USB Groundloop Isolation

[dalpozlead]

Another one here fighting against USB groundloop noise when connected USB controller with audio output...

 

I`ve found some online recomendations as below, but wonder what you guys are using...

 

https://www.amazon.com/dp/B06XB9YBHJ/ref=cm_sw_r_cp_ep_dp_Onl4AbN6VB5CK

 

https://hifimediy.com/product/usb-isolator/

 

tks!

[Sam Mullins]

I use the idefender+. works great but is more expensive ($45-50) than what you have linked to. For a discussion of this and other solutions to similar situations (e.g. just getting a cheap audio plug that does ground lifting), scroll down within this thread about the CTS300:

 

https://forums.musicplayer.com/ubbthreads.php/topics/3014975/all/casiotone-s300-as-really-cheap-travel-keyboard

[dalpozlead]

I use the idefender+. works great but is more expensive ($45-50) than what you have linked to. For a discussion of this and other solutions to similar situations (e.g. just getting a cheap audio plug that does ground lifting), scroll down within this thread about the CTS300:

 

https://forums.musicplayer.com/ubbthreads.php/topics/3014975/all/casiotone-s300-as-really-cheap-travel-keyboard

 

tks so much!

[konaboy]

don't have a fix, but it's definitely an issue that doesn't get mentioned much, which I find strange that not more people run into it.

 

I multi-tracked a Moog subphatty, USB cable from PC to Moog to transmit midi whilst synth audio is captured on USB audio interface.

 

That grungy, whiny, humming interference really added up when playing back 6 recorded tracks.

 

Next time I run into this I will sacrifice a USB cable by slicing it open and cutting the ground wire, maybe that will fix it on the cheap.

[Dr Mike Metlay]

Arturia now packages some of its USB controllers with a USB isolator thrown into the box just 'cause. I wish more folks did this.

[Theo Verelst]

IN the past I've considered buying this 18 euros Olimex product, because of Hum and crackle and other issues with Usb audio interfaces. I know you'd have to test it first, because some audio interfaces don't tolerate intermediate buffering of USB connections.

 

My solution in general is threefold. The best solution is proper grounding (possibly even a separation transformer on the interface, maintaining proper safety. If your instrument, like the CP4 has full ground high impedance ground separation it isn't going to introduce hum if you just connect the audio outputs.

 

Another solution is using a DAC (can work for ADC as well) that has built in ground separation, like my Do It Yourself In Hong Kong XMOS based Usb interface with $29 very high quality DAC board has. That's abit of DIY but it has the advantage it also locks out audio clock generator ground and supply pollution from the output audio, and there's no delay in the USB connection functionality (like volume control). I recall there's an Asus high Q audio interface that does this as well.

 

Also, it's possible with pro equipment, similar to rack mount devices in a heavy metal rack, to get a very solid ground connection between all audio components. I this with a Yamaha MG16XU, a Lexicon MX400 (unfortunately discontinued) and the Kurzweil PC3, which all have thier audio output solid connected to ground/earth. COnnecting them via the normal audio and Usb connections will create ground currents (worse if your end amplifier would also have it's input ground connected to ground) and ground currents will introduce voltage over the resistance of the zero wires, and hence hum and so on. You could go balanced to circumvent this, which for pure mains hum may be ok, but very wide tolerance coupling capacitors at the aduio inputs and outputs make it such that all kinds of low frequency components will make it through the balancing efforts. Unless there's DC coupling, or accurate coupling transformers. Mainkly what I do is simply properly ground ("earth") those 3 pieces with the official earth prong on the supply cord, and then connect the output signal grounds together via heavy measurment cables with crocodile clamps on them, which makes the hum go away, the same way a metal rack would,

 

T

[Modler]

I have just been fighting a ghastly loop noise in my setup, with the two keyboards (PC4 and FA-06) both MIDI'ing to the laptop via USB, with the Roland also functioning as audio interface for the software.

The solution however was simple; balanced cables out from BOTH keyboards and the noise became unaudiable.