Noise when USB launch control XL connected

#1

i've got it set in a eurorack and without anything plugged in it sounds okay, albeit some slight digital artifact when the gain is cranked. Once the Novation controller is plugged in the sound is unusable. I know if got enough amps going to it but something is up. Any ideas?

#2

How is the Axoloti Core powered? Via eurorack bus, taking +5 or +12? Flying bus cable or bus board? Is this happening with or without usb-to-pc plugged in?
The noise comes from the voltage difference over the ground wire caused by the current draw, when the current consumption modulates - probably from the LED multiplexing in the LaunchControl - the ground reference is modulated too.
The first specs for a ribbon cable I found, list around 200 milliOhm per meter, when carrying a current of 500mA, that's a voltage drop of 100mV, and that's just the wire, not the connectors.
I have no golden solution but here are the approaches I can think of:

  • Reducing the resistance of the ground connection can help, using the 4 ground wires in parallel on the bus rather than only one, using the shortest possible ribbon cable from the busboard, or connecting a more solid ground wire between Axoloti Core and the eurorack power supply.
  • Another solution is using a separate power supply for Axoloti, isolated from the eurorack supply, like a wallwart, and only connecting ground to the eurorack supply and to Axoloti close to the analog parts, avoiding "digital" current on the analog ground path.
  • Yet another solution is using a USB power injector cable between Axoloti and the LaunchControl. Arturia recommends this approach for their Beatstep. But this also requires a separate power supply.
  • A more complex solution is compensating for the ground differential voltages at the audio input and output stage, Axoloti Core uses this approach for the on-board audio in- and output jacks. TI ground loop break circuit application report 143 In eurorack context you could probably use a separate ground wire of the bus bar as a "ground sense" wire for the input/output stage.
#3

Its powered via bus board off the 12v rail, and without the usb-to-pc plugged in.

i should note that i've got two in the rack, and they both sounds fine until the Novation is plugged in.

putting it back into a standalone case might be in order. Would daisy chaining them off a 9v 1amp wallwart be ok?

also thanks for the in-depth analysis, u rule.

#4

Oh another thing that could make a significant difference: enable the low power mode of the Launchpad!

9V/1A for two Axoloti Cores is fine, even when you use the USB Host port on both with a power-hungry USB device.

#5

so i've got them both wired into the novation controller but seem to be getting slight hum. It goes away once i touch the ground, and its not present when they are powered off usb. any ideas?

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#6

Where is the line out going into?
What sort of hum do you get? Typical mains 50 or 60Hz hum, or something different? Does the hum correlate with led activity on the launch control, or other activity?
Could you try a different power supply?

#7

the line out is split into 2 small jacks, and does not correlate with led activity. I've tried with a different power supply but not changes..it doesn't make noise when powered off micro USB (even when the usb is powering the controller)

it could very well be a 50 or 60hz hum, and it seems to go away when i touch something metal, like my mpc case (even if the mpc not turned on, but simply plugged into the same power strip)

#8

Can you check if the headphone out is free of hum (with headphones)?
Where is the sound going into, and how is that device powered?

#9

Hi got similiar problems with 2 Axos a Launchcontrol XL and Nanokontrol. The main frequency of the noise is 280hz, same for you @ilovedrums247

For me it seemed to be indeed connected to the Launchcontrols LEDs, for example when launchcontrol does its startup, you here the noise tones move with the lights. I tried powering the AXOS via a power supply for the usb hub and via a smartphone powerbank to the usb hub but even that didnt help get rid of the noise. When I power them via wallwart (both of the same wallwart) it works fine, with still some high pitched nosie frequencies left over.

Both Axos share the same external audio input, and send audio back and forth via the pins next to the jack connector and then have eacht one output going to a mixer. Since they share the same power supply i didnt do a ground connection. Any Ideas what the high pitched noises might be, @johannes?