Moog Music Forum

Hi,

In the past I've had the same issues that others seems to have regarding MIDI over USB, specifically with my Little Phatty connected to my laptop via USB. the symptoms were noisey output and the controls on the LP would develop a mind of their own. the solutions were either disconnect the laptop power supply, or use the MIDI ports instead of the USB port (which requires a MIDI adapter). Both which effectively isolated the LP form the laptop power supply.

Now to me, the source of the problem seems to be that the USB spec' doesn't include electrical isolation, whereas the MIDI spec' does. There appears to be the potential to create ground issues using USB that wouldn't have been possible in the past with MIDI.

Has anyone had any experience using devices like below to fix any grounding problems in their setup? I have a couple of pieces of equipment that have MIDI over USB that i have to use the MIDI ports on because of what i see as ground problems and i'm trying to find a solution.
http://www.bb-elec.com/product.asp?SKU= ... lType=Main
http://www.sealevel.com/store/accessori ... ports.html
http://www.circuitsathome.com/products- ... interfaces

Cheers,
Ben.

i purchased a circuits@home isolator and it fixed my USB problem... it came back again once i connected the audio out of my LPII into my soundbox (edirol FA-101).

the ultimate solution ended up being attaching a earth wire from the power-board of my rig to the grounding point of the FA-101. it works fine (much better???) now without the USB isolator, though there is still an earth loop there so I am still using the isolator.

i might try later to use one of the firewire isolators that disconnect the 2 power lines of the firewire and power the FA-101 externally to see if that also fixes my problem.

I think I know what you are talking about when you say the "the controls on the LP would develop a mind of their own". Though I'm not having any noise issues, I've had an issue where when I power up my LP Stage II the presets will not hold at all, and the modulation, oscillators, filter, and envelope generator will all change values. I'll be changing the presets, but they automatically turn off (the preset button changes color and the values on everything change). Does this sound like the same thing you have happening?

For me I've noticed that it only happens when I have my USB and/or Audio Output line inserted (my audio out is using a balanced cable which runs to a firewire interface). If I disconnect them from everything (so the LP is isolated) the presets hold and everything is great... but the second I plug anything in I get the same issue with the presets not holding.
It makes sense that it might be a grounding problem, especially considering that I get the issue not just with the USB but also my audio out (likely because of the shield).

The weird thing is I don't have the problem ALL THE TIME.... it seems to happen at random. Next time I have the problem I'll do some experimenting with the way I have things hooked up. I'm betting it's a grounding issue with the USB and Firewire bus on my PC. If so I think Sore_Knee's idea of using isolators (and cutting out the 5v rail) on the USB and firewire will do the trick.