Usb isolator

Random
#1

This isn’t really for my mod duo, but I have an alesis multimix that I use as a usb sound card to record the output from my duo and recently I’ve started getting a high pitched ground loop whine. There’s a few usb isolators for sale on amazon but it gets really expensive if you look at higher speed versions, not that I need the high speed version but some say the low speed versions don’t work with focusrite gear and I don’t want to rule out future purchases.

For now I’ve plugged in a usb extender cable and it’s mostly got rid of the problem in the volume range I normally use, but returns if I crank the volume on the mixer, so I’m just wondering if I’ll get better results with an isolator and if anyone can recommend one.

Dirty USB from the MOD Duo X host port
#2

Before you do that, try lifting the ground on the power for the mixer with one of those 3->2 prong power adapters… Assuming you’re in a country that uses Edison plugs, i.e. The USA.
I have some cheap stereo Behringer active DI boxes that sound completely excellent. Ground lift switches solve all kinds of issues AND it’s a more flexible/pro solution. Annnnnnd it has input pad switches so I run my Eurorack nonsense into a pair and hit the -40dB pad for maximum signal to noise ratio.
USB ground lifts are sub-optimal solution and snipping a ground wire on a balanced cable is far cheaper.

#3

Unfortunately I’m in the UK, so there appears to be no easy fix on the power supply side. I figure that considering I appear to have discovered that it’s the usb at fault then the easiest thing to do is isolate that.

#4

If you play into a mixer/amp/interface with balanced inputs, try a passive stereo DI box with a ground lift switch, just like you would connect a keyboard on stage :wink: Active DI boxes sometimes don’t help much against ground loop noise and for passive instruments like playing bass guitar with DI people sometimes would use an active and a passive DI box together.

#5

Thanks, unfortunately I have no experience of being on stage or of (musical) keyboards :slight_smile:

I’m just a linux/open source developer who has been playing guitar for a bit and wanted to avoid the proprietary stuff out there in the modelling guitar pedals which always seems to require windows/mac. I just have the guitar into the duo, then the duo into the mixer and then the usb to the PC.

I’m actually now thinking the easiest/cheapest thing would be to use netjack to put the mod duo output directly into my pc and remove the mixer from my setup

#6

unfortunately I have no experience of being on stage

Not yet :stuck_out_tongue:

For audio through netjack through USB there’s this guide on the wiki so yes, it’s probably the cheapest option. I’d guess you can get even lower latency and better sound with that solution than having the overhead of duo ADC - duo DAC - mixer ADC.

Anyway for ground loops it’s a lot safer not to cut any wires on power cords or USB (unless you really know what you’re doing) but instead use a cheap passive DI box like this one. Bonus life hack: Connected in reverse between you interface and a guitar amp with the -20dB pad switch it also works great for recording your own impulse responses or re-amping without spending hundreds on a reamp box :wink:

#7

Thanks for that, it’s good to have a recommendation for a cheap DI at least. I might pick one up anyway to give it a try.