[sdiy] How to design out "usb noise"?

[cheater cheater]

it makes sense to put the digital stuff on a separate pcb that's at
least 1cm away from the analog stuff. (or at least, strip off a huge
chunk of copper between them). This to prevent capacitive coupling.

On Fri, Feb 2, 2024 at 8:19 PM Mattias Rickardsson <mr at analogue.org> wrote:
>
> If I'm not mistaken, this is the ground loop that typically brings in computer/USB noise into audio:
>
> a) Computer
> b) USB cable to synth
> c) Digital system in synth
> d) Digital power domain in synth
> e) Analog power domain in synth
> f) Analog system in synth
> g) Analog audio cable to audio interface
> h) Analog system in audio interface
> i) Analog power domain in audio interface
> j) Digital power domain in audio interface
> k) Digital system in audio interface
> l) USB cable to computer
> a) Computer (again)
>
> If the ground is disconnected between any two stages in this loop, the noise can go away.
>
> Isolating USB itself at b) or l) has been mentioned, but can be problematic for higher bandwidth connections, like when streaming many channels of audio along with the MIDI data.
>
> Isolation between d) and e), together with data isolators between c) and f), is an alternative when building synths. But it seems very rare.
>
> Likewise, audio interfaces could have isolation between i) and j), as well as between h) and k). Do any manufacturers do it like this?
>
> It should be mentioned that g) can also play a role here. A balanced audio connection can suppress enough of the noise in some cases where the rest is designed well - for instance by introducing a resistance instead of tight ground connection somewhere in the ground loop.
>
> But it's all a very very hairy issue.
>
> /mr
>
>
> Den fre 2 feb. 2024 12:30René Schmitz <synth at schmitzbits.de> skrev:
>>
>>
>> Have a seperate USB uC as a front end that has an insulation barrier to
>> everything else.
>>
>> Or seperate the Audio Output. (Transformer, Optically)
>>
>>
>> Best,
>>
>>   René
>>
>>
>> Am 02.02.2024 um 12:01 schrieb Vladimir Pantelic via Synth-diy:
>> > have a look at e.g.
>> >
>> > https://waldorfmusic.com/legacy-nw1/
>> >
>> > they explicitly state:
>> >
>> > "...USB port with *galvanic isolation* for wavetable transfer and text
>> > input.."
>> >
>> >
>> > On 01.02.24 23:06, Mike Beauchamp wrote:
>> >> I recently stumbled across this post on reddit of someone showing usb
>> >> connection causing some serious noise:
>> >> https://www.reddit.com/r/synthesizers/comments/1aghqsa/how_to_get_rid_of_usb_noise/
>> >>
>> >> Some comments suggest to use DIN MIDI instead of USB MIDI as a
>> >> solution, but it got me wondering if there's a best practice for
>> >> implementing MIDI OVER USB output that wouldn't cause this. MIDI spec
>> >> includes schematics for hardware implementation of DIN MIDI
>> >> connections as we know, including the use of opto-isolator, but I
>> >> can't find the equivalent for the USB connection.
>> >>
>> >> A typical USB-B connector has the following pins:
>> >>
>> >> 1. VBUS
>> >> 2. D-
>> >> 3. D+
>> >> 4. GND
>> >> 5. SHIELD
>> >>
>> >> How do you think these connections should be handled inside the
>> >> synth, assuming a hostile environment where connections are also
>> >> being made to/from a PC with audio cables, MIDI cables, power
>> >> adapters to different outlets/circuits, etc.
>> >>
>> >> Mike
>> >>
>> >>
>> >>
>> >>
>> >>
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>> --
>> --
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>> http://schmitzbits.de
>>
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