I have a technical question regarding a modular synthesizer I’m building. I’m using the Kosmo format for my modules, and I’m using two Frequency Central Power Supplies for +12/-12/Gnd. The two power supplies are the same model built with the same parts, both driven by the same external power converter (120VAC to 12VAC).
The problem I have is that when I have modules plugged into both power supplies, there’s a short circuit that fries one of the ground wires. From my own investigation I found that there is a potential difference of around +/-8mV (it fluctuates, but who really knows with my crappy multimeter) between the two power supplies’ grounds (note this is the same whether or not modules are plugged into the power supplies). So because each module’s face plate is grounded and the face plates of all the modules touch, the two grounds are connected and it creates the short circuit. My question is this: is there a way to make the ground from both power supplies equal, and if not, is there a way to make sure that things still work properly with this voltage across the grounds? (Also, when the modules’ faceplates are not touching and I tap them together, there’s a noticeable spark, which my intuition tells me means there’s more than 8mV, but I don’t really know)
My first idea was to place a very small resistor between the modules of one of the power supplies and the ground connection to the power supply, which would mean it doesn’t create a short circuit because there’s a load in between, and I think a 10R 1/4W resistor would work (P=V^2/R with V=0.008V and R = 10Ω means P = 0.0000064W, much less than the 0.25W that the resistor is rated for), but I think that would mess up the modules it’s connected to (discharging capacitors would take longer and stuff like that). But then again, if the two grounds are connected, couldn’t those capacitors discharge through the other ground?
Basically I’m out of my depth and would love some advice. Thanks!