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 Grounding issue with PAiA and MFOS 
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Joined: Fri Sep 10, 2010 2:02 pm
Posts: 4
Post Grounding issue with PAiA and MFOS
I've got a PAiA Frac Rack with a couple PAiA 9700 modules, the MIDI to CV converter and the VCO module. They work correctly.

I just built a Music From Outer Space dual log/lin VCA module, fabricated my own frac rack panel for it and hooked it up to the power from the PAiA modules.

Well, the VCAs work, but there's a big, disappointing, frustrating, audible HUM.

The PAiA modules have four different power connections, V+, V-, G (power ground), and SG (signal ground) and the MFOS dual VCA only has V+, V- and G (common ground). Right now I have the MFOS module's ground hooked up to the PAiA unit's G (power ground) AND the SG. I also tried hooking up the MFOS's ground to the PAiA unit's G connection (no SG connection) and the same hum occurred. What should I be doing differently to eliminate this hum?


Sat Nov 10, 2012 7:27 pm
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Joined: Sun Nov 09, 2008 2:49 pm
Posts: 725
Post Re: Grounding issue with PAiA and MFOS
If the MIDI2CV8 is the power source, it being unregulated and ripple on the DC supplies might be the reason for hum.

Copy the power input circuitry of the PAiA 9720 VCO (with positive DC, power ground, signal ground, negative DC connections, into resistors, capacitors, voltage regulators, and, capacitors) point to point connected on an experimenter's board and you'll have regulated twelve volt supplies with this linked between the MIDI2CV8 and the VCA project.

Use G for the ground to these extra power supply parts and pass the SG on through as the ground for the VCA project.

G and SG return to a single point on the MIDI2CV8, so are the same, but just with different branches for different circuit sections.

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Mon Nov 19, 2012 2:36 pm
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Joined: Tue Nov 13, 2012 1:42 am
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Post Re: Grounding issue with PAiA and MFOS
:lol: PAiA-Scott is right, just do follow him :D

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Fri Dec 21, 2012 2:00 am
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