Why are there two zero volts?

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Cablebasher
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Why are there two zero volts?

Post by Cablebasher » Tue May 26, 2020 5:34 am

Hey guys

About to start my 5u system after years in eurorack DIY and have a question.

On the PSU there are 2 zero volts.

0VA and 0VB

Why do we need 2?

Sorry for the silly question it’s just I have not come across this before

Cheers.

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BananaPlug
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Re: Why are there Two zero volts?

Post by BananaPlug » Tue May 26, 2020 6:48 am

Less resistance. A more solid connection.

KSS
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Re: Why are there Two zero volts?

Post by KSS » Tue May 26, 2020 6:54 am

:agree: Same reason your Eurorack has 6 pins carrying 0v.

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Re: Why are there Two zero volts?

Post by KSS » Tue May 26, 2020 7:05 am

This paper by Tony Algood of Oakley Sound talks about other reasons to have more than one 0V-GND pin.
http://www.oakleysound.com/dizzy3-bg.pdf

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htor
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Re: Why are there Two zero volts?

Post by htor » Tue May 26, 2020 8:23 am

thanks for linking that paper! learning something new every day here. this is new to me.

in the intro he hints at his ideal situation using a 5-pin power connector:
"This would contain +15V, -15V and three grounds. One ground would be the safety ground; this would be connected to the front panels and then directly onto the main’s supply earth. The second would be a clean ground for all the analogue modules to take their supply reference, the zero volt line, ie. 0V. The third would be a dirty ground. This would be the ground reference for things like the noisy digital circuitry and LED switching. ... "
question: does separating analog ground and digital ground mean you route an IC's ground connection to one of these ground paths depending on their type? for instance if you have an op amp and a CMOS chip sitting in a circuit. the former should be analog grounded, but latter should be digitally grounded, via separate return paths? i gathered this is to reduce noise/crosstalk. i'm still planning how to do my power for my DIY modular, so using some extra pins for the different grounds seems like a good idea. and maybe then i don't have to think too much about component placement wtr. digital/analog ground return paths.

i see many eurorack schematics have all ground pins tied together at the module. i gathered this will reduce the resistance of the ground return path, but will it not make for a noiser situation when having digital/analog grounds mixed? potentially? i guess you can use different pcb traces for different grounds and join at the power connector, so maybe not an issue. but if they all instead join at the PSU, it'll be better, no?

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Re: Why are there Two zero volts?

Post by KSS » Tue May 26, 2020 8:51 am

It's a complex subject when you get into hybrid circuits. Tony has similar papers on his other modules and he's got a clear way of speaking that you might find helpful beyond this issue. And because power affects all your modules. Since he's chosen to have his system utilize two separate return paths, hearing how he's decided to arrange things can be useful.

But don't think having an extra return path makes you have to think less, it makes it necessary to think more.

Your last two lines summarize the situation nicely. Emphasis on your word "maybe".

As Graham Hinton has pointed out, the AES48 standard explains the hows and whys. Bottom line is that you need very low resistance on your common signal return paths, and Ground used for safety and screening should not be carrying signal return current.

Do a search of his posts here, and you'll quickly get up to speed on what good system power distribution can be. And see how many or most modular synth formats fall short of the ideal.

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htor
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Re: Why are there Two zero volts?

Post by htor » Tue May 26, 2020 10:08 am

thanks kss, will do more research!

Cablebasher
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Re: Why are there Two zero volts?

Post by Cablebasher » Wed May 27, 2020 5:00 am

Thanks guys for the quick and detailed responses. I feel like I learned something which is always nice!

Cheers!

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EATyourGUITAR
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Re: Why are there Two zero volts?

Post by EATyourGUITAR » Wed May 27, 2020 5:04 am

here is a real world example with a case study kinda

http://www.loopers-delight.com/tools/re ... se_mod.pdf
WWW.EATYOURGUITAR.COM <---- MY DIY STUFF

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