Grounding issue with PAiA and MFOS

Free-for-all discussion about PAiA products and the kinds of audio you produce with them.
Post Reply
Posts: 4
Joined: Fri Sep 10, 2010 2:02 pm
Hometown: Sacramento, CA, USA
Favorite topic: Girls
Super Robot Smashing Puzzle Time!: 12

Grounding issue with PAiA and MFOS

Post by danielwarner »

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?
User avatar
Posts: 733
Joined: Sun Nov 09, 2008 2:49 pm

Re: Grounding issue with PAiA and MFOS

Post by PAiA-Scott »

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.
Scott Lee
Posts: 5
Joined: Tue Nov 13, 2012 1:42 am
Hometown: London
Favorite topic: Big and hot
Super Robot Smashing Puzzle Time!: 12

Re: Grounding issue with PAiA and MFOS

Post by cooky24 »

:lol: PAiA-Scott is right, just do follow him :D
Post Reply