May 05 2014, 05:58PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Thanks Eric, I am using the Mini MIDI/DR controller from Paul Slawinski which does the job. Then between the computer and the controller I have the dreaded USB cable Trying to picture your setup and how it is different from what I am doing?

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