[sdiy] Eurorack Grounding Question

mark verbos markverbos at gmail.com
Sat Jan 2 20:15:45 CET 2021


Fun stuff. Reminds me of the PCB routing nightmare that I just went through with a small DC-DC switching power supply I made. I used TI Webbench Power Architect and found that some of the capacitors had to be moved directly onto the pins (of TSSOP ICs!)  of the ICs for the rail to start up. I redesigned the PCB with the parts moved to right next to the pins and found that the 1 or 2mm away from being on the actual pins made the same problem! Mind you, these are just caps from the power line to ground, but certain pins need them to be very close. Of course, once  the problem is found and a solution found, it seems obvious, but when searching for it...

Mark

> On Dec 31, 2020, at 11:48 AM, Ben Stuyts <ben at stuyts.nl> wrote:
> 
> Here are a couple of good app notes if you want to read up on it:
> 
> Grounding in mixed-signal systems demystified pt 1 & 2:
> https://www.ti.com/lit/an/slyt499/slyt499.pdf <https://www.ti.com/lit/an/slyt499/slyt499.pdf>
> https://www.ti.com/lit/an/slyt512/slyt512.pdf <https://www.ti.com/lit/an/slyt512/slyt512.pdf>
> 
> PCB Design Guidelines For Reduced EMI:
> https://www.ti.com/lit/an/szza009/szza009.pdf <https://www.ti.com/lit/an/szza009/szza009.pdf>
> 
> Ben
> 
> 
>> On 31 Dec 2020, at 09:01, Steven Cook via Synth-diy <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>> wrote:
>> 
>> Thank you for these answers. I think I'll go with Tony's recommendation. The reason I have input jacks connected to the digital ground is simply that they are connected to the microcontroller (via transistors and reverse voltage protection diodes), so I assumed that the jacks should be also - I'll change that.
>> 
>> I have a couple of follow-up questions:
>> 
>> 1. If I have a ground fill on the PCBs, which ground should it be connected to?
>> 
>> 2. Which ground should the DAC be connected to?
>> 
>> ------ Original Message ------
>> From: "Steven Cook via Synth-diy" <synth-diy at synth-diy.org <mailto:synth-diy at synth-diy.org>>
>> To: Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> Sent: 29/12/2020 09:30:46
>> Subject: [sdiy] Eurorack Grounding Question
>> 
>>> Hi, I'm designing a Eurorack module which uses a microcontroller. The PCB has separate analogue and digital grounds joined at the power input header, but I've realised since designing it that both grounds will also be shorted together by the front panel as there are input jacks connected to the digital ground and output jacks connected to the analogue ground. I assume this would create an ground loop. Would I be better off not bothering with separate grounds?
>>> 
>>> Regards,
>>> 
>>> Steven Cook
>>> 
>>> 
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>> 
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